m m girgis. . ,
TRANSCRIPT
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
ive
data
obta
ined
for
v-ke
to-d
imet
hine
cyan
ine
dyes
(2e
and
2r)
inm
ixed
solv
ents
at27
"C.
Exei
l.en
ergy
n ><Co
mpo
und
>-Sy
stem
CkJ
mol
-I)
nKr
zN
o.s;: trl
Pure
solv
ent
Pure
EtO
Hcl ><
2eCH
C13-
EtO
H21
3(CH
C13)
215
10.
015
ĐlH
20-E
tOH
216(
H20
)21
52
0.04
22e
CHC1
3-Et
OH
218(
CHCh
)22
11
0.19
6H
20-E
tOH
224(
H20
)22
12
0.05
2
0\ ......
VJ
614 A. I. M. KORAIEM ET AL.
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.
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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).