N. Altinolcek, A. Battal, C.N. Vardalli et al.
Journal of Molecular Structure 1239 (2021) 130494
to that, the thermal and electrochemical properties of compounds
C25H25NNaO [M+Na]+ 378.1828, found for [M+Na]+ 378.1817 (er-
ror: +3.1 ppm).
4 and 5 were compared with 7.
4-(9ꢀ-hexylcarbazol-3ꢀ-yl)benzylidenemalononitrile
(Cz-
ꢀ
ꢀ
Ph-CN: 5): 4-(9 -hexylcarbazol-3 -yl)-benzaldehyde
4
(300 mg,
2. Experimental section
0,84 mmol) and malononitrile (130 mg, 1,9 mmol) in
dichloromethane (10 ml) were mixed together and stirred at
room temperature for 10 min. One drop of pyrrolidine was added
to the reaction mixture. The reaction mixture was stirred for 24 h
at room temperature. After this, the crude product was dissolved
in dichloromethane and washed with water (3 × 20 mL). The com-
bined extracts were dried over sodium sulfate and then filtered.
Upon concentration under reduced pressure, the crude product
was obtained as a dark brown–orange sticky solid. Purification by
preparative thin layer chromatography (Hexane/Chloroform/EtOH,
4:3:0.2 v/v/v) gave the title compound (300 mg, 88%) as an orange
solid.
2.1. Materials and methods
Carbazole (95%), N-Bromosuccinimide (NBS) (99%), n-hexyl
bromide (99%), tetrabutylammonium iodide (TBAI) (98%) and
dichlorobis(triphenylphosphine)palladium(II)
(PdCI2(PPh3)2)
were purchased from Alfa-Aesar. Sodium hydroxide (NaOH),
4-formylphenylboronic acid, dimethylformamide (DMF) and potas-
sium carbonate (K2CO3) were purchased from Merck. Malononitrile
(≥99%) and pyrrolidine (99%) were purchased from Sigma-Aldrich.
Tetrahydrofuran (THF) and dichloromethane were purchased from
VWR. 3-Bromocarbazole (2) and N-hexyl-3-bromocarbazole (3)
was synthesised as previously described [35]. Inert reactions
were performed under an argon atmosphere. Nuclear magnetic
resonance (NMR) spectra were obtained on an Agilent Premium
Compact NMR spectrometer (600 MHz for 1H NMR, 150 MHz
for 13C NMR) with tetramethylsilane as internal standard. The
IR spectra were obtained (4000–400 cm−1) using a Shimadzu
IRAffinity-1S Fourier transform infrared spectrophotometer. The
mass spectra were obtained on Bruker microTOFq mass spectrom-
eters to obtain low- and high-resolution spectra using electron
ionisation (EI) or electrospray ionisation (ESI) techniques. UV,
PL and photoluminescence quantum yields were measured on
a Duetta two-in-one fluorescence and absorbence spectrometer
from Horiba Scientific. Both absorption and emission solutions
for reference and samples had a concentration of 10−6 M. CV
Rf (Hexane/Chloroform/EtOH, 4:2:0.1 v/v/v): 0.57. Melting point:
117–118.6 °C. 1H NMR (600 MHz, CDCI3) δ (ppm): 8.38 (s, 1H),
8.16 (d,
J
=
7.8 Hz, 1H), 8.00 (d,
J
=
8.4 Hz, 2H), 7.89 (d,
J = 8.4 Hz, 2H), 7.78–7.74 (m, 2H), 7.54–7.48 (m, 2H), 7.45 (d,
J = 8.4 Hz, 1H), 7.29 (t, J = 7.2 Hz, 1H), 4.34 (t, J = 7.2 Hz,
2H), 1.9 (p, 2 H), 1.44–1.24 (m, 6H), 0.87 (t, J = 6.6 Hz, 3H). 13C
NMR (150 MHz, CDCI3) δ (ppm): 159.25, 148.47, 141.03, 140.94,
131.59, 129.53, 128.89, 127.71, 126.35, 124.98, 123.65, 122.80,
120.51, 119.49, 119.28, 114.26, 113.14, 109.39, 109.16, 80.73, 43.33,
31.58, 28.99, 26.99, 22.56, 14.03. FT-IR (cm−1): 2967, 2922, 2867,
2852, 1697. MS (ESI+, m/z): 426.19. (M+Na)+. HRMS (ESI+, m/z):
calculated for C28H25N3Na [M+Na]+ 426.1941, found for [M+Na]+
426.1922 (error: +4.5 ppm). Anal. Calcd. for C28H25N3, C: 83.34, H:
6.24, N: 10.41; found: C: 83.57, H: 6.24, N: 10.48.
measurements were obtained using
a CH Instruments 602E
electrochemical workstation with iR compensation using dry
dichloromethane. Thermogravimetric analysis was conducted using
a Netzsch TG 209 F3 Tarsus Thermogravimetric Analyser under a
constant flow of nitrogen. Differential scanning calorimetry was
determined on a Netzsch DSC 214 Polyma instrument.
3. Results and discussion
3.1. Synthesis
Compounds 4, 5 and 7 were synthesised starting from carbazole
(1) in four steps as depicted in Scheme 1. The synthesis of 7 was
previously reported by us [35], whilst the preparation of 4 was re-
ported by Afroz et al. [14] and Naik et al. [49] as an intermediate
for dye-sensitized solar cells. Similar structures to 4 with differ-
2.2. Synthesis of compounds 4 and 5
ꢀ
ꢀ
4-(9 -hexylcarbazol-3 -yl)benzaldehyde
3-–bromo-9-hexylcarbazole (3) (200
4-formylphenylboronic acid (0.140
(Cz-Ph-CHO:
4):
mmol),
mmol),
ꢀ
ent alkyl groups (ethyl, butyl) on the 9 -position of carbazole were
mg,
mg,
0.60
0.90
also reported by others [50–52]. Very recently, Li et al. [20] re-
ꢀ
ported a synthesis with the octyl group at the 9 -position of car-
potassium carbonate (0.1 M, 7–8 mL) and dichloro-
bis(triphenylphosphine)palladium(II) (0.03 g, 0.04 mmol) were
dissolved in tetrahydrofuran (10 mL). The reaction mixture was
refluxed for 24 h under an argon atmosphere. After removing the
solvent, the crude product was dissolved in dichloromethane and
washed with water (3 × 20 mL). The combined extracts were
dried over sodium sulfate and then filtered. Upon concentration
under reduced pressure, the crude product was obtained as a dark
brown–green sticky solid. Purification by flash column chromatog-
raphy (1:40 Ethyl acetate/Hexane v/v) and recrystallization from
1:15 Ethyl acetate/Hexane v/v gave the title compound (161 mg,
75%) as a white solid.
bazole. However, this work reports the first known synthesis of
compound 5 and involves the Knoevenagel condensation of 4 with
malononitrile in dichloromethane at room temperature with a cat-
alytic amount of pyrrolidine. Compound 5 was obtained in excel-
lent yield (88%).
3.2. Thermal properties
The thermal properties of compounds 4 and 5 were investigated
by thermogravimetric analysis (TGA) for the first time by us. Com-
pounds 4 and 5 were heated to 650 °C at a rate of 20 °C/min un-
5%
Rf (Ethyl acetate/Hexane, 1:6 v/v): 0.43. Melting point: 80.5–
81 °C. 1H NMR (600 MHz, CDCI3) δ (ppm): 10.07 (s, 1H), 8.38
(s, 1H), 8.16 (d, J = 7.2 Hz, 1H), 7.98 (d, J = 7.8 Hz, 2H), 7.89 (d,
J = 8.4 Hz, 2H), 7.76 (d, J = 8.4 Hz, 1H), 7.52–7.47 (m, 2H), 7.44
(d, J = 8.4 Hz, 1H), 7.28 (t, J = 7.2 Hz, 1H), 4.33 (t, J = 7.2 Hz,
2H), 1.9 (p, 2 H), 1.45–1.25 (m, 6H), 0.87 (t, J = 7.2 Hz, 3H). 13C
NMR (150 MHz, CDCI3) δ (ppm): 192.01, 148.27, 141.00, 140.63,
134.45, 130.46, 130.38, 127.55, 126.15, 125.16, 123.53, 122.87,
120.49, 119.31, 119.26, 109.20, 109.04, 43.29, 31.60, 28.99, 27.00,
22.57, 14.04. FT-IR (cm−1): 2948, 2923, 2885, 2856, 2733, 1681.
MS (ESI+, m/z): 378.18 (M+Na)+. HRMS (ESI+, m/z): calculated for
der nitrogen atmosphere. The decomposition temperatures (Td
)
corresponding to 5% weight losses for 4 and 5 were 316 °C and
337 °C, respectively. These values give the opportunity to use these
compounds during high temperature operations [53–55]. When 4
and 5 were compared, it seems the dicyanovinyl group exerts an
extra thermal stability of 21 °C when compared to the formyl
group. When 4 was compared with previously reported Cz-Py-
CHO 7 [35], the benzene spacer in 4 exerts an extra stability of
9 °C in comparison to the pyridine spacer in 7 (see Table 1).
Moreover, the decomposition temperature was also affected by the
substituents; compound 4 bearing a formyl group decomposed at
2