M M Girgis. . ,

CROATICA CHEMICA ACT A CCACAA 63 (4) 603-616 (1990)

CCA-1964 YU ISSN 001-1643UDe 547.712.832

Original Scientific Paper

Electronic Absorption Spectra of New y-Keto-dimethine CyanineDyes and Apocyanines

. * . . **+ . ** *A. 1. M Koraiem , M M Girgis, Z. H KhalLl and R. M Abu El- Hamd

Chemistry Department, Aswan-Faculty of Science, Aswan, Egyptand

Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

Received October 2, 1989

New asymmetrical y-keto-dimethine cyanines (2.-f) were prepared through thecondensation of phenyl glycosal derivatives (l.-e) with 2-methyl pyridinium (qui-nolinium)-2yl salts. Such dyes were converted into the corresponding dyes (3a-g and4a-d) by cyclocondensation with hydrazines or hydroxylamine hydrochloride undersuitable conditions. The new synthesized cyanines were identified by elemental andspectral analyses. The U'V-visible absorption spectra of some selected dyes wereinvestigated in pure and mixed solvents as well as in aqueous buffer solutions. Mo-lecular complex formation with ethanol was verified by mixed solvent studies. Elec-tronic transitions were attributed to either locally excited or predominantly chargetransfer states. The spectral shifts were discussed in relation to molecular structureand in terms of medium effects. The variation of absorbance with pR was utilizedfor the determination of the pK. value for aselected compound (2e). The pho-tostability of some selected đyes (2e, 3g and 4d) was investigated.

INTRODUCIlON

Dimethine cyanine dyes have various applications as photosensitizers in pho-tographic processes! and as corrosion inhibitors.? Apocyanine dyes possess, also, va-rio us bactericidal activities.' In the present investigation, new y-keto-dimethinecyanines (2a-r) and their converted apocyanines (3a-g and 4a-d) were prepared to studytheir spectral behaviour for their possible photosensitization and to study their sol-

+ Adress for correspondence: Dr. Maher Mikhail Girgis, P.O. Box 161, Assiut,Egypt

604 A. I. M. KORAIEM Ef AL.

vatochromic-, acid-base behaviour. Photostability of some selectcd dyes (2e, 3g and4d) was also studied to help appropriate selection for their application as photo-sensitizers.

EXPERIMENT AL

All melting points are uncorrected. The IR spectra were determined with a Perkin ElmerInfrared 127 B spectraphotometer. The UV-visible absorption spectra were recorded on a Shi-madzu UV-Vis record ing spectrophotometer UV-240. The -n NMR spectra were record edwith a KEM-390 90 MHZ NMR spectrameter.

Phenyl glycosal derivatives (1a-e) were prepared in away similar to that described earlier.4

SolutionsThe stock solutions of the dyes were of the order 10-3 M. Solutions of low molarities used

in spectral measurements were obtained by accurate dilution.An accurate volume of 10-3 M ethanolic solution of the dye was placed in a 10 ml mea-

suring f1askcontaining the required volume of ethanoi, then completed to the mark with theother solvent (CHC13 or H20) to study the spectral behaviour in mixed solvents.

An accurate volume of 10-3 M ethanolic solution of the dye was added to 5 ml of buffersolution in a 10 ml measuring f1askand then completed to the mark with redistilled water. ThepH of this solution was checked before spactral measurements. A modified buffer series derivedfrom that of Britton22 was prepared.

A fresh ethanolic solution (10-3 M) of the dye was prepared, then diluted to (1.OxlO-4 M)in a 10 ml measuring f1askand exposed to the light source (white lamp 100 W). The solutionused in spectrophotometric measurements was kept at (27.0±0.5yC and measured at time in-tervals.

1. Synthesis of v-Keto-dimethine Cyanine Dyes (2a-f)

To a warm solution of dissolved equimolar amounts of phenyl glycosal (1a-e) and methylquaternary salts (a-picoline-or quinaldine ethiodide), 0.01 mol in ethanol (30 ml), aqueous al-coholic NaOH solution (50% (v/v)) was added dropwise with stirring. After complete addition,the solution was stirred for 3 hrs. Then the products were filtered and recrystallized fram etha-noi to give (2a-f). The resuits are !isted in Table I-I. IR("KBr cm-l) for 2b, 3000-2970 cm-lmax("EtI), 1670 cm-I ("C=O), 1600 cm-l ("C=C) and 3500 cm-I ("OH enoI). IH NMR (CDC13)for (2e),06.9-6.1 ppm (m, 12 H, aram. + heter. + olefinic pratons), 05.2 ppm (s, 1 H, enolicOH) , 02.7 ppm (q, 2H, CH2I), 05.7 ppm (s, 1 H, C=CH) and 01.7 ppm (t, 3H, CH3).

2. Apocyanine Dyes (3a-g and 4a-d):

a) Synthesis of saturated N-elhyl-2-azolylquinolinium salts (3a-g). - Equimolar amounts of(2a-e)and hydrazine, phenyl hydrazine and/er hydraxylamine hydrochloride (0.01 mol) were dis-solved in AcOH 7 (30 ml) and ref1uxed for 8-10 hrs. The reaction mixture was filtered hot,the filterate was concentrated and then cooled. The precipitated praducts after dilution withwater were collected and recrystallized from the appropriate solvent, yields 19-31%. The resu\ts

are summarized in Table (I-II). IR(" KBr cm-I) for (3b) is 2990-2800 cm-I (" EtI):maxb) Synthesis of unsaturated N-ethyl-2-azolylquinolinium salts (4a-d). - 1. To a mixture of

(2a or 2e) (0.04 mol) and hydrazine, phenyl hydrazine and/er hydroxylamine hydrochloride (0.02

CYANINE DYES 605

mol) in ethanol (50 ml), and alcoholic KOH (0.05 mol/SOml ethanoll was added. The reactionmixture was refluxed on a steam bath for 8 hrs. The precipitated products which were formedafter concentration were throughly washed with water to remove inorganic salts and recrystal-lized from absolute ethanol to give greenish crystals of (4a.d), yield 34-58%. The resu Its aresummarized in Table I-III.

2. Equimolar amounts of (3a and 3e.g, 0,01 mol) and the corresponding y-keto-dimethinecyanine (2a or 2e, 0.01 mol) were dissolved in ethanol (50 ml), to which an alcoholic KOHsolution (0,02 mol/SOml ethanoI) was added. The reaction mixture was refluxed for 6 hrs. Theprecipitated products were collected, washed with warm water and recrystallized from absoluteethanol to give the same products (4a.d) having the same m.p's and the other physical properties.

The resu Its are given in Table I-III. IR(vKBr crn") for (4d) is 1600 cm·1 (vC=C).max

RESULTS AND DISCUSSION

Interaction of phenyl glycosal derivatives (la.e)4 with 2-methyl quaternary am-monium saits in 50% aqueous alcoholic NaOH 5 afforded the corresponding y-ke-to-dimethine cyanine dyes (2a.f), Scheme (1). Their structures were confirmed byelemental analysis (Table I-I) IR and lH NMR spectral data." These ćornpoundsare coloured, soluble in non-polar and polar solvents, exhibiting slight green flu-rescence and release iodine on warming with conc. H2S04. The colour of their etha-nolic solutions is discharged on acidification.

y-Keto-dimethine cyanines (2a.f) when cyclocondensed with hydrazines or hydro-xylamine hydrochloride afforded the corresponding apocyanines (3a-g and 4a.d). Thecyclocondensation reaction products depend upon the molarity of y-keto-dimethinecyanines and on the nature of the catalyst used. Thus, the interaction of equimolarof y-keto-dimethine cyanines and hydrazines or hydroxylamine hydrochloride in thepresence of AcOH 7 gave the corresponding saturated N-ethyl-2-azolylquinoliniumsalts (3a.g), Table I-II, while the interaction of y-keto-dimethine cyanines with hy-drazines or hydroxylamine hydrochloride (2:1 molar rations) in the presence ofKOH 8 afforded the corresponding unsaturated N-ethyl-2-azolylquinolinium salts(4a-d), Table I-III. This reaction appears to proceed via dehydrogenation process ofdihydro azolyl group." This suggestion was confirmed by the interaction of (3a and3e.g) with excess of the corresponding y-keto-dimethine cyanine (2a or 2e) to givethe same isolated compounds (4a.d), Scheme 1. The structures of these compounds(2a.g, 4a.d) were confirmed by elementa I analyses (Table I) and IR spectra. The com-pounds (3a.g) are fairly soluble in most polar and non-polar organic solvents withno fluorescence while the corresponding apocyanine derivatives (4a.d) are colouredin solutions, exhibiting intense green to blue fluorescence depending upon the or-ganic solvent used. They are soluble in conc. H2S04, releasing iodine vapour on hea-ting.

Relation Between Molecular Structure and Spectral Behaviour of theSynthesized Cyanines

The visible absorption spectra of y-keto-dimethine cyanines (2•.r) in ethanolpossess different absorption bands. The Amaxand t:m•xvalues of these bands are col-lected in Table II-I. Substituting A=H in (2f) by A= C6H4-2yl salt moiety in (2e)causes a red shift of 13 nm with intensification of the longer wavelenght band at

606 A. I. M. KORAIEM ET AL.

542 nm. This can be attributed to the higher coplanarity of (2e) resulting from thegreater bulk of the quaternary heterocyclic moiety attached to the -CH=CH- centre.This leads to a strong interaction of the electrons within the molecule and hencea lower excitation energy is required. On the other hand, the shoulder located at

IX ~~-010 +H C ~ 5O%agu./. X~~-CH=Cl-l CrA~ 3 ~ alc/NaOH ~ ~~

) I Siir.3 hr . ) I

1a-e 2a_f

(la_e): X=H(a),E-CH3(b),E-OCH3(c), E-NOZ(d) and E-Cl(e).

(Za_f): A=C6H4-Zyl-saltj X=H(a), E-CH3(b), Q-OCH3(c),Q-NOZ(d),Q-Cl(e) andA=H-Zyl-salt j X=Q-Cl (f).

( 2a_f ) + ~N-Y

KOH/8 hrs.2 mole

X

c3 a-g): Y=NHj jX=H(a) 'E-C~ (b) ,Q-OCH 3(C) ,E-NOZ(d) ,Q-Cl(e) ,Y=N-phjX=E-Cl(f) andY=O jX=Q-Cl( g) .

(4a_d): Y=NH jX=H(a), Q-Cl(b),Y=N-phjX=Q-Cl(c) andY=O jX=Q-Cl(d).

Scheme 1.

TABL

Er

Cha

ract

eriz

atio

nof

y-ke

to-d

imet

hine

cyan

ine

dyes

(2a-

r)an

dth

eir

deri

ved

apoc

yani

nes

(3•.g

and

4•.d

).

Elem

enta

lan

alys

isM.

P.YH

!.1d

Calc

ulat

ed(F

ound

)Co

mpou

nd(a

C)Mo

lecu

lar

form

ula

(Mol

.wt.

)"

No.

CH

N

I.Y-

Keto

-dim

ethi

necy

anin

es(Z

a_f)

Z16

570

C ZOH 18

NOI

(415

)57

.83

(57.

80)

4.34

(4.3

7)3.

37(3

.35)

a Zb14

058

CZIH

ZONO

I(4

Z9)

58.7

4(5

8.75

)4.

66(4

.61)

3.26

(3.3

0)Z

135

43CZ

IHZO

NOZI

(445

)56

.63

(56.

70)

4.49

(4.4

6)3.

15(3

.16)

c 2d14

048

CZOH

17NZ

03I(

460)

52.1

7(5

Z.Z0

)3.

70(3

.75)

6.09

(6.1

3)

217

560

C 20H 17

NOCl

l(44

9.5)

53.3

9(5

3.38

)3.

78(3

.80)

3.11

0.09

)O

e-<

2 f16

018

C 16H I5

NOCI

I(39

9.5)

48.0

6(4

8.10

)3.

75(3

.70)

3.50

(3.5

5)>- Z Z tT1

II.

Apoc

yani

nes

(3a_ g)

d -< m3 a

210

31C2

0HZO

N31

(4Z9

)55

.94

(55.

96)

4.66

(4.7

0)9.

79(9

.80)

3 b21

5ZI

C Z1H ZZ

N 31(4

43)

56.8

8(5

6.88

)4.

97(4

.92)

9.48

(9.5

1)3

ZlZ

19C n

H ZZN 3OI

(459

)54

.90

(54.

92)

4.79

(4.8

2)9.

15(9

.13)

c 3 dZ0

5ZI

CZOH

19N4

0ZI(

474)

50.6

3(5

0.60

)4.

01(4

.08)

11.8

1(11

.80)

319

225

CZOH

I9N3

CII(

463.

5)51

.78

(51.

8rJ)

4.10

(4.1

1)9.

06(9

.05)

e 3 f17

130

C26H

23N3

CII(

539.

5)57

.83(

57.8

5)4.

26(4

.33)

7.78

(7.7

0)3

185

Z9C2

0HI8

N20C

II(4

64.5

)51

.67(

51.7

0)3.

88(3

.92)

6.03

(6.0

1)9

III.

Apoc

yani

nes

(4a_ d)

4a18

834

CZOH

18N3

I(4

Z7)

56.Z

1(56

.Z6)

4.2Z

(4.2

1)9.

84(9

.85)

4b18

544

C20H

17N3

Cl!(

461.

5)52

.00(

5Z.0

3)3.

68(3

.73)

9.10

(9.1

1)4

212

58C2

6HZI

N3Cl

l(53

7.5)

58.0

5(58

.10)

3.91

0.88

)7.

81(7

.80)

0\

cO

4d19

550

CZOH

16N2

0Cll

(46Z

.5)

51.8

9(51

.93)

3.46

(3.4

9)6.

05(6

.08)

-.l

0'1 o ex>

TABL

EII

Visi

ble

abso

rptio

nsp

ectr

ach

arac

teri

stic

sof

y-ke

to-d

imet

hine

cyan

ine

dyes

(2._r)

and

thei

rde

rive

dap

ocya

nine

s(3

.-gan

d4 a_ d)

inet

hano

lat

27"C

;>1.

Y-K

eto-

dim

ethi

necy

anin

es

22b

22d

ac

-3)

A(C

xW-3

)-3

-3)

Am

ax(c

max

xl0

maxmax

Am

ax(c

max

xlO

)>-

max(

Emax

xlO

--

--m

i(an2

,troC

l)nm

(an2

muC

I)on

(an2

moC

l)nm

(cm

2m

ol-I)

-40

0M!(2

.9)

400s

h(2

.9)

400a

h(9.

J)40

0(2.

9)42

5sh(

B.B)

49BM

!(B.l)

49B2

.!!(1

2.4)

49Bs

h(I0

.3)

520(

12.3

)51

9sh

(13.

5)51

B(13

.1)

525(

9.7)

555(

19.4

)55

5(21

.1)

55B(

15.9

)55

6(15

.5)

640s

h(2.

7)64

0sh(

2.1)

640s

h(3.

4)64

0sh(

1.7)

(20_

f) Z e (-3

Am

axEm

axxJ

G)

nm(an2

mol

-I)

5Z1s

h(11

.9)

555(

19.1

)

Zr,....

(-3)

Am

axEm

axxl

O

z :<: ~ ~ ~ :> r-

rm(0

1\2IroJ-I

)

400s

h(2.

4)

5Z0s

h(6.

3)54

2(JO

.l)

Tabl

eII

tobe

cont

inue

d

Tabl

eII

cont

inue

d

Il.Ap

ocya

nine

dyes

(3S-

9)

33 b

33 d

33 r

3a

ce

g

-3-3

-3)

A(E

xlO-3)

(-3)

(-3)

>max((max

xIO-3

>max

(Em

axxlO

)Amax(Em

axX10

)Amax(EmaxxlO

maxmax

Amax

EmaxxlO

Amax

E maxxlO

---

----

--------

rrn

(an2

moC1)

rm(on2

noel)

run(on2

mol-l)

run(an2

mar-I)

run(an2

mol-I)

run(002

mol-I)

nrn(an2

nol.-1)

522sh(5.4)

564(7.9)

57B(7.9)

492ah(6.6)

522(B.4)

552sh{7.0)

52Bsh(6.6)

565(B.6)

492sh(

5.4)

S2Bsh(6.4)

561(0.4)

5229h(

5.0)

563(7.B)

57B(7.B)

52B~(4.6)

560(6.9)

57Bsh(6.0)

52B9h(5.0)

560(7.

J)n -< ~ Z m tJ -< ~

Il!.

Apoc

yani

nedy

es(4

a_ d)

44b

44d

Bc

(-3

A(

10-3)

(-3)

Amax(EmBxxIO-3)

Amax

E maxx10

)m

axE:

max

XAmax

E mBxxlO

---

-run(an2

mol-I)

nn(an2

moCI)

ml(an2

mol-I)

run(an2

1T'01-1)

367(9.6)

419(12.B)

435(13.

9)

560sh

(1.4

)

366sh(6.5)

41B(9.2)

434(9.3)

560sh(2.3

)

416sh(9.6

)

433(9.4)

565(6.4)

..166(9.7

)

41B(11.2)

435(12.4)

565(3.2)

0\O 1.0

610 A. 1. M. KORAIEM ET AL.

518-525 nm is influenced by the nature of the aryl substituents (X) (Tablc II-I), aswell as the solvent nature, which can be attributed to an electronic transition ori-ginating from the carbonyl group as a source to the strong electron withdrawingni tro group as a sink (2d, X=p-N02). The other substituents (X) have minor effects.The Cl' that takes place can be representcd as follows:

A good linear relationship is obtained on plotting l/A.max (intramolccular C'I'band) vs the Hammett constant!" (-a) of the substituent X (Figure la) supportingthe C'I' nature of this band.

.o lU

t t'bxXlUtor<~

1·761·90L._-1. __ -L__ L-_-1. __ -L__ L-_-:-':__ ;-'-08 -06 -04 -0-2 o

Figure 1. (a) The l/A.mar versus -l lammctt constant (-a) plot for the CT bands of compounds(2a-e) in EtOH at 2rc.

(b) The l/A.mar versus Hammett constant (a) plot for the CT bands of compounds (3a-e)in EtOH at 27'C.

The band located at 542-558 nm is largely affected by the solvent polarity andits position is slightly affccted by the nature of the aryl substituents (X) (Table II-I).It can be assigned to an intramolecular C'I' transition originating from carbonylgroup as a source to the positively charged heterocyclic quaternary (N) atom as asinko This intramolecular C'I' transition can be represented as follows:

TABL

EIII

Elec

tron

icab

sorp

tion

spec

tra

char

acte

rist

ics

ofv=

keto

-dim

ethi

necy

anin

edy

es(2

ean

d2[

)in

pure

solv

ents

at27

'C

Wat

erD

MF

EtO

HCH

Ci3

CC14

Dio

xane

Com

poun

dN

o.Am

ax[em

axx10

-3)Am

ax[em

axx10

-3)Am

ax[e

maX

X10-3)

Amax

[emaxx

10-3)

Amax

[emaXX

10-3)

Amax

[emaxx

10-3)

2-1

2-1

2-1

2-1

2-1

2-1

nmcm

mol

nmcm

mol

nmcm

mol

nmcm

mol

nmcm

mol

nmcm

mol

2e19

8(27

.7)

-20

9(42

.7)

--

-o ><

228(

22.9

)-

228s

h(38

.2)

--

-;t> z

266(

12.6

)26

1(39

.0)

254(

27.4

)Z tI1

275s

h(6.

1)-

227s

h(12

.6)

278s

h(l1

.2)

277s

h(31

.9)

278s

h(20

.7)

tJ ><31

8(7.

5)31

5sh(

8.5)

315(

10.1

)31

5sh(

8.5)

316(

23.0

)31

5(14

.8)

m51

8sh(

3.0)

524s

h(10

.1)

521s

h(l1

.9)

525s

h(1O

.1)

527s

h(7.

0)52

2sh(

8.6)

552(

4.3)

559(

17.3

)55

5(19

.1)

560(

20.2

)56

3(88

.5)

556(

12.8

)

2f20

6(36

.6)

-21

0(31

.9)

261(

27.6

)-

255(

27.9

)27

0(18

.0)

260(

16.8

)26

0(27

.5)

31O

sh(9

.6)

31O

sh(l1

.6)

312s

h(15

.2)

312s

h(15

.2)

310s

h(12

.4)

31O

sh(1

4.8)

510s

h(1.

9)52

4sh(

6.7)

520s

h(8.

9)52

0sh(

7.8)

530s

h(4.

0)52

2sh(

1.3)

538(

2.2)

544(

9.0)

542(

10.1

)55

0(9.

3)55

6(4.

4)54

3sh(

0.8)

0\

'"""'

'"""'

612 A. J. M. KORAIEM ET AL.

The visible absorption band of compounds (3a-e) located at 552-565 nm is greatlyinfluenced by the substituent (X) (Table II-II) which can be attributed to an elec-tronic transition from the 4-aryl residue as a source to the N-heteroatom of pyra-zoline as a sinko The CT takes place can be represented schematically as follows:

A good linear relationship is obtaincd on plotting 1/?max (intramolecular CTband) vs the Hammett constant!" (o) of the substituent (X) (Figure 1b), supportingthe CT nature of this band. Substituting (Y=NH) 3e by (Y=N-ph) 3r or (Y=O)3g resu Its in a slight blue shift by 3 nm. This can be attributed to the retardationof this type of transition as a result of increasing the electron donating characterof the heterocyclic moiety (N-ph or (O) > NH)_

The longer wavelenght band of apocyanine dyes (4a-d), located at 560-565 nm,is influenced by the type of azolyl group (Table II-III). Thus, substituting (Y =NH)4b by (Y =N-ph) 4c intensifies the absorption band accompanied with a red shift by5 nm. This may be attributed to the increasing of the mesomeric effect of N-phenylpyrazolo moiety. Similar behaviour was also noticed for 4d (Y =0) due to the greaterelectron density of oxygen atom in isoxazoline moiety. The CT that transition takesplace can be represented as fol1ows:

Solvatochromic Behaviour of y-Keto-dimethine Cyanine Dyes (2e and 2f) inPure Solvents

The A.maxand €maxvalues of the absorption bands due to different electronic tran-sitions within the solute molecules (2e and 2r), obtained in pure solvents of differentdielectric constants!' (viz. H20, DMF, EtOH, CHCh, CCl4 and dioxane), are rep-resen ted in Table III.

The spectra of compounds (2e and 2r) in ethanol consist of six and five essentialabsorption bands, respectively. The UV-bands lying up to 315 nm can be assignedto x=n" transitions within the benzenoid and heterocyclic rings. These bands arelittle influenced by changing the polarity of the medium. As reported above, thepronounced shoulder located at 521 and 520 nm in compound (2e and 2r), respec-tively, was attributed to an electronic transition originating trom the carbonyl groupas a source to the (Cl) atom as a sinko While the visible band located at 555 and542 nm an 2e and 2[, respectively, was attributed to an intramolecular CT transitionoriginating from the carbonyl group as a source to the positively charged hetero-cyclic quaternary (N) atom as a sinko

Careful examination of the resuits reported in Table III reveals that the bandscorresponding to CT transitions showa red shift on changing the organic solventfrom EtOH to dioxane, DMF, CHCb and CCk The unexpected blue shift observed

TABL

EIV

Cum

ulat

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in the A.max of the two CT bands for the two compounds (2e and 2r) in ethanol canbe mainly explained as a result of intermolecular H-bond formation between ethanoland the lo ne pair of electrons of the oxygen of the y-keto group. Thus, the abilityof electron releasing power of the y-keto oxygen is decreased and consequently theobserved high excitation energy needed in ethanolic medium relative to the otherorganic solvents used. The stronger blue shift observed in A.maxof the two CT bandsof compounds (2e and 21) in water (dielectric constant » 78.54)11 relative to ethanol(24.3/ , as well as the lower extinction, can be ascribed to the stronger interactionof water molecule with the lo ne pair of the electrons on the oxygen of the y-ketogroup.

Spectral behaviour of 4-chlorphenyl-2-keto-dimethine quinolinium(pyridiniumi ethiodide (2e and 2f) in mixed solvents

This study was done to test the possibility of formation of H-bonded solvatedcomplex betwccn the solute molecules and ethanol/or water. The visible spectra ofcompounds (2e and 2r) in CHCh and H20 each containing successively increasedquantities of EtOH were studied.

The stability constant ~Kr) of the complex can be determined from a conside-ration of the behaviour'<! in the mixed solvents applied using the previously ap-plied relation (1).15,16

I A-Aminlog Kr:::: og - n log CEtOH

Amax-A

The values of Kr of the H-bonded molecular complex liable to form in solutionbetween the molecules of compounds (2e and 2r) and EtOH/or H20 are given inTable IV. The values of Kr and n(the number of EtOH/or H20 molecules whichare complexed with the solute molecule) indicate that a 1:1 complex is formed insolution bctween the molecule and ethanol whcreas a 1:2 complex is formed betweenthe solute and water molecules.

Examination of the results reported in Table IV indicates that the ability ofEtOH/or H2 to form solvated complexes depends 00. the nature of the solute used.

The plots of ~vof the longer wavelength band as a function of (D-1)/(D+1)17 .for compounds (2e and 2r) are nonlinear. Therefore, the CT band shift is govcrnedby other factors in addition to the dielectric constant of the medium.P These facto rsinclude solute-solvent interaction.

On drawing the excitation energy (E) of the CT band in the mixed solvent vsthe ethanol mole fractions, for compounds 2e and 2r, broken lines with three seg-ments are obtained for each. The first segment indicates the orientation of the sol-vent molecules around the solute molecule. The second one represents themolecular complex formation while the third segment represents the steady stateof the energy attained after the complete formation of the molecular complex.

CYANINE DYES 615

Acid-Base Properties of 2[4-ChlorophenyIJ-y-keto-quinolinium-2yl-saltDimethine Cyanine (2e) in Aqueous Universal Buffers

The solution of some selected y-keto-dimethine cyanines give a permanent co-lour in the basic medium discharged on acidification. This prompted us to studythe spectral behaviour of one of these compounds in aqueous buffer solution in or-der to ensure the optimal pH in the application of these dyes. The effectiveness ofthe compounds as photosensitizers increases when they are present in the ionicform, which has a higher planarity.

The electronic absorption spectra of dye (2e) in aqueous buffcr solutions of va-rying pHs (1.80-11.58) show regular changes with increasing pH of the medium,especially the CT bands. Increasing the pH of the medium results in increased ab-sorbance of the CT bands. As the pH of the medium decreases, the extinction ofthese bands becomes lower and disappears at pH :5 3.29. This behaviour can beinterpreted on the principle that the carbonyl group becomes protona ted in solutionof low pH values and, therefore, the CT interactionwithin the protonated form isexpected to be difficult, i.e. the protona ted form does not absorb energy in the visiblerefgion. On the other hand, as the pH of the medium increases (pH ~ 5.60), thecarbonyl group becomes deprtonated and, therefore, its mesom eric interaction withthe rest of the molecule is intensified. Consequently, the Cf interaction within thefree base is facilitated, i.e. the free base absorbs energy in the visible region.

The recorded visible absorption spectra of compound (2e) in aqueous buffer so-lutions of varying pH's were applied to the spectrophotometric determination of thepKa val ue. The absorbance-pH curve is a typical dissociation curve, supporting theacid-base equilibrium. The acid dissociation constant (pKa) was determined from thevariation of absorbance with pH usin:fi the spectrophotometric half-height, limitingabsorbance and Colleter methods.l": The mean pKa value is 6.1.

Photostability of Some Selected Synthesized Cyanine DyesThe photochemical stability of some selected cyanine dyes has been examined

to shed some light on the relation between the chemical structure and their pho-tostability. An ethanolic solution (1.Oxl0-4M) of y-keto-dimethine cyanine (2e) andits derived compounds (3g and 4d) were irradiated by a white lamp (100 W) for 0-12hrs for 1-5 days. The photostability was found to be in the order 2e > 3g > 4d.

REFERENCES

1. A. H. 11er z , Adv. Col/oid interface Sci., 8 (1977) 237.2. M. T. M a k h I o u f and Z. H. K haI i I , J. Chem. Techno!. Bioteehno!. 38 (1987) 89.3. E. P. O P ana s e n ko, G. K. P a II i and P. V. P r i s y a z h n y u k, Khim. Farm. Zh. 8 (1974) 18.4. A. I. Vo g el, A tea-book of practical organie chemistry, 3rd Edn. (Longmans, London) 1975.5. A. M. O s man, Kh. M. Ha s s a n and M. A. E I - Mag h rab y , Indian J. Chem., 148 (1976)

282.6. F. S h e i n man n, Nuclear magnetie resonance and infrared spectroscopy, Vo!' 1 (1970), p. 41-70.7. E. A. S o I ima n, M. M. A b d ala, M. M. M o ham med and A. M. E I g i n d y , Indian J. Chem.,

16B (1978) 505.8. A. Sam m o u r, M. I. B. S e I im, M. M. N o urE I - Dee n and M. A bdE I - HaI im, U.A.R

J. Chem., 13 (1970) 7.9. R. Fra n k and R. Ste ven, J. Amer. Chem. Soc., 71 (1949) 2629.


10. J. H i ne, Physical organic chemistry 2nd. Edn. (McGraw-HiIl Book Company, Inc., New York) 1962,p.87.

11. R. C. We a s t and M. J. As tle, CRC Handbook of chemistry and physics, 61 st Edn. (CRC Press,Inc.) (1980-1981) p. 56.

12. R. M. I s sa, M. M. G h o n e im, K. A. I d r i s s and A. A. H a r f o li S h , Z. phys. Chem. N.F.B.,94, 5 (1975) 135.

13. M. S. El - E z a by, I. M. S ale m , A. H. Ze w a i I and R. M. I s sa, J. Chem. Soc. (B) (1970)1293.

14. T. Ga n gal y and S. B. B ane r je e , Spectrochim. Acta. 34A (1978) 617.15. A. S. El - S h a h a wy, M. M. G i r g i s and Z. H. K haI i I , Croat. Chem. Acta. 60 (1987) 613.16. A. S. El - S h a h a w y, M. M. G i r g i s and Z. H. K haI i I , Z. phys. Chem. (Leipzig), in press.17. M. S. A. A bdE 1- M o t t ale b and Z. H. K haI i i, Z. phys. Chem. (Leipzig) 260 (1979) 650.18. K. A. I d r i s s , A. S. El - S h a h a w y , M. S. A b li B ake r , A. A. Ha rf o li S h and E. y. H a -

s h e m , Spectrochim. Acta, 4lA (1985) 1063.19. I. M. I s sa, R. M. I s sa, M. S. El - E z a b y and Y. Z. Ah med, Z. phys. Chem., 242 (1969)

169.20. R. M. I s sa, M. S. El - E z a b y and A. H. Ze w a i I, Z. phys. Chem., 244 (1970) 157.21. J. C. C o Il e ter, Ann. Chim. (France), 5 (1960) 415.22. H. T. S. B rit t o n, Hydrogen ions, 4th Edn. (Chapman and Hall, London) 1952, p. 313.

SAŽETAKElektronski apsorpcijski spektri novih y-keto-dimetin-cijaninskih boji\a i odgovarajućih

apocijanina

A. 1. M Koraiem, M M Girgis, Z. H Khalil i R. M Abu EI-Hamd

Kondenzacijom derivata fenil-glikosala (la-e) s 2-metilpiridinijevim ili 2-metilkinolinijevimsalima pripravljeni su novi asimetrični y-keto-dimetin-cijanini (2a-f), a iz njih (ciklokondenza-cijom s hidrazin-hidrokloridom ili s hidroksilamin-hidrokloridom) odgovarajuća bojila (3a-g, 4a-d). Snimljeni su UVNIS spektri odabranih bojila u različitim čistim i miješanim otapalima teu vodenim (puferskim) otopinama. Utvrđeno je nastajanje molekulskih kompleksa u etanolnirnotopinama. Opažen i elektronski prijelazi pripisani su dijelom lokalnim ekscitacijama, a dijelomprijenosu naboja. SpektraIni pomaci Objašnjeni su molekuIskom strukturom i(ili) utjecajem me-dija. Istraživana je i fotostabilnost odabranih bojila (2e, 3g, 4d).

M M Girgis. . ,

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Transcript of M M Girgis. . ,