Synthesis and spectral properties of merocyanine dyes derived from tetranitrofluorene and heterocycles of various electron-donating ability

Article abstract of DOI:10.1007/s10593-013-1245-x

Syntheses are reported for di-, tetra-, and hexamethine merocyanines derived from 2,4,5,7-tetra-nitrofluorene and heterocyclic fragments with various electron-donating ability. The absorption spectra of these compounds were studied in solvents of different polarities. A quantum-chemical analysis was carried out for the electronic structure and types of electronic transitions of these merocyanines by using the DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set. The electronic structure of these merocyanines varied from neutral polyene to polymethine and bipolar polyene with increasing electron-donating ability of the heterocyclic fragment and with solvent polarity. These differences were strongly reflected in the position, intensity, and shape of the absorption bands, vinylene shifts, and deviations, as well as the sign of solvatochromic effect.

Full text of DOI:10.1007/s10593-013-1245-x

Chemistry of Heterocyclic Compounds, Vol. 49, No. 2, May, 2013 (Russian Original Vol. 49, No. 2, February, 2013)
SYNTHESIS AND SPECTRAL PROPERTIES OF
MEROCYANINE DYES DERIVED FROM TETRA-
NITROFLUORENE AND HETEROCYCLES OF
VARIOUS ELECTRON-DONATING ABILITY
I. V. Kurdyukova1, A. A. Ishchenko1*, N. A. Derevyanko1, and D. D. Mysyk2
Syntheses are reported for di-, tetra-, and hexamethine merocyanines derived from 2,4,5,7-tetra-
nitrofluorene and heterocyclic fragments with various electron-donating ability. The absorption spectra
of these compounds were studied in solvents of different polarities. A quantum-chemical analysis was
carried out for the electronic structure and types of electronic transitions of these merocyanines by
using the DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set. The electronic structure of
these merocyanines varied from neutral polyene to polymethine and bipolar polyene with increasing
electron-donating ability of the heterocyclic fragment and with solvent polarity. These differences were
strongly reflected in the position, intensity, and shape of the absorption bands, vinylene shifts, and
deviations, as well as the sign of solvatochromic effect.
Keywords: merocyanines, 2,4,5,7-tetranitrofluorene, electronic structure, electronic spectra, quantum-
chemical calculations, solvatochromism.
There has recently been an increasing interest in donor-acceptor systems containing either a strong
electron-donating or a strong electron-withdrawing fragment. These compounds hold considerable promise in
light of their characteristic intramolecular charge transfer. This property may be utilized for obtaining organic
semiconductors and sensitizers for photothermoplastic holographic [1-6], photovoltaic [7], and
electroluminescent media [8]. Extensive work in this field has been devoted to donor-acceptor systems derived
from tetranitrofluorene [9-11]. However, tetranitrofluorene is more often used as a component of mixed
complexes with polymers or other electron-donor compounds. Thus, we undertook the preparation of
intramolecular donor-acceptor systems derived from this fluorene. Individual representatives of such
compounds have already been synthesized [2, 4], but they have not yet been subjected to a systematic study.
Merocyanine dyes hold an important position among donor-acceptor systems with intramolecular
charge transfer. These dyes have a broad range of useful properties, such as pronounced solvatochromism,
_______
*To whom correspondence should be addressed, e-mail: alexish@i.com.ua.
1Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska St., Kyiv 02094,
Ukraine.
2Donetsk National Technical University, 58 Artema St., Kyiv 02094, Ukraine, e-mail: mysyk@yandex.ru.
________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 305-317, February, 2013. Original
article submitted July 27, 2012.
0009-3122/13/4902-0281©2013 Springer Science+Business Media New York
281

capacity to undergo a significant change in dipole moment upon electronic excitation, and capacity to sensitize
various physicochemical processes. They are finding increasing application in optical electronics, nonlinear
optics, devices for recording and information processing, medicine, and biology [12, 13].
In the present work, we synthesized and studied a series of merocyanines derived from 2,4,5,7-tetra-
nitrofluorene containing heterocyclic fragments of various electron-donating ability.
NO2
O2N
Me
Me
NO2
NO2
Me
N
Me
N
CHO
O2N
O2N
1'
Me
2'
Ac2O, 
Me
2
NO2
NO2
1
O2N
Me
Me
–
ClO4
NO2
NO2
Ac
+
N
Me
Me
N
n
Ph
Me
n
Ac2O, Et3N, 
N
Me
NO2
3 n = 1, 4 n = 2
O2N
NO2
O2N
NO2
H
N
n
H+
O2N
N
O2N
Ph
Ph
Cl–
HC(OEt)3
1
Ac2O, 
Ac2O, 
Ph
3'(5')
N
O2N
n
Ac
O2N
EtO
6 n = 1, 7 n = 2
5
O2N
Ph
NO2
N
Me
Cl–
5
+
N
NO2
1'
Ac2O, Et3N
Het
2'
Ph
or
Py, Et3N
or
NO2
NO2
8, 11, 14
Me
BF4
Py, piperidine
+
N
O2N
–
Ph
NO2
Ph
O+
Ph
6 or 7
Ac2O, Et3N
Me
or
n
NO2
Py, Et3N
Het
–
BF4
9, 12, 15 n = 1; 10, 13, 16 n = 2
Ph
Ph
N
O
8–10 Het =
, 11–13 Het =
, 14–16 Het =
N
N
Ph
Ph
Ph
282

Cyanine condensation at the methylene group proceeded much more readily when the fluorene system
had strong electron-withdrawing nitro substituents, in contrast to the case of unsubstituted fluorene [14].
Merocyanines 2-4 were synthesized by the reaction of 2,4,5,7-tetranitrofluorene (1) [15] with an aldehyde and
hemicyanines derived from 1,3,3-trimethyl-3H-indole under the standard conditions for cyanine condensation.
1
We should note that the merocyanine 16 was sparingly soluble in solvents commonly used for H NMR
spectroscopy, which complicated the acquisition of a high-quality spectrum. Thus, the di-tert-butyl analog 17,
which was more soluble than merocyanine 16, was synthesized by an analogous procedure in order to confirm the
structure of compound 16.
O2N
NO2
NO2
t-
t-
Bu
O+
Bu
1'
3'
5'
7
Bu
t-
Me
6'
2'
4'
Py, Et3N
O
–
ClO4
NO2
-t
Bu
17
The spectral characteristics, namely, absorption maxima (λmax), extinction coefficients (ε), and
deviations (D) of merocyanines 2-4 and 8-17 are given in Table 1.
In contrast to common merocyanines [17], derivatives 2-4 and 8-17 have multiple bands in their
absorption spectra similar to symmetrical anionic polymethines with terminal tetranitrofluorene groups [16].
The shape of the absorption bands exhibited by merocyanines with heterocyclic fragments possessing moderate
(compounds 2-4) and strong electron-donating properties (compounds 8-10) differed markedly from the shape
exhibited by merocyanines 11-17, which contain weakly electron-donating heterocyclic fragments (Fig. 1, Table
1).
The absorption spectra showed narrowing and increased intensity of the short-wavelength band and the
opposite effect for the long-wavelength band for the series of merocyanines 2-4 and 8-17 with the electron-
donating ability of the heterocyclic fragment increasing from pyran and benzo[cd]indole to indole and
benzimidazole (Fig. 1).
Fig. 1. Electronic absorption spectra of merocyanines 3 (1), 9 (2), 12 (3), and 15 (4) in CH2Cl2.
283

TABLE 1. Spectral Properties of Merocyanines 2-4 and 8-17
Solvent
CH2Cl2
Com-
pound
Toluene
DMF
λmax
nm
,
ε·10–4
,
λmax
nm
,
ε·10–4
,
D,
nm
λmax
nm
,
ε·10–4
,
D, nm
l·mol-1·cm-1
l·mol-1·cm-1
l·mol-1·cm-1
2
640
612
502*
381
1.99
1.99
5.23
2.06
655
515*
381
1.71
5.49
2.24
673
524*
390
1.56
4.85
2.25
19.5
30.0
3
4
696
566*
369
4.31
4.43
1.86
718
597*
376
3.42
5.59
1.72
731
613*
392
2.76
6.50
1.77
32.0
44.5
9.0
6.5
773
5.90
3.87
1.57
805
675*
377
298
6.33
4.99
1.66
2.36
810
706*
397
299
5.20
6.13
1.71
2.39
627*
372
8
9
724
673
521*
394
302
1.31
1.24
6.05
2.13
1.89
747
522*
455
401
283
1.16
4.82
2.75
2.66
3.32
747
517*
450
413
294
0.85
3.21
3.06
2.96
2.47
11.0
5.5
11.5
9.0
790
729
603*
391
2.31
2.53
6.42
1.44
809
610*
405
289
1.79
8.57
2.19
3.07
826
602*
521
417
298
1.09
4.82
3.31
2.41
2.77
10
11
873
828
690*
391
5.83
6.17
6.43
1.82
3.87
2.62
2.05
1.26
1.77
856
692*
408
294
2.65
9.12
2.41
2.77
884
668*
417
326
1.16
4.41
2.37
2.53
13.5
66.5
29.0
—
696
642
575*
533
360
708
588
365
292
3.70
2.66
2.02
2.80
720
601
369
292
4.54
3.21
2.83
4.20
12
13
14
772
712
621*
369
5.21
4.67
2.53
1.95
795
732
656
372
294
5.53
4.52
3.19
2.44
3.13
89.0
85.0
800
739
670
377
296
4.98
4.61
3.28
2.11
2.75
—
—
—
773
—*2
865
809
696*
376
284
—*2
802
696*
383
289
4.15
3.33
2.00
3.33
655*
382
142.0
47.0
69.0
684
637
559*
529
381
3.91
3.38
3.19
2.72
2.84
687
566*
363
3.97
3.67
3.14
689
577*
366
3.84
3.58
3.04
15
16
17
761
699
631*
362
3.89
4.04
3.07
1.99
777
712
637*
370
—*2
778
720
658*
371
4.71
4.41
3.91
2.33
—
—
—
748
697*
352
3.66
3.36
2.50
868
796
693*
364
3.19
4.81
4.25
2.31
871
796
690*
373
2.95
3.99
3.86
2.19
108.5
779
717*
369
4.92
6.03
1.75
827
765*
374
6.14
5.69
1.85
824
748*
376
5.30
5.28
1.69
_______
*Polymethine bands.
*2Not determined due to low solubility in the given solvents.
284

The results of our quantum-chemical calculations indicated that the calculated absorption spectra of
merocyanines 2-4 and 8-17, although possessing multiple peaks, were caused by π-π* electronic transitions (Table 2).
The large number of calculated absorption bands, as in the case of symmetrical polymethine dyes derived from
tetranitrofluorene [16], resulted from additional energy levels localized on the nitro groups. The major bands of the
theoretical absorption spectra are different in nature.
Fig. 2. Change in electron density in merocyanine 4 for the S0 → S1 transition
( – increase,  – decrease in electron density).
The long-wavelength band in the calculated spectrum of merocyanine 4 was the result of an electron
density transfer along the long axis of the molecule from the electron-donating heterocyclic fragment to the
electron-withdrawing fluorene moiety (Fig. 2). This band may be considered as a charge transfer band.
The short-wavelength band was accompanied by an electron density transfer between adjacent atoms of
the polymethine chain and a partial increase in electron density on the fluorene nitro groups (Fig. 3). This
corresponded to the polymethine nature of the absorption band.
The shortest wavelength band due to interaction of fluorene system and nitro group orbitals was found
in the calculated spectra of all these merocyanines. This band was caused by one of the higher electronic
transitions, such as S0 → S7 in the case of merocyanine 4, and this calculated band virtually matched the
experimental short-wavelength absorption band at 370-400 nm.
The position, intensity, and shape of the shortest wavelength band remained virtually unchanged with
increasing the length of the polymethine chain or upon changing from one heterocyclic fragment to another. The
solvatochromic shifts were small and did not exceed 5 nm. The same band was found in the spectra of
symmetrical anionic dyes derived from tetranitrofluorene. All these findings suggest that this band is a
characteristic absorption feature of the tetranitrofluorene system.
Fig. 3. Change in electron density in merocyanine 4 in the transition S0 → S2.
285

The conclusion concerning the nature of the transitions is also in accord with the much larger increase in
calculated dipole moments of merocyanines upon transition to the S1 state, compared to a transition to the S2 state,
and suggests that the electronic state of merocyanine in the ground and excited states was considerably more
different, compared to the polymethine transition.
TABLE 2. Results of Quantum-chemical Calculations of the Absorption
Maxima (λmax.theor), Oscillator Strength (ftheor), and Dipole Moments in the
Ground (μ), First (μ*) and Higher Excited States (μ**) of Merocyanines
2-4 and 8-16
Com-
pound
λmax.theor
nm
,
Com-
pound
λmax.theor,
nm
ftheor
μ, D μ*, D μ**b, D
ftеор
μ, D
μ*, D μ**b, D
2
3
4
635
455a
401
367
0.13 15.18 33.54 33.91
11
12
13
672
517a
446
378
0.19
0.73a
0.10
0.15
14.63
35.09
43.19
51.75
20.07
23.81
30.57
0.28a
0.70
0.25
676
489a
434
373
0.20 18.27 42.00 36.47
707
551a
383
360
0.30
1.19a
0.13
0.12
17.18
19.42
0.85a
0.63
0.25
722
529a
471
460
378
0.28 20.97 50.46 39.55
755
590a
488
387
375
0.41
1.62a
0.14
0.12
0.17
1.46a
0.15
0.41
0.22
8
9
701
486
415a
376
0.12 17.89 32.68 17.01c
0.12
0.90a
0.29
14
15
642
482a
429
375
370
331
0.21
0.97a
0.27
0.10
0.16
0.12
17.67
20.38
34.32
43.12
19.74
23.19
742
514
457a
377
0.17 22.22 42.51 28.51c
0.55
1.05a
0.27
695
525a
460
454
382
370
355
0.29
1.53a
0.13
0.14
0.15
0.16
0.10
10
788
552a
491
380
0.25 25.96 51.97 40.41
16
743
567a
483
385
372
357
0.40
2.02a
0.18
0.14
0.14
0.11
22.77
51.61
28.71
1.32a
0.72
0.25
_______
aPolymethine bands.
bDipole moments in the second excited state (S2).
cDipole moments in the fourth excited state (S4).
According to the Franck-Condon principle, the intensity of light absorption in the charge transfer transition
should be lower than in the polymethine transition. This conclusion is also supported by the theoretical
oscillator strengths ftheor (Table 2) obtained in quantum-chemical calculations. Indeed, the experimental long-
wavelength absorption bands are less intense than the analogous short-wavelength bands (Table 1).
The increase in the calculated dipole moments upon excitation indicates positive solvatochromism for the
S0 → S2 transition in all the merocyanines studied (Table 2). Indeed, any increase in the solvent polarity in the
merocyanine series 2-4 and 11-17 containing medium and weakly electron-donating fragments, and in going from
toluene to dichloromethane for merocyanines 8-10 caused bathochromic shifts of the short-wavelength absorption
bands. A positive solvatochromism sign indicated that for these dyes a neutral polyene ground state structure
predominated among the three possible limiting structures (neutral polyene, ideal polymethine, and dipolar polyene).
286

The shift of electron density from the heterocycle to the polymethine chain increased with higher
electron-donating ability of the heterocycle in the series from pyran and benzo[cd]indole to indole and
benzimidazole, which led to enhanced alternation of the positive and negative charges on the chain atoms and
leveling of the bond orders in the chain. In other words, the electronic structure of the merocyanines approached
an ideal polymethine structure [13]. This conclusion was supported not only by the above-mentioned intensity
increase and narrowing of the short-wavelength bands, but also by the increase in the vinylene shifts of these
bands with higher electron-donating ability of the heterocyclic fragments. The vinylene shifts in the spectrum of
merocyanine 9 reached 88 nm, which was comparable to the values of these shifts for common merocyanines,
such as malononitrile derivatives (90 nm) and symmetrical dyes (~100 nm). Still further evidence for the
increasing contribution of polymethine structure in going from pyran and benzo[cd]indole to indole and
benzimidazole was found in the deviation change calculated for the short-wavelength bands. These values
dropped with increasing electron-donating ability of the heterocyclic fragment from 108.5 nm in the spectrum of
merocyanine 16 to 13.5 nm in the spectrum of derivative 10.
The vinylene shifts, deviations, band intensity, band shape, and especially the width of bands
determined the trends for polyene-polymethine electronic relaxation variations in donor-acceptor systems, since
these factors reflected the extent of bond order alternation in the chromophore. An increase in bond order
alternation led to decreasing vinylene shifts and band intensity, but greater deviation and wider bands [18].
Fig. 4. Electronic absorption spectra of merocyanine 3 in toluene (1), CH2Cl2 (2), and DMF (3).
Increased solvent polarity had an effect on the absorption spectra of merocyanines 2-4 that was similar
to increased electron-donating ability of the heterocycles, as illustrated by the short- and long-wavelength band
intensity redistribution in the case of dye 3 (Fig. 4). This effect was related to the stabilization of charge
separation in the chromophore by polar solvents, and was especially pronounced for merocyanines 8-10, which
had the strongest electron-donating heterocycle (1,3-diphenylbenzimidazole). The slight increase in polarity
upon replacing toluene with dichloromethane was accompanied by a bathochromic shift of the absorption band
(positive solvatochromism), while the further increase in polarity to DMF led to a hypsochromic shift (negative
solvatochromism). Hence, merocyanines 8-10 have reversible solvatochromism. Such behavior suggests that
dyes 8-10 are closest to an ideal polymethine structure in a specific solvent, in this case, dichloromethane. This
is supported by the maximum extinction coefficient values (Table 1). Higher polarity of the medium favored a
dipolar polyene structure, while a decrease in polarity led to a neutral polyene structure, resulting in reversible
solvatochromism.
287

We note that the long-wavelength band for all the merocyanines studied underwent only bathochromic
shifts upon any increase in solvent polarity. This served as an additional proof that this band was due to charge
transfer, since charge transfer in all neutral compounds always causes a greater dipolarity of the excited state
than the ground state, thus the excited state energy was decreased more strongly than the ground state energy
upon solvation by a polar solvent.
A decrease in the vinylene shifts and increase in deviations of the short-wavelength band upon
increasing the length of the polymethine chain provided evidence for an increased contribution of the neutral
polyene structure in merocyanines 2-4 and 11-16 (Fig. 5, Table 1). The redistribution of short- and long-
wavelength band intensities with increasing value of n was also in accord with this conclusion.
On the other hand, an increase of the polymethine chain length in merocyanines 8-10 was accompanied
by an increased contribution of polymethine structure in toluene and dichloromethane (Fig. 6, Table 1). Similar
behavior was apparent in DMF, when going from dimethinemerocyanine 8 to the tetramethinemerocyanine 9.
However, a further increase in chain length, judging from the drop in the extinction coefficient and broadening
of the short-wavelength band of dye 10, was linked with an increased contribution of a dipolar polyene
structure.
Fig. 5. Electronic absorption spectra of merocyanines 2 (1), 3 (2), and 4 (3) in CH2Cl2.
Fig. 6. Electronic absorption spectra of merocyanines 8 (1), 9 (2), and 10 (3) in CH2Cl2.
288

Thus, we were able to predictably control the electronic structure of merocyanines based on 2,4,5,7-tetra-
nitrofluorene in the range of limiting ideal structures (neutral polyene, polymethine, and dipolar polyene) by
changing the electron-donating ability of the heterocyclic fragment and solvent polarity. The position, intensity,
and shape of the absorption bands, as well as the sign of solvatochromic effect were altered correspondingly.
EXPERIMENTAL
The absorption spectra were recorded on a Shimadzu UV-3100 spectrophotometer in 1-cm cells. The
1
concentration of the dissolved samples was 10-5 mol/l. The H NMR spectra were recorded on a Varian VXR-
300 spectrometer at 300 MHz for merocyanines 6, 7, and 11-17 and a Jeol Eclipse-400 spectrometer at 400
MHz for compounds 2-4 and 8-10, with TMS as internal standard. The elemental analysis was carried out on a
Carlo Erba Strumentazione Elemental Analyzer 1106. The melting points were determined in an open capillary
and not corrected. The purity of the dyes was checked by thin-layer chromatography on Silufol UV-254 plates
with acetonitrile as the eluent. The solvents were purified by reported methods [19]. Dichloromethane was
stabilized by adding 1% of absolute ethanol.
The ab-initio DFT quantum-chemical calculations were carried out using the PC Gamess/Firefly
software package in the B3LYP/6-31G(d,p) basis with prior optimization of the ground state geometry in the
same basis set. The TDDFT method was used to calculate the electronic transitions. In describing the calculated
spectra, electronic transitions with oscillator strength greater than 5% of the transition intensity at the greatest
osccilator strength were taken into account.
(2E)-1,3,3-Trimethyl-2-[2-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)ethylidene]indoline (2). A solution
of (2E)-(1,3,3)-trimethyl-1,3-dihydro-2H-indol-2-ylidene)acetaldehyde (20 mg, 0.1 mmol) and 2,4,5,7-tetra-
nitrofluorene (1) (35 mg, 0.1 mmol) in acetic anhydride (2 ml) was heated at reflux for 3-4 min. The precipitate
was filtered off, washed with acetic anhydride and then with acetone (310 ml) to give indoline 2. Yield 52 mg
1
(99%). Dark-green powder; mp >270°C (acetic acid). Rf 0.40. H NMR spectrum (DMSO-d6), δ, ppm (J, Hz):
1.86 (6H, s, C(CH3)2); 3.83 (3H, s, NCH3); 6.91 (1H, d, J = 14.4, H-1'); 7.28 (1H, t, J = 6.8, H Ar); 7.42 (1H, d,
J = 6.8, H Ar); 7.43 (1H, s, H Ar); 7.45 (1H, t, J = 7.2, H Ar); 7.62 (1H, d, J = 7.6, H Ar); 8.57 (1H, d, J = 1.6,
H Ar); 8.74 (1H, d, J = 14.4, H-2'); 9.34 (2H, d, J = 1.6, H Ar). Found, %: С 58.73; Н 3.36; N 13.01.
C26H19N5O8. Calculated, %: С 58.98; Н 3.62; N 13.23.
(2E)-1,3,3-Trimethyl-2-[(2E)-4-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)but-2-enylidene]indoline
(3). A mixture of 2-{(1E,3E)-4-[acetyl(phenyl)amino]buta-1,3-dienyl}-1,3,3-trimethyl-3H-indolium perchlorate
(45 mg, 0.1 mmol) and 2,4,5,7-tetranitrofluorene (1) (35 mg, 0.1 mmol) was dissolved with heating at reflux in
acetic anhydride (2 ml) over 3-4 min, and then Et3N (1 ml) was added. A precipitate formed immediately. The
reaction mixture was cooled. The precipitate was filtered off and washed with acetic anhydride, then with
acetone (310 ml) to give indoline 3. Yield 55 mg (99%). Dark-green powder with a bronze sheen; mp >270°C
1
(acetic acid). Rf 0.43. H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): 1.76 (6H, s, C(CH3)2); 3.64 (3H, s,
NCH3); 6.52 (1H, d, J = 13.6, H-1'); 7.22 (1H, t, J = 7.6, H Ar); 7.31 (1H, d, J = 7.6, H Ar); 7.39 (1H, t,
J = 14.4, H-3'); 7.39 (1H, t, J = 7.6, H Ar); 7.56 (1H, d, J = 7.6, H Ar); 8.31 (1H, t, J = 12.8, H-2'); 8.53 (2H, s,
H Ar); 8.70 (1H, d, J = 13.2, H-4'); 9.32 (2H, s, H Ar). Found, %: С 60.40; Н 3.68; N 12.89. C28H21N5O8.
Calculated, %: С 60.54; Н 3.81; N 12.61.
(2E)-1,3,3-Trimethyl-2-[(2E,4E)-6-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)hexa-2,4-dienylidene]-
indoline (4).
A
mixture of 2-{(1E,3E,5E)-6-[acetyl(phenyl)amino]hexa-1,3,5-trienyl}-1,3,3-trimethyl-
3H-indolium perchlorate (47 mg, 0.1 mmol) and 2,4,5,7-tetranitrofluorene (1) (35 mg, 0.1 mmol) was dissolved
with heating at reflux in acetic anhydride (2 ml), and Et3N (1 ml) was added. The mixture was heated at reflux
for an additional 2-3 min. The precipitate was filtered off, washed with acetic anhydride and then with acetone
1
(410 ml) to give indoline 4. Yield 44 mg (75%). Dark-green powder, mp >270°C (acetic acid). Rf 0.48. H
NMR spectrum (DMSO-d6), δ, ppm (J, Hz): 1.67 (6H, s, C(CH3)2); 3.53 (3H, s, NCH3); 6.17 (1H, d, J = 13.2,
289

H-1'); 6.78 (1H, t, J = 12.4, H-2'); 7.14 (1H, t, J = 7.2, H Ar); 7.19 (1H, d, J = 7.6, H Ar); 7.34 (1H, t, J = 7.2,
H Ar); 7.39 (1H, t, J = 12.8, H-4'); 7.46 (1H, d, J = 7.2, H Ar); 7.70-7.89 (2H, m, H-3',5'); 8.41 (1H, d, J =14.0,
H-6'); 8.55 (2H, s, H Ar); 9.27 (2H, s, H Ar). Found, %: С 61.75; Н 3.73; N 11.90. C30H23N5O8. Calculated, %:
С 61.96; Н 3.99; N 12.04.
N-Phenyl-N-[(1E)-3-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)prop-1-enyl]acetamide (6). A solu-
tion of 2,4,5,7-tetranitrofluorene (1) (173 mg, 0.5 mmol) and N-[3-anilinoprop-2-enylidene]anilinium chloride
(130 mg, 0.5 mmol) in acetic anhydride (3 ml) was heated at reflux for 2-3 min. The product precipitated
immediately. The precipitate was filtered off and washed with acetic anhydride and ethanol to give acetamide 6.
1
Yield 255 mg (99%). Brown powder; mp 265-266°C (acetic acid). H NMR spectrum (acetone-d6), δ, ppm (J,
Hz): 2.06 (3H, s, СОCH3); 6.20 (1H, t, J = 12.6, H-2'); 7.58 (2H, d, J = 8.1, H Ar); 7.73 (3H, t, J = 7.5, H Ar);
8.37 (1H, d, J = 1.8, H Ar); 8.59 (1H, d, J = 1.8, H Ar); 8.61 (1H, d, J = 12.3, H-1); 8.62 (1H, d, J = 1.8, H Ar);
8.72 (1H, d, J = 13.2, H-3); 9.14 (1H, d, J = 1.8, H Ar). Found, %: С 55.45; Н 2.81; N 13.39. C24H15N5O9.
Calculated, %: С 55.71; Н 2.92; N 13.54.
N-Phenyl-N-[(1E,3E)-5-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)penta-1,3-dienyl]acetamide (7). A
solution of 2,4,5,7-tetranitrofluorene (1) (173 mg, 0.5 mmol) and N-[5-anilinopenta-2,4-dienylidene]anilinium
chloride (143 mg, 0.5 mmol) in acetic anhydride (3 ml) was heated at reflux for 2-3 min. The product
precipitated immediately. The precipitate was filtered off and washed with acetic anhydride and ethanol, to give
1
acetamide 7. Yield 260 mg (96%). Shiny black powder; mp 270-271°C (acetic acid). H NMR spectrum
(acetone-d6), δ, ppm (J, Hz): 2.14 (3H, s, CH3); 5.63 (1H, t, J = 12.6, H-2); 7.40 (2H, d, J = 7.2, H Ar);
7.49-7.68 (5H, m, H-3,4, H Ar); 8.15 (1H, d, J = 13.8, H-1); 8.72 (1H, d, J = 10.5, H-5); 8.64 (1H, s, H Ar);
8.67 (1H, s, H Ar); 9.09 (1H, s, H Ar); 9.15 (1H, s, H Ar). Found, %: С 57.28; Н 3.19; N 13.00. C26H17N5O9.
Calculated, %: С 57.46; Н 3.15; N 12.89.
1,3-Diphenyl-2-[2-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)ethylidene]-2,3-dihydro-1H-benzimidazole
(8). A solution of 2-methyl-1,3-diphenyl-3H-benzimidazol-1-ium chloride (32 mg, 0.1 mmol) and 9-(ethoxy-
methylene)-2,4,5,7-tetranitro-9H-fluorene (5) (40 mg, 0.1 mmol) in pyridine (3 ml) with Et3N (1 ml) was heated at
reflux for 2-3 min. The precipitate was filtered off and washed with cold pyridine and acetone to give benzimidazole
1
8. Yield 42 mg (66%). Gray powder with a blue sheen; mp >270°C (pyridine). Rf 0.42. H NMR spectrum
(DMSO-d6), δ, ppm (J, Hz): 6.22 (1H, d, J = 14.6, H-1'); 7.11 (1H, d, J = 15.2, H-2'); 7.11 (2H, dd, J = 6.4, J = 2.6,
H Ar); 7.51 (2H, dd, J = 6.4, J = 2.6, H Ar); 7.71-7.82 (10H, m, H Ar); 8.28 (2H, d, J = 2.0, H Ar); 8.81 (2H, d,
J = 2.0, H Ar). Found, %: С 63.43; Н 3.08; N 12.97. C34H20N6O8. Calculated, %: С 63.75; Н 3.15; N 13.12.
1,3-Diphenyl-2-[(2E)-4-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)but-2-enylidene]-2,3-dihydro-1H-benz-
imidazole (9). A solution of 2-methyl-1,3-diphenyl-3H-benzimidazol-1-ium chloride (32 mg, 0.1 mmol) and
acetamide 6 (52 mg, 0.1 mmol) in pyridine (3 ml) with Et3N (1 ml) was heated at reflux for 3-4 min. The
precipitate formed was filtered off and washed with pyridine and acetone to give benzimidazole 9. Yield 36 mg
(54%). Gray-green powder; mp >270°C (pyridine). Rf 0.45. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): 6.17
(1H, d, J = 15.2, H-1'); 6.75 (1H, dd, J = 15.2, J =11.6, H-2'); 6.99 (1H, dd, J = 14.8, J =11.6, H-3'); 7.29 (2H,
dd, J = 6.4, J = 2.6, H Ar); 7.34 (1H, d, J = 14.8, H-4'); 7.54 (2H, dd, J = 6.4, J = 2.6, H Ar); 7.83-7.95 (10H, m,
H Ar); 8.27 (2H, d, J = 2.0, H Ar); 8.99 (2H, d, J = 2.0, H Ar). Found, %: С 64.53; Н 3.09; N 12.42.
C36H22N6O8. Calculated, %: С 64.87; Н 3.33; N 12.61.
1,3-Diphenyl-2-[(2E,4E)-6-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)hexa-2,4-dienylidene]-2,3-dihydro-
1H-benzimidazole (10). A solution of 2-methyl-1,3-diphenyl-3H-benzimidazol-1-ium chloride (32 mg,
0.1 mmol) and acetamide 7 (55 mg, 0.1 mmol) in pyridine (3 ml) was heated at reflux for 3-4 min. The
precipitate formed was filtered off and washed with acetone to give benzimidazole 10. Yield 30 mg (43%).
1
Dark-green powder; mp >270°C (pyridine). Rf 0.51. H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): 6.05 (1H,
d, J = 14.4, H-1'); 6.44 (1H, t, J = 11.2, H-3'); 6.51 (1H, t, J = 11.6, H-2'); 6.68 (1H, t, J = 13.2, H-4'); 6.92 (1H,
dd, J = 15.2, J = 11.2, H-5'); 7.32 (2H, dd, J = 6.4, J = 3.2, H Ar); 7.60 (2H, dd, J = 6.0, J = 3.2, H Ar); 7.82–7.91
(10H, m, H Ar); 7.93 (1H, d, J = 15.2, H-6'); 8.26 (2H, d, J = 2.0, H Ar); 9.18 (2H, d, J = 2.0, H Ar). Found, %:
С 65.61; Н 3.24; N 11.98. C38H24N6O8. Calculated, %: С 65.90; Н 3.49; N 12.13.
290

(2E)-1-Benzyl-2-[2-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)ethylidene]-1,2-dihydrobenzo[cd]indole
(11). A mixture of 1-benzyl-2-methylbenzo[cd]indolium tetrafluoroborate (35 mg, 0.1 mmol) and 9-(ethoxy-
methylidene)-2,4,5,7-tetranitro-9H-fluorene (5) (40 mg, 0.1 mmol) in acetic anhydride (2 ml) was heated at
reflux until the starting compounds were completely dissolved (2-3 min). Then Et3N (1 ml) was added. The
precipitate formed was filtered off and washed with acetic anhydride, hot ethanol, and acetone to give
dihydrobenzoindole 11. The pure compound is readily soluble in polar aprotic solvents. Yield 50 mg (80%).
Dark-green powder; mp >270°C (acetic acid), Rf 0.25. 1H NMR spectrum (pyridine-d5), δ, ppm (J, Hz): 5.73 (2H,
s, NCH2Ph); 7.25-7.32 (3H, m, H Ar); 7.34 (1H, d, J = 13.6, H-1'); 7.37-7.48 (2H, m, H Ar); 7.49-7.56 (1H, m,
H Ar); 7.64-7.75 (2H, m, H Ar); 7.78-7.85 (1H, m, H Ar); 8.15 (1H, d, J = 8.0, H Ar); 8.84 (1H, s, H Ar); 8.91
(1H, s, H Ar); 8.95 (1H, d, J = 8.0, H Ar); 9.15 (1H, s, H Ar); 9.23 (1H, d, J = 14.0, H-2'); 9.54 (1H, s, H Ar).
Found, %: С 64.33; Н 3.01; N 11.14. C33H19N5O8. Calculated, %: С 64.60; Н 3.12; N 11.41.
(2E)-1-Benzyl-2-[(2E)-4-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)but-2-enylidene]-1,2-dihydrobenzo-
[cd]indole (12). A mixture of 1-benzyl-2-methylbenzo[cd]indolium tetrafluoroborate (35 mg, 0.1 mmol) and
acetamide 6 (52 mg, 0.1 mmol) in acetic anhydride (2 ml) was heated at reflux until the starting compounds
completely dissolved (3-4 min). Then Et3N (1 ml) was added. The precipitate formed was filtered off, washed
with ethanol, and dried. The crude product was transferred to a flask and heated at reflux in chloroform (10 ml).
The precipitate was filtered off and dried to give dihydrobenzoindole 12. Yield 43 mg (67%). Green powder
1
with a bronze sheen; mp >270°C (acetic acid). Rf 0.27. H NMR spectrum (pyridine-d5), δ, ppm (J, Hz): 5.34
(2H, s, NCH2Ph); 6.96 (1H, d, J = 13.5, H-1'); 7.02 (1H, d, J = 6.9, H Ar); 7.27-7.41 (6H, m, H-2', H Ar); 7.41-
7.67 (3H, m, H Ar); 7.87 (1H, t, J = 12.6, H-3'); 7.97 (1H, d, J = 7.2, H Ar); 8.28 (1H, d, J = 7.2, H Ar); 8.64
(1H, t, J = 13.5, H-4'); 8.81 (1H, s, H Ar); 8.86 (1H, s, H Ar); 9.28 (1H, s, H Ar); 9.33 (1H, s, H Ar). Found, %:
С 65.58; Н 3.14; N 10.77. C35H21N5O8. Calculated, %: С 65.73; Н 3.31; N 10.95.
(2E)-1-Benzyl-2-[(2E,4E)-6-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)hexa-2,4-dienylidene]-1,2-di-
hydrobenzo[cd]indole (13). A mixture of 1-benzyl-2-methylbenzo[cd]indolium tetrafluoroborate (52 mg,
0.15 mmol) and acetamide 7 (81 mg, 0.15 mmol) in pyridine (3 ml) was heated at reflux for 2-3 min, then Et3N
(1 ml) was added. Heating at reflux was continued until a precipitate began to form (2-3 min). The precipitate
was filtered off and washed with acetone (35 ml) to give dihydrobenzoindole 13. Yield 50 mg (75%). Black
powder with a green sheen; mp >270°C (pyridine). Rf 0.31. 1H NMR spectrum (DMSO-d6), δ, ppm ( J, Hz): 5.35
(2H, s, NCH2Ph); 6.54 (1H, d, J = 12.0, H-1'); 6.99 (1H, t, J = 12.3, H-3'); 7.03 (1H, d, J = 6.4, H Ar); 7.22-7.55 (6H,
m, H-2', H Ar); 7.62 (1H, t, J = 12.0, H-4'); 7.72-7.89 (2H, m, H Ar); 7.93-8.05 (3H, m, H-5', H Ar); 8.28 (1H, d,
J = 6.4, H Ar); 8.49 (1H, d, J = 12.0, H-6'); 8.65 (2H, s, H Ar); 9.30 (2H, s, H Ar). Found, %: С 66.43; Н 3.28;
N 10.19. C37H23N5O8. Calculated, %: С 66.77; Н 3.48; N 10.52.
2,6-Diphenyl-4-[2-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)ethylidene]-4H-pyran (14). A solution
of 4-methyl-2,6-diphenylpyrilium tetrafluoroborate (33 mg, 0.1 mmol) and 9-(ethoxymethylidene)-2,4,5,7-
tetranitro-9H-fluorene (5) (42 mg, 0.1 mmol) in pyridine (3 ml) with piperidine (0.5 ml) was heated at reflux for
2-3 min. A precipitate formed upon cooling, which was filtered off and washed with ethanol and hot acetone to
give pyran 14. Yield 30 mg (50%). Green powder with a bronze sheen; mp >270°C (pyridine). Rf 0.39. 1H NMR
spectrum (D2SO4), δ, ppm (J, Hz): 4.11 (1H, s, H-1'); 6.86-7.11 (6H, m, H Ar); 7.38-7.59 (4H, m, H Ar);
7.62 (2H, s, H Ar); 8.21 (1H, s, H Ar); 8.29 (1H, s, H Ar); 8.44 (1H, d, J = 12.9, H-2'); 9.92 (2H, s, H Ar).
Found, %: С 63.53; Н 2.88; N 9.01. C32H18N4O9. Calculated, %: С 63.79; Н 3.01; N 9.30.
2,6-Diphenyl-4-[(2E)-4-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)but-2-enylidene]-4H-pyran (15). A
mixture of 4-methyl-2,6-diphenylpyrilium tetrafluoroborate (33 mg, 0.1 mmol) and acetamide 6 (52 mg,
0.1 mmol) in pyridine (2-3 ml) with Et3N (1 ml) was heated at reflux for 3-4 min. The precipitate formed was
filtered off and washed with acetone (35 ml) to give pyran 15. Yield 40 mg (63%). Black powder with a green
1
sheen; mp >270°C (pyridine). Rf 0.44. H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): 6.58 (1H, d, J = 12.8,
H-1'); 7.53 (1H, t, J = 13.2, H-2'); 7.55-7.71 (6H, m, H Ar); 7.95-8.14 (6H, m, H Ar); 8.32 (1H, t, J = 12.2,
H-3'); 8.51 (1H, d, J = 12.8, H-4'); 8.62 (2H, s, H Ar); 9.27 (2H, s, H Ar). Found, %: С 64.73; Н 3.04; N 8.77.
C34H20N4O9. Calculated, %: С 64.97; Н 3.21; N 8.91.
291

2,6-Diphenyl-4-[(2E,4E)-6-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)hexa-2,4-dienylidene]-4H-pyran
(16). A solution of 4-methyl-2,6-diphenylpyrilium tetrafluoroborate (34 mg, 0.1 mmol) and acetamide 7 (54 mg,
0.1 mmol) in pyridine (3 ml) was heated at reflux for 3 min, then Et3N (1 ml) was added. The precipitate formed
was filtered off and washed with pyridine and acetone to give pyran 16. Yield 12 mg (18%). Black powder with
a green sheen; mp >270°C (pyridine). Rf 0.41. Found, %: С 65.83; Н 3.12; N 8.41. C36H22N4O9. Calculated, %:
С 66.06; Н 3.39; N 8.56.
2,6-Di-tert-butyl-4-[(2E,4E)-6-(2,4,5,7-tetranitro-9H-fluoren-9-ylidene)hexa-2,4-dienylidene]-4H-
pyran (17). A solution of 4-methyl-2,6-di-tert-butylpyrilium perchlorate (31 mg, 0.1 mmol) and acetamide 7
(54 mg, 0.1 mmol) in pyridine (3 ml) was heated at reflux for 3 min, then Et3N (1 ml) was added. The
precipitate formed was filtered off and washed with pyridine and acetone to give pyran 17. Yield 50 mg (81%).
Black powder with a bronze sheen; mp >270°C (pyridine). Rf 0.56. 1H NMR spectrum (CDCl3), δ, ppm (J, Hz):
1.25 (9H, s, C(CH3)3); 1.31 (9H, s, C(CH3)3); 5.82 (1H, d, J = 12.6, H-1'); 5.98 (1H, d, J = 1.5, H Ar); 6.39 (1H,
d, J = 1.5, H Ar); 6.59 (1H, t, J = 12.3, H-2'); 7.28-7.35 (2H, m, H-3',4'); 7.89 (1H, t, J = 12.6, H-5'); 8.72 (1H,
d, J = 1.5, H Ar) Found, %: С 62.17; Н 4.48; N 8.99. C32H30N4O9. Calculated, %: С 62.54; Н 4.92; N 9.12.
This work was carried out using the computer facilities of the Computer Unit of the Scientific-
Technological Complex "Institute of Monocrystals" and Institute of Scintillation Materials of the National
Academy of Sciences of Ukraine as part of the Ukrainian National Grid.
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