374 JOURNAL OF CHEMICAL RESEARCH 2017
Computational methods
All of the calculations were performed using the DFT method with
the B3LYP functional31 as implemented in the Gaussian 03 program
package32 and the 6-311++G(d,p) basis set.
First, the geometry of the compound 3b was fully optimised in the
EtOAc solution. Here, one self-consistent reaction field method,
the sophisticated polarised continuum model (PCM),33 was used
for investigation of the solvent effects. The PCM calculations were
performed in EtOAc solution and the zero-point corrections were
considered to obtain energies. Based on the optimised geometries and
using TD-DFT34–36 methods, the electronic spectrum of compound 3b
was predicted.
Synthesis of compounds 3a–d from 1a–d and 2; general procedure
1-alkyl-5-nitro-1H-indazoles 1a–d (10 mmol) and 1-naphthylaceto-
nitrile (2) (13 mmol) were added with stirring to a solution of KOH
(20 g, 357 mmol) in methanol (40 mL). The mixture was stirred at r.t.
for 48 h. After concentration at reduced pressure, the precipitate was
collected by filtration, washed with water, followed by cold EtOH and
acetone, and then air dried to give the crude products 3a–d. Further
purification was achieved by crystallisation from a suitable solvent
such as EtOH or acetone.
3-Methyl-3H-benzo[a]pyrazolo[3,4-j]acridine-13-carbonitrile
(3a): Shiny yellow needles (acetone); m.p. 320–322 °C; yield 73%;
IR (KBr) (νmax cm–1): 2223 (CN); 1H NMR (300 MHz, CDCl3): δ 4.17
(3H, s, NCH3), 7.78–7.99 (7H, m, ArH), 8.09 (1H, d, J = 9.3 Hz, ArH),
9.42 (1H, s, ArH), 9.98 (1H, d, J = 7.5 Hz, ArH); 13C NMR (75 MHz,
CDCl3): δ 36.2, 107.3, 115.3, 116.4, 120.5, 123.2, 124.1, 126.0, 127.5,
128.1, 128.3, 129.0, 129.3, 129.3, 132.5, 133.4, 135.5, 137.4, 145.7,
147.6; MS (m/z) 308 [M]+ found: C, 78.05; H, 3.94; N, 17.90; calcd for
C20H12N4 (308.3): C, 77.91; H, 3.92; N, 18.17%.
Fig. 4 The HOMO and LUMO maps of compound 3b.
3-Ethyl-3H-benzo[a]pyrazolo[3,4-j]acridine-13-carbonitrile (3b):
Shiny yellow needles (EtOH); m.p. 288–289 °C; yield 66%; IR (KBr)
molecules, and has a determining role in, for example, electronic
properties, electronic spectra and photochemical reactions.
As can be seen in Fig. 4, the frontier molecular orbitals of 3b
are mainly composed of p atomic orbitals in the HOMO and
LUMO maps of dye 3b, so the electronic transitions in the
spectra above correspond to π–π* electronic transitions. The
energy separation between the HOMO and LUMO is 3.09 eV
(401.2 nm). As can be seen, the three-dimensional maps are
mostly localised on the centre of the ring system.
1
(νmax cm–1): 2221 (CN); H NMR (300 MHz, CDCl3): δ 1.68 (3H, t,
J = 7.2 Hz, NCH2CH3), 4.62 (2H, q, J = 7.2 Hz, NCH2CH3), 7.80–8.01
(7H, m, ArH), 8.09 (1H, d, J = 9.3 Hz, ArH), 9.42 (1H, s, ArH), 9.98
(1H, d, J = 7.5 Hz, ArH); 13C NMR (75 MHz, CDCl3): δ 15.5, 44.5,
107.7, 116.0, 116.1, 120.8, 123.3, 124.1, 126.0, 127.7, 128.0, 128.4, 129.1,
129.2, 129.3, 132.3, 133.0, 135.3, 137.5, 145.7, 146.8. MS (m/z) 322 [M]+
found: C, 78.29; H, 4.40; N, 17.21; calcd for C21H14N4 (322.4): C, 78.24;
H, 4.38; N, 17.38%.
The TD-DFT electronic spectra calculations for 3b
demonstrate that there is an electronic transition band: a
relatively sharp peak at 433.6 nm (oscillator strength: 0.4208)
that can be linked to ð–ð* transitions (donor endocyclic nitrogen
(N3) to the acceptor CN group). This electronic transition
band is comparable to the experimental value of 420 nm. The
calculated electronic absorption spectral data of compound 3b
are provided in Table S2 the ESI.
3-Propyl-3H-benzo[a]pyrazolo[3,4-j]acridine-13-carbonitrile (3c):
Shiny yellow needles (MeOH); m.p. 268–270 °C; yield 67%; IR (KBr)
1
(νmax cm–1): 2225 (CN); H NMR (300 MHz, CDCl3): δ 1.05 (3H, t,
J = 7.2 Hz, NCH2CH2CH3), 2.07–2.14 (2H, m, NCH2CH2CH3), 4.54
(2H, t, J = 7.2 Hz, NCH2CH2CH3), 7.81–8.04 (7H, m, ArH), 8.13 (1H,
d, J = 9.3 Hz, ArH), 9.44 (1H, s, ArH), 9.98 (1H, d, J = 7.5 Hz, ArH);
13C NMR (75 MHz, CDCl3): δ 12.1, 24.9, 49.3, 107.5, 116.3, 116.1, 120.7,
123.1, 124.5, 125.8, 127.4, 127.7, 128.5, 129.2, 129.2, 129.5, 132.6, 133.1,
135.3, 137.6, 145.6, 146.7. MS (m/z) 336 [M]+ found: C, 78.79; H, 4.83; N,
16.49; calcd for C22H16N4 (336.4): C, 78.55; H, 4.79; N, 16.66%.
Experimental
3-Butyl-3H-benzo[a]pyrazolo[3,4-j]acridine-13-carbonitrile (3d):
Shiny yellow needles (MeOH); m.p. 260–262 °C; yield 70%; IR (KBr)
Absorption and fluorescence spectra were recorded on a Varian
50-bio UV-Vis spectrophotometer and
a Varian Cary Eclipse
1
(νmax cm–1): 2224 (CN); H NMR (300 MHz, CDCl3): δ 1.01 (6H, d,
spectrofluorophotometer. UV-Vis and fluorescence scans were recorded
from 200 to 1000 nm. All measurements were carried out at r.t. The IR
(as KBr discs) spectra were obtained on a Tensor 27 spectrophotometer
and only noteworthy absorptions are listed. The 1H NMR and 13C NMR
spectra (300 and 75 MHz, respectively) were recorded on a Bruker Avance
DRX-300 FT spectrometer in CDCl3. Chemical shifts are reported in ppm
downfield from TMS as an internal standard. Electron impact ionisation
mass spectra were recorded on a Varian Mat CH-7 instrument at 70 eV.
Elemental analysis was performed on a Thermo Finnigan Flash EA
microanalyser. Melting points were measured on an Electrothermal type
9100 melting point apparatus.
J = 6.9 Hz, NCH2CH2CH2CH3), 1.41–1.45 (1H, m, NCH2CH2CH2CH3),
2.02–2.05 (1H, m, NCH2CH2CH2CH3), 4.57 (2H, d, J = 7.2 Hz,
NCH2CH2CH2CH3), 7.81–8.03 (7H, m, ArH), 8.12 (1H, d, J = 9.3 Hz,
ArH), 9.43 (1H, s, ArH), 9.98 (1H, d, J = 7.5 Hz, ArH); 13C NMR (75
MHz, CDCl3): δ 13.3, 22.3, 32.8, 46.8, 107.2, 116.1, 116.2, 120.5, 123.0,
124.3, 125.7, 127.4, 127.5, 128.1, 129.3, 129.0, 129.6, 132.1, 133.3,
135.6, 137.8, 145.4, 146.9. MS (m/z) 350 [M]+ found: C, 78.98; H, 5.20;
N, 15.79; calcd for C23H18N4 (350.4): C, 78.83; H, 5.18; N, 15.99%.
Acknowledgement
Compounds 1a–d25 and 226,27 were synthesised according to the
literature procedures. Other reagents and solvents were purchased
from Merck. All solvents were dried according to standard procedures.
We express our sincere gratitude to the Research Office,
Mashhad Branch, Islamic Azad University, Mashhad-Iran, for
financial support of this work.