UHODWLRQVKLSV - UCSBresearch.mrl.ucsb.edu/~ewert/articles/pccp_model_chromophores.pdfmaterials,...

PRIVILEGED DOCUMENT FOR REVIEW PURPOSES ONLY

1

Prof. Dr. Claus D. Eisenbach

Institut für Angewandte Makromolekulare Chemie, Universität Stuttgart, Pfaffenwaldring

55, D-70569 Stuttgart

1HZ�GRQRU�DFFHSWRU�FKURPRSKRUHV�IRU�SKRWRUHIUDFWLYH

FRPSRVLWHV��VWUXFWXUH�SURSHUW\�UHODWLRQVKLSV

Kai Ewert,a)d) Heidi Hayen,b) Stefan Schloter,c) Dietrich Haarer,c) Claus D.

Eisenbach*a)

a) Institut für Angewandte Makromolekulare Chemie, Universität Stuttgart, Pfaffenwaldring 55,

D-70569 Stuttgart (Germany), [email protected]

b) Makromolekulare Chemie I, Universität Bayreuth, D-95440 Bayreuth (Germany)

c) Experimentalphysik IV, Universität Bayreuth, D-95440 Bayreuth (Germany)

d)current address: Materials Research Lab, University of California, Santa Barbara CA 93106-

5121 (USA)


2

$EVWUDFW

A series of donor-acceptor-type electrooptic (NLO) chromophores for use in

photorefractive guest-host materials has been synthesized and characterized.

Donor substituents (alkoxy or dialkylamino) as well as chromophore type

(azo-, stilbene-, tolane- and dicyanovinylbenzene-type) were varied

systematically to improve both the sample stability and index modulation,

and to investigate structure-property relationships. The optical, thermal and

electrochemical properties of the chromophores were studied by using

UV/VIS-spectroscopy, differential scanning calorimetry (DSC) and cyclic

voltammetry (CV). The chromophore’s donor substituents and bridging

groups have a strong influence on the spectral characteristics and the

oxidation and reduction potentials as well as on the melting behavior. Key

parameters were found to be the donor strength, the ability of the bridging

group to effect conjugation between the aromatic rings, and the bulkiness of

the donor groups. Some important chromophore properties such as

electrochemical properties and crystallinity can be tailored independently

from each other. Ternary composites of these chromophores with photo-

conducting poly(methyl-(3-(9-carbazolyl)propyl)-siloxane)siloxane and

2,4,7-trinitro-fluorenone were prepared and their photorefractive properties

studied using two-beam coupling and degenerate four-wave mixing. The

composites show high index modulations (up to 10-2) and photorefractive


3

gain. The influence of chromophore structure on these properties and the

holographic response times as well as the long-term stability are discussed.

_____________________________________________________________

,QWURGXFWLRQ

Organic photorefractive materials have attracted a rapidly increasing interest

since the first description of this type of compounds in 1991.1,2,3,4 This is

due to the unique features of the photorefractive effect, which distinctively

differs from all other types of light-induced modulation of a material’s

refractive index (e.g. photochromism, thermochromism)5 and allows for

numerous applications.6 In photorefractive systems, photogenerated charges

drift under the influence of an external field and get trapped, building up a

space charge field which in turn modulates the material’s refractive index

via the Pockels and the Kerr effect. This means that the refractive index

modulation is spatially shifted with respect to the light intensity pattern,

resulting in an asymmetric energy transfer between incident laser beams.

Other features of the photorefractive effect that are of great interest

concerning potential applications are its sensitivity (making the use of diode

lasers possible) and its reversibility (allowing real-time applications). 5,7

From the mechanism of grating formation, it follows that photorefractive

materials must combine photoconducting and electrooptic properties. This is

the case for a number of inorganic crystals, e.g. lithium niobate LiNbO3,


4

where the photorefractive effect was first observed in 1966.8 In organic

materials, different approaches exist for incorporating the essential

functions. In guest-host or composite systems, an amorphous matrix is

provided by a polymer which may be inert9 or bearing either

photoconducting units10,11,12,13,14,15,16 or nonlinear-optical (NLO)

chromophores.1,17 Photoconducting low molecular weight glasses have also

been used as the amorphous matrix.18 In contrast to guest-host systems,

incorporating more than one functional unit into either a polymer19 or a low

molar weight glass20 results in bifunctional or multifunctional

photorefractive materials. These do not suffer from phase separation or

chromophore crystallization, but they require higher synthetic efforts,

especially when the aim is to vary individual components. To encounter this

problem, we have developed and successfully applied a building block

approach for photorefractive polymers.21

The advent of organic photorefractive materials has renewed the interest in

NLO chromophores, a field that has been studied extensively.22 For the use

in photorefractive composites, new demands have to be met by electrooptic

dyes. Contributions to the modulation of the refractive index following the

buildup of a modulated space charge field in the material5 not only stem

from the electrooptical or Pockels effect but also from a contribution of the

chromophores’ birefringence after they reorient in the field (Kerr effect).

The term “orientational enhancement effect” has been coined for the latter


5

phenomenon,23 which frequently dominates the refractive index modulation

in photorefractive composites.16 Taking both effects into account, a tentative

figure-of-merit for photorefractive chromophores

N700)

αµµβ ∆+=229

has been proposed.24,25 Here ∆α is the polarization anisotropy, k is

Boltzmann’s constant and T the temperature; M is the chromophores’

molecular weight, β its first hyperpolarizability and µ its ground-state

dipole moment.

While the model used to derive the figure of merit is incomplete even for the

description of the refractive index modulation since it neglects the field-

induced dissociation of dimeric chromophore aggregates,26 chromophores

with a large figure-of-merit are likely to exhibit large index modulations.

This has been shown experimentally, e.g. for chromophores of the

merocyanine type.27,28,24,20e However, the high dipole moments of

chromophores with optimized FOM lead to strong aggregation which is

detrimental for photorefractive performance, and chromophores with the

highest reported FOMs were found to be inactive in photorefractive

composites.26,29,30 On the other hand, chromophores with comparatively low

FOM such as 2,5-dimethyl-4-(4-nitrophenylazo)-anisole (DMNPAA),10,11 its

substituted analog EHDMNPAA,13,31 a 4-cyano-4'-alkoxy-tolane32 or amino-


6

dicyanovinylbenzenes16,37,42 give composites of remarkable performance,

especially when the response times are taken into consideration. Other

important characteristics of photorefractive composites such as sample

stability, optical absorption and the speed of the photorefractive response are

also influenced strongly by the chromophores. They are, however, not

addressed by the above figure-of-merit.33 Investigations on the influence of

chromophore photoisomerization39 revealed this to be another property of

importance for photorefractive performance. Early studies on guest-host

materials in which the chromophore was varied16,34,35 did not compare series

of different chromophore type or did not investigate the influence of single

chromophore properties on the performance of guest-host photorefractive

materials. More recently, the importance of the electrochemical properties of

the chromophores has been realized and assessed.16,36,37 and structure

property relationships of newly designed chromophore types have been

investigated more systematically.27,30,38

While the understanding of structure property relationships for

chromophores used in photorefractive composite materials is still

incomplete, development of new improved materials has proceeded rapidly.

This has yielded composites showing total internal diffraction,11 refractive

index modulations (∆n) around 0.0127,39,40 and holographic rise times faster

than 10 ms.14,15,32,41,42


7

In this paper, we present our approach to systematically and independently

vary important chromophore characteristics (e.g. dipole moment, HOMO-

energy, crystallization enthalphy) to determine their influence on the

performance of photorefractive guest-host materials. For this purpose, we

have synthesized a series of new NLO-chromophores, which include the

well-known chromophore DMNPAA10,11 for comparison. We have prepared

chromophores of different type (π-system) and donor substitution and

characterized them using UV/VIS spectroscopy, differential scanning

calorimetry (DSC) and cyclic voltammetry (CV). Photorefractive

composites prepared from the chromophores, a photoconducting siloxane

polymer and 2,4,7-trinitrofluorenone (TNF) were characterized using DSC,

their stability towards chromophore recrystallization was assessed and their

photorefractive properties were measured. While the chromphores in this

study have not been optimized with regard to their photorefractive figure of

merit, their facile synthesis allowed the investigation of other properties

relevant to photorefractive composites by systematic structural variations.

Nevertheless, the stationary the performance of these chromophores is

impressive with index modulations as high as 10-2.

([SHULPHQWDO�6HFWLRQ

*HQHUDO� 0HWKRGV� Nuclear magnetic resonance (NMR) spectra were

obtained using a Bruker AC 250 spectrometer with tetramethylsilane as the


8

internal standard. Infrared (IR) spectra were recorded on a DIGILAB-

DIVISION BIO-RAD 3240-SPC FTS-40 instrument. Absorption spectra

were measured on a Perkin Elmer LAMBDA 15 spectrometer in

tetrahydrofurane (THF) of spectrophotometric quality. Mass spectrometry

(MS) was performed using a Finnigan MAT 8500 mass spectrometer. A

Perkin Elmer DSC 7 apparatus was used for thermal analysis. Samples of

photorefractive composites were heated to well above their glass transition

temperature and quenched in liquid nitrogen before the measurement. Flash

chromatography was performed using silica gel 60 from Merck (particle size

40 - 63 µm).

&\FOLF� YROWDPPHWU\� A three electrode cell and a potentiostat assembly

from EG&G Princeton Applied Research were used. The measurements

were performed at a sweep rate of 50 mV/s using a glassy carbon working

electrode in dry THF or 1,2-propylene carbonate (both purchased from

Aldrich) containing 0.1 M Bu4N+ PF6

-. The reference electrode was Ag/0.1 M

AgNO3 in acetonitrile and the redox standard was ferrocene (-4.80 eV

HOMO). Reversible redox processes were evaluated according to standard

procedures.43 For irreversible reactions, the potential used for the HOMO-

energy calculation was approximated as 1/2 (Epeak, anodic + Epeak, cathodic) if

there was both an anodic and a cathodic peak. If there was only one peak,

half the difference in potential of the peaks of ferrocene was added to /

subtracted from the peak potential for the irreversible reduction / oxidation.


9

The aim of this procedure was to allow comparison of reversibly and

irreversibly reacting chromophores.

3KRWRUHIUDFWLYH� FKDUDFWHUL]DWLRQ� The techniques for photorefractive

sample preparation as well as the detailed experimental procedures for the

characterization of the photorefractive composites have been given

elsewhere.39 In brief, solutions of the compounds in 1,4-dioxane were mixed

at appropriate ratios and freeze-dried. The resulting powder was melted and

filled into ITO glass cells (“Test cells for LC”, 20-40 µm, EHC, Japan) by

capillary action. The setup for the degenerate four-wave mixing (DFWM)

and two-beam coupling experiments consisted of two diode-laser beams

with an intensity of 1 W/cm2 and a wavelength of 670 nm which were

intersected at an angle of 17.2° in the sample. The bisector of the beams was

tilted 45° with respect to the sample normal. Thus, a grating spacing of 4 µm

resulted.

0DWHULDOV� 4-Dimethylamino-4’-nitrostilbene (DANS, ��H) was purchased

from Kodak. Ethylcarbazole and Poly(N-vinylcarbazole) (PVK) were

purchased from Aldrich. The other starting materials were purchased from

Fluka, Aldrich or Merck. TNF (Aldrich) was recrystallized from ethanol. 4-

Nitroaniline (Merck) was recrystallized from ethanol-water. All other

materials were used as received. DMNPAA (��H) was prepared as described

by v. Auwers44, and 4-Dimethylamino-4’-nitrotolane (11,11-dimethyl-4-[2-

(4-nitrophenyl)-1-ethynyl]aniline, DANT, ��I) was synthesized according to


10

the method of Akiyama et al.45 The photoconducting poly(methyl-(3-(9-

carbazolyl)propyl)-siloxane) (PSX) was prepared as described by

Strohriegl.46 The cyclic siloxane 1,3,5,7-Tetrakis-(3-(9-carbazolyl)propyl)-

1,3,5,7-tetramethyl-cyclotetrasiloxane (D4-4CZ, cf. Fig. 2) was synthesized

by hydrosilylation of N-allylcarbazole with 1,3,5,7-Tetramethyl-

cyclotetrasiloxane (Gelest) as described for PSX.46

6\QWKHVLV�� Representative experimental procedures are given below.

Procedures and spectral data for all compounds are given in the

supplementary information.

1��HWK\OKH[\O��1��PHWK\ODQLOLQH� ��E�� To a stirred mixture of

117.9 mL (116.6 g, 1.088 mol) N1-methylaniline and 3.08 g tetrabutyl-

ammonium iodide, 108.6 mL (100 g, 0.518 mol) 2-ethylhexyl bromide were

added slowly under an inert atmosphere. After stirring for 24 hours at 85 °C,

the mixture was poured into 700 mL water. The resulting solution was made

alkaline by adding potassium hydroxide while cooling and extracted three

times with diethyl ether. The combined organic layers were washed with

water, dried (Na2SO4) and the solvent was evaporated. The residue was

fractionally distilled in vacuo (10-3) to yield 83.7 g (74%) of a colorless

liquid, bp. 90 °C (1.7⋅10-2 mbar).

�+�105 (CDCl3): δ / ppm = 0.89 ( ”t”, J = 8 Hz, 6 H, CH-CH2-C+3, CH-

(CH2)3-C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85

(m, 1 H, CH2-C+(Et)(Bu)), 2.93 (s, 3 H, N-C+3), 3.16 (”d”, J = 7 Hz, 2 H,


11

N-C+2-C(H)(Et)Bu), 6.55-6.80 (m, 3 H, +ar R-NRR’, +ar S-NRR’), 7.10-

7.30 (m, 2 H, +ar P-NRR’); ��&�105 (CDCl3): δ / ppm = 10.7, 14.1 (CH-

CH2-&H3, CH-(CH2)3-&H3), 23.2, 24.0 ( CH-&H2-CH3, CH-(CH2)2-&H2-

CH3), 28.7, 30.7 (CH-(&H2)2-CH2-CH3), 37.8, 39.3 (N-&H3, CH2-

&H(Et)(Bu)), 57.1 (N-&H2), 111.8 (H&ar R-NR2), 115.5 (H&ar S-NR2),

128.9 (H&ar P-NR2), 149.7 (&ar LSVR-NR2); ,5 (Film): ν / cm-1 = 3094 (w),

3063 (w), 3027 (w), 2959 (s), 2929 (s), 2873 (s), 2839 (s), 1600 (s).

��>��HWK\OKH[\O��PHWK\O�DPLQR@EHQ]DOGHK\GH ��E��47� Under an argon

atmosphere, 24.7 mL (27.0 g, 200 mmol) N-methylformanilide were mixed

with 18.2 mL (30.6 g, 200 mmol) phosphoroxy chloride and kept for 45

minutes at room temperature. Keeping the temperature below 25 °C, 43.9 g

(200 mmol) ��E were added within one hour with stirring. The mixture was

kept for 15 hours at room temperature and poured into 500 mL of cold

water. After extraction with ether (twice), combining and drying (Na2SO4)

the organic layers followed by removal of the solvent gave a colorless oil.

The crude product was fractionally distilled in vacuo (10-3 mbar) to yield

32.7 g (66%) of a colorless oil, bp. 130 °C (4⋅10-2 mbar).

�+�105 (CDCl3): δ / ppm = 0.80-1.00 (m, 6 H, CH-CH2-C+3, CH-(CH2)3-

C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1

H, CH2-C+(Et)(Bu)), 3.06 (s, 3 H, N-C+3), 3.30 (”d”, J = 7 Hz, 2 H, N-


12

C+2-C(H)(Et)Bu), 6.70 (”d”, J = 9 Hz, 2 H, +ar R-N), 7.71 (”d”, J = 9 Hz, 2

H, +ar P-N), 9.72 (s, 1 H, C+O).

�1��(WK\O��KH[\O��1�PHWK\O�DPLQR��¶�QLWUR�D]REHQ]HQH ��E�� A

cooled suspension of 6.45 g (46.9 mmol) 4-nitroaniline in 14 mL water and

14 mL conc. hydrochloric acid was diazotized with a solution of 3.3 g

(47 mmol) sodium nitrite in 3.5 mL water at 0 to 5 °C. Excess nitrite was

removed by addition of little amidosulfuric acid. The resulting solution was

added dropwise to a cooled solution of 8.76 g (40.0 mmol) ��E in 23 mL

conc. hydrochloric acid at 0 to 5 °C. After stirring for one hour, the solution

was neutralized using saturated sodium acetate solution. Filtration gave a

crude product which was purified by recrystallization from methanol and

subsequent flash chromatography using cyclohexane (CyH)-ethyl acetate

(EAc) (9:1, v/v) as the eluent to yield 5.1 g (35%) red crystals, mp. 96.5 °C.


C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1


C+2-C(H)(Et)Bu), 6.74 (”d”, J = 9 Hz, 2 H, +ar R-NRR’), 7.80-7.95 (m, 4

H, +ar P-NRR’, +ar P-NO2), 8.31 (”d”, J = 9 Hz, 2 H, +ar R-NO2); ,5

(KBr): ν = 2957 (m), 2931 (m), 2871 (w), 2857 (m), 1602 (s), 1585 (s),

1519 (m), 1507 (s), 1379 (m), 1327 (vs), 1307 (s), 1137 (s), 1102 (s), 857

(m); 06 (EI, 70 eV): m/z (%) = 368 (18, M+·), 270 (31, M - C7H14), 269

(40, M - C7H15), 223 (9, M - C7H15, - NO2), 119 (18, C8H9N).


13

1��HWK\OKH[\O��1��PHWK\O��>�(��QLWURSKHQ\O��HWKHQ\O@DQLOLQH

��E��48� To 3.0 g (12.2 mmol) ��E and 2.21 g (12.2 mmol) 4-

nitrophenylacetic acid, 3 droplets of piperidine were added and the mixture

was stirred at 160 °C for 6 hours.. After cooling, recrystallization of the

crude product from methanol followed by flash chromatography using CyH-

EAc (4:1, v/v) as the eluent yielded 3.1 g (70 %) orange crystals, mp.

121 °C.


C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1


C+2-C(H)(Et)Bu), 6.67 (”d”, J = 9 Hz, 2 H, +ar R-NRR’), 6.90 (d, 3Jtrans =

16 Hz, 1 H, =C+-C6H4-NO2), 7.20 (d, 3Jtrans = 16 Hz, 1 H,

+C=CH-C6H4-NO2), 7.42 (”d”, J = 9 Hz, 2 H, +ar P-NRR’), 7.55 (”d”, J =

9 Hz, 2 H, +ar P-NO2), 8.17 (”d”, J = 9 Hz, 2 H, +ar R-NO2); ,5 (KBr): ν =

2959 (m), 2930 (m), 2872 (w), 1606 (m), 1585 (s), 1524 (m), 1507 (s), 1337

(s), 1188 (m), 836 (m); 06 (EI, 70 eV): m/z (%) = 366 (11, M+·), 267 (40,

M - C7H15), 221 (9, M - C7H15, - NO2).

1��HWK\OKH[\O��1��PHWK\O��LRGRDQLOLQH� ��E��To a stirred mixture of

10 g (45.6 mmol) ��E, 5.7 g (68.4 mmol) sodium hydrogencarbonate and

50 mL water, 11.7 g (45.6 mmol) iodine were added in portions. After

stirring for 3 h, the mixture was extracted three times with dichloromethane.

The combined extracts were washed with water, dried (Na2SO4) and the


14

solvent was evaporated. The residue was purified by flash chromatography

using CyH-dichloromethane (15:1, v/v) as the eluent (Rf = 0.49) to yield

8.6 g (55%) of a colorless oil.


C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1


C+2-C(H)(Et)Bu), 6.42 (”d”, J = 9 Hz, 2 H, +ar R-N), 7.41 (”d”, J = 9 Hz, 2

H, +ar P-N); ��&�105 (CDCl3): δ / ppm = 10.7, 14.1 (CH-CH2-&H3, CH-

(CH2)3-&H3), 23.1, 23.9 ( CH-&H2-CH3, CH-(CH2)2-&H2-CH3), 28.7, 30.7

(CH-(&H2)2-CH2-CH3), 37.6, 39.3 (N-&H3, CH2-&H(Et)(Bu)), 56.7 (N-

&H2), 76.1 (&ar LSVR-I), 114.1 (H&ar R-NR2), 137.4 (H&ar P-NR2), 149.1

(&ar LSVR-N).

1��HWK\OKH[\O��1��PHWK\O��>��QLWURSKHQ\O��HWK\Q\O@DQLOLQH

��E�� To a solution of 4 g (11.6 mmol) ��E and 1.69 g (11.7 mmol) 1-(1-

ethynyl)-4-nitro-benzene (�) in 44 mL diethylamine, a mixture of 0.16 g

(0.23 mmol) bis(triphenylphosphine)palladium(II) chloride and 0.02 g

(0.11 mmol) copper(I) iodide was added in small portions under an argon

atmosphere. After stirring for 18 hours, the diethylamine was distilled off.

Water was added to the residue, and the mixture was extracted three times

with dichloromethane. The combined organic layers were dried (Na2SO4)

and the solvent was evaporated. The crude product was purified by

recrystallization from ethanol and subsequent flash chromatography using


15

CyH-dichloromethane (3:1, v/v) as the eluent (Rf = 0.29) to yield 1.8 g

(43%) orange crystals, mp. 95 °C.


C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1

H, CH2-C+(Et)-CH2), 3.00 (s, 3 H, N-C+3), 3.24 (”d”, J = 7 Hz, 2 H, N-

C+2-C(H)(Et)Bu), 6.63 (”d”, J = 9 Hz, 2 H, +ar R-NRR’), 7.40 (”d”, J = 9

Hz, 2 H, +ar P-NRR’), 7.58 (”d”, J = 9 Hz, 2 H, +ar R-NO2), 8.17 (”d”, J = 9

Hz, 2 H, +ar P-NO2); ��&�105 (CDCl3): δ / ppm = 10.7, 14.1 (CH-CH2-

&H3, CH-(CH2)3-&H3), 23.1, 24.0 ( CH-&H2-CH3, CH-(CH2)2-&H2-CH3),

28.7, 30.7 (CH-(&H2)2-CH2-CH3), 37.9, 39.4 (N-&H3, CH2-&H(Et)(Bu)),

56.7 (N-&H2), 86.4, 97.4 (-&≡&-), 107.7 (H&ar S-NRR’), 111.4 (H&ar

R-NRR’), 123.6 (&ar R-NO2), 131.5, 133.2 (&ar S-NO2, H&ar P-NRR’��H&ar

P-NO2), 146.1 (&ar LSVR�NRR’), 150.8 (&ar LSVR-NO2); ,5 (KBr): ν = 2957

(w), 2931 (w), 2872 (w), 2857 (w), 2202 (m), 2183 (m), 1610 (m), 1584 (s),

1503 (m), 1334 (s), 1137 (m), 1105 (m), 850 (w); 06 (EI, 70 eV): m/z (%)

= 364 (52, M+·), 266 (40, M - C7H14), 265 (100, M - C7H15), 219 (17, M -

C7H15, - NO2).

��>��HWK\OKH[\O��PHWK\O�DPLQR@SKHQ\OPHWK\OHQH�PDORQRQLWULOH

��E��34 Following the addition of 10 droplets of piperidine, a stirred solution

of 6.00 g (24.3 mmol) ��E and 3.23 g (48.6 mmol) malononitrile in THF-

methanol 1:1, v/v was warmed to 40 °C. After stirring for 4 hours, the


16

solvent was evaporated. The resulting residue was dissolved in

dichloromethane and washed with aqueous sodium chloride solution, 0.1 N

hydrochloric acid and again aqueous sodium chloride solution. The organic

layer was dried (Na2SO4) and the solvent evaporated. Purification of the

crude product by flash chromatography using diethyl ether-petrol ether (40-

60 °C) (1:9, v/v) as the eluent yielded 7.5 g (63%) orange crystals, mp.

59 °C.


C+3), 1.20-1.50 (m, 8 H, CH-C+2-CH3, CH-(C+2)3-CH3), 1.65-1.85 (m, 1


C+2-C(H)(Et)Bu), 6.68 (”d”, J = 9 Hz, 2 H, +ar R-N), 7.44 (s, 1 H,

+C=C(CN)2), 7.79 (”d”, J = 9 Hz, 2 H, +ar P-N); ,5 (KBr): ν = 2959 (s),

2931 (s), 2873 (s), 2216 (s), 1614 (s), 1575 (s), 1565 (s), 1525 (s), 1400 (s),

1206 (s), 1191 (s), 816 (m); 06 (EI, 70 eV): m/z (%) = 295 (12, M+·), 196

(100, M - C7H15).

5HVXOWV�DQG�'LVFXVVLRQ

'HVLJQ�RI�FKURPRSKRUHV� We have synthesized a series of chromophores in

which the donor and acceptor parts were varied independently and

systematically. Thus, as shown in Table 1, we obtained azo- (��D�H),

stilbene- (��D�H), tolane- (��D�H) and dicyanovinylbenzene-chromophores

(��D�H), suited to study the structure-property relationships of donor-acceptor


17

chromophores for photorefractive applications. The well known

chromophore DMNPAA (��H),11 for example, has a relatively weak donor

group (OMe), resulting in a moderate dipole moment and

hyperpolarizability.33 Its small size might be advantageous with regard to

fast orientation by an electric field in a polymer matrix, but the chromophore

is quite prone to crystallization due to its compact structure. Therefore, we

first increased the strength of the donor by replacing OMe with NMe2

(chromophore ��G) while maintaining the small size of the chromophore,

and secondly introduced bulky donor groups in chromophores ��D and ��E

(in ��E, the alkyl residue is also racemic) in order to inhibit crystallization.

The medium-sized allyl group of chromophore ��F may be used to attach this

chromophore to cyclic or polymeric siloxanes via hydrosilylation.

By varying the type of the chromophore we aimed to control

photoisomerization, which gives rise to undesired polarization gratings in

addition to the photorefractive grating.49 Azo-chromophores readily undergo

reversible photoisomerization, a phenomenon which has been widely used,

e.g. in polymer chemistry.50,51 Photoisomerization of stilbenes is not

thermally reversible, while tolanes and dicyanovinylbenzenes do not

undergo structural changes upon irradiation, thereby eliminating the

possibility of polarization gratings. As we show below, the chromophore

type also influences the electrochemical and electrooptical properties.52


18

6\QWKHVLV��Efficient synthesis of the chromophore series was achieved by

using intermediates parallelly in sequences leading to different chromophore

types as shown in Schemes 1 and 2. Thus, in the first step, donor-substituted

benzene derivatives were obtained from suitable anilines. From the donor-

substituted benzenes, we prepared azo chromophores by coupling with the

diazonium salt derived from 4-nitroaniline and benzaldehydes by a

Vilsmeyer-Haack53 procedure. Those aldehydes in turn were used for both

the synthesis of the dicyanovinylbenzene and the stilbene chromophores as

also shown in Scheme 1. We applied a piperidine-catalyzed condensation

with malonodinitrile34 to obtain the dicyanovinylbenzene chromophores. To

yield WUDQV-stilbenes, the aldehydes were reacted with 4-nitro-

triphenylphosphoniumbromide54,55 or with 4-nitro-phenylacetic acid and

piperidine.48 The synthesis of the tolane chromophores (Scheme 2) applies

two Heck-type coupling reactions as key steps.56,57 First, 4-bromo-

nitrobenzene was coupled with trimethylsilylacetylene to yield 1-(1-

ethynyl)-4-nitrobenzene (�) after deprotection. Compound � was then

coupled with substituted iodobenzenes, obtained by direct iodination of the

respective donor-substituted benzenes, to yield the corresponding tolanes.

$EVRUSWLRQ�VSHFWURVFRS\� Increasing the donor strength of donor-acceptor

chromophores incresases their dipole moment as well as their

hyperpolarizability, which leads to a desirable increase in the photorefractive

FOM. On the other hand, an increase in donor strength typically effects a


19

red-shift of the absorption maximum which can be undesired since

chromophore absorption at the wavelength of the lasers used should be

negligible. To investigate whether this limits the possibilities of tailoring

NLO-chromophores for photorefractive applications and to get information

on relative donor strengths, we measured the UV/VIS spectra of our

chromophore series. The absorption maxima as obtained from dilute

solutions in THF are listed in Table 2. The value for the azo parent

compound ��I was taken from the literature.58 For chromophores of different

type but identical donor substitution, the wavelength of the absorption

maxima drops in the order azo > stilbene > dicyanovinylbenzene > tolane.

The shape and structure of the absorption is quite similar for the

chromophore types, showing two maxima. For the azo chromophores, this

means that the strong π-π*-band completely overlaps with the n-π*-

absorption (“pseudo stilbene behavior”59), as otherwise two long-

wavelength absorption maxima would be expected. Only for compound ��H,

a slight shoulder resulting from the n-π*-absorption is visible. This

demonstrates the relatively small influence of substitution on the n-π*-

transition,59 implying that tuning the chromophore’s absorption in the red

region is difficult for azo-chromophores. This is different for the other

chromophore types, as the donor substitution has a pronounced effect on the

π-π*-transition. The chromophores with dialkylamino-donors absorb at the

longest wavelengths, while a strong blue-shift occurs on changing the donor-


20

group from NMe2 to OMe. Methyl-substitution on the aromatic ring confers

a blue-shift of the absorption maximum for both azo- and stilbene-

chromophores, probably by increasing the dihedral angle between the

aromatic rings. In contrast, no similar blue-shift is observed for

dicyanovinylbenzene chromophores (e.g. comparing compounds ��G and

��E). Likely, the dicyanovinyl-acceptor is twisted out of the plane of the

phenyl ring even for unsubstituted derivatives due to sterical interactions

with the ring hydrogen atoms as shown in Figure 1.60 Therefore, no further

reduction of the conjugation occurs with methyl substitution of the phenyl

ring.

7KHUPDO� FKDUDFWHUL]DWLRQ� RI� WKH� FKURPRSKRUHV� The high chromophore

content of photorefractive composites frequently gives rise to phase

separation and chromophore crystallization.10, 11 This leads to strong

scattering of light or dielectric breakdown of the samples and is

unacceptable for devices.

Different approaches towards improving the stability of photorefractive

composites and to prevent crystallization-driven segregation processes have

been pursued. Hendrickx et al.61 used a random isomeric mixture of

chromophores, while Meerholz et al.62 applied an eutectic mixture. Liquid

chromophores have also been used successfully.63,12 As a more general

approach, the use of plasticizers can serve to inhibit crystallization and

simultaneously lower the glass transition temperature (Tg) of the


21

composite,11,14,16,27,28,41 but the plasticizer can reduce the concentration of

functional components. Another widely applicable approach, the

introduction of a bulky alkyl-groups, was first used by Cox et al. with a

DMNPAA-like chromophore,31 and has been employed frequently in recent

work.13,27,30,40

To rationalize these different approaches, we can consider a photorefractive

composite material in a simplifying approach as a two component system

with no miscibility in the solid state. For the material to be stable,

miscibility of chromophor and photoconductor in the melt or

“compatibility” (which is increased by alkyl substituents) and lowering of

the melting point of the chromophore to below the temperature of operation

by the mixing are required. This shows why a low melting point of the

chromophore is crucial, a criterion that also holds if the goal is to inhibit

recrystallization kinetically, i.e. to achieve a very slow crystallization

velocity at room temperature (as in most DMNPAA composites). In the

latter case, a low melting enthalpy also is important, as it increases the

critical size of a crystallization nucleus and thus decreases the probability of

such a nucleus being formed.

The melting points of the chromophores and their melting enthalpies as

determined by DSC are listed in Table 5. Unsubstituted chromophores such

as DANS (��I) or the corresponding tolane derivative DANT (��I) do not

melt below 220 °C; as expected, we were not able to prepare photorefractive


22

composites from these chromophores due to their facile crystallization.

Increasing the number or the bulk of substituents lowers the melting point

very effectively: e.g. compare ��I� with ��G, where unsymmetric methyl

substitution on the donor ring has been introduced; ��H�with ��G, where the

methyloxy-substituent has been replaced by a dimethylamino group; ��F

with ��E, where the allyl group has been replaced by the 2-ethyl-hexyl

group. Introducing bulky donor groups as in the series D and E is

synthetically easier than adding substituents on the phenyl ring and is a very

efficient means of reducing the melting point and, in most cases, the melting

enthalpy. The effect of a given donor substituent, however, is not identical

for chromophores of different type: a comparison of compounds ��D/E and

��D/E shows that it can not be predicted a priori which donor group is more

effective in reducing the melting point, even if the overall structure of the

chromophores is very similar.

&\FOLF� YROWDPPHWU\� The relative HOMO and LUMO energies of the

chromophore and the photoconducting compound (corresponding to their

oxidation and reduction potentials, respectively) are an important means to

understand trapping in photorefractive composites.36,37,38,64,65 For the

chromophores to act as traps - either directly by trapping holes or indirectly

by providing the compensator for radical-anions of the sensitizer which act

as traps37 - their HOMO-energy must be higher than that of the

photoconductor.


23

In Table 3, the HOMO- and LUMO-energies of the chromophores are given

as determined by CV using ferrocene as the standard.66 Additionally, it is

indicated whether the observed oxidation / reduction is reversible or

irreversible. For illustration, the cyclic voltammograms of the oxidation of

chromophore ��G� and the reduction of chromophore ��H are shown in

Figure 2. The plots are typical examples of an irreversible oxidation and a

reversible reduction, respectively.

We have measured the LUMO-energy of the sensitizer TNF under identical

conditions as those of the chromophores and found it to be –3.90 eV

(reversible reaction). The chromophores’ LUMO-energies are much higher

and thus no reduction of the chromophores will take place in the composites.

The HOMO-energies are strongly affected by the donor substitution for all

chromophore types. The weaker methoxy donor group (series H) leads to a

much lower HOMO-energy than the dialkylamino groups. Variation of the

HOMO-energies with the structure of the dialkylamino donor is smaller, but

correlates roughly with the donor strengths as obtained from the analysis of

the UV/VIS-spectra. For example, the chromophores �-��D exhibit the

lowest HOMO-energies in the respective chromophore series. The decrease

of electron withdrawing properties of the acceptor / bridging group in the

order dicyanovinylbenzene > azo > stilbene > tolane parallels an increase in

the HOMO-energy for chromophores of different type but with identical

donor substitution.


24

If the chromophores contribute to the trap manifold, reversibility of the

oxidation is important to avoid unwanted side effects like the formation of

permanent gratings. For azo- and dicyanovinylbenzene-chromophores,

reversibility of the oxidation reaction depends on the donor-substitution.

The reaction is irreversible for allyl-methyl-amino and methoxy-substituted

derivatives. The double bond in the allyl-residue of chromophores ��F and

��F is a probable cause for the irreversibility while in the case of the

compounds ��H and ��H, the high reactivity of the radical cations formed by

oxidation (evidenced by their high oxidation potential) is the likely cause.

For all stilbene- and tolane-chromophores, the oxidation reaction is

irreversible, even though their oxidation potentials are lower than those of

the other chromophores.

For comparison with the chromophore oxidation potentials, we have

measured the HOMO-energies of PVK and the model compounds

ethylcarbazole and D4-4CZ. No reduction of these compounds was observed

in the solvent window of THF. Their structures are depicted in Figure 3

together with that of the polymeric siloxane PSX used in the photorefractive

composites. Ethylcarbazole has been used by others as a model compound

for PVK in electrochemical measurements.37

The HOMO-energies of the carbazole derivatives are given in Table 4. To

illustrate the typical behavior, the voltammogram of ethylcarbazole is shown

in Figure 4 a). As for all carbazole compounds investigated, the oxidation is


25

irreversible. In the second cycle of the measurements, a reversible oxidation

is observed at a significantly lower potential. We suggest that the carbazole

units undergo a coupling reaction after oxidation to the radical cation in

analogy to the electrochemical coupling reaction of triphenylamines.67 The

role of this reaction in the bulk is not clear. We note, however, that dimers

produced by the reaction would be able to act as deep traps in pure PVK,

decreasing the hole mobility. The voltammogram of PVK is shown in

Figure 4 b). The coupling reaction here leads to crosslinking and therefore

experimental difficulties. As there is no oxidation peak, the HOMO-energy

of PVK can only be estimated, taking the sharp rise in current at 824 mV as

peak onset.

Comparing the HOMO energies of the chromophores with those of the

carbazole derivatives, it is evident that the HOMO-energy of the

chromophore can be varied in a range is large enough to cover both a regime

where the chromophores’ HOMO-energy is significantly lower than that of

the photoconducting matrix (alkyloxy donor and not stilbene type) and one

where the HOMO-energy is low enough to be close to that of carbazole

dimers (stilbenes with dialkylamino donors). Chromophores with alkoxy

donor groups are the best choice for electrochemically inert dopants, and the

irreversibility of their oxidation is of no concern since their HOMO energies

are below that of the photoconductor.


26

As a final consideration regarding the electrochemical properties of the

chromophores, the injection of holes at the electrode interfaces will become

more probable when the HOMO-energy of chromophore or photoconductor

are close that of the ITO-electrodes (ca. –4.8 eV) unless there is an

insulating layer between the ITO and the composite. This increases the

likelihood of dielectric breakdown of the samples. Of the chromophores

investigated, stilbenes are the most likely to exhibit this problem.

&KDUDFWHUL]DWLRQ� RI� SKRWRUHIUDFWLYH� FRPSRVLWHV�� We have prepared

photorefractive guest-host materials from the photoconducting polysiloxane

PSX,46 TNF and a number of the chromophores. Their composition, glass

transition temperature, shelf lifetime and important physical characterization

data are compiled in Table 6. In the context of shelf lifetimes, we refer to a

sample as stable if upon storage no processes are observed that are

detrimental for its use in photorefractive experiments, e.g. crystallization of

the chromophore or phase separation leading to opaque samples.

7KHUPDO�FKDUDFWHUL]DWLRQ� To achieve optimized specimen characteristics,

the Tg of the composites as measured by DSC was adjusted to room

temperature where all measurements of the photorefractive properties were

performed. In composites with a higher glass transition temperature,

chromophore orientation is very slow, while a low Tg made samples prone

to dielectric breakdown. The adjustment of the glass transition temperature

was achieved by varying the ratio of chromophore and photoconductor.


27

Azo- and stilbene-chromophores of identical donor substitution, e.g. � D and

� D or ��H and ��H, had to be mixed with PSX in approximately the same

weight portion, reflecting their very similar structure and molecular weight.

A much smaller weight portion of the tolane- and dicyanovinylbenzene-dyes

was needed to lower Tg to room temperature. Such a smaller weight fraction

of the chromophore typically corresponds to greater stability of the

composite. This is evident in the stability of the composites made from

chromophores ��H and ��H, where ��H even has a higher melting point than

DMNPAA. The composites made from the corresponding azo and stilbene

chromophores DMNPAA (��H) and ��H are only stable for a limited time

before crystallization occurs. Thus, for composites with chromophore

contents of more than 40% by weight, only chromophores with bulky donor

substituents yield stable samples. The donor substituent approach to create

chromophores that yield morphologically stable samples is therefore

superior over substitution directly on the aromatic ring.

3KRWRUHIUDFWLYH� &KDUDFWHUL]DWLRQ� Evaluating the photorefractive

properties of the composites compiled in Table 6, we find that all but one

are “high performance materials” according to the definition by Moerner et

al..3 Only the composite based on chromophore � H fails to satisfy these

criteria (diffraction efficiency > 5%, gain coefficient > 50 cm-1) due to its

relatively small gain coefficient of 23 cm-1. This demonstrates that for

common donor-acceptor type NLO-chromophores, several properties (e.g.


28

HOMO-energy, ability to photoisomerize) may be varied without severely

compromising the photorefractive refractive index modulation.

For a detailed discussion of the photorefractive performance, we will focus

on the composites made from compounds �-�� H, where the chromophore

type was varied while maintaining identical substitution. For compounds

��H, ��D and ��E, the results of extensive investigations have been published

elsewhere.39

We investigated whether a polarization grating, stemming from

photoisomerization of the chromophores, was present in the composites.

This grating is best observed for s-polarized reading beams, because the

writing beams in the DFWM-measurements are s-polarized as well.68 To

measure the small refractive index modulation ∆npolariz. resulting from

photoisomerization, the grating translation technique69,70,71 was used at E0 =

0 V/µm. The values determined for ∆npolariz. are given in Table 6. Due to

their facile and thermally reversible photoisomerization, azo chromophores

show the largest refractive index modulations at zero field. The stilbenes

exhibit a small ∆npolariz., which is larger for ��D than for ��H. This may be

attributed to the higher absorption coefficient (13 cm-1) of ��D compared to

��H�(3 cm-1). Finally, the use of tolane chromophores, which are not able to

undergo structural changes upon irradiation, prevents the formation of a

polarization grating. Thus, variation of the chromophore type can be used to

control the extent of polarization gratings.39


29

The phase shift Φ between the photorefractive grating and the light intensity

pattern was also determined using the grating translation technique. The

results for the chromophores �-��H are plotted against the field E0 in

Figure 6. At small external fields (E0 ≤ 20 V/µm), the phase shift strongly

depends on E0. In this regime, Φ rises with E0 for the tolane chromophore

while it drops for the azo- and the stilbene-chromophore (compounds ��H

and ��H). The initial high phase shift is due to the polarization grating for

which Φ = 180 °. The phase shift drops to that of the photorefractive grating

once the refractive index modulation of the later becomes dominant. Since

there is no polarization grating in the composite with the tolane �� H, Φ

steadily rises due to the increasing strength of the drift field, which enables

the charges to propagate further before being trapped.

The effective trap density Neff in the composites was calculated based on

results from the standard model for organic photorefractive materials7 as

previously reported.39 The trap densities as listed in Table 6 rise with

decreasing HOMO energy. This has been found by others37 and is expected

both if the chromophores themselves were to act as traps and if they

provided a compensating charge for sensitizer radical anions. Higher trap

densities yield smaller values for the phase shift Φ at high field E0, which

thus also is influenced by the chromophores HOMO energy.


30

All materials exhibit net-gain. The gain coefficients Γ for the series �-��H are

plotted against the external drift-field E0 in Figure 5. The dependence of Γ

on E0 is quadratic and the gain coefficients (and therefore the refractive

index modulations) for s- and p-polarized writing beams have opposite sign.

Both these results are predicted for materials in which the refractive index

modulation is predominantly due to the orientational enhancement effect.23

The gain coefficients span an order of magnitude for the chromophores

investigated, with the highest values observed for DMNPAA and its stilbene

analog ��H. Since index modulations are high in our materials, the main

factor limiting Γ is the phase shift, which in turn is related to the trap

densities and thus to the HOMO energies of the chromophores.

As a final quantity to compare the steady state performance of the

composites, the refractive index modulations ∆n for both s- and p-polarized

reading beams were obtained from the respective diffraction efficiencies in

DFWM experiments. We use the refractive index modulation rather than the

diffraction efficiency for comparison of the chromophores since ∆n is a

quantity that is less dependent on experimental parameters (e.g. sample

thickness). The dependence of ∆n on E0 is quadratic for all composites,

again demonstrating the dominance of the orientational enhancement

effect.72 The index modulations ∆n observed for the tolane composites

(chromophores ��E and ��H) are comparatively small, but this must in part be


31

attributed to their lower chromophore content. The very high ∆np of the

composite with chromophore ��D, which leads to total internal diffraction at

a sample thickness of only 40 µm and a field of ca. 75 V/µm, is presumably

due to the strong dialkylamino donor group which leads to a higher

hyperpolarizability52 and thus to a larger contribution by the Pockels-effect

to the refractive index modulation.

The ratio of contributions from birefringence and Pockels effect to the index

modulation, ABR/AEO (given in Table 6) allow us to evaluate this more

quantitatively.23 These values drop as the donor strength increases, e.g

comparing chromophores ��D and ��H or ��E and ��H. Since ABR/AEO = -1/3

∆α/β µ/kT, we can conclude that an increase in donor strength increases β

significantly more than ∆α·µ for our chromophores. For compound ��H

(DMNPAA), our value of –5.5 for ABR/AEO agrees well with published

results (ABR/AEO = -5.3) on a DMNPAA/PVK composite.73

The characteristic response times the photorefractive grating were

determined by fitting the early decay of the diffraction efficiency to a single

exponential η = η0·exp(-2t/τ) as performed by other groups.39,41,36,74 The

factor two in this equation takes the quadratic dependence of the diffraction

efficiency on the refractive index modulation into account. For the

chromophore series �-��H, the decay times are plotted against the field E0 in

Figure 7. For all chromophores, the decay times decrease with increasing

field strength. For high field strengths (> 40-50 V/µm), this incremental


32

decrease becomes small. Thus, the decay times τ at high field strength are

compiled in Table 6. They are quite similar for the chromophores �-��H, but

significantly longer for the other compounds. The response times are quite

long and the main limiting factor for applications of our composites. It is

therefore important to try and identify the process or processes that limit τ,

which could be any of the processes charge generation, charge transport,

charge trapping and chromophore orientation (As the time required for the

electrooptic response is less than a microsecond, we do not consider it here).

The response time rises as the size of the chromophore increases. However,

experiments in which the rotational mobility of the chromophores was

probed by in-situ measurements of second-harmonic generation (SHG)

showed that larger donor groups do not reduce the speed of orientation.75

Furthermore, Kippelen et al. found that even at a response time of 4 ms,

orientation was not limiting for a tolane-based composite.32 Therefore,

chromophore orientation is not limiting τ for our composites. It is also

unlikely that the time required for charge trapping limits the response times

since they increase with the trap density in our composites (cf. Table 6). On

the other hand, this correlation between trap density and response times may

indicate that charge transport is the limiting process, as the charge carrier

mobility will be decreased by the introduction of deep traps. This reasoning

is supported by the observation that the response times also rises with

increasing dipole moment of the chromophores. As the presence of dipoles


33

in organic photoconductors leads to a broadening of the trap energy

distribution and thus to an increased energetic disorder76 in the model of

Bässler et al.,77 the charge carrier mobility is also decreased. The dipole

moments of the chromophores may be estimated from those of model

compounds with similar substitution given in Table 7.52 For chromophores

�-��H and � E the dipole moment will be quite similar to that of the model

compounds, but it will be higher for compound ��D due to the additional

ester groups.60

To investigate the influence of charge generation and corroborate that of

charge mobility, further experiments using different sensitizers and

photoconductors, respectively, are required. Improving the photoconducting

component has a strong effect on the response time of photorefractive

composites.13,14

&RQFOXVLRQV

To study their structure property relationships, we have synthesized and

characterized a number of new NLO-chromophores specifically designed for

the use in photorefractive composites. Donor substitution and chromophore

type were varied systematically using an efficient synthetic scheme.

The absorption spectra of the chromophores give information on donor

strengths and the tunability of light absorption through structural

modifications. Chromophore melting points and melting enthalpies were


34

greatly lowered by introducing bulky alkyl substituents, which allowed the

preparation of photorefractive composites with long-term stability towards

chromophore recrystallization. These modifications do not compromise

chromophore orientation or tuning of the HOMO levels. By varying donor

strength and chromophore type, the HOMO-energies of the chromophores

can be tuned to cover a range of ±0.5 eV around the HOMO of carbazole-

based photoconducting host polymers. Fluorination of the chromophores38 is

another way of tuning the HOMO energy which we did not explore in this

study. This might constitute an especially promising approach for stilbene

chromophores which showed the highest HOMO energies. The trap density

in the photorefractive composites rises with the HOMO-energies of the

chromophores. It has a significant influence on both the photorefractive

phase shift and the charge mobility, which in turn determines the

holographic response time. Whether photocharge generation also limits the

response times remains to be investigated by variation of the sensitizer.

While the response times require improvement, possibly by use of modified

photoconducting matrix, all chromophores investigated allow for high

refractive index modulations and the formation of polarization gratings can

be inhibited by using chromophores which are not capable of

photoisomerization reactions.


35

(OHFWURQLF� 6XSSOHPHQWDU\� ,QIRUPDWLRQ� DYDLODEOH� Experimental details

for the preparation of all compounds and their spectroscopic

characterization; absorption spectra and normalized DSC-traces for selected

compounds (PDF, 19 pages). This material is available free of charge via the

Internet or from the authors.

$FNQRZOHGJHPHQWV

We thank A. Göpfert and W. Joy for technical assistance and I. Otto for

preparation of the photorefractive samples. We are thankful to Dr.

Mukundan Thelakkat (MC I, University of Bayreuth) for an introduction to

CV measurements and helpful discussions and to Prof. H.-W. Schmidt for

his supportive interest in this work. Financial support by the Bayerische

Forschungsstiftung within FOROPTO II is gratefully acknowledged.

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37

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K. Ewert and C.-D. Eisenbach, -��2SW��6RF��$P��%, 1998, ��, 2560; e) M. S. Bratcher, M.

S. DeClue, A. Grunnet-Jepsen, D. Wright, B. R. Smith, W. E. Moerner and J. S. Siegel,

-��$P��&KHP��6RF�,�1998, ��, 9680; f) M. Döbler, C. Weder, P. Neuenschwander, U. W.

Suter, S. Follonier, C. Bosshard and P. Günter, 0DFURPROHFXOHV, 1998, ��, 6184.

20 a) Y. Zhang, T. Wada, L. Wang and H. Sasabe, &KHP��0DWHU�, 1997, �, 2798; b) C.

Hohle, U. Hofmann, S. Schloter, M. Thelakkat, P. Strohriegl, D. Haarer and S. J. Zilker, -�

0DWHU��&KHP�, 1999, �, 2205; c) K. Ogino, S.-H. Park and H. Sato, $SSO��3K\V��/HWW�, 1999,

��, 3936; d) H. J. Bolink, C. Arts, V. V. Krasnikov, G. G. Malliaras and G. Hadziioannou,

&KHP��0DWHU��1997, �,�1407; e) P. M. Lundquist, R. Wortmann, C. Geletneky, R. J. Twieg,

M. Jurich, V. Y. Lee, C. R. Moylan and D. M. Burland,�6FLHQFH,�1996, ��, 1182; f) O.

Ostroverkhova, D. Wright, U. Gubler, W. E. Moerner, M. He, A. Sastre-Santos and R. J.

Twieg, $GY��)XQFW��0DWHU�, 2002, ��, 621.

21 K. Ewert, S. Schloter, U. Hofmann, K. Hoechstetter, D. Haarer and C. D. Eisenbach,

3URF��63,(, 1998, ��,�134.

22 a) C. Bosshard, K. Sutter, P. Prêtre, J. Hullinger, M. Flörsheimer, P. Kaatz and P. Günter,

2UJDQLF�1RQOLQHDU�2SWLFDO�0DWHULDOV��$GYDQFHV�LQ�1RQOLQHDU�2SWLFV��9RO��; Gordon and

Breach: Amsterdam, 1995; b) J. J. Wolff and R. Wortmann, $GY��3K\V��2UJ��&KHP�, 1999,

��, 121; c) T. Verbiest, S. Houbrechts, M. Kauranen, K. Clays and A. Persoons, -��0DWHU�

&KHP�, 1997, �, 2175.


38

23 W. E. Moerner, S. M. Silence, F. Hache and G. C. Björklund, -��2SW��6RF��$P��%, 1994,

��, 320.

24 R. Wortmann, C. Poga, R. J. Twieg, C. Geletneky, C. R. Moylan, P. M. Lundquist, R. G.

DeVoe, P. M. Cotts, H. Horn, J. E. Rice and D. M. Burland,�-��&KHP��3K\V�,�1996, ��,

10637.

25 B. Kippelen, F. Meyers, N. Peyghambarian and S. R. Marder, -��$P��&KHP��6RF�, 1997,

��, 4559.

26 F. Würthner, S. Yao, T. Debaerdemaeker and R. Wortmann, -��$P��&KHP��6RF�, 2002,

��, 9431.

27 F. Würthner, S. Yao, J. Schilling, R. Wortmann, M. Redi-Abshiro, E. Mecher, F.

Gallego-Gomez and K. Meerholz, -��$P��&KHP��6RF�, 2001, ��, 2810.

28 B. Kippelen, S. R. Marder, E. Hendrickx, J. L. Maldonado, G. Guillernet, B. L. Volodin,

D. D. Steele, Y. Enami, Sandalphon, Y. J. Yao, J. F. Wang, H. Röckel, L. Erskine and N.

Peyghambarian, 6FLHQFH, 1998, ��, 54.

29 S. Beckmann, K.-H. Etzbach, P. Krämer, K. Lukaszuk, R. Matschiner, A. J. Schmidt, P.

Schuhmacher, R. Sens, G. Seybold, R. Wortmann and F. Würthner, $GY��0DWHU�, 1999, ��,

536.

30 F. Würthner, R. Wortmann, and K. Meerholz, &KHP3K\V&KHP, 2002, �, 17.

31 A. M. Cox, R. D. Blackburn, D. P. West, T. A. King, F. A. Wade and D. A. Leigh, $SSO�

3K\V��/HWW., 1996, ��, 2801.

32 J. A. Herlocker, K. B. Ferrio, E. Hendrickx, B. D. Guenther, S. Mery, B. Kippelen and N.

Peyghambarian, $SSO��3K\V��/HWW�, 1999, ��, 2253.

33 C. R. Moylan, R. Wortmann, R. J. Twieg and I. McComb, -��2SW��6RF��$P��%,�1998, ��,

92.

34 S. M. Silence, M. C. J. M. Donckers, C. A. Walsh, D. M. Burland, R. J. Twieg and W. E.

Moerner, $SSO��2SW�, 1994, ��, 2218.


39

35 S. M. Silence, J. C. Scott, J. J. Stankus, W. E.; Moerner, C. R. Moylan, G. C. Bjorklund

and R. J. Twieg, -��3K\V��&KHP�,�1995, ��, 4096.

36 G. G. Malliaras, V. V. Krasnikov, H. J.; Bolink and G. Hadziioannou, $SSO��3K\V��/HWW�,

1995, ��, 1038.

37 A. Grunnet-Jepsen, D. Wright, B. Smith, M. S. Bratcher, M. S. DeClue, J. S. Siegel and

W. E. Moerner, &KHP��3K\V��/HWW�, 1998, ��, 553.

38 E. Hendrickx, Y. Zhang, K. B. Ferrio, J. A. Herlocker, J. Anderson, N. R. Armstrong, E.

A. Mash, A. P. Persoons, N. Peyghambarian and B. Kippelen, -��0DWHU��&KHP�, 1999, �,

2251.

39 S. Schloter, U. Hofmann, P. Strohriegl, H. W. Schmidt and D. Haarer, -��2SW��6RF��$P��%,

1998, ��, 2473.

40 U. Gubler, M. He, D. Wright, Y. Roh, R. J. Twieg and W. E. Moerner, $GY��0DWHU�,

2002, ��, 313.

41 A. Grunnet-Jepsen, C. L. Thompson, R. J. Twieg and W. E. Moerner, $SSO��3K\V��/HWW�,

1997, ��, 1515.

42 D. Wright, M. A. Diaz-Garcia, J. D. Casperson, M. DeClue and W. E. Moerner, $SSO�

3K\V��/HWW�,�1998, ��, 1490.

43 G. A. Mabbott, -��&KHP��(G�, 1983, ��, 697.

44 K. v. Auwers, F. Michaelis, %HU��'WVFK��&KHP��*HV�, 1914, ��, 1275.

45 S. Akiyama, K. Tajima, S. Nakatsuji, K. Nakashima, K. Abiru and M. Watanabe, %XOO�

&KHP��6RF��-SQ�, 1995,��, 2043.

46 P. Strohriegl, 0DNURPRO��&KHP��5DSLG�&RPP�, 1986, �, 771.

47 L. F. Tietze and T. Eicher, 5HDNWLRQHQ�XQG�6\QWKHVHQ�LP�RUJDQLVFK�FKHPLVFKHQ

3UDNWLNXP�XQG�)RUVFKXQJVODERUDWRULXP; Thieme: Stuttgart, 1991.

48 P. Pfeiffer and S. Sergiewskaja, %HU��'W��&KHP��*HV�, 1911, ��, 1107.


40

49 K. Anderle, R. Birenheide, M. Eich and J. H. Wendorff, 0DNU� &KHP��5DSLG�&RPP�,

1989, ��, 477.

50 C. D. Eisenbach, 0DNURPRO��&KHP�, 1978, ��, 2489.

51 C. D. Eisenbach, Ber. Bunsenges. Phys. Chem., 1980, 84, 680.

52 a) L. T. Cheng et al., L.-T. Cbeng, W. Tam, S. H. Stevenson, G. R. Meredith, G. Rikken

and S. R. Marder, -��3K\V��&KHP�, 1991, ��, 10631. b) L.-T. Cbeng, W. Tam, S. R. Marder,

A. E. Stiegman, G. Rikken and C. W. Spangler, -��3K\V��&KHP�, 1991, ��, 10643.53 A. Vilsmeyer, A. Haack, %HU��'WVFK��&KHP��*HV�, 1927, ��, 119.

54 G. Wittig, G. Geissler,�-XVWXV�/LHELJV�$QQ��&KHP�, 1953, ��, 44.

55 A. R. Tatchell, 9RJHO¶V�7H[WERRN�RI�3UDFWLFDO�2UJDQLF�&KHPLVWU\; John Wiley & Sons:

New York, 1989.

56 R. Zentel, D. Jungbauer, R. J. Twieg, D. Y. Yoon and C. G. Willson, 0DNURPRO��&KHP�,

1993, ��, 859.

57 J. Wong, P. Masson and J.-F. Nicoud, 3RO\PHU�%XOO�, 1994, ��, 265.

58 H. Mustroph and J. Epperlein, -��SUDNW��&KHP., 1980, ��, 305.

59 H. Rau in 3KRWRFKURPLVP (Eds.: H. Dürr and H. Bouas-Laurent); Elsevier: Amsterdam,

New York, 1990.

60 This also results from semiempirical quantum mechanical calculations performed using

the MOPAC6 package (AM1 parametrization) of cerius2 by msi.

61 E. Hendrickx, J. F. Wang, J. L. Maldonado, B. L. Volodin, Sandalphon, E. A. Mash, A.

Persoons, B. Kippelen and N. Peyghambarian, 0DFURPROHFXOHV, 1998, ��, 734.

62 K. Meerholz, R. Bittner, Y. De Nardin, C. Bräuchle, E. Hendrickx, B. L. Volodin, B.

Kippelen and N. Peyghambarian, $GY��0DWHU., 1997, �, 1043.

63 M. C. J. M. Donckers, S. M. Silence, C. A. Walsh, F. Hache, D. M. Burland, W. E.

Moerner and R. J. Twieg, 2SW��/HWW�, 1993, ��, 1044;

64 O. Ostroverkhova and K. D. Singer, -��$SSO�3K\V�, 2002, ��, 1727.


41

65 E. Hendrickx, D. Van Steenwinckel, A. Persoons, C. Samyn, D. Beljonne and J.-L.

Brédas, -��&KHP��3K\V�, 2000, ��, 5439.

66 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bässler, M. Porsch and J. Daub,

$GY��0DWHU�, 1995, �, 551.

67 M. Yano, M. Furuichi, K. Sato, D. Shiomi, A. Ichimura, K. Abe, T. Takui and K. Itoh,

6\QWK��0HW�, 1997, ��, 1665.

68 Sandalphon, B. Kippelen, N. Peyghambarian, S. R. Lyon, A.B. Padias and H. K. Hall, Jr.

, 2SW��/HWW�, 1994, ��, 68.

69 K. Sutter and P. Günter, -��2SW��6RF��$P��%, 1990, �, 2274.

70 C. A. Walsh and W. E. Moerner, -��2SW��6RF��$P��%,�1992, �, 1642.

71 C. A. Walsh and W. E. Moerner, -��2SW��6RF��$P��%, 1992, ��, 753.

72 M. Kuzyk, M. in &KDUDFWHUL]DWLRQ�7HFKQLTXHV�DQG�7DEXODWLRQV�IRU�2UJDQLF�1RQOLQHDU

2SWLFDO�0DWHULDOV (Eds: Kuzyk, M.; Dirk, C.), Vol. 60, Marcel Dekker, Inc., New York

��.

73 Sandalphon, B. Kippelen, K. Meerholz and N. Peyghambarian, $SSO��2SW�, 1996, ��,

2346.

74 Y. Zhang, S. Ghosal, M. K. Casstevens and R. Burzynski, 3RO\PHU�3UHSU�, 1994, ��, 233.

75 K. Hoechstetter, S. Schloter, U. Hofmann and D. Haarer, -��&KHP��3K\V�, 1999, ��,

4944.

76 P. M. Borsenberger and J. J. Fitzgerald, -��3K\V��&KHP� 1993, ��, 4815.

77 H. Bässler, 3K\V��6WDW��6RO��%, 1981, ��, 9.


42

7DEOHV

7DEOH�� 6WUXFWXUHV�DQG�QXPEHULQJ�RI�WKH�GRQRU�DFFHSWRU�FKURPRSKRUHV�

N

O

OO

O

N N N O N

← Donor part a)

Acceptor part a) ↓

��D ��E ��F ��G ��H c) �b)N NO2N

��D ��E ��F ��G ��H ��I d) CH NO2HC

��D ��E �b) �b) ��H ��I e) C NO2C

��D ��E ��F ��G ��H �b) CNCN

a) The curved line represents the single bond to the acceptor/donor part, respectively.b) Chromophore not prepared. c) commonly denominated DMNPAA. d) commonly denominated

DANS. e) commonly denominated DANT.


43

7DEOH�� /RQJHVW�ZDYHOHQJWK� DEVRUSWLRQ�PD[LPD�RI� WKH�GRQRU�DFFHSWRU� W\SH� FKURPRSKRUHV

LQ�7+)�VROXWLRQ��)RU�WKH�VWUXFWXUHV�RI�WKH�FKURPRSKRUHV�FI��7DEOH��

λPD[ / nm (ε / M-1cm-1)

Acceptor

Donor Nitrophenyl-azo(�)

Nitrostilbene(�)

Nitrotolane(�)

Dicyanovinyl-phenyl(�)

D 461 (3.13 × 104) 428 (3.05 × 104) 399 (2.39 × 104) 420 (4.24 × 104)

E 477 (2.84 × 104) 443 (2.91 × 104) 416 (2.23 × 104) 431 (5.16 × 104)

F 461 (2.63 × 104) 434 (2.71 × 104) - 425 (4.25 × 104)

G 429 (2.08 × 104) 397 (2.08 × 104) - 419 (2.34 × 104)

H 397 (2.36 × 104) a) 385 (2.18 × 104) 354 (2.22 × 104) 371 (2.70 × 104)

I 475 (3.16 × 104) d) 433 (2.93 × 104) b) 409 (2.49 × 104) c) -

a) chromophore commonly denominated DMNPAA. b) chromophore commonly denominated

DANS. c) chromophore commonly denominated DANT. d) From reference 29.


44

7DEOH�� +202�� DQG� /802�HQHUJLHV� RI� WKH� FKURPRSKRUHV� DV� GHWHUPLQHG� E\� F\FOLF

YROWDPPHWU\�� 7KH� OHWWHUV� µL¶� DQG� µU¶� LQGLFDWH� LUUHYHUVLEOH� DQG� UHYHUVLEOH� UHDFWLRQ�

UHVSHFWLYHO\��)RU�WKH�VWUXFWXUHV�RI�WKH�FKURPRSKRUHV�FI��7DEOH��

E / eVHOMO (LUMO)

Azo-Type (�) Stilbene-Type (�) Tolane-Type (�) Dicyanovinylben-zene-Type (�)

D -5.55 r (-3.36 r) -5.18 i (-3.12 r) -5.41 i (-3.20 r) -5.65 r (-2.90 i)

E -5.39 r (-3.31 r) -5.05 i (-3.13 r) -5.30 i (-3.17 r) -5.53 r (-2.87 i)

F -5.43 i (-3.33 r) -5.07 i (-3.12 r) b) -5.60 i (-2.91 i)

G -5.36 r (-3.34 r) -5.09 i (-3.15 r) b) -5.46 ic) (-3.08 i)

H -5.99a) i (-3.37 r) -5.62 i (-3.15 r) -5.87a) i (-3.21 r) -6.21a) i (-2.99 i)

a) measured in 1,2-propylene carbonate. b) chromophore not synthesized. c) irrev. at 20 mV/s.


45

7DEOH�� +202�HQHUJLHV�RI�FDUED]ROH�GHULYDWLYHV�DV�GHWHUPLQHG�E\�F\FOLF�YROWDPPHWU\�

Compound E / eVHOMO

E / eVHOMO Dimer

Scan rate/ mVs-1

Ethylcarbazole -5.59 -5.22 50

PVK -5.56…-5.61a) - 50

D4-4CZ -5.62 -5.26 50

a) estimated as described in the text.


46

7DEOH�� 0HOWLQJ� SRLQWV� �SHDN� RQVHW�� DQG� PHOWLQJ� HQWKDOSLHV� RI� WKH� GRQRU�DFFHSWRU� W\SH

FKURPRSKRUHV�DV�GHWHUPLQHG�E\�'6&��7KH�VWUXFWXUHV�RI�WKH�FKURPRSKRUHV�DUH�JLYHQ

LQ�7DEOH��

ΤPHOW / °C (∆+PHOW�/ J g-1)

Acceptor

Donor Nitrophenyl-azo(�)

Nitrostilbene(�)

Nitrotolane(�)

Dicyanovinyl-phenyl(�)

D 114 (50.1) 84 (51.5) 95 (54.7) 101 (86.7)

E 96 (103.0) 119 (71.2) 88 (96.6) 53 (69.4)

F 120 (98.6) 156 (90.4) 109 (149.6)

G 114 (92.0) 92 (87.3) 148 (150.9)

H 164 (124.4) a) 125 (93.1) 137 (109.2) 178 (166.9)

I - 250 (subl.) b), c) 220 b), d) -

a) chromophore commonly denominated DMNPAA. b) Determined using a Kofler hot stage. c)

chromophore commonly denominated DANS. d) chromophore commonly denominated DANT.

PR

IVIL

EG

ED

DO

CU

ME

NT

FO

R R

EV

IEW

PU

RP

OS

ES

ON

LY

47

7DE

OH��

3K\

VLFDO�FKDUDFWHUL]DWLRQ

�RI�SK

RWRUHIUDFWLYH�FRPSR

VLWHV�SU

HSDUHG

�IURP�7

1)��36;

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FWXU

H�JLYHQ�LQ�)

LJ��

��DQ

G�VHOHFWHG�FKURP

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UHV��IRU�VWUXFWXUHV�FI�

7DE

OH��/LVWHG�DUH�WKH�FRPSR

VLWLRQ

�RI�WKH�VDPSOHV��WKH

LU�VKH

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ODVV�WUDQVLWLRQ�WHPSH

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J

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RWRUHIUDFWLYH�JD

LQ�Γ�IRU�V��DQ

G�S�

SRODUL]HG�OLJ

KW�DV�ZHOO�D

V�KR

ORJUDS

KLF�ULVH�WLP

HV�τ��J

UDWLQJ

�SKD

VH�VKLIW�Φ

��HIIHFWLYH�WUDS�GH

QVLW\�1

HII

��UHIUDFWLYH�LQGH[�PRG

XODWLRQ�IRU�V��DQG

�S�SRODUL]HG�EHDPV�

∆QV

DQG�

∆QS

��UHIUDFWLYH�LQGH[�PRG

XODWLRQ�GX

H�WR�WKH

�SRODUL]DWLRQ�JUDWLQJ�

∆QSRODUL]�

�DQG

�WKH

�UDWLR�RI�FRQWULEX

WLRQ

V�WR�WKH�UHIUDFWLYH�LQGH[�PRG

XODWLRQ�E\

�ELUHIULQJ

HQFH

�$%5

��DQ

G�3RFNHOV�HIIHFW��$

(2

��$

%5

��$

(2

��

Chr

omo-

phor

eC

ompo

sitio

nPS

X:C

hrom

:TN

FSh

elf

lifet

ime

of s

ampl

esT

g / °

CG

ain

Γ p (

Γ s)

/ cm

-1τ

/ sΦ

/ °

(Nef

f / 1

017 c

m-3

)∆n

p (∆

n s)

/ 10-3

∆npo

lari

z.

/ 10-5

AB

R /

AE

O

��D

49:5

0:1

> 1

yea

ra)26

.7

��D

51:4

8:1

> 1

yea

ra)26

.5-5

3 (7

)60

4 ±

2 (4

± 2)

-10.

5 (1

.7)

-1-2

.2 ±

0.6

��D

56:4

2:2

> 1

yea

ra)22

.5

��E

78:2

1:1

> 1

yea

ra)25

.4-2

3 (6

)40

11 ±

4 (

1.4 ±

0.5

)-2

.3 (

0.7)

--4

.2 ±

0.7

��H

53:4

6:1

2-4

wee

ks23

.7-2

21 (

56)

430

± 3

(0.

4 ± 0

.1)

-5.8

(1.

8)-1

0-5

.5 ±

1.0

��H

52:4

7:1

ca. 8

wee

ks24

.0-1

19 (

33)

614

± 3

(0.

9 ± 0

.2)

-5.9

(1.

7)-0

.5-5

.1 ±

1.3

��H

78:2

1:1

> 1

yea

ra)23

.2-5

6 (1

6)7

11 ±

3 (

1.1 ±

0.3

)-2

.9 (

0.9)

--6

.2 ±

1.1

��H

68:3

1:1

> 1

yea

ra)25

.2

a) N

o cr

ysta

lliza

tion

obse

rved

to d

ate

(afte

r ≥

20 m

onth

s).


49

7DEOH�� 'LSROH�PRPHQWV�RI�'013$$��H��DQG�PRGHO�FRPSRXQGV��

Chromophore Solvent µ /

10-18 esu

NO2N

��I

CHCl3 6.6

NO2N

��I

CHCl3 6.1

NN

OO2N

��H

CHCl3 5.5

OO2N

1,4-dioxane 4.5

OO2N1,4-dioxane 4.4


50

)LJXUH�DQG�VFKHPH�FDSWLRQV

6FKHPH�� 6\QWKHVLV�RI� WKH�D]R�� VWLOEHQH��DQG�GLF\DQRYLQ\OEHQ]HQH�

FKURPRSKRUHV�� D��2�1�3K�&+

��33K

�

�� %U�� 1D+�� '062�

E��2�1�3K�&+

��&2

�+��SLSHULGLQH�

6FKHPH�� 6\QWKHVLV� RI� WKH� WRODQH�FKURPRSKRUHV� E\� +HFN�W\SH

FRXSOLQJ�UHDFWLRQV�

)LJXUH�� 6WHULFDO� LQWHUDFWLRQV� RI� WKH� GLF\DQRYLQ\O� DFFHSWRU�JURXS

ZLWK�ULQJ�K\GURJHQ�DWRPV�

)LJXUH�� 7\SLFDO� F\FOLF� YROWDPPRJUDPV� REWDLQHG� IRU� WKH

FKURPRSKRUHV� LQ� 7+)� VROXWLRQ�� D�� 2[LGDWLRQ� RI

FKURPRSKRUH� ��G�� 7KH� LUUHYHUVLELOLW\� RI� WKH� SURFHVV� LV

HYLGHQW� IURP� ODFN�RI� D� UHGXFWLRQ� SHDN� IRU� WKH� JHQHUDWHG

UDGLFDO� FDWLRQ�� E�� 5HGXFWLRQ� RI� FKURPRSKRUH� ��H�� 7KH

UHGXFWLRQ��SURFHVV�LV�UHYHUVLEOH�DV� MXGJHG� �E\�KHLJKW�DQG

SRVLWLRQ� RI� WKH� R[LGDWLRQ� SHDN� IRU� WKH� JHQHUDWHG� UDGLFDO

DQLRQ�� 7KH� VWUXFWXUHV� RI� WKH� FKURPRSKRUHV� DUH� JLYHQ� LQ

7DEOH��


51

)LJXUH�� 6WUXFWXUHV� RI� WKH� KROH� WUDQVSRUWLQJ� SRO\PHUV� SRO\�1�

YLQ\OFDUED]ROH�� 39.�� SRO\�PHWK\O��

FDUED]RO\O�SURS\O��VLOR[DQH��36;��WKH�PRGHO�FRPSRXQGV

HWK\OFDUED]ROH� DQG� ��WHWUDPHWK\O��WHWUDNLV��

��FDUED]RO\O�SURS\O��F\FORWHWUDVLOR[DQH� �'��&=�� DQG

WKH�VHQVLWL]HU��WULQLWURIOXRUHQRQH��71)��

)LJXUH�� &\FOLF� YROWDPPRJUDPV� RI� D�� HWK\OFDUED]ROH� �ZLWKRXW

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53

6FKHPHV

D R

R N N

NO2

��E�G

G R = Me, D = NMe2

H R = Me, D = OMe

D�� R = H, D =

NMe

NMe

E R = H, D =

F R = H, D =

NO2

N2+ Cl

-

NO

O 2

HC(O)NMePh

POCl3

NC CN

piperidinea) or b)

NOHOH

NHNH2

NaH , BrR’

( KI )

D

R

R

��D�H

D

O

R

R

H

��D�H

D

CN

CN

R

R

��D�H

D R

R

NO2

��D�H

Et3N

PivCl,Me2SO4

6FKHPH��

K. Ewert et al.


54

NO2

Br

2. KOH, MeOH

1. (Ph3P)2PdCl2 , CuI

Et2NH

I2 , base

SiMe3

H

+

(Ph3P)2PdCl2 , CuI

Et2NH

NO2

H

�

I

D

R

R

��D�E�H

D

NO2

R

R

��D�E�H

D

R

R

��D�E�H

H

R = Me,

D = OMeN

MeE

R = H,

D = N

O

O

O

O

D

R = H,

D =

6FKHPH��

K. Ewert et al.


55

)LJXUHV

D

HN

N

)LJXUH��

K. Ewert et al.


56

0 100 200 300 400 500 600 700 800

10 µA

E vs. reference electrode / mV

-1400 -1200 -1000 -800 -600 -400 -200 0

10 µA


D�

E�

)LJXUH��

K. Ewert et al.


57

O

NO2

NO2

O2N

TNF

nO Si

(CH2)3

N

Me

PSX

4O Si

(CH2)3

N

Me

D4-4CZ

n

N N

EthylcarbazolePVK

)LJXUH��

K. Ewert et al.


58

D�

E�

-400 -200 0 200 400 600 800 1000 1200

second cycle

first cycle5 µA


-400 -200 0 200 400 600 800 1000 1200

second cycle

first cycle10 µA


)LJXUH��

K. Ewert et al.


59

(56:43:1)

(52:47:1)

(68:31:1)

E / V/ mµ

Γ / c

m-1

Γ / c

m-1

Γ / c

m-1

0

)LJXUH��

K. Ewert et al.


60

E / V/ mµ0

Φ /

degr

eep

Φ /

degr

eep

Φ /

degr

eep

PSX:4e:TNF (56:43:1)

PSX:5e:TNF (52:47:1)

PSX:6e:TNF (68:31:1)

)LJXUH��

K. Ewert et al.


61

PSX:4e:TNF(56:43:1)

PSX:5e:TNF(52:47:1)

PSX:6e:TNF(68:31:1)

E / V/ mµ

τ /

s

0

)LJXUH��

K. Ewert et al.

UHODWLRQVKLSV - UCSBresearch.mrl.ucsb.edu/~ewert/articles/pccp_model_chromophores.pdfmaterials,...

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