Abstract Larisa En

Faculty of Chemistry and Chemical Engineering

“Babes-Bolyai” University

M. Kogălniceanu 1, 400082

Cluj-Napoca, Romania

Larisa-Natalia POPA (MĂTĂRÂNGĂ-POPA)

NOVEL PRECURSORS FOR CHARGE-TRANSPORT MATERIALS

BASED ON PHENOTHIAZINE DERIVATIVES

- ABSTRACT –

Scientific Advisors:

Prof. Dr. LuminiŃa SILAGHI-DUMITRESCU

Prof. Dr. Ioan A. SILBERG

- Cluj-Napoca 2009 -

PhD Abstract Thesis – Larisa Natalia Popa (c. Mataranga-Popa)

- 2 - 2

Faculty of Chemistry and Chemical Engineering

“Babes-Bolyai” University

M. Kogălniceanu 1, 400082

Cluj-Napoca, Romania

Larisa-Natalia POPA (MĂTĂRÂNGĂ-POPA)

- Phd Abstract Thesis -

Jury

President

Prof. Dr. Ion Grosu, “Babeş-Bolyai” University, Cluj-Napoca, Romania

Reviewers

Prof. Dr. Ionel Mangalagiu, “Al. I. Cuza” University, Iasi, Romania

Assoc. Prof. Dr. Castelia Cristea, “Babeş-Bolyai” University, Cluj-Napoca, Romania

Assoc. Prof. Dr.Antal Csampai, „ ELTE” University, Budapesta, Hungary

Scientific Advisors

Prof. Dr. LuminiŃa Silaghi-Dumitrescu, “Babeş-Bolyai” University, Cluj-Napoca,

Romania

Prof. Dr. Ioan A. Silberg, “Babeş-Bolyai” University, Cluj-Napoca, Romania

Defence: 7th of October 2009


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Table of contents

1. Introduction…………………………………………………………………………….. 6

2. General presentation of the phenothiazines ….…………………………………. 9

2.1 Generalities about the synthesis and the reactivity of phenothiazines….. 10

3. ORIGINAL CONTRIBUTIONS 17

3.1 Cyano(oligo)phenothiazines ………………………...…………………….. 18

3.1.1 Literature data on the aromatic nitriles……………………………. 18

3.1.2 Literature data on the oligophenothiazines………………………. 20

3.1.3 Synthesis and electronic properties of cyano (oligo)phenothiazines..... 24

3.2 Aminomethylene(oligo)phenothiazines……………………………………….. 39

3.2.1 Literature data on the mesoporous silicas……………………….. 39

3.2.2 Synthesis and electronic properties of aminomethylen

(oligo)phenothiazines………………………………………………..

39

3.3 Diphenothiazine dumbbells bridged by heterocycles……………………... 45

3.3.1 Literature data on the N, N- aryl substituted phenothiazines…... 45

3.3.2 Synthesis and electronic properties of diphenothiazine dumbbells

bridged by heterocycles………………………………..

48

3.4 Photoactive binaphthyl phenothiazine derivatives…………………………. 66

3.4.1 Literature data on the binaphthyl derivatives…………………….. 66

3.4.2 Synthesis of photoactive binaphthyl phenothiazine derivatives... 70

3.5 Phenothiazine Tröger Base derivatives………………………………………. 75

3.5.1 Literature data on the Tröger Base derivatives………………….. 75

3.5.2 The syntheses and electronic properties of phenothiazine Tröger

Base derivatives……………………………………………

76

4. Experimental part………………………………………………………...................... 84

4.1. General considerations………………………………………………………. 85

4.2. Syntheses of the precursors…………………………………………………. 86

4.2.1 Syntheses of N-Alkylphenothiazine……………………………….. 86

4.2.1.1 Synthesis of N-Methylphenothiazine (1)………………... 87

4.2.1.2 Synthesis of N-Hexylphenothiazine (2)…………………. 87


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4.2.2 Synthesis of bromophenothiazine derivatives…………………… 88

4.2.2.1 Synthesis of3-Bromo-10-methyl-10H-phenothiazine(4). 88

4.2.2.2 Synthesis 3-Bromo-10-hexyl-10H-phenothiazine (5)..... 89

4.2.2.3 Synthesis of 3,7´´-Dibromo-10,10´,10´´-trihexyl

10H,10´H,10´´H- [3´,7;7´,3´´]terphenothiazine (10)......

90

4.2.3 Synthesis of 10-Hexyl-3-(4,4,5,5-tetrametyl-1,3,2-dioxaborolan-2-

yl)-10H-phenothiazine (39)...............................

91

4.2.4 Synthesis of 3-bromo-10,10´´-dihexyl-10H,10´ H-[3,3´]

bisphenothiazine (7)...................................................................

92

4.2.5 Synthesis of 2,5- Dibromofurane (24)…………………………….. 93

4.2.6 Synthesis of 3,6 - Dibromo-9,9-dihexyl-9H-fluorene (28)............ 93

4.2.7 Synthesis of (RS)-N,N’-diacetyl-1,1’-binaphthalene-2,2’

diamine (40)…………………………………………………………

94

4.2.8 Synthesis of (RS)-N,N’-Diacetyl-6,6’-dibromo-1,1’ binaphthalene-

2,2’-diamine (41)………………………………….

94

4.2.9 Synthesis of (RS)-6,6’-Dibromo-1,1’-binaphthalene-2,2’-

diamine (42)………………………………………………………….

95

4.2.10 Synthesis of (R,S) 6,6’-Dibromo-1,1’-binaphthalene-2,2’-

dicarbonitrile (43).......................................................................

95

4.2.11 Synthesis of (R)-1,1’-Binaphthyl-2,2’-dimethyl ether(42)……… 96

4.2.12 Synthesis of (R) 6,6′-Dibromo-2,2′-dimethoxy-1,1′-binaphthyl

(43)…………………………………………………………………….

96

4.3 Syntheses of the (oligo)phenothiazinyl nitriles 11 – 18……………………. 97

4.3.1 Synthesis of 3-Cyano-10-methyl-10H-phenothiazine (11)……… 103

4.3.2 Synthesis of 3-Cyano-10-hexyl-10H-phenothiazine (12)……….. 103

4.3.3 Synthesis of 3,7-Dicyano-10-hexyl-10H-phenothiazine (13)…… 104

4.3.4 Synthesis of 3-Cyano-10,10´-dihexyl-10H,10´H-3´,7-

bisphenothiazine (14)……………………………………………… 105

4.3.5 Synthesis of 3,7´-Dicyano-10,10´-dihexyl-10H,10´H-3´,7-

bisphenothiazine (15)………………………………………………

106

4.3.6 Synthesis of 3-Cyano-10,10´,10´´-trihexyl-10H,10´H,10´´H-[3´,7;


- 5 - 5

7´,3´´]terphenothiazine (17)………………………………... 106

4.3.7 Synthesis of 3,7´´-Dicyano-10,10´,10´´-trihexyl 10H,10´H,10´´H-

[3´,7; 7´,3´´]terphenothiazine (18)……………..

107

4.4 Synthesis of aminomethylen (oligo)phenothiazines 19 – 25……………… 108

4.4.1 Synthesis of 10-Methyl-10H-phenothiazine- 3-methylenamine

(19)…………………………………………………………………….

109

4.4.2 Synthesis of 10-Hexyl-10H-phenothiazine- 3-methylenamine

(20)…………………………………………………………………….

109

4.4.3 Synthesis of 10-Hexyl-10H-phenothiazine- 3,7

dimethylenamine (21)………………………………………………

110

4.4.4 Synthesis of 10,10´-Dihexyl-10H,10´H-3´,7-bisphenothiazine-3-

methylenamine (22)……………………………………………...

110

4.4.5 Synthesis of 10,10’-diheyl-10H, 10H’-3,3’-biphenothiazine-7,7’-

diyl dimethylenamine (23)…………………………………….

111

4.5 Synthesis of new phenothiaizine dyads 30, 31, 32, 33, 34, 35 and 37….. 112

4.5.1 Synthesis of10, 10’-Biphenothiazinyl-2,5-furane (30)…………… 114

4.5.2 Synthesis of 10, 10’-Biphenothiazinyl-3,6-pyridazine (31)……… 114

4.5.3 Synthesis of 10, 10’-Biphenothiazinyl-2,5-pyridine (32)………… 115

4.5.4 Synthesis of 10, 10’-Biphenothiazinyl-2,6-pyridine (33)………… 115

4.5.5 Synthesis of 3,6-[10,10’]Biphenothiazinil-9,9-dihexyl-9H- fluorene

(34)………………………………………………………...

116

4.5.6 Synthesis of 10, 10’-Biphenothiazinyl-2,5-thiophene (35)……… 117

4.5.7 Synthesis of 10-Acenaphtalen-5yl-10H-phenothiazine (37)……. 117

4.6 Synthesis of (R,S) 6,6’-Bis-(N-hexylphenothiazin-3-yl)-1,1’-binaphthalene -

2,2’-dicarbonitrile (44)………………………………………

118

4.7 Synthesis of (R,S) 2,2’ –Bis (N-hexylphenothiazin-3-yl) 1,1’-binaphthalene

(45)………………………………………………………….

119

4.8 Syntheses of 2-aminophenothiazines……………………………………… 119

4.8.1 Synthesis of 10H-phenothiazine- 2-amine (50)………………… 120

4.8.2 Synthesis of 10- Methyl-10H-phenothiazine- 2-amine (51)…… 120

4.9 Syntheses of phenothiazines Tröger’s Bases…………………………….. 121


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4.9.1 Synthesis of 6H, 2H-tetrahydro-10’H, 10’’H-phenothiazinyl-[1,5]

diazocine (52)…………………………………………………

121

4.9.2 Synthesis of 6H, 2H-tetrahydro-10’Me, 10’’Me-phenothiazinyl

-[1,5]diazocine (53)…………………………………………………

122

5. General conclusions………………………………………………………………….. 123

6. References……………………………………………………………………………… 127

Appendix (A)………………………………………………………………........................... 139

A.1 Abbreviations…………………………………..…………………………….... 140

A.1.1. General abbreviations……………………………………………. 140

A1.2 Abbreviations for groups and substituents………………. 141

A1.3 Abbreviations for NMR, IR and mass spectra…………... 141

A.2 Crystal data and structural refinement……………………………………… 143

A2.1 Data for 2,5-Di(10H-phenothiazin-10-yl)thiophen 35.........…… 143

A2.2 Data for 3,6-[10,10’]Biphenothiazinil-9,9-dihexyl-9H-fluorene

34……………………………………………………………………

144

A.3 Coordinates of 10, 10’-Biphenothiazinyl-3,6-pyridazine 31 and

10,10’-Biphenothiazinyl-2,5-thiophene from molecular modelling 35…...

145

A 3.1 Cartezian coordinates (B3LYP/6-31+G(d,p)) of 31……………. 145

A 3.2 Cartezian coordinates (B3LYP/6-31+G(d,p)) of 35……………. 146

A.4 List of the synthesized compounds…………………………………………. 149

List of scientific communications………………………………………………………...

152

Keywords: Phenothiazine, nitrilephenothiazine, dumbbell-shaped diphenothiazines,

binapthyl-phenothiazine, Tröger’s base, palladium, fluorescence, cyclic votammetry.


- 7 - 7

1. Introduction

The chemistry of phenothiazine derivatives is a long-standing and continuously

active field, inspired in part by their application in medicine and these derivatives have

become important spectroscopic probes in molecular and supramolecular arrangements.

The main purpose of this work is to obtain phenothiazine precursors for novel

charge-transport materials.

The original results for the synthesis and characterisation of new phenothiazine

derivatives with different subtituentes like nitriles, amines, heterocycles, their reactivity

and potential application in materials science are presented.

We have synthesized the 3-cyano and 3,7-dicyano (oligo)phenothiazines, which

were obtained in good to very good yields from bromo (oligo)phenothiazines via the

Beller cyanation protocol either under conductive or under dielectric heating using NMP

as a solvent. These cyano(oligo)phenothiazines display large Stokes-shifts (5800–8300

cm-1

) and substantial quantum yields (11–27%).

Dumbbell-shaped diphenothiazines with heterocyclic bridges display tunable

redox and in some cases, fluorescence properties. New phenothiazine dyads were

synthesized in good to very good yields using the Buchwald-Hartwig amination of

phenothiazine with different dibromo aromatic heterocycles: electron-deficient units such

as pyridine, pyridazine and electron-rich units like thiophene, furane, fluorene. The

symmetrical dumbbell-shaped phenothiazine dyads bridged by heterocycles show intense

electronic coupling between the redox-active phenothiazine moieties. The fluorescence of

the pyridyl-bridged derivatives can be controlled by pH change giving reversibly

switchable redox-active bielectrophore dyads.

The preparation of new phenothiazin - binaphthalene derivatives following a

rational synthetic approach based on Suzuki or Negishi arylation of suitable precursors, is

discussed. These compounds are candidates for new molecular materials with potentially

efficient photoinduced electron transfer properties due the low-oxidation potential and

high tendency to form stable radical cations of the phenothiazine units.

The first synthesis of innovative phenothiazine Tröger’s base derivatives was

prepared and their conformations are proposed and has been investigated using DFT


- 8 - 8

calculations. These derivatives present remarkable Stokes-shifts (6900-7400cm -1

) and

substantial quantum yields (29 - 40%).

3. ORIGINAL CONTRIBUTION

3.1 Synthesis and electronic properties of cyano(oligo)phenothiazines

Due to their rich transformation potential and with regard to grafting and fine-

tuning of electronic properties we have focussed on cyano(oligo)phenothiazines.

Cyanophenothiazines are usually prepared either by de novo synthesis of the phenothiazinyl

core or by elimination from amides or oximes1.

(Oligo)phenothiazinyl nitriles were synthesized in good to very good yields from

bromo (oligo)phenothiazines via the Beller cyanation protocol either under conductive or

under dielectric heating using NMP as a solvent (Scheme 1).

N

S Br

nhexyl

H

n

N

S CNH

n

K4[Fe(CN6)], Na2CO3

[Pd(OAc)2, dppf], NMP120 °C, 20 h

orMW (160 °C), 1 h

N

S Br

nhexyl

Br

n

N

S CN

nhexyl

NC

n

nhexyl

5: n = 1 7: n = 210: n = 3

K4[Fe(CN6)], Na2CO3

[Pd(OAc)2, dppf], NMP120 °C, 20 h

orMW (160 °C), 1 h

12: n = 1 14: n = 2 17: n = 3 11-82%

7: n = 1 8: n = 210: n = 3

13: n = 1 15: n = 2 18: n = 3 35-86%

Scheme 1. Synthesis of cyano(oligo)phenothiazines 11 - 18

The structures of the (oligo)phenothiazinyl nitriles 11-18 are unambiguously supported

by 1H and

13C NMR spectroscopy and mass spectrometry and correct combustion

analysis. All the nitrile derivatives show in carbon-nuclear magnetic resonance spectrum

1 a) Vowinkel, E.; Bartel, J. Chem. Ber. 1974, 107, 1221; b) Burger, A.; Schmalz, C. J.

Org. Chem. 1954, 19, 1841; c) Cauquil, G.; Casadevall, A. Bull. Soc. Chim. Fr.

1955, 1061; d) Abramov, I. G.; Zhandarev, V. V.; Smirnov, A. V.; Kalandadze, L. S.;

Goshin, M. E.; Plakhtinskii, V. V. Mendeleev Commun. 2002, 3, 120.


- 9 - 9

the characteristic signal for the carbon atom from CN group in δ = 105-110 ppm region

(Figure 1). In the case of bisnitrilephenothiazine derivatives NMR spectra show the Cs

symmetry which becomes clear by half number of signals. In the IR spectra the absobtion

due to the vibration of CN group appears at 2220-2250 cm-1

, which reveal the typically

absorptions for phenothiazinnitrile derivatives.

Figure 1. The 1H NMR (500 MHz) and

13C NMR (125 MHz) of 12 in CD2Cl2

Their electronic properties (Table 3) were determined by absorption and emission

spectroscopy and cyclic voltammetry. All compounds display intense blue to greenish-

blue daylight fluorescence with fluorescence quantum yields between 11 and 27 % and

remarkable Stokes shifts (5800-8300 cm-1

). These substantial Stokes shifts can be

attributed to significant geometrical changes upon excitation from a highly non-planar

ground-state to a largely planarized excited state2. According to absorption and emission

spectra the effective conjugation length is already reached with two conjugatively linked

phenothiazinyl units. In particular, the emission data can be attributed to the presence of a

3-cyano phenothiazinyl moiety (17) which seems to be the dominant fluorophore.

2 L. Yang, J.-K. Feng, A-M Ren, J. Org. Chem. 2005, 70, 5987–5996.


- 10 - 10

Table 1. Electronic properties of the cyano (oligo)phenothiazines 11-18.

Compound

Absorption

λmax,abs

[nm][a]

Emission

λmax,em

[nm][a]

Quantum

yield

[%][b]

Stokes

shift

(cm-1

)

E00/+1

[mV] [c]

E0+1/+2

[mV]

E0+2/+3

[mV]

11 267, 336 475, 505

(sh) - 8600 - - -

12 268, 340 474, 491

(sh.) 11 8300 952 - -

13 277, 335,

366

479, 507

(sh.) 19 6400 1179 - -

14 279, 324,

375

481, 507

(sh.) 25 5800 711 1040 -

15 281, 333,

376

481, 510

(sh.) 18 5900 936 1098 -

17 282, 328,

376

474, 491

(sh.) 27 5800 631 781 1012

18 281, 333,

377

474, 491

(sh.) 22 5800 656 981 1030

[a] Recorded in CH2Cl2 [b] Determined with coumarine 1 as standard. [c] Recorded in

CH2Cl2, 20 °C, v = 100 mV/s, electrolyte: nBu4N

+ PF6

-, Pt working electrode, Pt counter

electrode, Ag/AgCl reference electrode.


- 11 - 11

3.2 Synthesis and electronic properties of aminomethylene(oligo)phenothiazines

Since the discovery of mesoporous silicas in 19923,4

,

research on these materials

has rapidly developed. They can be readily obtained by micellar condensation of silicic

acid derivatives.

Our goal was to synthesize new molecules which contain both 10H-phenothiazine

and triethoxysilyl units for adsorption on silica surfaces. In this way, functionalized silica

surfaces which exhibit phenothiazine properties (fluorescence, redox activity, etc.) can be

obtained. The cyanophenothiazines 11, 12, 13 and 14 were reduced to the corresponding

amines 19, 20, 21 and 22 with LiAlH4 in diethyl ether (Scheme 2). Unfortunately, we

didn’t succeed to reduce the dicyano dyads, monocyano and dicyano triads because of the

low solubility of these compounds in diethyl ether, THF and toluene. In order to reduce

the dicyanophenothiazynil dyad we have tried to used the tetra-n-

butylamoniumborohydrid5 as reducing agent in CH2Cl2 (Scheme 2). This procedure

afforded the corresponding amino derivatives in 83% yields.

N

S

R

N

S

R

CNXNH2Y

LiAlH4, Et2Oreflux

or

Bu4NBH4

CH2Cl2, ref lux

n n

11 : n =1, R = Me, X = H12 : n =1, R = Hex, X = H13 : n =1, R = Hex, X = CN14 : n =2, R = Hex, X = H15 : n =2, R = Hex, Y = CN

19 : n =1, R = Me, Y = H

20 : n =1, R = Hex, Y = H

21 : n =1, R = Hex, Y = CH2NH2

22 : n =2, R = Hex, Y = H

23 : n =2, R = Hex, Y = CH2NH2

40-92%

Scheme 2. Synthesis of amino(oligo)phenothiazines.

The structures of the (oligo)phenothiazinyl methylen amines 19-23 are

unambiguously supported by 1H and

13C NMR spectroscopy and mass spectrometry and

correct combustion analysis.

3 a) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature

(London, U.K.) 1992, 359, 710; b) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M.

E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W.;

McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834. 4 a) Soler-Illia, G. J. de A. A.; Sanchez, C.; Lebeau, B.; Patarin, J. Chem. ReV. 2002, 102,

4093; b) Widenmeyer, M.; Anwander, R. Chem. Mater. 2002, 14, 1827. 5 T. Wakamatsu, H. Inaki, A. Ogawa, M. Watanabe, Y. Ban, Heterocycles 1980, 14 (10),

1437


- 12 - 12

The electronic properties of the (oligo)phenothiazine amines 19 - 23 were investigated

by absorption and emission spectroscopy and cyclic voltammetry (table 2). Furthermore,

the fluorescence quantum yield of 22 was determined with coumarine 1 as standard.

Table 2. Electronic properties of the amino (oligo)phenothiazines 19 - 23.

PT

Absorption

λmax,absnma

Emission

λmax,em [nm][a]

Quantum

yield[%][b]

E00/+1

[mV] [c]

E0+1/+2

[mV]

Stokes-

Shifts

(cm-1

)

19 260, 286 - - 701 - -

20 260, 314 - - 743 - -

21 260, 316 479, 507 (sh) - 739 - 11700

22 270, 325, 284 460, 485 (sh.) 13 634 853 9030

23 288, 237, 370d 470, 504 (sh)

d - 628 845 5700

[a] Recorded in CH2Cl2 [b] Determined with coumarine 1 as standard. [c] Recorded in

CH2Cl2, 20 °C, v = 100 mV/s, electrolyte: nBu4N

+ PF6

-, Pt working electrode, Pt counter

electrode, Ag/AgCl reference electrode [d] Recorded in DMSO

3.3 Synthesis and electronic properties of diphenothiazine dumbbells bridged by heterocycles

New phenothiazine dyads were synthesized in good to very good yields using the

Buchwald-Hartwig amination of phenothiazine with different dibromo aromatic

heterocycles. Electron-deficient units were used as spacer like pyridine, pyridazine and

electron-rich units like thiophene, furane, fluorene.


- 13 - 13

Scheme3. Synthesis of new phenothiazines dyads.

The structures of the phenothiazine dyads 30-35 are unambiguously supported by

1H and

13C NMR spectroscopy, mass spectrometry and correct combustion analysis.

The electronic structures of some heterocycle-bridged phenothiazine dyads 31 and

35 was considered by computations on the DFT level of theory (B3LYP/6–

31+G(d,p))6.The structures of 3,6-pyridazine- 31 (Figure 2) and 2,5-thiophene- 35

(Figure 3) bridged phenothiazine dyads were geometry optimized and for further

discussion the electron density distribution in the frontier orbitals (HOMO and LUMO)

of these lowest energy conformation structures was exclusively taken into account.

donors whilst the thiophene moiety serves as an acceptor.

Figure 2. LUMO(left) and HOMO(rigth) of the N,N’-pyridazine bridged biphenothiazine

31

6 M. J. Frisch, et al., Gaussian 03, Revision C.03; Gaussian, Inc.,Wallingford, CT, USA,

2004.


- 14 - 14

Figure 3. LUMO(left) and HOMO(right) of the N,N’-thiophene bridged biphenothiazine

35.

Most characteristically, the butterfly structure of the phenothiazinyl moieties is

reproduced by the computations. Futhermore, both phenothiazine units adopt the

pseudo-equatorial intra-configuration, which is typical for N-aryl phenothiazines7.

Due to symmetry, the computed HOMO (Figure 19, right) is predominately localized

on both phenothiazine moieties, whereas the LUMO (Figure 19, left) is localized on

the central thiophene. This also represents the intuitive notion, where phenothiazine

units can be regarded as strong electron donors whilst the thiophene moiety serves as

an acceptor. The electronic structure of 31 with respect to the frontier orbitals reveals

a significantly different electron distribution (Figure 20) in comparison with the

thiophene derivative 35. While the LUMO (Figure 20, left) of 31 is located mostly in

the pyrazidine moiety, the HOMO (Figure 20, right) represents a largely delocalized

structure, i.e. electron density in all fragments of the molecule.

The electronic properties of the phenothiazine dyads 30 – 35 were investigated by

absorption and emission spectroscopy and cyclic voltammetry (table 3). Optical

spectroscopy studies (UV/Vis and fluorescence spectra) of systems 30 – 35 displays

weak fluorescence with emission of blue-green light and enormous Stokes shifts (9600-

10600 cm-1

). Since pyridazine itself is essentially non-fluorescent8, expectedly, the

pyridazine bridged phenothiazine derivative 31 does not show any detectable emission.

7 J.-P. Malrieu and B. Pullman, Theor. Chim. Acta 1964, 2, 293. 8 H. Li, P. Dupre and W. Kong, Chem. Phys. Lett. 1997, 273, 272.


- 15 - 15

Table 3. Electronic properties of the phenothiazines 30 – 36.

Compound Absorption

λmax,abs [nm][a]

Emission

λmax,em [nm][a]

Stokes

Shifts

[cm-1

]

E00/+1

[mV] [b]

E0+1/+2

[mV] [b]

30 252, 304 443, 503 (sh.) 10300 608 954

31 253, 303 - - 851 1155

32 253, 283, 309 517, 556 (sh.) 13000 736 1132

33 288, 251, 333 516, 552 (sh.) 10600 891 1276

34 259, 280, 308 477, 506 (sh.) 11500 761 -

35 256, 311 444, 512 (sh.) 9600 640 1072

36 260, 299, 313 473 10800 716 -

[a] Recorded in CH2Cl2 [b] Recorded in CH2Cl2, 20 °C, v = 100 mV/s, electrolyte: nBu4N

+ PF6

-, Pt working electrode, Pt counter electrode, Ag/AgCl reference electrode.

The fluorescence was monitored upon titration with trifluoroacetic acid (TFA)

in methylene chloride (Figure 4). The fluorescence of both compounds 32 and 33

develops in a similar fashion upon continuous addition of aliquots of TFA. Whereas

the free bases 32 and 33 display emission at 516 nm and 517nm, respectively, after

addition of 0.1-5 equivalents of TFA the emission is noticeably quenched.

Figure 4. Emission spectra of 32 (left) and 33(right) in the presence of increasing

amounts of TFA(recorded in CH2Cl2, c(9) = 10-6

M, T = 293k)

According to cyclic voltammetry symmetrical dumbbell-shaped phenothiazine

dyads bridged by heterocycles show intense electronic coupling between the redox-active

350 400 450 500 550 600 6500

50

100

150

200

250

300

350

Em

issio

n

wavelength [nm]

0 eq

0.1eq

0.2eq

0.3eq

0.5eq

1eq

2eq

3eq

5eq

350 400 450 500 550 600 6500

50

100

150

200

250

300

0 eq

0.1 eq

0.2 eq

0.3 eq

0.5 eq

1 eq

2 eq

3 eq

10 eq

5 eq

Em

issio

n

Wavelength [nm]


- 16 - 16

phenothiazine moieties. Futhermore, the fluorescence of the pyridyl-bridged derivatives

can be controlled by pH change giving reversibly switchable redox-active bielectrophore

dyads.

3.4 Photoactive binaphthyl phenothiazine derivatives

We aimed to prepare a series of binaphthyl derivatives bearing phenothiazine

groups at positions 2,2’ and/or 6,6’. Investigation of the photochemical and

electrochemical properties of such derivatives should give as valuable information about

electronic communication among these groups via binaphthyl spacer as a background for

construction of optoelectronic devices.

The preparation of new bis-(10-alkyl-phenothiazin-3yl)-1,1’-binaphthalene

derivatives following a rational synthetic approach based on Suzuki or Negishi arylation

of suitable precursors, is discussed. Positive results were obtained by Suzuki arylation of

the (RS)-6,6’-dibromo-[1,1’-binaphthalene]-2,2’-dicarbonitrile with 10-Hexyl-3-(4,4,5,5-

tetrametyl-1,3,2-dioxaborolan-2-yl)-phenothiazine and Negishi arylation of the (RS)-2,2’-

diiodo-[1,1’-binaphthalene] with 3-bromo-10-hexyl-phenothiazine.

CN

CN

Br

Br

S

N

nHex

B

O

O

(Ph3P)4Pd

DME

80o C

CN

CN

S

N

nHex

S

N

nHex

43 39 44

72 %

S

N

nHex

Br

5

S

N

nHex

S

N

nHex45

I

I

DIBN

Pd[(PPh3)4]

27%

Scheme 4. Synthesis of new binaphtalen phenothiazines 44 and 45

The structure of compound 44 is supported by 1H-NMR and

13C-NMR. The values of

chemical shifts and the coupling constants for the protons of the oligomer 44 are


- 17 - 17

presented in Table 4. Most characteristically for all N-hexyl-subtituted phenothiazines the

methylene protons apeear as a triplet at δ = 3.80 ppm with vicinal coupling constant of

7.3 Hz. For the aromatic phenothiazinyl binapthyl protons resonances, well resolved

coupling patterns of the signals are found between δ = 6.80 – 8.42 ppm. In particular, the

nitril binaphtyl phenothiazine 44 can be clearly identified by the diagnostic appearance

by quaternary carbon nuclei at δ = 99 ppm in the 13

C-NMR spectra. The characteristic

CN- triple bond of 44 stretching vibration at 2160 cm-1

in the IR spectra reveal the

typically absorptions for nitrile derivatives.

Table 4. The values of chemical shifts and coupling constants of the protons in the

structure of diciano binaphtalen phenothiazine 44.

Type of compound Type of proton

Chemical shift

δ (ppm)

Coupling

constant

J (Hz)

t 6H

m 12H

m 4H

t 4H

m 12H

m 6H

d 2H

dd 3H

dd 3H

0.87

1.29

1.67

3.80

6.80

7.60

7.84

8.17

8.42

7.3 (J)

7.3 (J)

8.5 (J)

2.0 (J) 8.5 (J)

2.0 (J) 8.5 (J)


- 18 - 18

3.5 Phenothiazine Tröger Base derivatives These work is dedicated to Prof.Univ. Dr. Ioan A. Silberg

Tröger’s base was first synthesized in 1887 by Julius Tröger9, and its V-shaped

and rigid structure has attracted a lot of attention in the past years10

that has led to

applications in the design of various receptors for the recognition of neutral organic

molecules such as menthol11

or adenine12

as well as for the recognition of dicarboxylic

acids13

, and it has been used as a chiral auxiliary for the enantioselective synthesis of

aziridines14

.

Our approach is aimed at the formation of self-assembled helical phenothiazine

Troger Base.

We found that the heating the mixture at 60°C for 4h and after that the mixture

was stirred at room temperature for 48h give us the better yields of the Troger’base

analogues 52 (23%) and 53 (40%) in oil bath (Scheme 5).

Scheme 5. Synthesis of the phenothiazine Troger Base derivatives 52 and 53

The structures of the aminophenothiazine and Troger’s Base derivatives are

unambiguously supported by IR, 1H NMR spectroscopy and mass spectrometry.

9 J. Tröger, J. Prakt. Chem. 1887, 36, 225.

10 M. Valik, R. M. Strongin, V. Kral, Supramol. Chem. 2005, 17, 347.

11 a) M. D. Cowart, I. Sucholeiki, R. R. Bukownik, C. S. Wilcox, J. Am. Chem. Soc.

1988, 110, 6204; b) T. H. Webb, H. Suh, C. S. Wilcox, J. Am. Chem. Soc. 1991, 113,

8554. 12

a) J. C. Adrian Jr, C. S. Wilcox, J. Am. Chem. Soc. 1989, 111, 8055; b) J. C. Adrian Jr,

C. S. Wilcox, J. Am. Chem. Soc. 1991, 113, 678; c) J. C. Adrian Jr, C. S. Wilcox, J. Am.

Chem. Soc. 1992, 114, 1398. 13

a) S. Goswami, K. Ghosh, Tetrahedron Lett. 1997, 38, 4503– 4506; b) S. Goswami, K.

Ghosh, S. Dasgupta, J. Org. Chem. 2000, 65, 1907. 14

Y.-M. Shen, M.-X. Zhao, J. Xu, Y. Shi, Angew. Chem. 2006, 118, 8173.


- 19 - 19

The electronic properties of the phenothiazine derivatives 52 and 53 were investigated

by absorption and emission spectroscopy (Table 5). Furthermore, the fluorescence

quantum yields of these push-pull chromophores were determined with coumarine 1 as

standard.

Table 5. Electronic properties of the phenothiazines 50 - 53

Compounds

Absorption

λmax,abs

[nm][a]

Emission

λmax,em

[nm][a]

Quantum

yield

[%][b]

Stokes

shift

(cm-1

)

52

259, 339 442 40 6900

53

282, 342

460 29 7400

[a] Recorded in acetonitrile [b] Determined with coumarine 1 as standard.

Optical spectroscopy studies (UV/Vis and fluorescence spectra) of systems 52 -

53 display considerable fluorescence with emission of blue-green light with highest

fluorescence quantum yields between 29 and 40% and remarkable Stokes shifts (6900 –

7400 cm-1

). These substantial Stokes shifts can be assigned to significant geometrical

changes upon excitation from a highly non-planar ground-state to a largely planarized

excited state.


- 20 - 20

5. General conclusions

The goal of this thesis was the synthesis and structural characterizaion of novel

phenothiazines derivatives with tunable electronic properties as precursors for charge-

transport materials.

During the work in this field, the obtaining of conjugated phenothiazine

containing heterocycless was analyzed and pursued.

The original contributions of this work, presented in chapters 3, are related to the

preparation and structural characterisation of nitril, amino phenotiazine oligomers,

dumbbell-shaped phenothiazine dyads, napthalen-phenothiazines and Tröger base

phenothiazines.

The results are summarized here:

seven nitrile phenothiazine oligomers were obtained and fully characterised.

We have transposed the Beller cyanation to electron rich phenothiazines,

predominantly under dielectric heating, giving rise to the formation of

(oligo)phenothiazinyl nitriles and dinitriles. The electronic properties, as determined

by absorption and emission spectroscopy and cyclic voltammetry, reveal a class of

highly fluorescent extended p-electron systems with large Stokes-shifts (5800-8300

cm -1

) and substantial quantum yields (11-27%). Furthermore, these

fluorophores are reversibly oxidized at potentials that correlate with the number of

phenothiazinyl units.

five aminomethylene phenothiazianes were obtained from the corresponding

cyano derivatives using two different reducing agents: LiAlH4 in EtO2 and

nBu4NBH4 in CH2Cl2 – solubility problems and they was fully characterised. Our

goal was to synthesize new molecules which contain both 10H-phenothiazine and

trietoxysilyl units for adsorption on silica surfaces. In this way, functionalized

silica surfaces which exhibit phenothiazine properties (fluorescence, low

oxidation potential etc.) can be obtained. The target molecules can be prepared

by reacting amines with phenothiazine units and 3-(triethoxysilyl)-propyl-

isocyanate.


- 21 - 21

seven dumbell-shaped phenothiazines were obtained and fully characterised. We

have presented the synthesis and electronic properties of dumbbell-shaped

phenothiazine dyads. The introduction of the heterocyclic bridge can be easily

accomplished by the Buchwald-Hartwig aryl amination. The symmetrical

systems 37, 40 and 42 show intense electronic coupling between the redox-

active phenothiazinyl units as shown by cyclovoltammetry. Futhermore, we

could demonstrate that the emission of derivatives 39 and 40 in CH2Cl2 can

be switched off by the addition of TFA and switched on by neutralizing the

sample solution as a consequence of the enhanced basicity of the pyridines by

the electron rich phenothiazine moieties.

two binaphthyl - phenothiazines were obtained and characterised by 1H and

13C

NMR. Despite the difficulties in coupling two electron-rich aromatic systems, the

results obtained using the palladium catalyzed cross-couplings reactions,

especially the Negishi coupling involving phenothiazinil-zincchloride derivatives

as intermediates, and the Suzuki coupling involving phenothiazinil borate

intermediates, opened us the way to achieve the synthesis of phenothiazine-

binaphthyl derivatives. The attempts to synthesize the full-conjugated tetra

substituted binaphthalene with phenothiazine have lead to complex mixtures. The

1HNMR experiments have revealed some characteristic signals of the desired

compounds, unfortunately, this compound could not been isolated in order to

perform a full characterization. The exploitation of cross-coupling methodologies

opens flexible strategies to various functionalization of naphthalen and

phenothiazinyl derivatives.

two phenothiazines Troger’s base were obtained and characterised by 1H NMR,

IR and MS spectroscopy. We have observed for the first time the formation of

phenothiazinyl Troger’s bases, which are the chiral amine with two stereogenic

nitrogen atoms and are bonded by a methylen bridge. The electronic properties, as

determined by absorption and emission spectroscopy, reveal a class of highly

fluorescent π-electron systems with remarkable Stokes-shifts (6900 - 7400cm-1

) and

substantial quantum yields (29 - 40%).


- 22 - 22

The electronic properties of these derivatives were interesting related to the correlation

between structure and redox potential. Electronic coupling of the donor and the acceptor

in the excited state can be observed, which is in prospect an application of the substance

class for photoinduced electron transfer (PET) studies. Furthermore, for the bridged and

unbridged oligophenothiazines there is also a strong dependence of the electronic

communication between aromatic units on the distance of electrophores and the nature of

the bridge.

List of scientific communications

Published Pappers

1. Adam W. Franz, Larisa N. Popa, Frank Rominger and Thomas J. J. Müller, Org.

Biomol. Chem., 2009, 7, 469–475.

“First synthesis and electronic properties of diphenothiazine dumbbells bridged by

heterocycles”.

2. Adam W. Franz, Larisa N. Popa and Thomas J. J. Müller Tetrahedron Letters, 2008,

49(20), 3300-3303.

”First synthesis and electronic properties of cyano(oligo)phenothiazines”

3. Larisa N. Popa, M. Putala, Studia, 2007, LII, 4, 43-50.

“Photoactive binapthyl pehnothiazine derivatives”

Poster Presentations

1. “Dumbbell-shaped Phenothiazine Dyads Bridged by Heterocycles”

Larisa Natalia Popa, Adam Franz, Luiza Gaina, Luminita Silaghi-Dumitrescu, Thomas

J.J. Müller

2. „Utilisation des pheromones sexuelles des insectes pour la protection des arbres”

Popa Larisa, Pojar-Feneşan Maria, Oprean Ioan, Balea Ana, Pirlea Maria

Actes du troisieme Colloque Franco-Roumain de Chimie Applique COFrROCA , 22-26

septembrie 2004, Slanic-Moldova, Bacau – Romania.

Abstract Larisa En

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