Synthesis, photochemical and luminescent properties of (E)-2-(2-hydroxyarylethylene)-3-phenylquinazolin-4(3H)-ones

Article abstract of DOI:10.1007/s11172-014-0764-7

Photoinduced transformations of 2-styrylquinazolinones in solutions were studied using absorption and NMR spectroscopy methods. A possibility of control of the photochemical isomerization rate of quinazolinone 2-(hydroxyaryl)ethenyl derivatives by changin

Full text of DOI:10.1007/s11172-014-0764-7

Russian Chemical Bulletin, International Edition, Vol. 63, No. 11, pp. 2467—2477, November, 2014
2467
Synthesis, photochemical and luminescent properties
of (E)ꢀ2ꢀ(2ꢀhydroxyarylethylene)ꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀones*
I. G. Ovchinnikova,a G. A. Kim,a E. G. Matochkina,a M. I. Kodess,a
N. V. Barykin,b O. S. El´tsov,b E. V. Nosova,b G. L. Rusinov,a and V. N. Charushina,b
aI. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
22 ul. S. Kovalevskoi, 620041 Ekaterinburg, Russian Federation.
Tel: +7 (343) 369 3058. Eꢀmail: iov@ios.uran.ru
bUral Federal University named after the First President of Russia B. N. Yeltsin,
19 ul. Mira, 620002 Ekaterinburg, Russian Federation
Photoinduced transformations of 2ꢀstyrylquinazolinones in solutions were studied using
absorption and NMR spectroscopy methods. A possibility of control of the photochemical
isomerization rate of quinazolinone 2ꢀ(hydroxyaryl)ethenyl derivatives by changing the pH of
the medium was demonstrated. The bases and the solvent nature also affect the luminescence
intensity of solutions of these compounds in the wavelength range of 550—650 nm. The differꢀ
ences in the steric organization of the orthoꢀhydroxystyryldiazinone system in crystals and in
solutions related to the turn of the aryl group were found. Their influence on the competing
processes of luminescence and photochemical transformation of the ethylene fragment were
shown. The fact of reversible photo/thermal E—Zꢀisomerization was established for (E)ꢀ2ꢀ(2ꢀ
hydroxystyryl)ꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone.
Key words: (E)ꢀ2ꢀstyrylquinazolinꢀ4(3H)ꢀones, orthoꢀhydroxystyrylquinazolinones, lumiꢀ
nescence, reversible photo/thermal isomerization, photoswitching.
Diarylethenes and their heterocyclic analogues form
the basis of modern electroluminescent and photochroꢀ
mic materials, successfully used in nonlinear optics, lasers
with tunable frequency, optoelectronic devices for recordꢀ
ing and storage of information, molecular photoswitchꢀ
es.1,2 Among hetarylstilbenes, their unsymmetric derivaꢀ
tives3,4 are of particular interest. Owing to the contribuꢀ
tion of the n,*ꢀstate, the presence of an acceptor azine
(azinone) core in addition to the donor (aryl) one in stilꢀ
bene molecules can have a considerable influence on
photochemical and photophysical behavior of the lumiꢀ
nophores.5 However, there are fewer publications on the
studies of the corresponding systems than of the symmetric
(het)arylethenes.4 In particular, there are several works on
the synthesis of (E)ꢀ2ꢀstyrylquinazolinꢀ4(3H)ꢀones and
the study of their photophysical properties.4,6—10 It should
be noted that compounds of this type with a specific emisꢀ
sion ability and a tendency to a photoinduced E—Zꢀisoꢀ
merization9,10 can be quite promising for the development
of pHꢀsensitive photochromic materials. We think that
the introduction of a hydroxy group at the orthoꢀposition
of the arylethenyl fragment of quinazolinones can generꢀ
ate photocontrolled processes related to the E–Zꢀisomerꢀ
ization with a proton transfer in the course of tautomeric
transformations and heterocyclization to the correspondꢀ
ing spiropyrans.
Experimental
IR spectra were recorded on a PerkinꢀElmer Spectrum One
IR Fourierꢀtransform spectrometer using a diffuse reflectance
sampling accessory (DRA). Electron absorption spectra were
recorded on a UVꢀ2401 PC doubleꢀbeam spectrophotometer
(Shimadzu, Japan) in the range of 190—700 nm with the waveꢀ
length setting accuracy of 0.3 nm using a Shimadzu Scan stanꢀ
dard program. Fluorescence spectra were recorded on a Varian
Cary Eclipse fluorescence spectrophotometer with mutually perꢀ
pendicular beams, the wavelength setting accuracy of 0.5 nm.
The measurements were carried out in the range of 190—800 nm
in SUPRASIL 111ꢀQS 10 quartz cells (Hellma, Germany), the
bandwidth around the stationary point of excitation/emission
was 10 nm. The wavelength of the excitation stationary point
was assigned based on the maximum in absorption and emission
spectra each time, the wavelength of the emission stationary
point, based on the maximum in excitation spectra. The PEM
bias was 600 V. The solvent luminescence was taken into acꢀ
count in the spectra. The relative quantum yields of solutions
were measured at 22 1 C according to the procedure, given at
* Dedicated to Academician of the Russian Academy of Sciences
Yu. N. Bubnov on the occasion of his 80th birthday and to the
60th anniversary of A. N. Nesmeyanov Institute of Organoꢀ
element Compounds of the Russian Academy of Sciences.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2467—2477, November, 2014.
1066ꢀ5285/14/6311ꢀ2467 © 2014 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014
Ovchinnikova et al.
www.jyhoriba.co.uk (Jobin Yvon Ltd. 2 Dalston Gardens, Stanꢀ
more, Middlesex HA7 1BQ UK). The control samples were
(CArom—H); 3320 (OH). Found (%): C, 77.58; H, 4.77; N, 8.21.
C22H16N2O2. Calculated (%): C, 77.63; H, 4.74; N, 8.23.
A solution of Eꢀ3c in a 20ꢀfold excess of the base
(Me4NOH•5H2O)20. 1H NMR (500 MHz, DMCOꢀd6), : 5.85
(ddd, 1 H, H(19), J = 7.5 Hz, J = 6.8 Hz, J = 1.0 Hz); 6.16 (dd,
1 H, H(17), J = 8.4 Hz, J = 1.0 Hz); 6.40 (d, 1 H, H(), J = 16.3 Hz);
6.71 (ddd, 1 H, H(18), J = 8.4 Hz, J = 6.8 Hz, J = 1.8 Hz);
6.74—6.80 (m, 4 H, H(6), H(10), H(14), H(20)); 6.91 (tt, 1 H,
H(12), J = 7.4 Hz, J = 1.1 Hz); 7.17 (ddd, 1 H, H(7), J = 8.4 Hz,
J = 7.3 Hz, J = 1.7 Hz); 7.23 (m, 2 H, H(11), H(13)); 7.74
(d, 1 H, H(), J = 16.3 Hz); 7.97 (dd, 1 H, H(5), J = 7.3 Hz,
J = 1.7 Hz); 8.73 (br.d, 1 H, H(8), J = 8.4 Hz). 13C NMR
(125.76 MHz, DMCOꢀd6), : 107.43 (C(19)); 111.60 (C());
118.40 (C(8)); 118.59 (C(6)); 120.67 (C(12)); 121.66 (C(17));
122.07 (C(10), C(14)); 123.26 (C(15)); 125.14 (C(4a)); 127.02
(C(20)); 128.42 (C(11), C(13)); 128.99 (C(7)); 129.95 (C(18));
131.03 (C(5)); 136.13 (C());142.98 (C(8a)); 151.56 (C(9));
153.68 (C(2)); 170.07 (C(4)); 172.02 (C(16)).
fluoresceine11 ( = 0.85) in 0.1 N aqueous solution of KOH
abs
and quinine bisulfate11 ( = 0.55) in 0.1 N aqueous solution
abs
of H2SO4. 1H and 13C NMR spectra were recorded on Bruker
DRXꢀ400 (400 and 100 MHz) and Bruker AVANCEꢀ500 (500
and 126 MHz) spectrometers in DMSOꢀd6, using TMS and
DMSOꢀd6 (C 39.5) as references. 1H and 13C signals in
the NMR spectra were assigned using 2D experiments
1H—1H COSY, 1H—1H NOESY, 1H—13C HSQC, and HMBC.
Electron impact mass spectra of compounds were recorded on
a Shimadzu GCMSꢀQP2010 Ultra EI instrument (70 eV). Meltꢀ
ing points were measured on a Boetius heating microstage. Thinꢀ
layer chromatography was carried out on Silufol UVꢀ254 plates.
Spots were visualized under the light of a lowꢀpressure mercury
lamp (6 W) or in iodine vapors.
2ꢀMethylꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone (1). Aniline (0.7 g,
7.5 mmol) and P2O5 (1 g) were added to 2ꢀmethylꢀ3,1ꢀbenzꢀ
oxazinꢀ4ꢀone (1.2 g, 7.5 mmol) (obtained by reflux of anthraꢀ
nilic acid in freshly distilled acetic anhydride12) in pyridine
(15—20 mL). The reaction mixture was heated for 26 h at 90—95 C.
After the reaction reached completion, the solvent was evapoꢀ
rated, water (50 mL) was added to the residue. The product was
filtered off and purified on a chromatographic column (SiO2),
eluent ethyl acetate—hexane, 3 : 2. The yield was 1.5 g (89%).
Analytical characteristics of this compound agreed with those
given in the literature.13
(Z)ꢀ2ꢀ(2ꢀHydroxystyryl)ꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone (Zꢀ3c).
A solution of isomer Eꢀ3c (10 mg, 0.03 mmol) in DMSOꢀd6
(1 mL) was placed into a 1ꢀcm pathlength hermetically sealed
quartz cell and exposed to the light of a DRShꢀ250 mercury
discharge lamp (250 W) using an UFSꢀ6 light filter at the disꢀ
tance of 13 cm with air cooling. The reaction progress was monꢀ
1
itored by NMR. After 32 h of exposure, the H NMR spectrum
showed that the solution contained ~88% of photoinduced
Zꢀisomer. 1H NMR (400 MHz, DMSOꢀd6), : 5.92 (d, 1 H, H(),
J = 12.4 Hz); 6.66 (d, 1 H, H(), J = 12.4 Hz); 6.66 (t, 1 H,
H(19), J = 7.3 Hz); 6.77 (d, 1 H, H(17), J = 7.9 Hz); 7.09 (ddd,
1 H, H(18), J = 7.9 Hz, J = 7.6 Hz, J = 1.7 Hz); 7.23 (dd, 1 H,
H(20), J = 7.6 Hz, J = 0.9 Hz); 7.35 (dm, 2 H, H(10), H(14),
J = 7.1 Hz); 7.49—7.53 (m, 4 H, H(11), H(13), H(12), H(8));
7.55 (ddd, 1 H, H(6), J = 7.8 Hz, J = 7.2 Hz, J = 0.7 Hz); 7.81
(ddd, 1 H, H(7), J = 8.0 Hz, J = 7.2 Hz, J = 1.1 Hz); 8.15 (dd, 1 H,
H(5), J = 7.8 Hz, J = 1.1 Hz); 9.80 (br.s, 1 H, OH).
(E)ꢀ2ꢀStyrylquinazolinꢀ4(3H)ꢀones (general method). A corꢀ
responding aldehyde 2a—d (1.7 mmol) and an equimolar amount
of H3BO3 (1.3 mmol) were added to compound 1 (0.3 g, 1.3 mmol)
in acetic acid (30 mL). The reaction mixture was refluxed for
6—8 h. After the reaction reached completion, the solvent was
evaporated, the product was purified by chromatography from
different impurities, first of all, of the Zꢀisomer formed in small
amounts (2—7%). Chromatographic separation was carried out
on a column with SiO2, eluent ethyl acetate—hexane, the proꢀ
portion of concentrations from 1 : 4 to 4 : 1, respectively. The
target product was crystallized from ethanol (3a—c) or acetoꢀ
nitrile (3d). Analytical characteristics of (E)ꢀ3ꢀphenylꢀ2ꢀstyrylꢀ
quinazolinꢀ4(3H)ꢀone (3a) (93% yield, 0.4 g) and (E)ꢀ2ꢀ(2ꢀ
(naphthalenꢀ1ꢀyl)vinyl)ꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone (3b)
(89% yield, 0.43 g) agreed with those given in the works.10,13
(E)ꢀ2ꢀ(2ꢀHydroxystyryl)ꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone (Eꢀ3c).
The yield was 82% (0.36 g), m.p. 275—276 C. 1H NMR
(500 MHz, DMSOꢀd6), : 6.56 (d, 1 H, H(), J = 15.6 Hz); 6.76
(t, 1 H, H(19), J = 7.5 Hz); 6.84 (br.d, 1 H, H(17), J = 7.9 Hz);
7.12—7.17 (m, 2 H, H(18), H(20)); 7.45 (dm, 2 H, H(10), H(14),
J = 7.1 Hz); 7.52 (ddd, 1 H, H(6), J = 7.8 Hz, J = 7.2 Hz, J =
= 0.7 Hz); 7.55—7.64 (m, 3 H, H(11), H(13), H(12)); 7.78 (br.d,
1 H, H(8), J = 8.0 Hz); 7.87 (ddd, 1 H, H(7), J = 8.0 Hz, J = 7.2
Hz, J = 1.1 Hz); 8.08 (d, 1 H, H(), J = 15.6 Hz); 8.13 (dd, 1 H,
H(5), J = 7.8 Hz, J = 1.1 Hz); 10.12 (s, 1 H, OH). 13C NMR
(125.76 MHz, DMSOꢀd6), : 116.11 (C(17)); 119.39 (C(19));
119.86 (C()); 120.43 (C(4a)); 121.69 (C(15)); 126.25 (C(6));
126.38 (C(5)); 127.10 (C(8)); 128.86 (C(20)); 128.92 (C(10),
C(14)); 129.02 (C(12)); 129.58 (C(11), C(13)); 130.81 (C(18));
134.67 (C(7)); 135.42 (C()); 137.24 (C(9)); 147.54 (C(8a));
(E)ꢀ2ꢀ[2ꢀ(2ꢀHydroxynaphthalenꢀ1ꢀyl)vinyl]ꢀ3ꢀphenylquinꢀ
azolinꢀ4(3H)ꢀone (3d). The yield was 72% (0.37 g), m.p.
257—258 C. 1H NMR (500 MHz, DMSOꢀd6), : 6.91 (d, 1 H,
H(), J = 15.5 Hz); 7.14 (d, 1 H, H(17), J = 9.0 Hz); 7.33 (ddd,
1 H, H(20), J = 8.0 Hz, J = 7.1 Hz, J = 0.8 Hz); 7.46–7.51 (m, 3 H,
H(10), H(14), H(21)); 7.53 (ddd, 1 H, H(6), J = 7.9 Hz,
J = 6.8 Hz, J = 1.3 Hz); 7.56 (m, 1 H, H(12)); 7.62 (tm, 2 H,
H(11), H(13), J = 7.5 Hz); 7.76 (d, 1 H, H(18), J = 9.0 Hz); 7.80
(dd, 1 H, H(19), J = 8.0 Hz, J = 1.0 Hz); 7.85 (dd, 1 H, H(8),
J = 8.2 Hz, J = 1.3 Hz); 7.89 (ddd, 1 H, H(7), J = 8.2 Hz,
J = 6.8 Hz, J = 1.5 Hz); 8.02 (br.d, 1 H, H(22), J = 8.6 Hz); 8.15
(dd, 1 H, H(5), J = 7.9 Hz, J = 1.5 Hz); 8.62 (d, 1 H, H(),
J = 15.5 Hz); 10.50 (s, 1 H, OH). 13C NMR (125.76 MHz,
DMSOꢀd6), : 113.24 (C(15)); 118.19 (C(17)); 120.41 (C(4a));
121.95 (C(22)); 123.01 (C(20)); 123.44 (C()); 126.17 (C(6));
126.39 (C(5)); 127.19 (C(21)); 127.24 (C(8)); 128.04 (C(18a));
128.73 (C(19)); 128.95 (C(10), C(12)); 129.58 (C(11));
131.13 (C(18)); 132.05 (C()); 132.51 (C(22a)); 134.66 (C(7));
137.42 (C(9)); 147.63 (C(8a)); 152.72 (C(2)); 155.72 (C(16));
161.46 (C(4)). IR (DRA), /cm–1: 615, 624, 647; 689, 732, 754,
762, 795, 812 (Arom); 846, 859, 909, 973, 1014, 1032, 1079,
1117, 1180, 1208, 1219, 1248, 1270, 1329, 1344, 1430, 1469,
1491; 1511, 1534, 1608, 1625 (C=C, C=N); 1655 (C=O);
3062, 3075 (CArom—H); 3343 (OH). Found (%): C, 79.64;
H, 4.45; N, 7.17. C26H18N2O2. Calculated (%): C, 79.98;
H, 4.65; N, 7.17.
152.18 (C(2)); 156.60 (C(16)); 161.36 (C(4)). IR (DRA), /cm–1
:
599, 650; 693, 714, 746, 770 (Arom); 855, 910, 981, 1014, 1094,
1155, 1232, 1246, 1304, 1351, 1455, 1470, 1489; 1546, 1569,
1602, 1628 (C=C, C=N); 1655, 1667 (C=O); 3036, 3064

2ꢀHydroxyarylethyleneꢀ3ꢀphenylquinazolinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014 2469
Studies of photophysical and photochemical properties of
Eꢀisomers 3a—d. Solvents were distilled and dried according to
the standard procedures. Preparation and spectrophotometric
studies of solutions were carried out in red light. Photochemical
transformations in solutions were carried out in 1ꢀcm pathlength
hermetically sealed quartz cells in a photochemical reactor usꢀ
ing a DRShꢀ250 mercury discharge lamp (250 W) with air coolꢀ
ing (23 2 C). Solutions were irradiated from a distance of 13 cm
with a light flux, passing through the system of focusing lenses
and SZSꢀ7 or SZSꢀ26 light filters (thermal filter) and UFSꢀ6, in
the short wavelength range of 364—456 nm. The lumen output
(150 mW) was determined using an IMOꢀ2N meter of average
power and laser irradiation energy.14 The light flux was directed
into the meter using quartz optical fibers.
Kinetic studies by absorption spectroscopy. 1. Photochemical
transformations of compounds Eꢀ3a—d (2•10–5 M) in nꢀbuꢀ
tanol, acetonitrile, and dimethylformamide were carried out by
recording UV spectra of irradiated solutions with allowance for
the initial absorption every 2 s (in the case of isomers 3b,c),
1 min (3d), and 5 min (3a) until persistent state of the solutions.
2. Thermal transformations of photosteady solutions of comꢀ
pound Zꢀ3c (2•10–5 M) thermostated at 35, 55, 65, and 75 C
were carried out by recording UV spectra every 10 min.
Table 1. Crystalographic data and parameters of the
Xꢀray diffraction experiment for crystal Eꢀ3c
Parameter
Value
Molecular formula
Molecular weight
C22H16N2O2
340.37
Crystal system
Z
Space group
a/Å
b/Å
c/Å
Triclinic
2
P–1
8.8760(18)
9.6168(14)
10.734(2)
91.142(15)
113.02(2)
98.448(14)
831.1(3)
1.360
/deg
/deg
/deg
3
V/Å
dcalc/g cm–3
F(000)
356
(MoꢀK)/mm–1
Crystal size/mm
Type/region of scanning
on /deg
Ranges of reflection
indices
0.088
0.250.200.15
3.03—26.42
5  h  11,
12  k  12,
13  l  13
7271
3. Spectrophotometric titration of solutions of Eꢀ3c,d
(2•10–5 M) with strong bases (Me4NOH or ButOK) were carꢀ
ried out until persistent state, using a series of solutions with the
ratio of concentrations CEꢀ3 : Cbase from 1 : 1 to 1 : 25.
Reflections collected
Kinetic studies by NMR. The studies by NMR were carried
out for 3•10–5 M solutions of compounds Eꢀ3a—d in DMSOꢀd6
(1 mL), using a technique similar to that described above for
absorption spectroscopy. Photochemical transformations of comꢀ
pounds Eꢀ3a—d were carried out by recording 1H NMR spectra
of irradiated solutions every hour for 6 h and then every 4—6 h
(over 30—32 h). In the case of compound Eꢀ3d, a mixture of
photoproducts was separated by chromatography (eluent ethyl
acetate—hexane, 1 : 2). The fractions with individual compounds
4a—c were characterized by mass spectrometry. MS (EI, 70 eV)
4a, m/z (Irel (%)): 390 [M]+ (100), 373 [M – OH]+ (71),
313 [M – C6H5]+ (15), 298 [M – C6H5NH]+ (37), 284 [M –
– C6H5—CHO]+ (5), 270 [M – C6H5NH—CO]+ (12), 244
[M – C6H5NH—CO—CN]+ (45), 221 [M – C12H8O—H]+ (26),
193 [M – C12H8O—H—CO]+ (12), 168 [M – C14H10N2O]+
(36), 140 [M – C14H10N2O—CO]+ (29), 139 [M – C14H10N2O—
CO—H]+ (55), 119 (40), 77 (80). MS (EI, 70 eV) 4b, m/z
(Irel (%)): 388 [M]+ (100), 371 [M – OH]+ (91), 359 [M – CHO]+
(5), 269 [M – C6H5NCO]+ (4), 221 [M – C12H7O]+ (7), 194
[M – C12H7O—HCN]+ (10), 179 [M – C12H7O—NCO]+ (5),
139 [M – C15H9N2O2]+ (15), 77 (38). MS (EI, 70 eV) 4c, m/z
(Irel (%)): 222 [M]+ (100), 221 [M – H]+ (91), 193 [M – CO]+
(10), 167 [M – CO—CN]+ (7), 129 (12), 119 [M – C7H5N]+
(23), 102 (10), 77 (72).
Number of independent
reflections
Rint
Number of reflection with I > 2(I)
Rꢀfactors on I > 2(I)
R1
wR2
Rꢀfactors (on all reflections)
R1
wR2
3375
0.0217
2096
0.0354
0.0763
0.0568
0.0788
1.001
Qꢀfactor on F2
Residual electron
density, min/max, e Å
3
–0.240 / 0.167
SHELXS–97 and SHELXLꢀ97 programs.16 Hydrogen atoms
were placed in geometrically calculated positions and they were
included in the refinement using a riding model with dependent
thermal parameters. The experimental Xꢀray diffraction data
(Table 1) were deposited with the Cambridge Structural Dataꢀ
base (CCDC 1033803).
Results and Discussion
Xꢀray diffraction studies. Crystals of compound Eꢀ3c were
obtained by slow concentration of acetonitrile solution. Xꢀray
diffraction analysis of the compound was carried out on a Xcaliꢀ
bur 3 automated diffractometer with a CCD detector (MoꢀK
radiation,  = 0.71073 Å, graphite monochromator, /2 scan
technique, with a 1 step) at 150(2) К. The set of reflections was
obtained and processed using the CrysAlis software.15 The strucꢀ
tures were solved by direct method and refined by fullꢀmatrix
least squares method first in isotropic and then in anisotropic
approximation on F2 for all nonhydrogen atoms using the
In order to carry out comparison studies of the photoꢀ
chemical and photophysical behavior of (E)ꢀ2ꢀstyrylꢀ
quinazolinꢀ4(3H)ꢀones in solutions, a series of derivatives
3a—d (Scheme 1) was synthesized. The C=C bond formaꢀ
tion techniques in (het)arylstilbenes often have a specific
nature, while the condensation of 2ꢀmethylazines with
aromatic aldehydes in the presence of zinc chloride or
sodium acetate does not always ensure a high yield of the

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Ovchinnikova et al.
target compounds.4 The use of boric acid as a catalyst in
the final stage of the synthesis, the condensation of
2ꢀmethylꢀ3ꢀphenylquinazolinꢀ4(3H)ꢀone (1a) with aroꢀ
matic aldehydes 2a—d, allowed us to obtain various diaziꢀ
nones 3a—d and, most importantly, their hydroxy derivaꢀ
tives in high yields.
unchangeable level (Fig. 2, Table 2). At that, considerable
temporal differences of photochemical transformations in
solutions of compounds 3a,d and 3b,c were observed. For
isomers Eꢀ3a,d, possessing fluorescence in the 350—550 nm
range, this time period was larger by one or two orders of
magnitude (see Table 1), which indicates an interrelation
between the emission ability of styrylquinazolinones and
the rate of their photochemical transformations in solutions.
The formation of the photosteady state in solutions of
(het)arylstilbenes is generally related to a reversible photoꢀ
isomerization of the —C=C— bond, which is induced by
light in the 350—450 nm wavelength range. The presence
of isobestic points in the absorption spectra of the exposed
solutions of compounds Eꢀ3 (see Fig. 2) can be an indicaꢀ
tion of the emergence of such a photosteady state in these
solutions. However, the decrease in the intensity of the
long wavelength absorption band in the UV spectra can
also be a result of competing processes (of [2 + 2]ꢀcycloꢀ
addition type), also related to photochemical transformaꢀ
tions of the —C=C— bond. The questions about the naꢀ
ture of the photosteady state of the system, about the
photoproducts and their ratio were answered using NMR
spectroscopy.
Scheme 1
According to the 1H NMR spectra of the exposed soluꢀ
tions of Eꢀ3a—c (3•10–2 mol L–1) in DMSOꢀd6, the
photoinduced products of E—Zꢀisomerization and [2 + 2]ꢀ
cycloaddition are the main ones, but there are some difꢀ
ferences in the priorities of the processes taking place.
Thus, the photoinduced E—Zꢀisomerization is characterꢀ
istic of the molecules of compound Eꢀ3c. In the process of
exposure of solutions of Eꢀ3c in DMSOꢀd6 after 2 h the
ratio of isomers Eꢀ3c to Zꢀ3c reached 16 to 84%, respecꢀ
tively. In the next 30 h of exposure the equilibrium in the
solution was retained with little change of the Zꢀform conꢀ
tent (within 84—88%). The formation of the Zꢀisomer
was confirmed by the presence of doublets of vicinal
protons of the C=C bond in the  5.9—6.7 region with the
R1
=
(a),
(b),
(c),
(d)
Reagents and conditions: i. (MeCO)2O; ii. R—NH2, C5H5N,
P2O5, ; iii. R1—CHO (2a—d), MeCOOH, H3BO3, .
Photoinduced transformations of (E)ꢀ2ꢀstyrylquinazolꢀ
inꢀ4(3H)ꢀones 3a—d in neutral media were studied and
some regularities were identified using absorption and
NMR spectroscopy. Thus, the presence of a hydroxy group
(compounds 3c,d) and/or an annulated aromatic fragment
(compounds 3b,d) in the (E)ꢀ2ꢀstyrylquinazolinꢀ4(3H)ꢀ
one molecules leads to a bathochromic shift of the absorpꢀ
tion band maximum to the 290—450 nm range (Fig. 1) in
the electron absorption spectra of their solutions. Fluoresꢀ
cence with an emission maximum at 428 nm (ex = 343 nm)
(see Fig. 1, a; Table 2) can be seen in the emission spectra
of compound 3a. When going to hydroxy derivative 3c, the
radiation intensity considerably decreases. For naphthyl
derivatives the opposite is true (see Fig. 1), namely an
increase in the intensity of the long wavelength emission
band in the wavelength region of 350—550 nm when going
from compound 3b to 3d. Thus, the emission ability of
(E)ꢀ2ꢀstyrylquinazolinꢀ4(3H)ꢀones in this region does not
depend directly on the presence of the OH group, which
normally quenches the luminescence of fluorophores.1
A tendency of (E)ꢀ2ꢀstyrylquinazolinꢀ4(3H)ꢀones in
a solution to transform photochemically when being exposed
to ultraviolet light of a DRSh–250 lamp (an UFCꢀ6 light
filter) was confirmed by a decrease of the long wavelength
absorption band intensity in their UV spectra to a specific
1
spinꢀspin coupling constant of 12.4 Hz in the H NMR
spectra of the exposed solution of compound 3c. Conseꢀ
quently, in the case of isomer Eꢀ3c, a photosteady equilibꢀ
rium is said to be established in solutions under these
conditions.
In the case of photochemical transformation of Eꢀisoꢀ
mers 3a,b in solutions against the background of the equiꢀ
librium mixture of Eꢀ and Zꢀisomers formed in the first
several hours upon long exposure, there was a graduꢀ
al appearance of a photodimerization product. In the
1H NMR spectra of the exposed solution of 3a,b in DMSOꢀd6
this is evidenced by the proton signals of the photoproduct
cyclobutane ring as a characteristic17 AA´BB´ spin system
in the  4.0—5.0 region (Fig. 3). Apparently, the high
concentration of reagents in the exposed solutions in
DMSOꢀd6 and the absence of the orthoꢀsubstituent in their
styryl fragment facilitates the [2 + 2]ꢀphotocycloaddition
reaction of quinazolinꢀ4(3H)ꢀones. On the whole, after

2ꢀHydroxyarylethyleneꢀ3ꢀphenylquinazolinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014 2471
a
b
A
I (arb. units)
A
I (arb. units)
0.8
80
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
80
70
60
50
40
30
20
10
0.7
70
60
50
40
30
20
10
1
0.6
3
0.5
0.4
1
2
0.3
0.2
0.1
3
2
300
400
500
600
/nm
300
400
500
600
/nm
c
d
A
I (arb. units)
A
I (arb. units)
0.5
0.4
0.3
0.2
0.1
80
70
60
50
40
30
20
10
250
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1
200
150
100
50
1
2
3
3
2
300
400
500
600
/nm
300
400
500
600
/nm
Fig. 1. Electron absorption spectra (1), excitation spectra (2), and fluorescence emission spectra (3) of compounds Eꢀ3a (a), Eꢀ3b (b),
Eꢀ3c (c), and Eꢀ3d (d) (2•10–5 mol L–1, in nꢀbutanol, the optical pathlength is 10 mm). The excitation and emission wavelengths,
/nm: 343 and 428 (a); 286 and 426 (b, c); 336 and 430 (d), respectively.
a
b
A/AE
1.0
A
4
3
1.0
0.8
0.6
0.4
0.2
h
0.9
0.8
0.7
0.6
0.5
2
1
h
1
2
200
250
300
350
400
450 /nm
20
40
60
80 t/min
Fig. 2. (a) The changes in the electron absorption spectra of a solution of compound 3c (2•10–5 mol L–1, acetonitrile) in the process of
EꢀZꢀphotoisomerization: 1 is the spectrum of the starting Eꢀisomer, 2 is the spectrum of the photosteady mixture with the Zꢀisomer.
(b) Kinetic curves of the dependence of the change in optical density (the ratio of the measured optical density to the optical density of
the Eꢀisomer, A/AE) at  = 350 nm of the photosteady solution with Zꢀ3c (2•10–5 mol L–1, acetonitrile) on the heating time at 35 (1),
55 (2), 65 (3), 75 C (4).

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Ovchinnikova et al.
Table 2. Photophysical and photochemical characteristics of styrylquinazolinones Eꢀ3a—d
Compound
Solvent

a/nm

c/nm (
max
td/s
fl
( b (%))
rel
Starting
Eꢀisomer
Reaction
mixture
3a
3b
3c
3d
nꢀButanol
Acetonitrile
DMF
nꢀButanol
Acetonitrile
DMF
nꢀButanol
Acetonitrile
DMF
nꢀButanol
DMF
428 (0.15)
111—
111—
426 (—)
111—
111—
426 (—)
111—
111—
430 (0.2)
111—
335 (21050)
350 (22400)
338 (20300)
355 (20150)
350 (21150)
355 (16550)
358 (18500)
350 (21150)
358 (20100)
389 (20000)
385 (21260)
325 (15200)
325 (13550)
337 (18550)
355 (6250)
350 (10550)
355 (8650)
358 (5250)
350 (9550)
358 (9950)
407 (2350)
407 (2450)
1140
4620
>1200
14
16
14
16
16
16
690
1080
a The long wavelength luminescence maximum.
b Relative quantum yield of the long wavelength luminescence of Eꢀisomers.
c The absorption maxima and the corresponding extinction coefficients11 (L mol–1 cm–1) of styrylꢀ
quinazolinones 3 (2•10–5 mol L–1).
d Duration of photochemical reactions of solutions upon exposure to irradiation.
30 h of exposure the Zꢀform (33% for compound 3a, 58%
for compound 3b) and the photodimerization product
(7—10%) were observed in the reaction mixture, along
with the Eꢀisomer.
UV spectral data of the reaction mixtures of compounds
3a,b upon prolonged keeping in dark or heating of the
solutions without exposure to light, no changes in the ratio
of Eꢀ and Zꢀisomers were observed. On the contrary, the
studies of the photosteady solutions of 3c by NMR indiꢀ
cated a reversible isomerization of the Zꢀform in the dark.
When the exposed solutions with Zꢀ3c as a major compoꢀ
nent was allowed to stand in dark for 2—3 days, the equiꢀ
librium shifted in the direction of the starting isomer Eꢀ3c.
In turn, heating of Zꢀ3c solutions in DMSOꢀd6 for 4 h
(105—110 C) also led to a complete transformation of
the latter into the Eꢀform.
Using UV spectroscopy, additional confirmation of the
thermal Z—Eꢀinversion of compound 3c was obtained. In
the UV spectra of the acetonitrile photosteady solutions of
compound Zꢀ3c, the dark Z—Eꢀisomerization was accomꢀ
panied by a gradual increase of the long wavelength abꢀ
sorption maximum in the 350 nm range until the formaꢀ
tion of the absorption spectrum characteristic of the startꢀ
ing Eꢀisomer (see Fig. 2). Kinetic studies of the dependꢀ
1
The analysis of the H NMR spectra of the exposed
solution of isomer Eꢀ3d in DMSOꢀd6 showed that in this
case the photoproducts differ from those synthesized at
the photochemical transformation of molecules 3a—c by
the absence of Eꢀ, Zꢀisomers and cyclobutaneꢀcontaining
adducts. After chromatographic separation, the three main
photoproducts were characterized by EI mass spectra. The
analysis of the mass spectrometric fragmentation and the
values of the molecular ion peaks of the composition
[C26H18N2O2] with m/z 390 (4a), [C26H16N2O2] with m/z
388 (4b), and [C14H10N2O] with m/z 222 (4c) allows us to
assign the synthesized structures to spironaphthopyran 4a
and the products of its rearrangement and decomposition
4b,c (Scheme 2).
Stilbens, as it is known,18 tend to reversibly photo and/or
thermally Z—Eꢀisomerize. In our studies of 1H NMR and
4.5
4.0

2
1
8.0
7.0
6.0
5.0

Fig. 3. 1H NMR spectra (400 MHz) of compound 3a in DMSOꢀd6 (3•10–2 mol L–1) before (1) and after 32 h of irradiation (2).

2ꢀHydroxyarylethyleneꢀ3ꢀphenylquinazolinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014 2473
Scheme 2

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Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014
Ovchinnikova et al.
ence of the Z—Eꢀinversion of compound 3c on temperaꢀ
ture based on UV spectral data demonstrate an acceleraꢀ
tion of the reaction from 28 h for solutions thermostated
at 35 C to 40 min at 75 C (see Fig. 2, b). Several cycles of
photo/thermal E—Z—Eꢀisomerization under these conꢀ
ditions demonstrated the stability of the conjugated sysꢀ
tem of compound 3c to destruction and side transformaꢀ
tions. Since the duration of photo E—Zꢀ and dark Z—Eꢀ
isomerization for compound 3c differs by two orders of
magnitude and the photoisomerization reaction is signifiꢀ
cantly shifted in the direction of the Zꢀform, we can conꢀ
clude that the electron absorption spectrum of the photoꢀ
steady solution of 3c is very similar to the spectrum of the
Zꢀisomer (see Table 2, Fig. 2, a).
Thus, as a result of exposure, orthoꢀhydroxystyrylꢀ
quinazolinones 3 in a solution demonstrates two types of
transformations (see Scheme 2), related to reversible E—Zꢀ
(in the case of 3c) and valence isomerization (in the case
of 3d). Clearly, the choice of one of two possible competꢀ
ing mechanisms is determined not only by the properties
of the electron structure of the orthoꢀhydroxystyryl fragꢀ
ment, but also by the spatial position relative to the diꢀ
azinone core. Thus, according to the Xꢀray diffraction
studies (see Fig. 4), the molecule Eꢀ3c has a practically
planar styrylquinazolinone conjugation system, where
the angle between the mean square planes passing
the (het)aryl fragments C(1)N(1)C(2)C(3)C(8)N(2) and
C(17)C(18)C(19)C(20)C(21)C(22) is 14.72. The modꢀ
ules of the torsion angles in the conjugated ethylene fragꢀ
ment N(2)C(1)C(15)C(16) and C(15)C(16)C(17)C(18)
are 12.41 and 27.42, respectively. The phenyl subꢀ
stituent at the N(1) atom of the diazinone ring (see
Fig. 4) is turned relative to the conjugation plane of
the chromophoric core. The angle between the mean
square planes passing N(2)C(1)N(1)C(2)C(3)C(8) and
C(9)C(10)C(11)C(12)C(13)C(14) is 70.25. The ethylene
fragment with transꢀconfiguration is stabilized in "pseudoꢀ
cisoid" conformation relative to the —N=C— bond of the
heterocycle, while the hydroxy group of the styryl moiety
is turned in the direction of the N(2) atom of the heteroꢀ
cycle. The C—C bond lengths of the ethylene bridge
C(1)—C(15)=C(16)—C(17) are equal to 1.459(2),
1.325(2), and 1.460(2) Å, respectively. Such a lengthening
of C—C single bonds can ease the conformational transꢀ
formations of terminal groups in this fragment in solutions.
Indeed, according to the NMR data in solutions the
conjugated system in molecules Eꢀ3c breaks down as
a result of a considerable turn of the 2ꢀhydroxyphenyl
substituent around the C—C single bond relative to the
ethenylquinazolinone framework. This is evidenced by the
cross peaks of practically equal intensities between H(),
H() and each of the protons of the H(20) and OH group
1
of the styryl fragment in the 2D H—1H NOESY specꢀ
trum of compound Eꢀ3c in DMSOꢀd6. A selected correlaꢀ
tion of protons is shown in Scheme 2. At the same time,
the "pseudocisoid" (relative to the C=N bond) conformaꢀ
tion and the conjugation of the ethylene fragment with the
heterocycle are retained, which is evidenced by the strong
cross peaks between the H() atom and the spatially close
to it orthoꢀprotons H(10) and H(14) of the phenyl substitꢀ
uent. Thus, the turn of the 2ꢀhydroxyphenyl moiety from
the plane of conjugation of the ethenylhetaryl core in
molecules Eꢀ3c is the reason of the activation of the
—CH=CH— bond, the acceleration of photochemical
E—Zꢀisomerization proceeding by the rotational mechaꢀ
nism,18 and the luminescence quenching in the 350—550 nm
range (see Fig. 1, c). The mechanism of thermal Z—Eꢀ
inversion of compound 3c (see Scheme 2), in turn, can be
related either to the double tautomeric transformation
through the quinonoid form during the reversible transfer
b
a
C(13)
C(14)
C(12)
C(11)
O(2)
C(9)
C(2)
C(10)
C(18)
C(1)
C(15)
N(1)
C(8)
C(4)
C(3)
C(6)
C(20)
C(19)
C(22)
C(16)
C(17)
O(1)
C(21)
N(2)
C(5)
C(7)
Fig. 4. (a) The molecular structure of compound Eꢀ3c based on Xꢀray diffraction studies (thermal ellipsoids are given with 50%
probability). (b) Molecular packing, formed by centrosymmetric dimers with intermolecularly close photosensitive C=C groups at
...
a distance of 4.7 Å and stabilized by intermolecular hydrogen bonds (O(2) H(1)O(1) 1.78 Å).

2ꢀHydroxyarylethyleneꢀ3ꢀphenylquinazolinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014 2475
A
of the OH group proton to the N(1) atom of the heteroꢀ
cycle, located close in space, or to the formation of the
spiropyrane intermediate. The absence of characteristic
proton signals of the spirobenzopyrane adduct19 in the
region  4.5—6 in the H NMR spectra of the reaction
mixture of Zꢀ and Eꢀisomers indicates that the former
a
0.40
0.30
0.20
0.10
1
mechanism is preferred.
In compound Eꢀ3d, according to the cross peaks beꢀ
tween the H() atom and the spatially close orthoꢀprotons
H(10) and H(14) of the phenyl substituent in the 2D 1H—1H
NOESY spectra, the isomer molecules in a solution have
a "pseudocisoid" conformation of the ethylene fragment
similar to Eꢀ3c (see Scheme 2). At the same time, a conꢀ
siderable increase in the intensity of the cross peak beꢀ
tween protons H(22) and H() of the naphthyl moiety as
compared to that of protons H(22) and H() indicates
a conjugation of this fragment with the ethenylhetaryl core
of Eꢀ3d. This is confirmed by broad luminescence band in
the 350—550 nm range in the emission spectra of soluꢀ
tions of Eꢀ3d (see Fig. 1, d). In addition, in experiments
using a mercury lamp of medium pressure (100 W) the
decrease in intensity of the luminous flux of the emitter
leads to a discontinuation of the photochemical transforꢀ
mations of molecule Eꢀ3d in solutions (unlike Eꢀ3a—c).
In 1H NMR spectra of the exposed solutions, only signals
of Eꢀisomer were present. Consequently, the stabilization
in solutions of the flattened chromophore structure not
only contributes to the appearance of noticeable luminesꢀ
cence, and, consequently, to the decrease of the rate of the
photochemical transformations of molecule Eꢀ3d, but also
assumes a mechanism of isomerization of the —C=C—
bond different from the one which takes place for comꢀ
pound Eꢀ3c. Apparently, the photochemical transformaꢀ
tion is caused by the appearance of the STꢀstate during
charge transfer11 from the donor (naphthyl fragment) to
the acceptor (diazinone fragment) part of the excited chroꢀ
mophoric molecular system. At that, the conformational
turn around the —C()—C()— bond of terminal groups
can be caused by the formation of the intermediate A in
the course of the tautomeric transformations (see Scheme 2).
Further photochemical transformations of the excited
molecule Eꢀ3d probably can proceed through both the
intermediate C (ionic mechanism), and the intermediate
B in the course of the photochemically allowed electroꢀ
cyclic reaction.19,20
300 350 400 450 500 550 600 650
/nm
b
A
I (arb. units)
0.30
0.25
0.20
0.15
0.10
0.05
120
100
80
1
2
3
60
40
20
300
400
500
600
/nm
Fig. 5. (a) The changes in the electron absorption spectra of
solutions of compound Eꢀ3c (2•10–5 mol L–1, DMF) in the
course of UV spectrophotometric titration with Me4NOH (the
change in the concentration of 3c : Me4NOH in molar ratio
from 1 : 0 to 1 : 20). (b) Electron absorption spectra (1), excitaꢀ
tion spectra (2), and fluorescence emission spectra (3) of the
quinonoid form of 3c (2•10–5 mol L–1) in DMF (optical pathꢀ
length 10 mm, excitation and emission wavelength, /nm:
512 and 606, respectively).
Table 3. Selected photophysical characteristics of the quinonoid
form of 3c,d (2•10–5 mol L–1) in basic media (Me4NOH or
ButOK)
a
b
Comꢀ
pound
Solvent
C
Eꢀ3 : Cbase




rel
(%)
When studying the influence of the medium pH on the
photophysical properties of quinazolinones, no changes in
the photoinduced behavior of compounds 3a,b upon the
addition of CH3COOH or ButOK (pH 3—4 and 8—12)
were observed. For hydroxy derivatives 3c,d, on the other
hand, this influence was considerable. Moderate acceleraꢀ
tion of the E—Zꢀisomerization of compound 3c was obꢀ
served in acidic media (CH3COOH, pH 3—4). Spectroꢀ
photometric titration of solutions of diazinones 3c,d with
strong bases Me4NOH or ButOK (Fig. 5, Table 3) was
ex
em
/cm–1
nm
3c
3d
nꢀButanol
Acetonitrile
DMF
nꢀButanol
DMF
1 : 20
1 : 20
1 : 20
1 : 12
1 : 12
450 600
486 604
512 606
468 580
548 595
5556
4020
3029
4126
1441
5.6
5.9
12.5
0.18
0.63
a The molar ratio of concentrations.
b Stokes shift.

2476
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014
Ovchinnikova et al.
accompanied by a decrease of the light absorption maxiꢀ
mum in the max 369 nm and 387 nm range and an appearꢀ
ance of a long wavelength band at 520 and 548 nm (for 3c
and 3d, respectively) in their electron absorption spectra.
The change of the solution color from pale yellow to crimꢀ
son orange was accompanied by an appearance of noticeꢀ
able broadband luminescence in the visible region with
a maximum at 580—607 nm (see Fig. 5). At that, the
influence of the solvent nature on the long wavelength
emission band intensity, the Stokes shift, and the relative
quantum yields of the studied compounds were noted
(see Table 3).
a
1
2
3
4
8.5
8.0
7.5
7.0
6.5
6.0

Such a considerable change in the spectral properties
of compounds 3c,d are related not only to the formation of
the anionic forms as a result of a CTCꢀtransition11 in the
intermolecular complex, but also to a significant redistriꢀ
bution of electron density in the chromophore conjugaꢀ
tion system itself. The tautomeric transformations in the
course of titration of solutions of 3c,d in DMSOꢀd6 with
bases were confirmed by the changes in the chemical shifts
of protons in the 1H NMR spectra (Fig. 6). The presence
of several sets of proton signals with the spinꢀspin couplꢀ
ing constants of vicinal protons H() and H() varying
in the 14.6—16.2 Hz range in the spectra, indicated the
stabilization of possible intermediates of type A, B, and C
(Scheme 3) with the transoid21 conformation of the
=CH()—CH()= fragment. In strongly basic media, the
equilibrium is completely shifted in the direction of one of
the conformers of the suggested intermediate C, which is
indicated by the comparison of the results of spectroꢀ
photometric titration of compounds 3c,d and the correꢀ
b
2
1
C(16)
C(9)
C(2)
150
C(4a)
C()
C()
C(8a)
C(4)
170
160
140
130
120
110

Fig. 6. (a) 1H NMR spectra (400 MHz) of the titration of
a solution of Eꢀ3c in DMSOꢀd6 (3•10–2 mol L–1) upon the adꢀ
dition of Me4NOH in the molar ratio of 1 : 0 (1), 1 : 5 (2), 1 : 10 (3),
1 : 15 (4). (b) 13C NMR spectra (125.76 MHz) of solutions in
DMSOꢀd6 of compounds Eꢀ3c (3•10–2 mol L–1, DMF) (1) and
Eꢀ3c : Me4NOH in the molar ratio of 1 : 20 (2).
1
sponding H and 13C NMR spectra (see Fig. 6). In the
Scheme 3

2ꢀHydroxyarylethyleneꢀ3ꢀphenylquinazolinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 11, November, 2014 2477
13C NMR spectra of compound 3c, the quinonoid strucꢀ
ture22 of the aryl moiety of isomer C was confirmed by
a considerable downfield shift of the carbon atom C(16)
signal to  172.02 (see Fig. 6). In turn, the transfer of the
negative charge to the oxygen atom of the acceptor
quinazoline core of the tautomer might be quite responꢀ
sible for the shift of the carbon atoms C(4) and C(9) signals
to  170.07 and 151.56 of the low field, respectively. The
probability of charge transfer to the mentioned oxygen
atom of the heterocycle is partly confirmed by the shortꢀ
ened (1.78 Å) intermolecular hydrogen bonds in crystals
Eꢀ3c, as shown by Xꢀray diffraction studies (see Fig. 4).
In the case of compound Eꢀ3c, an increase of the conꢀ
centration of the base in solutions leads to a shift of the
equilibrium from the photochemical processes of isomerꢀ
ization to luminescence. In the course of titration of soluꢀ
tions of 3c in DMSOꢀd6 with ButOK followed by irradiaꢀ
tion, the ratio of Zꢀ and Eꢀisomers were found to change
with an increase of the latter based on 1H NMR data.
In conclusion, using compound Eꢀ3c as an example,
we demonstrated the ability of orthoꢀhydroxystyrylquinꢀ
azolinones to reversible photo/thermal switch in solutions.
The process of E—Zꢀisomerization is initiated by light in
the 300—400 nm range, the reverse Z—Eꢀinversion is
a dark process and significantly accelerates at elevated
temperatures. Using Xꢀray diffraction analysis and NMR
spectroscopy the differences in the spatial organization of
the orthoꢀhydroxystyryldiazinone system of Eꢀ3c,d in crysꢀ
tals and in solutions related to the turn of the aryl moiety
were determined. We showed the influence of the conforꢀ
mation on the equilibrium shift in the direction of either
the photochemical or luminescence process. Taking into
account this factor and the ability to undergo tautomeric
transformations of the chromophoric core of orthoꢀhydrꢀ
oxystyrylquinazolinones, we suggest two mechanisms of
photoinduced isomerization of the disubstituted ethylene
fragment: the rotational mechanism18 (for molecules Eꢀ3c)
and the mechanism (for molecules Eꢀ3d) induced by the
excited STꢀstate.11 We determine the interrelation of the
effects of a strong base, the nature of the solvent and the
luminescence intensity of solutions of Eꢀ3c,d, the formaꢀ
tion of the charge transfer complex being accompanied by
the tautomeric transformation of the conjugated system
into the quinonoid form. It was shown that the photoꢀ
chromic and luminescent properties of such compounds
can be regulated by changing the pH of the medium.
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 14ꢀ03ꢀ00340).
Received February 7, 2014;
in revised form July 17, 2014