Synthesis and spectral properties of merocyanine dyes based on fluorene and its derivatives

Article abstract of DOI:10.1134/S1070363212040172

The di-, tetra- and hexamethine merocyanines, the derivatives of fluorene, diphenyl 9H-fluorene-2,7-disulfonate, and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-disulfonate, as well as the derivatives of the heterocycles of moderate (indolyliden

Full text of DOI:10.1134/S1070363212040172

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 4, pp. 703–719. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.V. Kurdyukova, N.A. Derevyanko, A.A. Ishchenko, D.D. Mysyk, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 4,
pp. 617–633.
Synthesis and Spectral Properties of Merocyanine Dyes
Based on Fluorene and Its Derivatives
I. V. Kurdyukovaa, N. A. Derevyankoa, A. A. Ishchenkoa, and D. D. Mysykb
a Institute of Organic Chemistry, National Academy of Sciences of Ukraine,
ul. Murmanskaya 5, Kiev, 02094 Ukraine
e-mail: alexish@i.com.ua
b Donetsk National Technical University, Donetsk, Ukraine
Received August 1, 2011
Abstract—The di-, tetra- and hexamethine merocyaninуes, the derivatives of fluorene, diphenyl 9H-fluorene-
2,7-disulfonate, and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-disulfonate, as well as the derivatives
of the heterocycles of moderate (indolylidene and benzotiazolylidene), weak (benzo[c,d]indolylidene and 2,6-
diphenylpyrane) and strong (2,6-diphenylpyridine) electron-donor properties were synthesized and their
absorption spectra in solvents of different polarity were studied. The quantum-chemical analysis of electronic
structure of the synthesized merocyanines was performed and the types of electronic transitions in them were
found by the DFT and TDDFT methods with the B3LYP/6-31G(d,p) basis.
DOI: 10.1134/S1070363212040172
Merocyanine dyes, due to a wide range of
practically important properties, like pronounced
solvatochromism, the ability to significantly alter the
dipole moment at the electron excitation and sensitize
various physical and chemical processes, find an
increasingly wide application in optoelectronics,
nonlinear optics, recording media and information
processing, medicine and biology [1, 2].
of the merocyanines containing heterocyclic fragments
with various electron-donating properties.
We failed to carry out the cyanine condensation at
the methylene group of fluorene because of its
insufficient C–H acidity (pKa = 20.5) [5] even in the
presence of strong bases like 1,8-diazabicycloundec-7-
ene (DBU) and a “proton sponge” 1,8-bisdimethyl-
aminonaphthalene. The merocyanines based on the
unsubstituted fluorene (III–V) were synthesized by
Wittig reaction using the fluorene tributylphosphorus
ylide I [6] (Scheme 1).
Traditionally, the end groups of the merocyanines
are the residues of heterocyclic compounds [1, 2]. The
search for new heterocycles is the basis for creating the
dyes with a deep color, that is, absorbing light at long
wavelengths [3]. In this work we aimed at exploring a
possibility to synthesize the merocyanines based on
aromatic carbocycles. We selected the fluorene
framework as the carbocycle. The choice is due to the
expanded π-system, the high electronic symmetry and
the presence of a methylene group, which can be
potentially active in the reactions of cyanine condensa-
tion owing to its conjugation with the benzene ring [4].
The introduction to the fluorene core of acceptor
substituents with the moderate and strong acceptor
properties, the phenoxysulfonyl group (for SO2OPh
σm
=
0.36, σp
=
0.33 [7]) and octafluoro-
phentyloxysulfonyl group (σm = 0.78, σp = 0.88 [8]),
respectively, facilitated considerably the cyanine
condensation at the methylene group of the fluorene
frame. The merocyanines based on the fluorene
derivatives IX–XVI, XVIII–XIX, XXII–XXIII were
synthesized in the reaction of the substituted fluorene
with heterocyclic aldehydes and heterocyclic
hemicyanines (Scheme 2) under usual conditions of
the cyanine condensation. The merocyanines with
pyridine ring (XXIV–XXV) were obtained from
We synthesized and studied a number of mero-
cyanines based on the unsubstituted fluorene and sub-
stituted analogs, diphenyl 9H-fluorene-2,7-disulfonate,
and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-
2,7-disulfonate, not utilized previously in the synthesis
703

704
KURDYUKOVA et al.
Scheme 1.
Me
Me
Me
Me
Δ
+
N
o-xelene
n
N
O
Me
n
PBu3
Me
III_V
I
IIa_IIc
n = 0 (IIa), 1 (IIb), 2 (IIc).
Scheme 2.
Ph
O
R
R
Ph
O
IIa
XX
VIa, VIb
Ph
X
O
A
Ph
N
A
Y
N
N
A
n
n
Ph
OEt
R1
Ac
Ph
XXI
VIIa, VIIb; VIIIa, VIIIb
XVIIa, XVIIb
R
Ph
R
R
X
O
N
n
n
N
Ph
R1
n
Ph
R
R
R
IX_XVI
XXII, XXIII
XVIII, XIX
VIa, R = SO2OPh; VIb, R = SO2OCH2(CF2)3CHF2; VIIa, X = C(Me)2, R1 = Me, n = 1, A = ClO4; VIIb, X = C(Me)2, R1 =
Me, n = 2, A = ClO4; VIIIa, X = S, R1 = Et, n = 1, A = BF4; VIIIb, X = S, R1 = Et, n = 2, A = TosO; XVIIa, Y = N(Me)2,
n = 1, A = BF4; XVIIb, Y = OEt, n = 2, A = BF4; XXI, A = BF4; IX–XIV, X = C(Me)2, R1 = Me; XV–XVI, X = S, R1 = Et;
IX–XI, XV–XVI, XVIII–XIX, XXII–XXIII, R = SO2OPh; XII–XIV, R = SO2OCH2(CF2)3CHF2; IX, XII, XVIII, XXII,
n = 0; X, XIII, XV, XIX, XXIII, n = 1; XI, XIV, XVI, n = 2.
pyrilium compounds XXII–XXIII in the reaction with
previously. The hemicyanines (VII, VIII) were
methylamine (Scheme 3).
synthesized by the known conventional methods [15].
Compounds IIa, IIb [9], IIc [10], XVII [11, 12],
XX [13], and XXI [14] have been described
Merocyanines can be considered as hybrids of two
types of symmetric dyes, cationic and anionic, one of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
705
Scheme 3.
SO2OPh
Ph
SO2OPh
Ph
Me
O
N
MeNH2
DMSO
n
n
Ph
Ph
PhOO2S
PhOO2S
XXII, XXIII
XXIV, XXV
n = 0 (XXII, XXIV), 1 (XXIII, XXV).
SO2OPh
PhOO2S
n
n
K
SO2OPh
PhOO2S
DBU H
XXIX_XXXI
XXVI_XXVIII
X
X
N
N
n
I
R
R
XXXII_XXXVI
Ph
Ph
O
O
Ph
Ph
N
N
R
n
n
ClO4
BF4
R
XXXVII
XXXVIII
Ph
Ph
Me
Me
Ph
N
N
Ph
n
BF4
XXXIX
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

706
KURDYUKOVA et al.
which has a longer polymethine chain, and another a
shorter chain than merocyanine. To calculate the
deviations, we used in this work the anionic dyes
XXVI–XXXI [16–18], and the cationic dyes XXXII–
XXXIX [16, 17].
strong electrophilic solvation, including the formation
of hydrogen bonds.
The main parameters describing the electron
absorption spectra are the absorption maximum (λmax
)
and molar extinction coefficient (ε). However, the λmax
value does not always reflect objectively the spectral
pattern, because it may be affected by various vibronic
transitions [16]. In addition, the maximum may be
determined with insufficient accuracy in the case of
broad, diffuse or highly structured bands. The curves
with such shape are characteristic of merocyanines
III–V, IX–XVI, XVIII–XIX, and XXII–XXIII, in
contrast to the corresponding symmetrical ionic dyes.
The chosen solvents are the almost non-polar
hexane (nD = 1,3751, εD = 1.890, B = 0 cm–1, E = 0),
which provides the polarity range approaching that in a
vacuum, and toluene (nD = 1.4961, εD = 2,37, B = 58 cm–1,
E = 1.3), low-polar dichloromethane (nD = 1.4242,
εD = 8.9, B = 23 cm–1, E = 2.7), polar acetonitrile (nD =
1.3441, εD = 36.2, B = 160 cm–1, E = 5.2) and DMF,
(nD = 1.4303, εD = 36.7, B = 291 cm–1 , E = 2.6), as
well as a typical proton-donor ethanol (nD = 1.3611,
εD = 24.3, B = 235 cm–1, E = 11.6) [16]. The latter is
regarded primarily as a solvent potentially prone to
We performed a mathematical treatment of long-
wavelength absorption bands of the synthesized dyes
by the method of moments [16]. This allowed us a
Table 1. Characteristics of long-wavelength absorption bands of merocyanines III–V, IX–XVI, XVIII–XIX, and XXII–
XXV in n-hexane, toluene, dichloromethane, acetonitrile, DMF, and ethanol.
Comp. no.
Solvent
Hexane
λmax, nm
Dλ, nm
ε×10–4, l mol–1 cm–1
M–1, nm
DM, nm
f
429
452
6.82
5.71
422.0
0.93
III
Toluene
441
460
4.91
4.34
436.1
0.73
CH2Cl2
EtOH
447
439
451
471
485
491
482
496
106.5
109.5
102.5
6.10
6.01
5.32
7.80
5.94
6.85
6.81
6.30
442.0
433.7
444.2
452.7
470.5
480.0
433.9
485.6
471.1
0.93
0.95
0.87
1.13
0.95
1.15
0.94
1.08
1.32
DMF
92.9
Hexane
Toluene
CH2Cl2
EtOH
IV
151
152.5
141.5
DMF
Hexane
480
503
7.53
7.80
V
Toluene
CH2Cl2
EtOH
509
516
504
520
5.62
7.17
7.18
6.91
492.4
504.5
490.7
508.7
475.3
0.98
1.30
1.34
1.31
0.63
232.5
235.5
223
DMF
Hexane
475
503
4.09
5.80
IX
Toluene
CH2Cl2
EtOH
518
519
515
519
525
5.54
5.86
5.67
5.73
5.85
488.6
495.1
489.0
492.4
496.6
0.67
0.73
0.75
0.80
0.86
CH3CN
DMF
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
707
Table 1. (Contd.)
Comp. no.
Solvent
Hexane
λmax, nm
532
564
555
583
564
562
567
580
581
600
608
601
600
614
480
509
521
523
516
520
524
543
575
Dλ, nm
ε×10–4, l mol–1 cm–1
6.49
M–1, nm
DM, nm
f
521.5
0.88
X
5.30
6.13
5.61
5.56
Toluene
545.7
0.91
CH2Cl2
EtOH
107
99.5
93.5
84
549.0
544.0
544.6
560.9
554.3
578.7
585.4
583.7
585.2
594.7
478.5
0.90
0.96
0.96
0.85
1.00
1.11
1.21
1.22
1.27
1.22
0.83
5.69
94.1
CH3CN
DMF
5.41
90.95
5.13
Hexane
Toluene
CH2Cl2
EtOH
6.47
XI
6.55
170.5
168.5
163.5
154.5
6.57
168.9
155.8
146.3
143.1
6.48
CH3CN
DMF
6.43
6.04
Hexane
4.94
7.56
7.05
XII
Toluene
CH2Cl2
EtOH
488.4
490.6
483.3
487.3
490.9
535.0
0.87
0.93
0.93
0.95
0.93
0.91
6.96
6.41
CH3CN
DMF
6.38
6.35
Hexane
6.62
5.96
XIII
Toluene
CH2Cl2
561
587
570
589
563
570
578
593
610
617
604
603
613
556
612
620
617
621
631
607
627
637
635
634
648
6.17
5.98
6.30
6.29
6.28
6.24
5.97
7.97
7.66
7.49
7.42
7.04
6.89
552.1
557.5
0.93
1.01
EtOH
547.9
550.4
557.9
570.4
587.7
597.25
585.7
585.9
596.0
547.5
569.8
577.3
574.9
577.1
585.4
577.1
604.7
618.1
614.0
614.8
626.7
1.05
1.08
1.02
1.20
1.25
1.33
1.43
1.39
1.33
CH3CN
DMF
Hexane
Toluene
CH2Cl2
EtOH
XIV
158.5
162.5
156.5
152.5
CH3CN
DMF
Hexane
Toluene
CH2Cl2
EtOH
CH3CN
DMF
XV
6.98
8.03
7.70
7.71
7.80
1.08
1.22
1.21
1.24
1.20
54
53.5
73.85
71.15
40.5
61.4
Hexane
Toluene
CH2Cl2
EtOH
XVI
6.83
7.01
5.85
6.43
5.36
1.10
1.24
1.09
1.25
1.04
147.5
146
143.85
134.35
120.35
111.3
CH3CN
DMF
133
130
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708
KURDYUKOVA et al.
Table 1. (Contd.)
Comp. no.
Solvent
λmax, nm
Dλ, nm
ε×10–4, l mol–1 cm–1
M–1, nm
DM, nm
f
Hexane
Toluene
CH2Cl2
EtOH
566
579
579
576
576
574
606
621
614
609
604
618
506
537
521
550
519
548
517
544
522
543
530
552
546
566
567
566
562
573
571
608
587
625
624
621
620
628
646
699
551.8
566.9
566.7
564.3
564.8
564.0
577.5
598.5
598.7
593.9
593.7
605.4
502.5
XVIII
4.73
5.49
5.11
5.24
7.36
0.65
0.77
0.73
0.77
1.01
CH3CN
DMF
Hexane
Toluene
CH2Cl2
EtOH
XIX
5.92
5.74
6.10
5.40
5.34
0.91
0.93
1.04
0.90
0.89
168
147.05
140.8
166.5
169.5
162
CH3CN
DMF
Hexane
XXII
Toluene
CH2Cl2
EtOH
4.04
4.30
4.20
4.47
4.30
4.49
4.23
4.37
4.06
4.34
520.7
518.9
515.2
516.4
513.8
0.83
0.89
0.93
0.91
0.92
CH3CN
DMF
Hexane
Toluene
CH2Cl2
EtOH
531.4
556.7
557.2
553.4
550.2
560.1
566.5
XXIII
XXIV
5.48
5.64
4.72
5.41
4.66
1.07
1.17
1.00
1.17
1.00
177.5
175.5
157.35
153.1
CH3CN
DMF
Hexane
Toluene
6.36
586.0
0.79
CH2Cl2
EtOH
9.80
9.46
584.6
583.2
583.4
590.2
619.6
0.93
0.90
0.86
0.90
CH3CN
DMF
9.80
10.34
Hexane
XXV
Toluene
CH2Cl2
EtOH
668
724
671
726
669
724
719
8.13
7.24
7.94
11.73
7.46
11.72
14.97
654.6
668.4
666.3
1.19
1.28
1.25
49.5
–5.5
14.1
4.6
CH3CN
DMF
–6.5
677.9
682.1
1.22
1.18
726
14.69
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
709
reliable estimation of the relevant parameters of the
position (M–1) and intensity (f) of the bands. The value
of M–1, averaged over all vibronic transitions and
corresponding to the average position of the band (in
the wavenumber scale, it is the center of gravity of the
BLA (bond length alternation) and BOA (bond order
alternation) are most often used [19], which represent a
difference between the average lengths (orders) of
single and double bonds of the polymethine chain in
the resonance structure of uncharged polyene [20]. The
BLA parameter takes positive values for the structures
A1 and intermediate between A1 and A2, and negative
in the case of structures A3 and those in the A2–A3
interval [19]. The BOA parameter has opposite signs
in these structures. Both parameters are zero for the
structures of type A2.
–
band: ν = 107/M–1), makes it possible to compare
objectively the curves differing in shape, in contrast to
λmax. Similarly, the integral intensity (oscillator strength
f) is more advantageous compared with the peak
intensity (extinction ε).
Table 1 lists the spectral characteristics of
merocyanines III–V, IX–XVI, XVIII–XIX, and
XXII–XXV. The data for anionic XXVI, XXX–XXXI
and cationic XXXII–XXXIX cyanines are given in
[17] and the monograph [16], respectively.
In addition to the BLA and BOA, we calculated the
parameter ΔPch [16]:
m
m
ΔPch = 1/m Σ |Pav – Pi|, ΔPav = 1/m Σ Pi,
i=1
i=1
Note that merocyanines III–V, in spite of the fairly
well-developed π-system of the core, are colored
rather highly (Table 1). Their λmax and M–1 values are
in the regoion of much shorter wavelengths than the
related values of the classic merocyanines based on the
indolylidene [2,11,12]. This indicates in them the more
pronounced alternation of bond orders in the
chromophore. This conclusion is clearly confirmed by
the unusually high values of the deviations compared
with the known merocyanines (Table 1, [2]). Thus, the
Dλ value of dye V reaches 232.5 nm.
where Pav is the average bond order over the chain, Pi
is the bond order of ith bond in the chain, m is the
number of bonds.
The alternation of bonds in the chromophore
determines the trends in the change of the vinylene
shifts, deviations, and the band shapes, especially their
width. The stronger alternation, the less vinylene
shifts, larger deviations, and wider bands [16].
The BLA and BOA parameters of the merocyanines
III–V are respectively positive and negative (Table 2).
Quantum-chemical calculations found in them much
greater alternation of bond length in polymethine
chains than in the corresponding symmetric cationic
and anionic dyes, and close to that in the
cyclooctatetraene, which is used as a model of ideal
neutral polyene [19] (Table 2). Dipole moments of
merocyanines III–V increase at excitation. All this
suggests that in merocyanines III–V the S0 state is
most close to the structure A1 in a vacuum.
The electronic structure of the merocyanine dyes is
clearly described as a superposition of three basic
boundary structures A1–A3 (Scheme 4) [2],
corresponding to the three ideal states: neutral polyene
(A1), polymethine (A2) and charged polyene (A3).
The above spectral effects in merocyanines III–V
can occur when the electronic structure of the ground
state S0 approaches one of the structures with
alternating single and double bonds A1 or A3.
The approach of the electronic structure of
investigated dyes to one of the ideal structures A1, A2,
and A3 can be estimated from the degree of alternation
of the bond lengths or orders in the chromophore [19].
To quantify the alternation in merocyanines parameters
The unambiguous choice between these structures
can be made considering a sign of solvatochromism of
the merocyanines. The positive solvatochromism
shows the prevalence of structure A1 in the ground
state (dipole moment is higher in the excited than in
Scheme 4.
δ+
δ−
D
A
D
A
A
D
n
n
n
A1
A2
A3
D and A are donor and acceptor ends of the chromophore, respectively.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

710
KURDYUKOVA et al.
Table 2. The results of quantum-chemical calculations of the parameters of bond orders alternation and dipole moments in
the ground and first excited states of merocyanines III–V, IX–XI, anionic (XXVI–XXXI) and cationic (XXXII–XXXIV)
dyes, and cyclooctatetraene XL
theor
Comp. no.
BLA
BOA
ΔРch
δ
λ
, nm
ftheor
μ, D
μ*, D
max
0.06
–0.401
–0.383
–0.376
–0.307
0.178
0.4119
0.4350
0.4429
0.2946
405.0
445.7
485.1
448.4
395.1
486.1
1.104
1.639
2.107
0.678
0.363
1.301
4.0
5.2
6.1
5.3
9.9
14.2
18.7
17.8
III
IV
V
0.061
0.061
0.044
0.1838
0.1843
0.1362
IX
0.049
–0.305
0.1466
0.3078
7.5
21.4
X
0.05
0
–0.31
0
0.1519
0
0.3243
0.1623
528.6
461.1
417.9
492.5
1.821
0.615
0.189
1.395
9.2
0.2
26.1
0.1
XI
XXVI
0.006
–0.046
0.023
0.1404
0.2
0.2
XXVII
0.006
0
0.011
0
0.0249
0
0.1454
0.1951
541.2
546.0
435.5
587.9
473.8
632.3
523.4
456.5
2.092
0.289
0.303
0.486
0.765
0.958
0.784
1.268
0.1
1.9
0.7
3.1
XXVIII
XXIX
0.006
–0.026
–0.021
0.013
0.2022
0.1706
0.8
0.1
0.7
0.3
XXX
0.0005
0.0118
XXXI
0
0.015
0.0075
0.0078
0.2717
0.2066
2.9
2.7
2.3
2.6
XXXII
0.003
–0.017
503.1
545.1
195.5
1.877
2.519
0.38
XXXIII
0.004
0.131
–0.028
–0.800
0.014
0.441
0.1526
2.02
2.5
0
3.1
0
XXXIV
XL
ground state), while negative sign, on the contrary,
corresponds to A3 structure (dipole moment in the
ground state is higher than in the excited state) [2]. For
the correct determination it is necessary to compare the
spectral shifts of the bands in a pair of solvents whose
nD values are similar while macroscopic (εD) and
microscopic (B and E) parameters of polarity are
significantly different. In this study we selected
dichloromethane and DMF. The latter is significantly
more polar and nucleophilic than the former while
their nD and E values are similar. Consequently, the
observed red shift of bands of merocyanines III–V in
going from CH2Cl2 to DMF is associated with the
increased polarity of the medium and demonstrates the
positive solvatochromism of these dyes.
a more polar ethanol, unlike the replacement by DMF,
causes blue rather than red shift of λmax and M–1. The
same effect was observed with other dyes. It may be
concluded that these merocyanines have a negative
solvatochromism. However, the reason for this shift is
the lower nD value of ethanol as compared with
CH2Cl2. It follows from the observed blue shift that
this factor dominates over the effect of increasing εD
and E parameters at the use of ethanol.
Consequently, the electronic structure of the
merocyanines III–V in the ground state approaches the
neutral polyene structure A1.
The positive solvatochromism of merocyanines
III–V is small and varies little with increasing
polymethine chain length. The replacement of CH2Cl2 by
DMF leads to a red shift of λmax and M–1 by 4 nm
820 cm–1) and 2.2 nm (112 cm–1) only, respectively, in
the case of merocyanine III and by 4 nm (149 cm–1)
and 4.6 nm (180 cm–1) in the case of the compound V
(Fig. 1).
By the example of the spectra of merocyanines III–
V we can illustrate the above considered often
appearing problem of incorrect determination of the
sign of solvatochromism. Thus, in the case of
merocyanine III the replacement of dichlorometane by
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
The insignificant positive solvatochromism of
711
merocyanines III–V while deviations are significant
points to the proximity of their electronic structure in
the ground state to that of ideal neutral polyene. This
conclusion is confirmed by the numerical values of
coupling constants of the polymethine chain protons in
the 1H NMR spectra of the dyes III–V. Note that usual
1H NMR spectra do not allow unambiguous
assignment of the signals.
Me Me
2
4
6
5
1
3
N
Me
V
λ, nm
Fig. 1. Absorption spectra of merocyanines III–V in
dichloromethane (solid) and DMF (dashed): (1) III, (2) IV,
and (3) V.
Therefore, we recorded COSY and ROESY spectra
of the dye V. Considering the 1H–1H correlations in the
homonuclear COSY spectrum we were able to assign
unambiguously all the proton signals of the polymethine
chain starting with the proton H1. In the ROESY spectrum,
at the saturation of the signal of proton H1 were
recorded the responses of both the proton H3 and the
protons of indolenine N-methyl group that indicates
the correctness of the initial assignment of the signal of
H1. At the saturation at the frequency of the signal of
H2 proton responses were observed of the protons of
isopropylidene group and H4 proton, as well as the
responses of lower intensity of the protons H1 and H3.
The proton H6 interacts with the protons of fluorene
framework and a proton H4, proton H3, with the
protons H1 and H5. The values of J12, J23, J34, J45, and
J56 of compound V are 12.0, 14.1, 11.4, 13.2, and
11.7 Hz respectively, indicating that the electronic
structure of merocyanines III–V in the ground state is
close to A1. We also note that the values of coupling
constants indicate all-trans structure of these mero-
cyanines.
The vinylene shifts in the spectra of merocyanines
III–V decrease with increasing chain length to the
values close to those characteristic of the carotenoids
in both non-polar and polar solvents. For example, the
first and second shifts in this series of dyes are
respectively 44 and 25 nm in CH2Cl2 and 45 and
24 nm in DMF. These values are significantly less than
those of traditional merocyanines. For example, in the
structural analogs of merocyanines III–V, in which the
fluorene core is replaced by the residue of
malononitrile, the first and second vinylene shifts are
90 and 75 nm respectively [18].
Increase in deviations and decrease in the vinylene
shifts at extending the polymethine chain indicate an
increase in the contribution of structure A1 in the
series of merocyanines III–V. This fact is consistent
with the broadening of the absorption bands in all
solvents with increasing n (Figs. 1, 2). In the absence
of strong intermolecular interactions with environment,
this may be due to increased vibronic interactions and
increased probability of the photoisomerization
processes due to reduced energy barrier for rotation
around a formally single bonds. If this mechanism
plays a dominant role, then the change in the band
width with the length of the polymethine chain would
be sharply different in the polymer film and liquid
solvents, as photoisomerization in the polymer film is
minimized. Inasmuch as the trends in the band width in
a liquid solvent and polyvinylethylal polymer film are
The extention of the polymethine chain increases
the deviation in the spectra of dyes III–V significantly:
it reaches the highest level among all known
merocyanines [2]. Thus, in the spectra of compound V
the Dλ value is 223 nm in DMF and 232.5 nm in
CH2Cl2. As can be seen from Table 1, the replacement
of CH2Cl2 by more polar solvents, both strongly
nucleophilic DMF and very electrophilic ethanol,
reduces the Dλ and DM. values. This indicates a slight
leveling of bond orders with increasing polarity of the
medium, associated with the change of the electronic
structure in the merocyanines III–V to the A2 side.
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712
KURDYUKOVA et al.
maximum of the dye V is higher than in the last
maximum, in contrast to compounds IV and I (Fig. 2).
A strong change in bond orders upon excitation,
leading to a change in the internuclear equilibrium
distances results in the fact that the band maximum is
determined by the transition to a higher vibrational
sublevel. This defines a symmetrical shape of the band
containing vibronic maxima at the short- and long-
wavelength sides of the main peak, due to the
transition to the higher and lower sublevels, respec-
tively, in relation to the most intense peak. Note that
the shape of the absorption bands of merocyanines III–
V in n-hexane is similar to that of typical neutral
polyene carotenoids [2].
Increasing the electron-acceptor properties of
fluorene framework by introducing phenoxysulfonyl or
2,2,3,3,4,4,5,5-octafluoropentoxysulfonyl substituents
should lead to a decrease in the bond order alternation
in the polymethine chain and approaching the mero-
cyanines IX–XIV to the polymethine state. Indeed,
according to quantum-chemical calculations, the
merocyanines IX–XI have smaller numerical values of
alternation of the bond lengths and bond orders, and
larger dipole moments than compounds of the III–V
series (Table 2). We can conclude that they are
somewhat more shifted towards structure A2. The
calculated values of BLA and BOA (absolute value),
λ, nm
Fig. 2. Absorption spectra of merocyanines III–V in
n-hexane: (1) III, (2) IV, and (3) V.
similar, we can conclude that they are associated
mainly with vibronic interactions. In the structures like
A1 and A3 the vibronic interactions reach higher level,
because bonds can change order at the excitation,
namely, from single to double and vice versa.
Therefore, in n-hexane and toluene, which are the least
polar among the studied solvents and are stabilizing
the A1 structure, the largest broadening of the bands
occurs.
ΔPch and
δ of the merocyanines IX–XI are
considerably less than similar values of the cyclo-
octatetraene, but higher than those of the correspond-
ing symmetric anionic XXVI–XXXI and cationic
XXXII–XXXIV dyes (Table 2). This indicates that in
a vacuum the electronic structure of the S0 state of the
former ones corresponds to the range of structures A1–
A2, but is shifted markedly to the structure of A1.
As a quantitative characteristic of vibronic inter-
actions in dyes [16] the value of the quadratic change
of bond order δ upon excitation, proportional to the
change in the internuclear equilibrium distances upon
excitation is used successfully.
m
δ = Σ (P∗ − P)2i ,
√
This theoretical conclusion is confirmed by
experimental data on λmax, M–1, red shift of the
absorption bands, decrease in deviations, growing first
and second vinylene shifts, band narrowing and
reduced alternation of proton coupling constants of the
polymethine chain relatively the compounds III–V.
These effects are somewhat greater in the case of
derivatives XII–XIV than of IX–XI, because the
2,2,3,3,4,4,5,5-octafluoropentyloxysulfonyl substituents
are stronger electron-acceptors than the phenoxy-
sulfonyl groups.
i=1
where i is the number of the bond, m is total number of
bonds, (P*–P) is the difference between the orders of
the ith bond in the excited and ground states.
The value of δ increases with the extention of the
polymethine chain in dyes III–V (Table 2). Therefore,
the broadening of the experimental absorption bands in
the series of merocyanines III–V (Table 1) is due to
the increase in the vibronic interactions. The streng-
thening of the vibronic interactions at the extention of
the polymethine chain is confirmed by the increase in
the intensity of the vibrational peak at the short-wave
side of absorption and a decrease in the main
maximum. As a cosequence, its intensity in the first
Similar trends in the spectral effects at the
elongation of the polymethine chain in merocyanines
IX–XIV and III–V indicate that in both the former and
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
713
Fig. 3. HOMO of dye V (isosurface lines 0.3, in the next
figures analogously).
Fig. 4. LUMO of dye V.
Fig. 5. HOMO of dye XI.
Fig. 6. LUMO of dye XI.
the latter the contribution of structure A1 in the
electronic structure of the ground state increases at the
chain elongation.
excitation, the electron density on the fluorene
fragment increases, while on the heterocyclic one
decreases (Figs. 7, 8). The orbitals localized on phen-
oxysulfonyl groups are not involved in the long-
wavelength transitions.
In going from merocyanines III–V to merocyanines
IX–XI the energy of both HOMO and LUMO levels
decreases, the energy gap also is reduced, which leads
to a red shift of λmax. theor. These findings are consistent
with large experimental absorption maxima of
compounds IX–XI. The energy of the main electronic
transition in the merocyanines III–V, IX–XI drops
with increasing chain length, and the magnitude of the
oscillator strength increases, as might be expected
from the calculation.
The long-wavelength transition in both groups of
merocyanines, III–V and IX–XI, are of π–π* type, and
93–97% of them occur between the HOMO and
LUMO orbitals. The calculated spectra of compounds
III–V, IX–XI include also the low-intensity transitions
to higher excited states.
In merocyanines V besides the main transition the
most intense is S0 → S3 trtransition. It corresponds to a
redistribution of electron density from the polymethine
chain on the fluorene and heterocyclic fragments.
The HOMO electron density of the dyes III–V,
IX–XI comprises the π-system of the entire molecule
(in dyes IX–XI the phenoxysulfonyl substituents are
not involved), but mostly is concentrated on the
polymethine chains, while LUMO is shifted signi-
ficantly to the fluorene framework (Figs. 3–6). At the
In the dye IX the S0 → S1 transition includes 90%
of the HOMO to LUMO transition and 9% of the
HOMO to LUMO+1 transition, and the S0 → S2
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714
KURDYUKOVA et al.
transition is a combination of 89% of the HOMO to
LUMO+1, and 9% of the HOMO to LUMO
transitions. Both transitions correspond to the transfer
of electron density from the indolenine framework and
polymethine chain on the fluorene fragment.
In the spectrum of merocyanines X–XI besides the
main transition there are intense enough S0 → S2
transitions from HOMO to LUMO+1. They are
characterized by the transfer of electron density from
indolenine fragment and the polymethine chain on the
fluorene framework and the sulfur and oxygen atoms
of the phenoxysulfonyl substituents.
Fig. 7. Change in the electron density at the S0 → S1
transition of the dye V (dark increase, light decrease;
isosurface lines 0.003).
In the series of dyes XV, XVI, XVIII, XIX, XXII–
XXV with the same acceptor fragments, the 2,7-
diphenoxysulfonyl-9H-fluorenylidene, and various
heterocyclic residues, regular changes are observed in
the spectral characteristics depending on the electron-
donating property of the heterocycle (Fig. 9).
The benzo[c,d]indolylidene and 2,6-diphenylpyran
residues are less electron-donating than indo-lylidene
[16]. Hence, we can expect that the electronic structure
of dyes XVIII, XIX, XXII, XXIII ap-proaches the
polyene state closer than merocyanines IX–XI. Larger
values of deviations, smaller vinylene shifts, broader
bandwidth in the former compared with the lattter
support this assumption (Table 1). Note that the values
of DM are more sensitive to changes in the electron-
donor properties of heterocycles than Dλ, due to
differences in the shape of the bands of merocyanines
XVIII–XIX, XXII–XXIII (Table 1).
Fig. 8. Change in the electron density at the S0 → S1
transition of the dye XI.
The replacement of the indolylidene residue in the
merocyanines IX, X by a more electron-donor
benzothiazolylidene should change the electronic
structure of the ground state of dyes XV, XVI, in
contrast to compounds XVIII, XIX, XXII, and XXIII,
to the side of the boundary structure A2, that is, bring
them closer to the polymethine state. This is reflected
by virtually all above spectral parameters. However,
large deviations, small vinylene shifts, low intensity,
and broad bands indicate the dominance of the polyene
structure A1 in merocyanines XV, XVI.
1.2
0.8
0.4
The nucleus of 2,6-diphenylpyridine is much more
electron-donating than the benzothiazolidene nucleus.
Consequently, for merocyanines XXIV, XXV even
greater approach to the ideal polymethine state is
expectable. Indeed, even in the nonpolar n-hexane a
significant increase occurs in vinylene shifts and
narrowing of the bands in the spectra of these
compounds compared with merocyanines XV, XVI.
λ, nm
Fig. 9. Absorption spectra of merocyanines X, XV, XIX,
XXIII, XXV in dichloromethane: (1) X, (2) XV, (3) XIX),
(4) XXIII, (5) XXV.
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
715
With increasing solvent polarity these effects are even
more contrasting. Already in dichorometane the
vinylene shifts increase up to 100 nm: this value is
typical of symmetrical polymethine dyes (Table 1).
The deviations virtually disappear (they are small
negative and positive in value for λmax and M–1,
respectively). The values of the proton coupling
constants in CDCl3 in the polymethine chain of the
merocyanine XXV are leveled compared with those of
compounds III–V, XV, XVI, XVIII, XIX, XXII,
XXIII: J12 = J23 = J34 = 13.2 Hz.
Decrease in DM, growth of ε and f, and narrowing
of the bands at the elongation of the polymethine chain
in merocyanines XXIV, XXV in contrast to
compounds III–V, XV, XVI, XVIII, XIX, XXII,
XXIII points to the decrease in polyene and increase
in polymethine character of the electronic structure of
the ground state.
Thus, the use of fluorene and its derivatives in the
cyanine condensation made it possible to obtain the
merocyanines with the structure maximally approach-
ing that of the ideal neutral polyene. They are charac-
terized by the maximum deviations, minimum
vinylene shifts, the large width of the vibrational struc-
ture at the short- and long-wavelength edges of the
bands and a slight positive solvatochromism. There-
with, by introducing electron-withdrawing substituents
in 2,7 positions of the fluorene framework and using
strong electron-donor heterocycles as the end groups it
is possible to create merocyanines with the structure of
at least ideal polymethines.
The growth of the solvent polarity facilitates the
displacement of electron density from the donor to the
acceptor fragment in the molecule of merocyanine, that
is, its bipolarity increases. This leads to an increase in
the order of the single bonds and a decrease in the
order of the double bonds in the chromophore, that is,
equalizes the bonds (making them closer to sesquialteral).
As a result, the electronic structure of merocyanines in
S0 state at increasing polarity of the solvent withdraws
from structure A1 and approaches structure A2.
EXPERIMENTAL
The maximal approach by merocyanines XXIV,
XXV to the ideal polymethine state is also seen from
the fact that their absorption bands have a universal
form with a pronounced vibration maximum at the
short-wavelength edge, characteristic of symmetric
polymethine dyes [16] (Fig. 9). In addition, the
narrowness of their spectra led to the highest values of
molar extinction coefficient among the studied
merocyanines. For merocyanines XXV in DMF ε×
10–4 = 14.69 l mol–1 cm–1, which is close to that of the
corresponding symmetrical dyes.
The absorption spectra were recorded on a
Shimadzu UV-3100 spectrophotometer with 1 cm cells
at a concentration of solute 10–5 M. Solvents were
purified by known methods [21]. CH2Cl2 was
stabilized by adding 1% of anhydrous ethanol.
Moments of the absorption bands are determined by
previously described [12, 16] method. For
merocyanines XV, XVI, XVIII, XIX, XXII–XXIV
the ε and f values were not determined because of
insufficient solubility in n-hexane. For chromato-
graphy silica gel 60 (Fluka) and aluminum oxide-90
(Merck) were used. The purity of dyes was monitored
The approach of the electronic structure of dyes
(XXIV, XXV) to the ideal polymethine state is also
reflected in the maximum deepening of their color among
the studied merocyanines, characteristic of this state
(Table 1). This effect is especially spectacular in a
seriesr of dyes of the same structural type XXII–XXV.
The merocyanines on the basis of pyridine XXIV,
XXV absorb by 76 and 159 nm more to the red side,
respectively, than their pyrilium counterparts XXII,
XXIII, whereas the pairs of related cationic symmetric
pyrido- and pyrilium-cyanines show reverse pattern [16].
Note that reacing the ideal polymethine state is difficult
even in the case of symmetric dyes, since the deviation
in electron-donating (electron-withdrawing) properties
of end groups from the average values to one or the
other side leads to the alternation of bond orders from
the heterocyclic residues to the center of the chain.
1
by TLC (Silufol UV-254), eluent acetonitrile). The H
NMR spectra were recorded on a Varian VXR-300 spec-
trometer (299.945 MHz), internal reference TMS. Two-
dimensional correlation spectra were recorded on a
Bruker-600 spectrometer (600.133 MHz). Melting points
were measured in open capillaries and were not corrected.
The quantum-chemical calculations were carried
out using the PC Gamess/Fierfly software package by
the non-empirical DFT method with a B3LYP/6-
31G(d,p) basis, with a preliminary geometry optimiza-
tion of the ground state in the same basis. Electronic
transitions were calculated by the TDDFT method.
(2Z)-2-[2-(9H-Fluoren-9-ylidene)ethylidene]-
1,3,3-trimethyl-2,3-dihydro-1H-indole (III) 183 mg
of tri-n-butylphosphoniumfluorenylide I and 101 mg
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

716
KURDYUKOVA et al.
of (2E)-(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-
ylidene)-acetaldehyde IIa was heated in 7 ml of o-
xylene for 4 h. The reaction process was monitored
spectrophotometrically. At the end of reaction the
solvent was removed at a reduced pressure, to the
residue ethanol was added and the mixture was
filtered. The precipitate was chromatographed on
Al2O3, using dichloromethane as eluent. Yield 120 mg
heated in 1 ml of acetic anhydride until they dissolved.
To the solution was added 5 drops of triethylamine and
the mixture was heated for 5 min. The reaction mixture
was treated with water. The precipitate formed was
isolated and recrystallized from chloroform. Yield 156
mg (94%), mp 217ºC. 1H NMR spectrum: 1.700 s [6H,
C(CH3)2], 3.32 s (3H, NCH3), 6.190 d (1H, J =
13.2 Hz, H1), 7.06–7.15 m (5H, ArH), 7.175 d (1H, J =
8.4 Hz, ArH), 7.24–7.42 m (7H, ArH), 7.498 d (1H,
J = 7.2 Hz, ArH), 7.718 d (1H, J = 8.4 Hz, ArH), 7.860 d
(1H, J = 8.1 Hz, ArH), 8.113 d (1H, J = 14.1 Hz, H2),
8.32–8.34 m (3H, ArH ), 8.452 d (1H, J = 8.1 Hz, ArH).
1
(69%), mp 166ºC. H NMR spectrum, δ, ppm: 1.774 s
[6H, C(CH3)2], 3.355 s (3H, NCH3), 6.377 d (1H, J =
12.9 Hz, H1), 6,751 d (1H, J = 7.5 Hz, ArH), 6.939 t
(1H, J = 7.5 Hz, ArH), 7.193–7.409 m (6H, ArH),
7.900 d (1H, J = 12.9 Hz, H2), 7.728 d (1H, J = 6.9 Hz,
ArH), 7.792 d (1H, J = 6.9 Hz, ArH), 7.852 d (1H, J =
6.9 Hz), (ArH ), 7.991 d (1H, J = 6.9 Hz, ArH).
Diphenyl 9-[(2E,4E)-2-(1,3,3-trimethyl-1,3-di-
hydro-2H-indol-2-ylidene)but-2-enylidene]-9H-fluo-
rene-2,7-disulfonate (X). 48 mg of compound ( VIa )
and 44 mg of 2-{(1E,3E)-4-[acetyl(phenyl)amino]
buta-1,3-dienyl}-1,3,3-trimethyl-3H-indolium perchlo-
rate (VIIa) was heated to dissolution in 1 ml of acetic
anhydride. 5 drops of triethylamine was`added and the
mixture was heated for 5 min. The reaction mixture
was treated with water. The resulting residue was
chromatographed on silica gel, and then again on
Al2O3 with dry chloroform as eluent. Yield 41 mg
(2Z)-2-[(2E)-4-(9H-Fluoren-9-ylidene)but-2-enyl-
idene]-1,3,3-trimethyl-2,3-dihydro-1H-indole (IV).
110 mg of compound (I) and 68 mg of (2E,4E)-4-
(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)but-
2-enal (IIb ) was heated in 3 ml of o-xylene for 2 h. The
solvent was distilled off at a reduced pressure, and the
residue was chromatographed on Al2O3 using dichloro-
methane as eluent. The solid was recrystallized from
1
1
ethanol. Yield 80 mg (71%), mp 193ºC. H NMR
(59%), mp 181ºC. H NMR spectrum: 1.617 s [6H,
spectrum: 1.669 s [6H, C(CH3)2], 3.215 s (3H, NCH3),
5.637 d (1H, J = 11.7 Hz, H1), 6.6.70 d (1H, J = 7.8 Hz,
ArH), 6.888 t (1H, J = 7.8 Hz, ArH), 7.150–7.410 m
(9H, ArH), 7.714-7.816 m (3H, ArH), 7.370 d (1H, J =
12.0 Hz, H4), 8.039-8.092 m (1H, ArH).
C(CH3)2], 3.335 s (3H, NCH 3), 5.925 d (1H, J = 12.9 Hz,
H1), 6.890–6.960 m (2H, ArH), 6.956–7.115 m (5H,
ArH), 7.164–7.358 m (9H, ArH), 7.672 d.d (1H, J1 =
4.3 Hz, J2 = 1.5 Hz, ArH), 7.767 d.d (1H, J1 = 3.9 Hz,
J2 = 1.2 Hz, ArH), 7.880 t (1H, J = 12.9 Hz, H2), 8.106
d (1H, J = 12.6 Hz, H4), 8.204 d (1H, J = 8.4 Hz,
ArH), 8.271 d (1H, J = 8.4 Hz, ArH), 8.301 s (1H,
ArH). 8.426 s (1, r–H). 8.426 s (1H, ArH).
(2Z)-2-[(2E,4E)-4-(9H-fluoren-9-ylidene)hexa-2,4-
dienylidene]-1,3,3-trimethyl-2,3-dihydro-1H-indole
(V). 100 mg of compound I and 69 mg of (2E,4E,6E)-
6-(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)
hexa-2,4-dienal (IIc) was heated in 3 ml of o-xylene
for 1 h. During the cooling of the solution a precipitate
formed. It was chromatographed on Al2O3 using dichloro-
methane as eluent and recrystallized from ethanol.
Diphenyl 9-[(2E,4E,6E)-2-(1,3,3-trimethyl-1,3-di-
hydro-2H-indol-2-ylidene)hexa-2,4-dienylidene]-9H-
fluorene-2,7-disulfonate (XI). 48 mg of compound
VIa and 48 mg of 2-{(1E,3E,5E)-6-[acetyl(phenyl)-
amino]hexa-1,3,5-trienyl}-1,3,3-trimethyl-3H-indolium
perchlorate (VIIb) was heated to dissolution in 1 ml of
acetic anhydride. 3 drops of triethylamine was added
and the mixture was heated for 5 min. The reaction
mixture was treated with water. The resulting residue
was chromatographed on Al2O3, using dry chloroform
1
Yield 75 mg (69%), mp 183ºC. H NMR spectrum:
1.614 s [6H, C(CH3)2], 3.157 s (3H, NCH3), 5.439 d
(1H, J = 12.0 Hz, H1), 6.335 d.d (1H, J1 = 14.1 Hz,
J2 = 11.4 Hz, H3), 6.639 d (1H, J = 7.8 Hz, ArH),
6.853 t (1H, J = 13.2 Hz, H5), 6.877 d (1H, J = 7.8 Hz,
ArH), 7.035 d.d (1H, J1 = 12.0 Hz, J2 = 14.1 Hz, H2),
7.148 d (1H, J = 6.0 Hz, ArH), 7.178 t (1H, J = 7.8 Hz,
ArH), 7.248–7.363 m (6H, ArH), 7.671–7.813 m (3H,
ArH), 7.972–8.048 m (1H, ArH).
1
an eluent. Yield 70 mg (98%), mp 120ºC. H NMR
spectrum: 1.576 s [6H, C(CH3)2], 3.234 s (3H, NCH3),
5.667 d (1H, J = 12.3 Hz, H1), 6.362 t (1H, J = 13.5 Hz,
H3), 6.809–6.877 m (2H, ArH), 6.959–7.166 m (6H,
ArH), 7.209–7.378 m (9H, ArH), 7.702–7.744 m (2H,
ArH), 7.812 d (1H, J = 8.4 Hz, ArH), 8.165 d (1H, J =
8.1 Hz, ArH), 8.241 d (1H, J = 8.4 Hz, ArH), 8.255 s
(1H, ArH), 8.359 s (1H, ArH).
Diphenyl 9-[(2E)-2-(1,3,3-trimethyl-1,3-dihydro-
2H-indol-2-ylidene)ethylidene]-9H-fluorene-2,7-di-
sulfonate (IX). 119 mg of diphenyl 9H-fluorene-2,7-
disulfonate (VIa) and 50 mg of compound IIa was
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
717
Bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9-[(2 Z)-2-
(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)ethyl-
idene]-9H-fluorene-2,7-disulfonate (XII). 75 mg of
bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-
disulfonate (VIb) and 20 mg of compound IIa was
heated in a minimal amount of acetic anhydride in the
presence of triethylamine, monitoring the reaction
course spectrophotometrically. The precipitate was
washed with alcohol. Yield 90 mg (98%), mp 165ºC.
1H NMR spectrum: 1.815 s [6H, C(CH3)2], 3.481 s
(3H, NCH3), 4.558 t (4H, J 13.5 Hz,OCH2), 6,021 min
(2H, J1 52.2 Hz. J2 5.4 Hz, CF2 H), 6.450 d (1H, J =
13.5, H1), 6.926 d (1H, J = 8.1 Hz, ArH), 7.094 t (1H,
J = 6.9 Hz, ArH), 7.323 t (1H, J = 7.2 Hz, ArH), 7.335
d (1H, J = 7.2 Hz, ArH), 7.854 d (1H, J = 7.8 Hz,
ArH), 7.912 d (1H, J = 8.1 Hz, ArH), 8.111 d (1H, J =
8.1 Hz, ArH), 8.174 d (1H, J = 7.8 Hz, ArH), 8.191 d
(1H, J = 14.1 Hz, H 2), 8.291 s (1H, ArH), 8.642 s (1H,
ArH).
chromatographed on Al2O3, using as eluent chloro-
form, and recrystallized from methanol. Yield 70 mg
(71%). mp H NMR spectrum: 1.578 s [6H, C(CH3)2],
1
3.166 s (3H, NCH3), 4,482 t.d (4H, J1 = 13.5 Hz, J2 =
9.6 Hz), 5.507 d (1H, J = 12.6 Hz, H1), 5.937 t.t (2H,
J1 = 52.2 Hz, J2 = 5.4 Hz, CF2H), 6.384 d.d (1H, J1 =
13.5 Hz. J2 = 10.5 Hz, ArH), 6.663 d (1H, J = 8.4 Hz,
ArH), 6.875 t ( 1H, J = 7.2 Hz, ArH), 6.997–7.158 m
(5H, ArH), 7.527 d (1H, J = 11.4 Hz, ArH), 7.804 d
(1H, J = 8.1 Hz, ArH), 7.867 d (1H, J = 8.1 Hz, ArH),
7.971 d (1H, J = 7.8 Hz, ArH), 8.025 d (1H, J =
8.1 Hz, ArH), 8.249 s (1H, ArH), 8.522 s (1H, ArH).
Diphenyl 9-[(2E,4E,6Z)-6-(3-methyl-1,3-benzo-
thiazol-2(3H)-ylidene)hexa-2,4-dienylidene]-9H-flu-
orene-2,7-disulfonate (XV). 48 mg of compound VIa
and 105 mg of 2-{(1E,3E)-4-[acetyl(phenyl)amino]buta-
1,3-dienyl}-3-ethyl-1,3-benzothiazol-3-ium tetra-
fluoroborate (VIIIa) was heated in acetic anhydride in
the presence of triethylamine.The reaction mixture was
quenched with water. The resulting precipitate was
filtered off and chromatographed on silica gel with the
toluene–chloroform (95:5 to 92:8) as eluent. The
merocyanine was crystallized from acetone-d6. Yield
Bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9-[(2E,4Z)-
2-(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)-
but-2-enylidene]-9H-fluorene-2,7-disulfonate (XIII).
75 mg of compound VIb and 46 mg of compound
VIIa was heated in a minimum amount of pyridine in
the presence of piperidine, monitoring the reaction
course spectrophotometrically. Aqueous methanol was
added and the precipitate formed was separated and
chromatographed on silica gel, eluent dichloromethane
with the addition of triethylamine. The solvent was
removed at a reduced pressure. The precipitate was
recrystallized from methanol. Yield 92 mg (96%), mp
203–204ºC. 1H NMR spectrum: 1.715 s [6H, C(CH3)2],
3.347 s (3H, NCH3), 4.538 t.d (4H, J1 = 13.5 Hz, J2 =
3.9 Hz, OCH2), 5.855 d (1H, J = 12.6 Hz, H1), 5,993 t.t
(J1 = 52.2 Hz, J2 = 5.4 Hz, CF2H), 6.803 d (1H, J =
7.8 Hz, ArH), 7.002 t (1H, J = 9.6 Hz, ArH), 7.082 t
(1H, J = 12.6 Hz, H3), 7.272 d (1H, J = 7.5 Hz, ArH),
7.598 t (1H, J = 12.6 Hz, H3), 7.689 t (1H, J = 12.6 Hz,
H2), 7.841 d (1H, J = 7.8 Hz, ArH), 7.909 d (1H, J =
8.1 Hz, ArH), 8.059 d (1H, J = 8.4 Hz, ArH),
8.114 ppm (1H, J = 8.1 Hz, ArH), 8.394 s (1H, ArH),
8.625 s (1H, ArH)
1
55 mg (79%), mp 230ºC. H NMR spectrum: 1.314 t
(3H, J = 7.2 Hz, NCH2CH3), 4.124 q (2H, J = 7.2 Hz,
NCH2CH3), 6.144 d (1H, J = 11.4 Hz, H1), 6.990 t
(1H, J 12.6 Hz, H3), 6.979–7.165 m (7H, ArH), 7.204–
7.487 m (12H, ArH), 7.552 d (1H, J = 7.8 Hz, ArH),
7.660 d.d (1H, J1 = 8.1 Hz, J2 = 1.5 Hz, ArH), 7.744
d.d (1H, J1 = 8.1 Hz, J2 = 1.5 Hz, ArH), 7.869 d (1H,
J = 8.1 Hz, ArH), 7.938 d (1H, J = 12.9 Hz, H4), 8.116
s (1H, ArH), 8.183 d (1H, J = 7.8 Hz, ArH), 8.231 d
(1H, J = 7.8 Hz, ArH), 8.254 d (1H, J = 7.8 Hz, ArH),
8.329 s (1H, ArH), 8.425 s ( 1H, ArH).
Diphenyl 9-[(2E,4Z)-2-(1-benzylbenzo[cd]indol-2
(1H)-ylidene)ethylidene]-9H-fluorene-2,7-disulfonate
(XVI). 48 mg of compound VIa and VIa and 110 mg
of 2-{(1E,3E,5E)-6-[acetyl(phenyl)amino]hexa-1,3,5-
trienyl}-3-ethyl-1,3-benzothiazol-4-ium methyl-
benzenesulfonate (VIIIb) was heated in 2.5 ml of
pyridine. The reaction mixture was diluted with water.
The resulting precipitate was filtered off and chromato-
graphed on silica gel with toluene–chloroform (95:5)
as eluent. The resulting merocyanine was recrystal-
Bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9-[(2E,4E,6Z)-
2-(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)-
hexa-2,4-dienylidene]-9H-fluorene-2,7-disulfonate
(XIV). 94 mg of compound VIb and 57 mg of
compound VIIb was heated in a minimal amount of
pyridine in the presence of piperidine, monitoring the
reaction course spectrophotometrically. The solvent
was removed at a reduced pressure. The residue was
1
lized from ethanol. Yield 36 mg (50%), mp 206ºC. H
NMR spectrum: 1.354 t (3H, J = 7.2 Hz, NCH2CH3),
3,916 q (2H, J = 7.2 Hz, NCH2CH3), 5.629 d (1H, J =
11.4 Hz, H1), 6.363 d.d (1H, J1 = 13.5 Hz, J2 = 11.4 Hz,
chain protons), 6.727 t (1H, J = 13.5 Hz, H3), 6.885 d
(1H, J = 8.1 Hz, ArH), 6.944–7.102 m (8H, ArH),
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718
KURDYUKOVA et al.
7.187–7.322 m (6H, ArH), 7.367 d (1H, J = 7.2 Hz,
ArH), 7.442 d (1H, J = 11.4 Hz, H6), 7.721 d.d (1H,
J1 = 8.1 Hz, J2 = 1.5 Hz, ArH), 7.754 d.d (1H, J1 =
8.4 Hz, J2 = 1.5 Hz, ArH), 7.908 d (1H, J = 8.1 Hz,
ArH), 7.955 d (1H, J = 7.8 Hz, ArH), 8.207 s (1H,
ArH), 8.452 s (1H, ArH).
chloromethane containing triethylamine. Yield 92 mg
(72%), mp 273ºC. 1H NMR spectrum: 6.585 d (1H, J =
13.2 Hz, H1), 6.772 d (1H, J = 1.5 Hz, β-H), 7.060 d
(2H, J = 7.8 Hz, ArH), 7.052 t (1H, J = 7.8 Hz, ArH),
7.166 d (1H, J = 1.5 Hz, β-H), 7.202–7.352 m (6H,
ArH), 7.485–7.604 m (5H, ArH ), 7.710 d.d (1H, J1 =
8.1Hz, J2 = 1.5 Hz, ArH), 7.773 d.d (1H, J1 = 8.1 Hz,
J2 = 1.5 Hz, ArH), 7.872 d (1H, J = 13.5 Hz, H2),
7.880 d.d (2H, J1 = 8.1 Hz, J2 = 1.5 Hz, ArH), 7.937 ppm
(1H, J = 8.1 Hz, ArH), 7.952 d.d (2H, J1 = 8.1 Hz, J2 =
1.5 Hz, ArH), 7.988 d (1H, J = 7.8 Hz, ArH), 8.345 s
(1H, ArH), 8.532 s (1H, ArH).
Diphenyl 9-[(2Z)-2-(1-benzylbenzo[cd]indol-2(1H)-
ylidene)ethylidene]-9H-fluoren-2,7-disulfonate (XVIII)
166 mg of compound VIa and 140 mg of 1-benzyl-2-
[(E)-2-(dimethylamino)vinyl]benzo[cd]indolium tetra-
fluoroborate XVIIa was heated in acetic anhydride,
and a few drops of DBU was added. To the reaction
mixture was added ethanol and the precipitate formed
was filtered off. The merocyanine was chromato-
rgaphed on silica gel with toluene–chloroform (3:1) as
Diphenyl 9-[(2E)-4-(2,6-diphenyl-4H-pyran-4-
ylidene)but-2-enylidene]-9H-fluorene-2,7-disulfonate
(XXIII). 96 mg of compound VIa and 110 mg of 4-
[(1E,3E)-4-ethoxybuta-1,3-dienyl]-2,6-diphenyl-
pyrilium tetrafluoroborate XXI was heated in a
minimal amount of pyridine, containing piperidine as a
base. The reaction mixture was treated with water. The
resulting precipitate was chromatographed on silica gel
and then on Al2O3 with dry chloroform as eluent. Yield
1
eluent. Yield 30 mg (40%), mp 242ºC. H NMR
spectrum: 5.201 (NCH2), 6.733 d (1H, J = 13.5 Hz,
H1), 6.927 d (1H, J = 6.6 Hz, ArH), 7.032 t (4H, J =
7.8 Hz, ArH), 7.154–7.231 m (2H, ArH), 7.271–7.360
m (6H, ArH), 7.383–7.546 m (5H, ArH), 7.701–7.830
m (3H, ArH), 7.951 d.d (3H, J1 = 7.8 Hz, J2 = 10.8 Hz,
ArH), 8.126 d (1H, J = 7.2 Hz, ArH), 8.235 s (1H,
ArH ), 8.235 d (1H, J = 12.9 Hz, H2), 8.444 s (1H, ArH).
1
80 mg (53%), mp 237ºC. H NMR spectrum: 6.038 d
(1H, J = 12.0 Hz, H1), 6.566 d (1H, J = 1.5 Hz, β-H),
6.986–7.103 m (6H, ArH), 7.080 t (1H, J = 12.0 Hz,
H3), 7.241–7.349 m (8H, ArH), 7.446–7.595 m (10H,
ArH), 7.743 d.d (2H, J1 = 8.4 Hz, J2 = 1.5 Hz, ArH),
7.713 d (2H, J = 7.5 Hz, ArH), 7.798 d.d (1H, J1 =
8.1 Hz. J2 = 1.5 Hz, ArH), 7.887 d.d (2H, J1 = 7.8 Hz,
J2 = 1.5 Hz, ArH), 7.918 d (2H, J = 8.4 Hz, ArH),
7.966 d (2H, J = 8.4 Hz, ArH), 8.249 s (1H, ArH),
8.467 s (1H, ArH).
Diphenyl 9-[(2E,4Z)-4-(1-benzylbenzo[cd]indol-
2(1H)-ylidene)but-2-enylidene]-9H-fluorene-2,7-di-
sulfonate (XIX). 108 mg of VIa and 96 mg of 1-
benzyl-2-[(1E,3E)-4-(N-phenylacetamido)buta-1,3-
dienyl]benzo[cd]indolium tetrafluoroborate XVIIb
was heated in acetic anhydride with a few drops of tri-
ethylamine. The reaction mixture was diluted with
ethanol. The precipitate formed was filtered off and
chromatographed on silica gel, washing out the mero-
cyanine with toluene. Yield 30 mg (37%), mp 260ºC.
1H NMR spectrum: 5.214 s (2H, NCH2), 6.221 d (1H,
J 13.5 Hz, H1), 6.666 d (1H, J = 6.5 Hz, ArH), 7.038 t
(5H, J = 7.0 Hz, ArH), 7.138 t (1H, J = 7.0 Hz, ArH),
7.200 t (2H, J = 7.0 Hz, ArH), 7.275–7.433 m (11H,
ArH), 7.598 d (1H, J = 12.5 Hz, H3), 7.713–7.845 m
(4H, ArH), 7.879 t (1H, J = 12.5 Hz, H2), 7.923 d (1H,
J = 7.5 Hz, ArH), 7.962 d (1H, J = 7.5 Hz, ArH), 8.168
d (1H, J = 7.0 Hz, ArH), 8.316 s (1H, ArH), 8.366 s
(1H, ArH).
Diphenyl 9-[2-(1-methyl-2,6-diphenylpyridine-4
(1H)-ylidene)ethylidene]-9H-fluorene-2,7-disulfonate
(XXIV). 60 mg of merocyanine XXII was dissolved in
DMSO containing 1.5 ml of 25% solution of methyl-
amine and heated on a silicone bath at a temperature of
95ºC for 10 min. The reaction mixture was treated with
a weak solution of sodium chloride. The resulting
precipitate was filtered off and chromatographed on
Al2O3, washing out the merocyanine with dichloro-
methane containing triethylamine. The compound ob-
tained was crystallized from acetoneitrile. Yield 50 mg
Diphenyl 9-[2-(2,6-diphenyl-4H-pyran-4-yliden)-
ethylidene]-9H-fluorene-2,7-disulfonate (XXII). 84 mg
of compound VIa and 79 mg of (2,6-diphenyl-4H-
pyran-4-ylidene)acetaldehyde XX was heated in a
minimal amount of acetic anhydride in the presence of
a few drops of triethylamine. The merocyanine
separated at cooling the reaction mixture. It was
chromatographed on silica gel, washing out with di-
1
(82%), mp 251ºC. H NMR spectrum: 3.157 s (3H,
NCH3), 6.357 d (1H, J = 14.1 Hz, H1), 6.542 d (1H,
J = 2.7 Hz, β-H), 6.942–7.031 m (5H, ArH), 7.133–
7.290 (m, 5H, ArH), 7.465–7.665 m (13H, ArH), 7.923
d (1H, J = 14.1 Hz, H2), 7.969 d (1H, J = 8.4 Hz,
ArH), 8.032 d (1H, J = 8.1 Hz, ArH), 8.237 s (1H,
ArH), 8.534 s (1H, ArH).
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SYNTHESIS AND SPECTRAL PROPERTIES OF MEROCYANINE DYES
719
7. Hansch, C. and Leo, A., Substituent Constants for
Correlation Analysis in Chemistry and Biology, New
York: Willey, 1979, p. 339.
Diphenyl 9-[(2E)-4-(1-methyl-2,6-diphenylpyridine-
4(1H)-ylidene)but-2-enylidene]-9H-fluorene-2,7-di-
sulfonate (XXV). 50 mg of merocyanine XXIII was
dissolved in DMSO containing 1.5 ml of 25% solution
of methylamine, and heated on a silicone bath at a
temperature of 95ºC for 10 min. The reaction mixture
was treated with a weak solution of sodium chloride.
The resulting precipitate was filtered off and chromato-
graphed on Al2O3 washing out merocyanine with the
dichloromethane containing triethylamine. The com-
pound obtained was crystallized from acetonitrile.
8. Popov, V.I., Skripkina, V.T., Protsyk, S.P., Skryn-
nikova, A.A., Krasovitskii, B.M., and Yagupol’skii, L.M.,
Ukr. Khim. Zh., 1991, vol. 57, no. 8, p. 843.
9. Meguellati, K., Spichty, M., and Ladame, S., Org. Lett.,
2009, vol. 11, no. 5, p. 1123.
10. Nesterenko, Yu.A., Briks, Yu.L., Kachkovskii, A.D.,
and Tolmachev, A.I., Khim. Geterotsikl. Soedin., 1990,
no. 2, p. 252.
1
11. Kulinich, A.V., Derevyanko, N.A., and Ishchenko, A.A.,
Yield 32 mg (63%), mp 228ºC. H NMR spectrum:
3.075 s (3H, NCH3), 5.810 d (1H, J = 13.2 Hz, H1),
6.282 s (1H, β-H), 6.741 s (1H, β-H), 6.870 t (1H, J =
13.2 Hz, H3), 6.940–7.074 m (4H, ArH), 7.192–7.314
m (6H, ArH), 7.378 t (1H, J = 13.2 Hz, H2), 7.420–
7.568 m (12H, ArH), 7.564 d (1H, J = 13.2 Hz, H4),
7.617 dd (1H, J1 = 8.4 Hz, J2 = 1.5 Hz, ArH), 7.673 d.d
(1H, J1 = 8.4 Hz, J2 = 1.5 Hz, ArH), 7.954 d (1H, J =
8.1 Hz, ArH), 8.001 d (1H, J = 8.1 Hz, ArH), 8.206 s
(1H, ArH), 8.492 s (1H, ArH).
Zh. Obshch. Khim., 2006, vol. 76, no. 9, p. 1503.
12. Kulinich, A. V., Derevyanko, N. A., and Ishchenko, A.A.,
Izv. Akad. Nauk, Ser. Khim., 2005, no. 12, p. 2726.
13. Reynolds, G.A. and VanAllan, J.A., J. Org. Chem.,
1969, vol. 34, no. 9, p. 2736.
14. Kudinova, M.A., Derevyanko, N.A., Dyadyusha, G.G,
Ishchenko, A.A., and Tolmachev, A.I., Khim.
Geterotsikl. Soedin., 1980, no. 7, p. 898.
15. Hamer, F.M., The Cyanine Dyes and Related
Compounds, New York: Intersci. Publ., 1964.
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