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structure, structural changes accompanying ICT in 9-aminoarylac-
ridines and corresponding acridinium ions were widely discussed
in the framework of the twisted intramolecular charge transfer
(TICT) model [15,18,22,23].
In our earlier study [27], we have briefly described the photoin-
duced synthesis of 9-diphenylamino-substituted acridine 1. More
recently [28], it was shown that its methyl derivative 2 exhibits a
well-pronounced solvatofluorochromic effect comparable with
that of well-known dye Nile Red. This feature of 2 was used to de-
velop polymer layers sensitive to vapors of polar solvents such as
acetone or ethanol [29]. Protonated 2 was used as molecular sensor
for recognition of ammonia vapor [30].
evaporated in vacuo and the residue then was purified as described
in Section 2.2. Compound 1 was obtained as a yellow crystalline
powder (yield 19%); m.p. 235–236 °C. 1H NMR (CDCl3) d: 6.97 (t,
2 H, 2 H(40), J = 7.3 Hz), 7.07 (d, 4 H, 2 H(20), 2 H(60), J = 8.6 Hz),
7.21 (t, 4 H, 2 H(30), 2 H(50), J = 7.9 Hz), 7.41 (m, 2 H, H(3), H(6)),
7.74 (m, 2 H, H(2), H(7)), 8.09 (d, 2 H, H(4), H(5), J = 8.6 Hz), 8.30
(d, 2 H, H(1), H(8), J = 9.2 Hz) ppm. 13C NMR (CDCl3) d: 121.09 (4
C), 122.20 (2 C), 124.59 (2 C), 125.34 (2 C), 126.45 (2 C), 129.43
(4 C), 130.11 (4 C), 147.58 (2 C), 147.77 (C(9)), 150.80 (2 C) ppm.
MS m/z: 346 [M+] (100), 267 (4), 242 (5), 177 (4), 167 (5), 148
(5), 101 (8), 84 (6), 69 (5), 57 (10). Calcd. for C25H18N2ꢂ0.6H2O: C
84.05, H 5.42, N 7.84; found: C 83.95, H 5.26, N 7.70%.
In order to better understand the relationship between the
structure of 9-diarylamino-substituted acridines and their absorp-
tion and fluorescent properties, we have performed X-ray diffrac-
tion analysis and carried out detailed spectroscopic studies of
three acridine derivatives 1–3 in their neutral and protonated
forms. In addition, DFT calculations of the structures and TD-DFT
calculations of the gas-phase excitation and emission energies of
neutral and protonated 1 were performed at the PBE0/SVP level
of theory.
2.2.2. 2,7-Dimethyl-N,N-bis(4-methylphenyl)acridin-9-amine (2)
2,7-Dimethyl-N,N-bis(4-methylphenyl)acridin-9-amine (2) was
obtained as a yellow crystalline powder (yield 16%); m.p. 178–
179 °C. 1H NMR (C6D6) d: 2.00 (s, 6 H, 2 Me), 2.02 (s, 6 H, 2 Me),
6.78 (d, 4 H, 2 H(20), 2 H(60), J = 8.4 Hz), 7.00 (d, 4 H, 2 H(30), 2
H(50), J = 8.4 Hz), 7.17 (dd, 2 H, H(3), H(6), J = 8.6 Hz, J = 1.8 Hz),
8.03 (br.s, 2 H, H(1), H(8)), 8.45 (d, 2 H, H(4), H(5), J = 8.6 Hz)
ppm. 13C NMR (C6D6) d: 20.54 (2 Me), 22.01 (2 Me), 121.11 (4 C),
122.98 (2 C), 126.16 (2 C), 130.36 (4 C), 131.10 (2 C), 131.18 (2
C), 132.40 (2 C), 136.47 (2 C), 146.09 (2 C), 146.18 (C(9)), 150.28
(2 C) ppm. MS m/z: 402 [M+] (100), 296 (6), 295 (5), 282 (3), 191
(3), 185 (3), 147 (3), 91 (6), 84 (7), 57 (6). Calcd. for C29H26N2: C
86.53, H 6.51, N 6.96; found: C 86.54, H 6.47, N 6.98%.
2. Experimental
2.1. General
All the solvents for optical studies (spectroscopic grade) were
purchased from Aldrich. Carbon tetrabromide, diphenylamine, di-p-
tolylamine, di[4-(1-methyl-1-phenylethyl)phenyl]amine, fluorescein
(forfluorescence studies) were used as received (Fluka, Aldrich, Merck).
The melting points (uncorrected) were measured in capillaries
on a Mel-Temp II instrument. The 1H and 13C NMR spectra were
2.2.3. 2,7-Bis(1-methyl-1-phenylethyl)-N,N-bis[4-(1-methyl-1-
phenylethyl)phenyl]acridin-9-amine (3)
2,7-Bis(1-methyl-1-phenylethyl)-N,N-bis[4-(1-methyl-1-phen-
ylethyl)phenyl]acridin-9-amine (3) was obtained as a yellow pow-
der (yield 21%); m.p. 185–186 °C. 1H NMR (CDCl3) d: 1.54 (s, 12 H, 4
Me), 1.67 (s, 12 H, 4 Me), 7.05 (d, 4 H, 2 H(20), 2 H(60), J = 8.5 Hz),
7.11 (d, 4 H, 2 H(200), 2 H(600), J = 7.3 Hz), 7.14 (d, 4 H, 2 H(30), 2
H(50), J = 8.5 Hz), 7.16 (t, 2 H, 2 H(400), J = 6.1 Hz), 7.20 (m, 6 H, 2
H(300), 2 H(400), 2 H(500)), 7.25 (m, 8 H, 2 H(200), 2 H(300), 2 H(500), 2
H(600)), 7.29 (br.d, 2 H, H(3), H(6), J = 9.2 Hz), 8.02 (d, 2 H, H(4),
H(5), J = 9.2 Hz), 8.05 (br.s, 2 H, H(1), H(8)) ppm. 13C NMR (CDCl3)
d: 29.91 (4 Me), 30.71 (4 Me), 42.43 (2 CMe2), 43.18 (2 CMe2),
119.94 (2 C), 121.33 (4 C), 123.62 (2 C), 125.56 (2 C), 125.79 (2
C), 126.65 (4 C), 126.70 (4 C), 127.77 (4 C), 127.96 (4 C), 128.13
(4 C), 129.57 (2 C), 131.08 (2 C), 144.70 (2 C), 146.08 (2 C),
147.30 (2 C), 147.62 (C(9)), 149.38 (2 C), 149.47 (2 C), 150.54 (2
C) ppm. ESI MS m/z: 841.4492 (calc. for C61H58N2ꢂNa+: 841.4498),
819.4672 (calc. for C61H58N2ꢂH+: 819.4678). Calcd. for C61H58N2:
C 89.44, H 7.14, N 3.42; found: C 89.34, H 7.18, N 3.44%.
recorded on
a Bruker DRX500 spectrometer (500.13 and
125.76 MHz, respectively) in CDCl3 and C6D6 at 25 °C using the
signal from the solvents as the internal standards (dH 7.27 and
7.15, dC 77.00 and 128.00, respectively). The chemical shifts were
measured with an accuracy of 0.01 ppm and the spin–spin
coupling constants were determined with an accuracy of 0.1 Hz.
The mass spectra were obtained on a Varian MAT 311A instrument
using a direct inlet system; the ionization energy was 70 eV.
High-resolution ESI mass spectra were measured on a Bruker
Daltonics MicrOTOF II instrument in the range of m/z = 50–3000
for positive ions (MeCN solution inlet, nitrogen gas flow, 4500 V
capillary voltage). Elemental analyses were performed at the
Laboratory of Microanalysis of the A.N. Nesmeyanov Institute of
Organoelement Compounds of the Russian Academy of Sciences
(Moscow).
2.3. X-ray crystallography
2.2. Synthesis of acridine derivatives 1–3 (general procedure)
Yellow crystals of compounds 1, 2 were grown by slow evapo-
ration of a solution in a mixture of CH2Cl2–hexane (ꢃ1:1, v/v) at
room temperature. Purple crystals of salts 1ꢂHClO4, 3ꢂHClO4 were
grown by slow saturation of a MeCN–benzene solution (ꢃ1:1, v/
v) of the compounds 1, 3 in the presence of excess perchloric acid
with a hexane–benzene mixture (ꢃ2:1, v/v) by the vapor diffusion
method at room temperature. Single crystals of each of the com-
pounds was coated with perfluorinated oil and mounted on a Bru-
A solution of a mixture of diarylamine (6 mmol) and carbon
tetrabromide (330 mg, 1 mmol) in hexane (50 mL) was placed in
Pyrex bulb and irradiated with sunlight for 4 weeks (Scheme 1).
The purple precipitate thus formed (hydrobromide of 1–3) was
decanted, dissolved in benzene, washed with NaHCO3 solution
(aq, sat.) and evaporated in vacuo. The residue was purified by
column chromatography on aluminium oxide (90 neutral, 0.063–
0.200 mm, Merck) using a 5:1 benzene–EtOAc mixture. The com-
pound 1–3 was re-crystallized from MeCN.
ker SMART CCD diffractometer (graphite monochromatized Mo K
a
radiation, k = 0.71073 Å,
x-scan mode) under a stream of cooled
nitrogen.
All the structures were solved by direct methods and refined
with full-matrix least-squares on F2 in anisotropic approximation
for all non-hydrogen atoms (except for O atoms of disordered per-
chlorate anion in 1ꢂHClO4 which were refined isotropically). The
positions of hydrogen atoms at carbon atoms were calculated
geometrically and then refined isotropically (for 2), using a riding
2.2.1. N,N-Diphenylacridin-9-amine (1)
N,N-Diphenylacridin-9-amine (1) was additionally purified
from an impurity of triphenylmethane dye on the stage of
hydrobromide salt separation. The solid hydrobromide of 1 was
extracted with acetone (3 ꢁ 20 mL), the mother solution was