Synthesis, absorption spectra, and luminescence properties of dihydrobenzoacridinone derivatives

Article abstract of DOI:10.1134/S1070427214060196

9,9-Dimethyl-12-[(5-aryl-2-furyl) (or 5-aryl-2-thienyl, or 5-aryl-1-methyl-1H-pyrrolyl)]-7,8,9,10,11,12-hexahydrobenzo[a]acridin-11-ones were synthesized, and their absorption and luminescence spectrum characteristics in ethanol at room temperature and at 77 K were studied. The spectra suggest the existence of these compounds in a liquid solution as mixtures of conformers, each of which is characterized by its own absorption and fluorescence spectra.

Full text of DOI:10.1134/S1070427214060196

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 6, pp. 780−786. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © N.G. Kozlov, S.L. Bondarev, Yu.D. Zhikharko, V.N. Knyukshto, R.Z. Lytvyn, Yu.I. Horak, M.D. Obushak, L.I. Basalaeva, 2014, published
in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 6, pp. 775−782.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Synthesis, Absorption Spectra, and Luminescence
Properties of Dihydrobenzoacridinone Derivatives
N. G. Kozlov, S. L. Bondarev, Yu. D. Zhikharko, V. N. Knyukshto,
R. Z. Lytvyn, Yu. I. Horak, M. D. Obushak, and L. I. Basalaeva
Institute of Physical Organic Chemistry, National Academy of Sciences of Belarus,
ul. Surganova 13, Minsk, 220072 Belarus
Minsk State Higher Radiotechnical College, pr. Nezavisimosti 62, Minsk, 220005 Belarus
Stepanov Institute of Physics, National Academy of Sciences of Belarus,
pr. Nezavisimosti 68, Minsk, 220005 Belarus
Ivan Franko National University, ul. Sychovych Strel’tsiv 14, Lviv, 79602 Ukraine
e-mail: loc@ifoch.bas-net.by
Received February 21, 2014
Abstract—9,9-Dimethyl-12-[(5-aryl-2-furyl) (or 5-aryl-2-thienyl, or 5-aryl-1-methyl-1Н-pyrrolyl)]-
7,8,9,10,11,12-hexahydrobenzo[а]acridin-11-ones were synthesized, and their absorption and luminescence
spectrum characteristics in ethanol at room temperature and at 77 K were studied. The spectra suggest the existence
of these compounds in a liquid solution as mixtures of conformers, each of which is characterized by its own
absorption and fluorescence spectra.
DOI: 10.1134/S1070427214060196
Proceeding with studies on synthesis of organic lumi-
nophores containing carbonyl group [1], we synthesized
new compounds with the carbonyl group incorporated in
the dihydrobenzoacridine core, following the procedure
that we developed (Scheme 1).
Azomethine IIIа–IIId, according to the suggested re-
action scheme, adds a dimedone molecule to form unsta-
ble intermediate A, which then decomposes into arylidene
diketone B and 2-naphthylamine. In 2-naphthylamine,
the electron density is the highest at the α-carbon atom
relative to the amino group, and it undergoes addition via
this atom to the double bond of arylidene diketone B to
form compound C whose heterocyclization with water
elimination yields the final products, 9,9-dimethyl-12-
[(5-aryl-2-furyl) (or 5-aryl-2-thienyl, or 5-aryl-1-methyl-
1Н-pyrrolyl)]-7,8,9,10,11,12-hexahydrobenzo[а]acridin-
11-ones Va–Vf. The possibility of the occurrence of such
transformations in the course of ternary condensation of
aromatic aldehydes, 1,3-diketones, and 2-naphthylamine
was reported in [2, 3].
Refluxing equimolar amounts of 2-naphthylamine I,
appropriate aldehyde IIа–IIf, and dimedone IV in an al-
coholic solution led to selective formation of 9,9-dimeth-
yl-12-[(5-aryl-2-furyl) (or 5-aryl-2-thienyl, or 5-aryl-1-
methyl-1Н-pyrrolyl)]-7,8,9,10,11,12-hexahydrobenzo[а]
acridin-11-ones Va–Vf.
Dihydrobenzoacridinones Va–Vd can be prepared
both by the reaction of azomethines IIIa–IIId with
2-naphthylamine and by the ternary condensation of
2-naphthylamine, aldehydes IIa–IId, and dimedone IV.
Dihydrobenzoacridinones Ve and Vf can be prepared only
by cascade condensation of 2-naphthylamine, aldehydes
IIe and IIf, and dimedone, because in reaction of 2-naph-
thylamine with N-methyl-5-arylpyrrole-2-carbaldehydes
IIe and IIf we failed to isolate the pure azomethines from
the reaction mixture.
The physicochemical constants of the synthesized di-
hydrobenzoacridinones Va–Vf are given in Table 1.
1
The H NMR spectra of dihydrobenzoacridinones
Va–Vf in all the cases are superpositions of the spectra
of different fragments and consist of three fragments:
(1) seven-spin system of aromatic protons belonging to
780

SYNTHESIS, ABSORPTION SPECTRA, AND LUMINESCENCE PROPERTIES
781
Scheme 1. Scheme of the synthesis of dihydrobenzoacridine derivatives
X = O, R = R = 4-NO2 (a), 2-NO2–4-ОCH3 (b); Х = S, R = 4-NO2 (c), 3-NO2 (d); Х = N-CH3, R = 4-Br (e), 2-Br (f).
the naphthalene core, АВ system of the heteroaromatic
ring, and four-spin system АА'ВВ' or АВCD depending
on the substituent position in the aromatic ring; (2) two
AB systems of the dimedone moiety in the aliphatic re-
gion; and (3) singlet from Н12 proton at 5.45–6.11 ppm.
The positions and multiplicities of the proton signals are
typical of the 1Н NMR spectra of related compounds [4].
The electronic absorption spectra of the synthesized
compounds in ethanol are characterized by a set of
vibronic bands in the UV range (Fig. 1, Table 2), which
can be subdivided into three groups. The first group
includes bands in the range 200–250 nm with high molar
extinction coefficient ε (30000–80000 L mol–1 cm–1);
the second group, bands at 250–320 nm (10 000–
38000 L mol–1 cm–1); and the third group, bands in the
range 320–450 nm (11 000–25 000 L mol–1 cm–1).
In the IR spectra of dihydrobenzoacridinones Va–Vf,
there are absorption bands of free (3440–3400 cm–1) and
associated (3275–3257 cm–1) amino groups. Such pattern
is observed at incomplete association of amines.
Each of these groups can be assigned to electronic
transitions Sn ← S0 (n = 1–3) characterized by the cor-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

782
KOZLOV et al.
Table 1. Yields, melting points, and elemental analyses of 9,9-dimethyl-12-[(5-aryl-2-furyl) (or 5-aryl-2-thienyl, or 5-aryl-1-
methyl-1Н-pyrrolyl)]-7,8,9,10,11,12-hexahydrobenzo[а]acridin-11-ones Vа–Vf
Found, %
Н
Calculated, %
Compound
Yield, %
Tm, °C
Formula
С
N
C
Н
N
Vа
Vb
Vc
70
62
60
310–312 75.00
288–290 80.21
279–280 72.52
5.26
5.97
С29Н24N2О4
С30Н27NО5
74.98
5.21
6.03
6.00
5.07
3.16
80.15
72.48
6.05
5.03
3.12
5.78
С29Н24N2О3S
5.83
S 6.70
S 6.67
Vd
Ve
Vf
47
50
44
210–212 72.42
5.00
5.47
5.46
5.81
S 6.67
С29Н24N2О3S
С30Н27ВrN2О
С30Н27BrN2О
72.48
70.15
70.15
5.03
5.32
5.83
S 6.67
>320
70.20
5.33
Br 15.38
5.48
Br 15.62
289–290 69.88
5.32
5.32
5.48
Br 15.49
Br 15.62
Va–Vf and, correspondingly, to high extent of allowance
responding oscillator strength f. The quantity f was cal-
culated by the formula [5]
→
of the S1 S transition.
←
0
The oscillator strength determined by the integral
extinction coefficient in accordance with Eq. (1) is the
measure of the probability of the electronic transition.
To estimate the probability of the S1 ← S0 transition in
Vа–Vf, let us perform comparative analysis of the oscil-
lator strengths given in Table 2 with those for benzene
and naphthalene (naphthalene in the form of the 2-amino
derivative participated in the synthesis of Vа–Vf). The
oscillator strengths for benzene and naphthalene were
determined in ethanol using the molar extinction coef-
ficients for benzene, 204 L mol–1 cm–1 at λmax = 254 nm,
and naphthalene, 350 L mol–1 cm–1 at λmax = 275 nm [7].
The oscillator strengths f for benzene and naphthalene
in ethanol, calculated from Eq. (1), appeared to be 0.002
and 0.0045. Comparison of these values with those ob-
tained for Vа–Vf shows that the oscillator strength for the
S1 ← S0 transition in Vа–Vf increases by one–two orders
of magnitude. Such a strong increase in the probability of
the S1←S0 transition is largely associated with changes
in the symmetry of the molecular structure. Indeed, in-
troduction of substituents into a benzene molecule (i.e., a
decrease in the molecular symmetry) leads to an increase
in the oscillator strength by an order of magnitude and
more [8].
(1)
~
where n is the refractive index of the solvent, and ν is
the wavenumber.
The values of f for the long-wave absorption band at
320–450 nm (Table 2) vary in the range 0.21–0.33, with
λmaabxs varying insignificantly (363–370 nm).
As seen from Table 2, the oscillator strength f of the
long-wave transition S1 ← S0 is high and proportional to
the rate constant k of the radiative transition S1 → S0,
calculated from the absorption and fluorescence spectra
calc
fl
[6] by the formula
(2)
~
where ν0 is the wavenumber of the 0–0 transition, deter-
mined from intersection of the absorption and fluores-
cence spectra.
calc
fl
As seen from the values of k
in Table 2, their
variation well correlates with the variation of f for the
calc
fl
The absorption spectra of compounds Va–Vf are main-
long-wave transition S1 ← S0. High values of f and k
ly formed on the basis of the absorption spectrum of the
are due to low symmetry of the molecular structure of
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

SYNTHESIS, ABSORPTION SPECTRA, AND LUMINESCENCE PROPERTIES
783
Table 2. Absorption and luminescence spectrum characteristics of Vа–Vf in ethanol solution at room temperature
max
abs
calc
fl
max
fl
eff
fl
× 10–8, s–1
Compound
λ
, nm (log ε [L mol–1 cm–1])
f
λ
, nm
Ф
× 103
k
Vа
Vb
Vc
Vd
Ve
230 (4.5), 280 (4.0), 370 (4.2)
235 (4.8), 290 (4.4), 363 (4.1)
235 (4.3), 285 (3.9), 370 (4.1)
235 (4.9), 290 (4.5), 368 (4.05)
240 (4.9), 290 (4.5), 363 (4.4)
240 (4.8), 280 (4.5), 363 (4.2)
0.27
0.24
0.23
0.21
0.33
0.28
2.2
2.1
2.1
2.0
2.5
2.3
440
0.52
470
465
410
445
450
8.4
0.4
5.0
1.6
2.0
Vf
naphthalene fragment (bands in the range 200–320 nm)
of the dihydrobenzoacridine moiety and also contain a
charge-transfer band. The band in the range 320–450 nm
is due to interaction of the dihydrobenzoacridine core and
hetaryl fragment bearing p-nitrophenyl or p-bromophenyl
substituents [9]. This interaction leads to the charge
transfer; hence, the band in the range 320–450 nm is the
charge-transfer band and can be assigned to the electronic
transition S1 ← S0. Depending on the structure of the heta-
ryl moiety, the shape of the charge-transfer band varies
from broad and smeared (Va, Vc) to structured, consisting
of several maxima (Vb, Vd–Vf). Their intensity relative
to the band at 200–320 nm varies. The charge-transfer
bands are characterized by high molar extinction coef-
ficients (Table 2), comparable or exceeding (in the case
of Va and Vc) those of the bands at 250–320 nm. For
Va and Vc (λmax 370 nm for both), log ε is 4.2 and 4.1,
compared to log ε = 4.0 and 3.9 at λmax 280 and 285 nm
for Va and Vc, respectively.
The charge-transfer bands are also revealed in the
spectra of the starting compounds from which compounds
Vа–Vf are synthesized. For example, 2-naphthylamine I
in ethanol exhibits a weak charge-transfer band with
a maximum at 340 nm, and 5-(4-nitrophenyl)furan-2-
carbaldehyde IIa has a strong charge-transfer band at
345 nm. In compound Va synthesized from these com-
ponents, the charge-transfer band is red-shifted and is
located at 370 nm.
The fluorescence spectra of the compounds studied,
recorded in ethanol at room temperature, consist of
max
fl
broad structureless bands with the maxima λ
in the
range 400–500 nm (Table 2). A specific feature of these
ε, L mol–1 cm–1
λ, nm
λ, nm
Fig. 2. (1, 2) Absorption and (3–6) fluorescence spectra of
(1, 3, 4) Va and (2, 5, 6) Vf in ethanol at 293 K. λexc, nm: (3, 5)
320 and (4, 6) 360. (I) Intensity and (λ) wavelength; the same
for Figs. 3 and 4.
Fig. 1. Absorption spectra of (1) Va, (2) Vb, (3) Vf, and (4) Vd
in ethanol at 293 K. (ε) Extinction coefficient and (λ) wave-
length.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

784
KOZLOV et al.
the molecule, the charge transfer occurs by the inductive
mechanism [9] and is controlled by mutual arrangement
of the donor and acceptor. Thus, the charge transfer ef-
ficiency depends of the angle of the turn around the single
bond, determining the existence of several conformers.
The rotation of the molecular fragments around a single
bond should depend on the viscosity of the medium.
Therefore, to study this effect, we performed the absorp-
tion and luminescence measurements at 77 K in ethanol,
when the molecules occur in solid glassy solutions.
In contrast to room temperature when only weak fluo-
rescence was detected, at 77 K, along with short-wave
fluorescence at 380–480 nm, a phosphorescence spectrum
was observed at 480–600 nm (Fig. 3), and the fluores-
cence and phosphorescence excitation spectra coincide
with the absorption spectra. The structured phosphores-
cence band is observed in the spectra of compounds Ve
and Vf whose molecules contain a heavy bromine atom.
Comparison of the phosphorescence spectra of Ve and
Vf with the published spectrum of 1-bromonaphthalene
in alcohol–ether mixture at 77 K [10] shows that these
spectra fully coincide. Thus, the phosphorescence in the
compounds studied is due to the naphthalene fragment
of the dihydrobenzoacridinone molecule. The energy of
the Т1 state, estimated from the 0–0 transition at 483 nm,
for Ve and Vf is 20 700 cm–1. The frequency of the 0–0
transition between the lower excited (S1) and ground
(S0) states of these compounds appeared to be equal to
26 300 cm–1.
λ, nm
Fig. 3. (1) Absorption, (3, 4) fluorescence + phosphorescence,
(5) phosphorescence, and (2) luminescence excitation spec-
tra of Vf in ethanol at 77 K. λexc, nm: (3) 320 and (4) 360;
(2) λreg 500 nm. Phosphorescence spectrum 5 was recorded
with a phosphoroscope.
max
fl
spectra is the dependence of λ on the excitation wave-
length λexc. The fluorescence spectra of Va and Vf, shown
in Fig. 2, are characterized, on the one hand, by a change
in the spectrum shape (for Vf) and, on the other hand, by
a bathochromic shift (Vа) on changing λexc from 320 to
360 nm. The corresponding values of λ are estimated at
430 and 450 nm. For Vb, on the contrary, the fluorescence
spectra undergo hypsochromic shift with increasing λexc
For example, at λexc = 320 nm, the fluorescence maximum
is observed at 550 nm, whereas at λexc = 360 nm λ
max
fl
.
Phosphorescence was also detected for the other four
compounds, but the spectrum was not always so clear and
structured as for Vf. For example, for Va, the phospho-
rescence spectrum consists of a broad weakly structured
band with a maximum at 490 nm (Fig. 4). Apparently,
in this case it is necessary to take into account stronger
influence exerted on the hetaryl moiety by the electron-
withdrawing nitro group.
max
fl
=
max
fl
450 nm. Therefore, in Table 2 we present the λ values
averaged over three values of maxima at λexc = 320, 340,
and 360 nm. The averaged fluorescence spectrum was
calc
fl
also used in calculation of λ . It should be noted that
the fluorescence excitation spectra do not coincide with
the absorption spectra. This fact suggests differences in
the sites that absorb radiation in the ground state and are
responsible for the emission. In other words, different
molecular structures of Va–Vf in the ground state coex-
ist in equilibrium. These structures are characterized by
slightly different absorption spectra and the correspond-
ing fluorescence spectra, which is also different.
As seen from Fig. 3, the fluorescence and phospho-
rescence spectra of Vf at 77 K, recorded at two essen-
tially different λexc values (320 and 360 nm), as well as
the absorption and fluorescence and phosphorescence
excitation spectra (λreg 420 and 500 nm), coincide al-
most fully. The same coincidence of the spectral pattern
under different conditions of excitation and registration
of fluorescence and phosphorescence was also observed
for other compounds. These facts unambiguously indicate
that in a solid solution, when the turn around a single bond
is impossible, there is only one conformer with its own
spectral characteristics.
Presumably, such molecular structures are conformers
differing in the turn of the hetaryl moiety around the single
bond. Rotation around this bond leads to a change in the
efficiency of the charge transfer from the dihydrobenzo-
acridine core. Because there is no common conjugation in
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

SYNTHESIS, ABSORPTION SPECTRA, AND LUMINESCENCE PROPERTIES
785
The compounds studied exhibit low emission ef-
ficiency at room temperature. Because the absorption
spectrum consisted of the spectra of separate conformers,
we were able to estimate only the effective quantum yield
eff
of fluorescence, Ф .
fl
eff
fl
The Ф values given in Table 2 do not exceed 1%,
which is due to strong fluorescence quenching as a result
of charge transfer. The strongest quenching effect was
observed for compounds Va and Vc (Table 2), in which
the strong electron-withdrawing nitro group is in the
p-position of the phenyl ring in the hetaryl moiety. For
eff
fl
these compounds, Ф is lower by an order of magnitude
than for compounds Vb and Vd containing the NO2
group in the o- or m-position. The nitro group in Va
and Vc also strongly affects the electronic absorption
spectra (Fig. 1) at 293 K and the luminescence spectra
at 77 K (Fig. 4).
λ, nm
Fig. 4. (1, 2, 3) Fluorescence and phosphorescence spectra of
Va, Vb, and Vf, respectively, in ethanol at 77 K for λexc 320 nm.
spectra recorded at different λexc with each other and of
the fluorescence and phosphorescence excitation spectra
with the absorption spectra.
Indeed, the absorption spectra of Vа and Vc in ethanol
are characterized by the most pronounced charge-transfer
band (320–450 nm) whose molar extinction coefficient
becomes comparable with that of the most intense band
in the spectra of the other compounds, 200–250 nm.Also,
strong differences between the luminescence spectra of
Vа, on the one hand, and Vb and Vf, on the other hand,
are observed at 77 K (Fig. 4). In the spectrum of Va, the
short-wave fluorescence band is virtually absent, and the
phosphorescence spectrum consists of a smeared struc-
tureless band. Thus, the nitro group in the p-position of
the phenyl ring of the hetaryl moiety, as in the case of
Va and Vc, exerts the strongest effect on the spectral and
photophysical characteristics, expressed in more efficient
fluorescence quenching at 293 K and in virtually full dis-
appearance of the fluorescence and of vibronic structure
in the phosphorescence spectra at 77 K.
EXPERIMENTAL
The IR spectra were recorded on a Nicolet Protege-460
Fourier spectrometer from thin films or KBr pellets. The
1Н NMR spectra were taken with an Avance-500 spec-
trometer (Bruker–Biospin) operating at 500 MHz. The
compounds were taken as 2–5% solutions in DMSO-d6;
the chemical shifts were determined relative to TMS as
internal reference. Elemental analysis was performed
with a VarioMICRO superuser CHNS analyzer, ser.
no. 15106057, except the halogenated compounds whose
elemental composition was determined by classical mi-
croanalysis.
The efficiency of the charge transfer depends both
on substituent positions in the phenyl ring of furan- (or
N-methylpyrrole-, or thiophene)carbaldehyde and on the
angle of turn of furan (or thiophene, or N-methylpyrrole)
rings around the single bond.As a result of such turns, the
compounds exist in a liquid solution at room temperature
as mixtures of conformers, each of which is character-
ized by its own absorption and fluorescence spectra.
The assumption that the compounds exist as mixtures of
conformers was confirmed by the absorption and lumines-
cence spectra recorded at 77 K, when only one conformer
remained in the solid solution owing to “freezing” of the
rotation of the hetaryl fragment around the single bond.
This is confirmed by coincidence of the luminescence
The absorption and fluorescence spectra of the solu-
tions were recorded with a Cary-500 spectrophotometer
(Varian, USA) and on an installation described in [11].
The substance concentration in solutions in these mea-
surements did not exceed 2 × 10–5 M. The effective
eff
fl
quantum yields of fluorescence, Ф , were measured by
the relative method using quinine sulfate in 1 N H2SO4
as reference (Ffl = 0.55 [12]). Low-temperature mea-
surements were performed in a quartz Dewar vessel for
ethanol solutions freezing at 77 K to form a transparent
glass. The measurement uncertainty was 20% for the
molar extinction coefficients ε and ~15% for the effective
quantum yields of fluorescence.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

786
KOZLOV et al.
ACKNOWLEDGMENTS
9,9-Dimethyl-12-[(5-aryl-2-furyl) (or 5-aryl-2-thie-
nyl, or 5-aryl-1-methyl-1Н-pyrrolyl)]-7,8,9,10,11,12-
hexahydrobenzo[а]acridin-11-ones Va–Vf. Procedure
а: To a solution of 0.01 mol of azomethine IIIa–IIId in
30 mL of ethanol, 1.40 g (0.01 mol) of dimedone was
added, and the mixture was refluxed for 2–3 h. The pre-
cipitate formed after cooling was filtered off, washed with
ether, and recrystallized with an alcohol–benzene mixture
(1 : 2) or washed with the same mixture.
The study was supported by the Belarussian Re-
publican Foundation for Basic Research (project
no. Kh13K-029) and by the State Foundation for Basic
Research of Ukraine (project no. F 54.3/004).
REFERENCES
1. Kozlov, N.G., Bondarev, S.L., Odnoburtsev, B.A., and
Basalaeva, L.I., Russ. J. Appl. Chem., 2007, vol. 80, no. 7,
pp. 1101–1104.
Procedure b:Asolution of 1.43 g (0.01 mol) of 2-naph-
thylamine I, 0.01 mol of appropriate aldehyde IIа–IIf,
and 1.40 g (0.01 mol) of dimedone in 30 mL of ethanol
was refluxed for 3–4 h. The precipitate formed after cool-
ing was worked up similarly to procedure а.
2. Kozlov, N.G., Basalaeva, L.I., and Dikusar, E.A., Russ. J.
Org. Chem., 2005, vol. 41, no. 11, pp. 1637–1646.
3. Kozlov, N.G., Bondarev, S.L., Kadutskii, A.P., and Ba-
salaeva, L.I., Russ. J. Org. Chem., 2010, vol. 46, no. 2,
pp. 202–208.
CONCLUSIONS
4. Dyer, J.R., Applications of Absorption Spectroscopy of
Organic Compounds, Prentice-Hall, 1965.
(1) The broad structureless band in the long-wave
region of the absorption spectrum (320–450 nm) is due
to charge transfer from the dihydrobenzoacridinone core
to the hetaryl fragment of the molecule.
5. Ferrante, C., Kensy, U., and Dick, B., J. Phys. Chem., 1993,
vol. 97, no. 51, pp. 13457–13463.
6. Forster, Th., Fluoreszenz organischer Verbindungen, Göt-
(2) The charge transfer processes play an important
role in photophysics and spectroscopy of the compounds
studied. This role is manifested most strongly, on the
one hand, in efficient fluorescence quenching at 293 K
for compounds Va and Vc containing the nitro group in
the p-position of the phenyl ring of the hetaryl moiety
and, on the other hand, in virtually full quenching of the
fluorescence and disappearance of the vibronic structure
in the phosphorescence spectra at 77 K.
tingen: Vandenhoeck und Ruprecht, 1951.
7. Kasha, M. and Rawls, H.R., Photochem. Photobiol., 1968,
vol. 71, pp. 561–566.
8. Stepanov, B.I., Vvedenie v khimiyu i tekhnologiyu or-
ganicheskikh krasitelei (Introduction to Chemistry and
Technology of Organic Dyes), Moscow: Khimiya, 1984,
pp. 60–78.
9. Iter, J. and Casodevoll, A., Bull. Soc. Chim. Biol., 1969,
pp. 2355–2359.
(3) In the ground and excited electronic states at room
temperature, the molecules of the compounds occur as
mixtures of conformers differing in the angle of turn of
furan (or thiophene, or N-methylpyrrole) rings around
single С–С bond. At 77 K, the rotation around this bond
is “frozen,” and only one conformer remains with its
specific absorption and luminescence spectra.
10. Ermolaev, V.L., Usp. Fiz. Nauk, 1963, vol. 80, no. 1,
pp. 3–40.
11. Borisevich, E.A., Knyukshto, V.N., Kozyrev, A.N., and
Solov’ev, K.N., Opt. Spektrosk., 1993, vol. 74, no. 1,
pp. 210–218.
12. Melhuish, W.H., J. Phys. Chem., 1969, vol. 65, pp. 229–
237.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014