Dyes and Pigments 6 (1985) 213-226

Chromophoric Chain fl-Aryl-Substituted Styryl Cyanines :Effect of Substituents on Visible Absorption Spectra

and Photosensitisation Properties

B. N . Jha

University Department of Chemistry, L, N . Mithila University,Kameshwar Nagar, Darbhanga-846004, Bihar, India

and

J. C. Banerji

6 Rajendra Nagar, Patna-800016, Bihar, India (Formerly Head ofthe Department of Chemistry, B.N. College, Patna-800004)

(Received : 6 September, 1984)

SUMMARY

A number of chromophoric chain f-aryl-substituted (CCBAS) styrylcyanines (hemicyanines) have been synthesised by condensing substitutedquaternised quinaldine bases with substituted benzophenones, with a viewto studying the effect of the aryl substituents on their visible absorptionand silver halide photosensitisation properties .

The dyes absorb at longer wavelengths than the unsubstitutedanalogues, showing uniform bathochromic shifts and extra photosensit is-ation properties, which corroborate the authors' previous findings .

Irrespective of the nature of the substituent attached to the chromo-phoric /3-phenyl group, electron withdrawing and donating groups resultin a bathochromic shift ofthe visible absorption band and extension oftheextra photosensitisation in most cases.

1 . INTRODUCTION

We have reported recently the spectroscopic and sensitisation propertiesof a number of hemicyanines . t -3 As a continuation of this work some

213Dyes and Pigments 0143-7208/85/$0390 © Elsevier Applied Science Publishers Ltd,England, 1985. Printed in Great Britain

214

B. N. Jha, J. C. Banerji

more CCBAS dyes have been prepared and the effect of the various fl-arylsubstituents on optical properties has been studied . These dyes wereprepared by condensing 4-dimethylamino-, 4dimethylamino-4'-nitro-,4-dimethylamino-2'-nitro- and 4-dimethylamino-3',5'-dinitro-benzophe-nones with different 6-substituted quinaldinium salts as summarised inScheme 1 .Absorption maxima (A.,) and the ranges of extra-sensitisation data

have been recorded and comparison made between the corresponding

X

0U~No CH 3 + O aC-

IIMe

X

Scheme 1

~MeN

Me

Dye X R Dye X R Dye X R

D,D,

HCI

HH

D,D, 6

HCI

4-nitro4-nitro

D,,D,,

MeOMe

2-nitro2-vitro

D,D,D5

BrIMe

HHH

D,,D, rD„

BrIMe

4-nitro4-nitro4-nitro

DyDi,D„

OEt5,6-BenzMe

2-nitro2-nitro3,5-dinitro

D6 OMe H D„ OMe 4-nitro DJ6 OMe 3,5-dinitroD7 OEt H D,, OEt 4-nitro D„ OEt 3,5-dinitroD6 5,6-Benz H D16 5,6-Benz 4-nitro Du 5,6-Benz 3,5-dinitro

D,

D=

D3

D`

Ds

D6

D7

De

Chromophoric chain /1-aryl-substituted styryl cyanines

215

X91"IiKJWA

Fig. 1 . Sensitisation spectrographs of the dyes .

216

B. N. Jha, J. C . Banerji

D9

DIG

D„

D12

D13

D14

DIS

D16

Alass

it w d,yfl1

∎

. illriAMM kffi

.

+' ~ilf"711AMi~i'ff I!F

Fig. 1-contd.

D21

D==

D23

Dy

Dr

Db

Dar

D32

Unbathed

Fig. I-conrd

218

B. N. Jha, J. C. Banerji

chain fl-substituted and fi-unsubstituted analogues.` The styrylcyanines have been examined extensively' -12 and earlier observationssuggest that substituents attached to a- or #carbon atom with respect tothe heterocyclic end group in the chromophoric chain cause hypso-chromic shifts of the absorption maxima compared with the unsubstitutedanalogues . 11-17

However, the dyes now described show invariably bathochromic shiftswhich confirm the authors' previously reported work . I - I

Since the fl-phenyl, fl-4nitrophenyl and fl-2-nitrophenyl substituentshave a strong resonance effect, it is possible that chromophoric chain#-substitution of this type may affect the resonance stabilisation of thedye molecule. However, the steric hindrance to the resonance stabilisationin the prime chromophoric chain due to the bulkiness of the fi-substituents may also be an important factor to consider .

2 . RESULTS AND DISCUSSION

Analytical and other experimental data for the dyes are summarised inTable 1 . Sensitisation spectrographs of photographic plates treated withthe dyes were obtained and compared with that of an undyed plate(Fig . 1). The absorption maxima (A..) of the iodide salts in ethanol arerecorded in Table 2 and the extra-sensitisation data in Table 3 .

2.1 . Visible absorption spectra

Comparison of the absorption data for the present CCBAS styryl cyaninedyes (series 1, series 2, D21_24 of series 3 and D29-32 of series 4), with thoseanalogues described previously" (Dn_2u of series 3, D2,,-,, of series 4 andseries 5) and with the fi-unsubstituted dyes" . ' (series 6) cited from theliterature permits the following generalisations to be made .

A chain fl-aryl substituent causes a general bathochromic shift ofthe absorption maximum of about 20-40 my relative to correspondingunsubstituted analogues,' , ' irrespective of the nature of any additionalgroups attached to the phenyl ring, i.e., whether they are electronattracting or electron donating or whether they are just space occupying .This is in contrast to the earlier observations that either a- or #-substitution generally leads to hypsochromic shifts . ) ' -17 The presentreport also corroborates the authors' previous investigations .` - '

TABLE

1An

alyt

ical

Dat

a of

the

Dye

s

Dye

symb

olMe

thio

dide

of b

ase

Dye

asmethiodide°

Crys

tal

colo

ur a

ndYi

eld

(%a

M.p

.(°

C)Mo

lecu

lar

form

ula

Foun

dCalc

.

shap

e°N

Hal.

NHa

l.

D1Q'

Mel

2-p-

DMA(

$-P)

-S-Q

MeI

dve

4613

0C,

6H„N

,15-

6325-76

5.69

2581

02

6-CI

Q'Mel

2-p-

DMA(

$-P)

-S-6

-CIQ

Me1

sdvc

4116

0C,

6H,4N,CB

5-28

3081

5-32

3086

D,6B

rQ'MeI

2pDM

A($-

P)S-

6BrQ

MeI

dvtn

4617

5C,

6H2,N,Brl

4-85

36-1

74-

9036

-25

D4

6IQ'

Mel

2-pD

MA(B

-P)-

S-6I

QMel

ivs'n

4421

2C,,He4N,I,

4-48

41-2

34-

5341

-10

Ds6M

eQ'M

eI2-pDMA(f-P)-S-6MeQMel

Idvt

n68

169

C,7H

I,N2

15.4

725

-05

5-53

2540

Ds6M

eOQ'Mel

2-pD

MA(B

-P)-

S.6MeOQMeI

gdvm

n61

185

C„H,

7N,I

O5.

3124

-39

586

2433

D,6E

tOQ'MeI

2-pDMA(f-P)-S-6EtOQMe1

Idw

6320

8C2

6H2gN,10

5.14

23-6

252

22369

0s

5,6B

zQ'MeL

2-p-DMA($-P)S-fl-NtQMeI

dvc

5121

2C,

0H,7N,

14-

9823-2

35.

022329

D,Q'

Mel

2pDMA($-4NP)-S-QMeI

dvc

4318

5C

36H„N

3I0,

7.76

2359

7.82

23-6

5D

106CIQ'Mel

2p-D

MA(d

-4NP

)-S-

6CIQ

Mel

sdvs"n

4520

4C,

6H,3N,C110,

7.31

28-4

278

528

-45

D„6-BrQ'Mel

2-pDMA(S-4NP)S-6BrQMeI

dw47

210

C,6H

2,N3

Br1O

,648

33-6

56.8

233

-62

D12

6IQ'

Mel

2-pDMA(f-4NP)S-6IQMeI

dvtn

5024

1C,

6H,3N,1,0,

629

3836

683

3881

D,,

6MeQ

'Mel

2pDMA(f-4NP)-S-6MeQM

eldr

vg'n

4619

7C2

7H24N

3102

7.57

2298

7.62

23-0

5D„

6MeO

Q'Mel

2pDMA(f-4-NP)-S6MeOQMel

dvtn

4721

4C,

7H,6N,IO,

786

2234

7.41

22-4

0D,,

6EtO

Q'MeI

2pDM

A( -

4NP)

-S-6

EtOQ

MeI

dvtn

6222

2C,

6H,6N,

103

7-18

21-8

172

32186

1316

5,6-BzQ'

Mel

2-p-

DMA(

$-4-

NP)-

S-$-

NtQM

eIdv

s"cw

rt'

4623

7C,

0H,6N,10,

7.09

2157

717

21-6

3

D21

6MeQ'M

eI2-

pDMA

{$-2

-NP)

S-6M

eQMe

ldv

tnwr

t'63

211

C27H

I1N,

102

7-58

2301

7-62

23-0

5D

2,6M

eOQ'MeI

2-p-

DMA(

fl-2

-NP)

-S-6

MeOQMeI

gdvm

n55

219

C,7H,6N,IO,

786

22-3

37.

4122

-40

D„6E

IOQ'Mel

2-p-DMA($-2-NP)-S-6EtOQMel

dvsn

4523

6C2

8H,8N,IO,

7.17

21-8

272

32186

D,4

5,6BzQ'Mel

2-p-

DMA(

$-2-

NP)-

S-$-

NtQM

eIdvs"Wc

4426

5C,

0H,6N,10,

7.11

2158

7-17

2-63

DB6M

eQ'M

el2-p-DMA($-3,5-DNP)-S-6MeQMel

dvtn

6716

8C,

7H2,

N,10

,9-

352-27

9-40

21-31

D,6MeOQ'Mel

2-p-

DMA(

$-3,

5-DN

P)-S

-6Me

OQMe

Isdvs"n

6917

2C,

7H,,N,10,

9-07

2041

945

2075

D„6EtOQ'Me1

2-p-DMA($-3,5-DNP)-S-6EtOQMeI

gdve'n

7018

1C,

6H,7N,10,

8-87

20-2

48-

9420

-29

D,2

5,6BzQ'Mel

2-p-

DMA(

$-3,

5-DN

P)-S

-$-N

tQMe

Igd

vtn

6520

3C,,H

2,N410

48-81

2003

8 86

20-0

9

° Q, quinoline

; Q'

, qu

inal

dine

; P, phenyl;

S, st

yryl;

Bz,

Ben

z; N

P, n

itro

phen

yl;

Nt,

naph

thyl

; DMA, dimethylamino

; DNP, dinitrophenyl

.6c

, Cr

ysta

ls; c', cl

uste

rs; d, dark;

g,glistening

;H,

glazing;

i,

inte

nse;

1, lustrous

; m, minute;

n,

need

les;

r, reddish;

s, shining;

s', slender

; s", small;

t,

tiny

;t',

tinge

; v, v

iolet

; w, with;

W,

wool

ly.

Y-.

TABLE

2Absorption Data of the Dyes (Methosalts in Absolute Ethanol)

X

0NO2

0O,

N

-

NO,

I

Present work'

'Values marked with an asterisk have been taken from Ref

.l.

a

MeN,-CH=

:CN~

I

Y

Me

Me

Reported w

ork

H

X 1

Series I

NO,

Series 2

Seri

es 3

Seri

es 4

N /\

MeMe

Seri

es 5

(ref

. 2)

Seri

es 6

(ref

s 4,

5)

Dye

A~

(MP)

Dye

A (my)

Dye

A (my)

Dye

A (my)

(mp)

(my)

HD,

562

D,56

3*D

17

564

*D~

569

568

530

ClD,

570

D„

570

*D13

578

*D26

578

577

548

BrD,

575

D11

575

*DI,

579

*D„

580

579

550

ID,

582

Du

584

*Dm

583

*Ds

584

585

552

MeD

S

545

DI,

569

D31

568

Dm

574

578

OMe

D*

548

D14

575

D3E

577

D„

578

580

OEt

D,

569

D17

578

D,,

579

D31

583

581

5,6-Benz

Ds

571

D1*

573

D„

574

D,,,

576

575

r-S

TABL

E3

Sensitisation Data of the Dyes (Methosalts)

X 0 YPr

een

wo,k

'

N ,M

e Me

02N--~~NO

2Y N Me

MeRepo

rted

wor

k

H

Valu

es m

arke

d wi

th an asterisk have bm taken from Ref I

" ac

, Al

most

con

tinu

ous;

ai, almost isolated

; au, almost uniform, c, con

tinu

ous;

dc, disconnected;

i, intense, ibvr, intense blue violet range

; it

, is

olat

ed; k, loosely connamd

; m,

mod

erat

e;

mi,

mode

rate

lyin

tens

e; m

p, m

ore

pronounced

; ub, uniform band, up, unpronounced

; vw, very weak; vwl, very weak Grace

; w.

weak.

D' D

esen

aibs

er

X

Series

ISeries

2Se

ries

3Se

ries

4Se

ries

5(ref 2)

Seri

es 6

(ref, 4, 5)

Range

(mp)

A.°

(mp)

Rang

e(m

y)

anwst

(mp)

Rang

e°(ma

)2ms

s

(mp)

Rang

e(n'p)

A-

(mp)

Dye

Range

(.a)

A. (mp)

Remark?

Dye

Rema

rk,°

Dye

Rema

rks°

Dye

Rang

eA.-

(eap)

(mp)

HDI

600

580

w,dc

D9630

570

w, al

ID17

620

560

w,dc

,Ibv

rD

asD

•

-63

0580

630

580

CID2

610

580

w, dc, mp

Din

640

540w

mini

DI5

630

590u

pmi, c

Day

D' -

680

S4Ou

p650

595

570m

(?600w)

580w

BrD3

620

590

i,au

DI1

640

580

ms, ac

'D19

630

590

ms,c

Dan

D'

-680

540w

650

595

(?600w)

580

660

wI

D4620

560

i,au

D12

650

580

i,c

'Da9

650

590

i,k

D>e

D'

-68

0540

650

60D

(?600m)

580m

i600

Me

DS610

550

i, au

DD

630

560

my u

bD2

562

0530

mi, k

Dg

D'61

0580

580

OW

11610

530

m, c

D14

640

565

6,

rib

DD

620

540m

w, k

Da9

D'

-68

0540vw

550

580w

(>60

0vwt)

580w

OEt

D762

D530

vu,c

Did

640

600

w,al

Dan

620

540

D31

D'

-68

0SWvw

550

580

(?60

Dvwt)

580w

5,6-

Benz

DS60

0525

ml,c

D16

690

-w, at

D24

620

580u

pW,

onD-

-64

0525.p

550

550

222

B. N. Jha, J. C. Banerji

It can also be seen that the nature of the fl-phenyl substituent (whereR = H, 4-nitro or 2-nitro) has little effect on the absorption maximum .It is interesting that the recently reported 4-dimethylaminophenylsubstituted dyes carrying electron donating substituents at the )3-positionhave, in all cases, Amax at longer wavelengths than the correspondingfl-aryl dyes containing electron withdrawing groups or no group in thephenyl ring. The effect of the 4-dimethylaminophenyl group is almostequivalent to the space occupying, but electronically ineffective, (f-3,5-dinitrophenyl group .

The influence of 6-substituents in the heterocyclic moiety on A max issmall but consistent for most of the series (1-3) . Thus the progressivebathochromic shifts in various series and in the series already reported'-2follow the sequence :

6-1 > 6-Br > 6-Cl > 6-Hand also

6-OEt > 6-OMe > 6-Me > 6-H

[except in series 1, where D, > both D 6 and D5] .The present results also confirm the earlier observations' s ,8 , 19 that the

nature and position of the substituents in the heterocyclic terminalresidue of the dye molecule can influence both the visible absorption bandand the sensitisation properties .

Absorption spectrographic properties of the dyes based on the con-densed fl-naphthaquinaldine system are anomalous, but even here, theeffect of fl-aryl groups is clearly operative and the dyes again absorb atlonger wavelengths than the fl-unsubstituted analogues .' , '

2.2 . Photosensitisation

Analysis of the sensitisation data does not permit any definite general-isation to be made. Although most of the newly prepared dyes (series 1, 2and 3) except the )3-3,5-dinitrophenyl dyes (series 4) are fairly goodsensitisers, the effect of the chromophoric chain #-substitution has noappreciable beneficial effect . The ranges of extra-sensitisation are ingeneral lower than those for the fl-unsubstituted analogues . This may bea steric effect, due to the CCBAS group projecting above and below theplane of the conjugated planar molecule ."

The fl-4-nitrophenyl dyes (series 2) are slightly better sensitisers when

Chromophoric chain fl-aryl-substituted styryl cyanines

223

compared with the $-2-nitrophenyl (series 3) and fl-phenyl (series 1) dyes .In some cases (D6-D., D10 and D31D23) two peaks can even be observed .In contrast the fi-3,5-dinitrophenyl dyes (series 4) are desensitisers, andthe intensity of the silver halide plates in the blue-violet range isdecreased . The desensitising property varies in the order

D28 < D 27 < D26 < D75and

D29 < D31 < D30 < D32It can also be seen that the extension of optical sensitisation induced by

6-substituents in the heterocyclic moiety follows the sequence :I>Br>Cl>H

andOEt >_ OMe ? Me >_ H

Moreover, it was also found that the present dyes were inferiorsensitisers in comparison with the fi-4dimethylaminophenyl dyes (series5), recently reported by the authors,' with regard to the range of extra-sensitisation, the extension of the sensitisation maxima, number of peaksand intensity of extra-sensitisation . Of the electron attracting chromo-phore, -NO 2 , and the electron donating auxochrome, -NMe 2 , thelatter is more effective than the former .

2.3 . General comparative conclusion

Comparison of the absorption data of the variously /I-substituted styryldyes leads to some interesting observations .The recently reported fl-4-dimethylaminophenyl substituted dyes'

(series 5) have consistently longer 'Lax values than the corresponding $-4-nitrophenyl substituted dyes (series 2) . The suggestion that the oppositemesomeric effect of the two substituents (A) and (B) is responsible for thecomparatively lower bathochromic shifts in the case of (B), does not appearto be valid. For, if this were the case, the fl-2-nitrophenyl substituteddyes (series 3) should have shown significant hypsochromic shifts, the2-nitrophenyl group (C) being more strongly electron attracting thanthe 4-nitrophenyl group (B), because of combined mesomeric andinductive effects . It may, however, be argued that the bulky /3-2-substituent causes out-of-plane twisting of the phenyl group, thus

224

B. N. Jha, J. C. Banerji

OT\O

MeNMe

O~ O(A)

(B)

(C)annulling the mesomeric effect and leaving only the inductive effectoperative .

The enhanced bathochromic shifts conferred by the fl-3,5-dinitrophenylsubstituent (series 4) suggests that steric effects are probably moreimportant than electronic effects . In this case the 3,5-dinitrophenyl groupwill have no mesomeric effect and only an insignificant inductive effect asa substituent .

It can also be seen for a given terminal hetero substituent that the fl-4dimethylaminophenyl substituted dyes' (series 5) are the best sensitisersamong those dyes studied by the authors . The obvious conclusion is thatthe strong electron donating effect to the conjugated system causes anenhanced bathochromic shift and a correspondingly enhanced sensitis-ation. On the other hand, the fl-4-nitrophenyl substituted dyes (series 2)are less effective sensitisers and absorb at a slightly shorter wavelength .The fl-4nitro substituted ring is not likely to lie exactly in the same planeand thus does not fully participate in resonance delocalisation, andconsequently its electron withdrawing effect is reduced .

The optical properties of the fi-2-nitrophenyl dyes (series 3) are moreinteresting. Although in the $-2-nitrophenyl compounds, the nitro groupcauses electron withdrawal due to both mesomeric and inductive effects,the mesomeric effect of the 2-nitrophenyl substituent is likely to beinsignificant, as steric interference would, in all probability, twist thebenzene ring out of the plane of the main conjugated system [model (D)],

NMe2

Chromophoric chain f-aryl-substituted styryl cyanines

225

thus inhibiting resonance delocalisation . Even so, the absorption andsensitisation properties of these dyes lie between those for the f-4dimethylaminophenyl 2 (series 5) and the fl-phenyl dyes (series 1) andclose to the Jf-4nitrophenyl dyes (series 2) .

3 . EXPERIMENTAL

3.1 . Chain substituted styryl cyanines

4Dimethylaminobenzophenone, 4-dimethylamino-4'-nitrobenzophenone,4-dimethylamino-2'-nitrobenzophenone and 4dimethylamino-3',5'-di-nitrobenzophenone (reported by Jha and Banerji') were obtained byadaptation of the method of . Shah et al. 21 The quaternary salts wereprepared by the general procedure suggested by Johnson and Adams ."

Condensation to give the dyes was effected, using the method reportedearlier." A mixture of the ketone and the quinaldinium salt (M : M)dissolved in the requisite volume of absolute ethanol/pyridine, wasrefluxed for about 2 h in the presence of piperidine as catalyst . The dyewhich precipitated after concentration was purified by recrystallisationfrom methanol .

3.2 . Absorption and sensitisation spectra

The absorption maxima (A max ) of ethanolic solutions (1/1000 = w/v) ofthe dyes were recorded on a Beckmann Spectrophotometer Model DU,adjusting the transmission of the dye solutions to between 40 and 60'/o'-The sensitisation spectra were recorded on an Adam Hilger WedgeSpectrograph, using process plates (N40, Ilford Ltd) and a 150 cp point-o-lite AC lamp, as light source . The plates were previously dipped in dyesolutions (1/50000 = w/v in 30 % ethanol) for 4min, drained and dried .Exposures of 4 min were given and plates were developed by the usualprocedure. The spectrograph of an unbathed plate was also recorded forcomparison (Fig . 1) .

ACKNOWLEDGEMENTS

Thanks are accorded to Professor Y . Thakur, Head of the UniversityDepartment of Chemistry, L . N . Mithila University, Kameshwarnagar,

226

B. N. Jha, J. C. Banerji

Darbhanga-846004 for his useful discussion and support . The financialassistance and encouragement of Dr (Mrs) D . Kumari Jha, Head of theChemistry Department, M . R . Mahila College, L . N . Mithila University,Darbhanga-846004 are also appreciatively acknowledged .

REFERENCES

I . B. N. Jha and J . C. Banerji, Dyes and Pigments, 1, 161 (1980) .2 . B. N . Jha and J . C. Banerji, Dyes and Pigments, 4, 77 (1983) .3 . B. N. Jha, Ph.D. Thesis, Bihar University, Muzaffarpur, Bihar . India

(1974) .4 . J . C. Banerji, A . K . Sinha and R. J . N. Sahay, J. Indian Chem . Soc ., 43,

225 (1966) .5 . J . C. Banerji and S . N . Sanyal, Indian J . Chem., 6, 346 (1968) .6 . F . M . Hamer, Cyanine dyes and related compounds, New York, Interscience

Publishers (1964), for a comprehensive survey of the subject with whichthis paper is concerned .

7 . J. C. Banerji, K . D. Banerjee, N . P. Bhattacharya and S . N . Sanyal,J. Indian Chem. Soc ., 45, 496 (1968) .

8. S . N . Sanyal, Ph .D. Thesis, Bihar University, Muzalfarpur, Bihar, India(1966) .

9 . N. Mishra, D, Patnaik, L . N . Patnaik and M . K . Rout, J. Indian Chem . Soc.,56, 367 (1979) .

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