Y.-F. Zhang, C.-Z. Zhang / Journal of Molecular Structure 1189 (2019) 225e232
227
(
0.72 g, 2 mmol) and PbO
2
(2.8 g, 12 mmol) were added into
3. Results and discussion
dichloromethane (DCM) (60 mL). The mixture was stirred for 25 h
at room temperature. Sediment was filtered. Solvent was removed
from filtrate to give a blue powder. The crude production was
recrystallized from tetrahydrofuran (THF) (20 mL) to get blue
3.1. Structure of the four compounds
3.1.1. Design and the synthetic methods of bisazo compounds with
antiaromatic five-membered rings
1
crystal, pure compound 1b (612 mg, 1.7 mmol, 85.0%). H NMR
(
CDCl
3
):
d
¼ 8.61 (d, J ¼ 7.2 Hz, 2H); 8.15 (d, J ¼ 7.2 Hz, 4H); 7.97 (d,
Antiaromatic compounds are usually oxidized or reduced to give
aromatic compounds [3,4,8]. Introduce of nitrogen atoms with
large electronegativity into the conjugated systems of antiaromatic
compounds would lower their LUMO energy levels and improve
their chemical stability [13,37]. In general, bisazo compounds were
synthesized by coupling reaction of azoic salt with phenol or ani-
line derivatives [18,19]. Yield of the coupling reaction are usually
low, therefore, a Schiff base reaction with high yield was used to
synthesize compounds 1a and 2a [26,34]. Then, the compounds 1a
J ¼ 8.4 Hz, 2H); 7.66 (dd, J ¼ 8.4, 7.2 Hz, 2H); 7.59 (m, 4H); 7.53 (m,
þ
þ
2
H). MS (ESI): m/z ¼ 360.14 [M ]; Calcd. for C24
16 4
H N [M ]: 359.99.
16 4
Elem. Anal. Calcd. for C24H N (360.4): C, 79.98; H, 4.47; N, 15.55.
Found: C, 80.01; H, 4.40; N, 15.49. IR (KBr):
Synthesis of 1,2-bis(4-bromophenylazo)acenaphthylene (2b).
Synthetic method of compound 2b was similar with that of com-
pound 1b [26,33,34]. Compound 2b was recrystallized from THF to
ꢀ
1
y
¼ 1665.0 (N]N) cm
.
1
give red crystal (Yield: 83.0%). H NMR (CDCl
3
):
d
¼ 8.62 (d,
J ¼ 6.8 Hz, 2H); 8.22 (d, J ¼ 8.0 Hz, 2H); 8.07 (m, 4H); 7.98 (m, 4H);
2
and 2a were oxidized by PbO to give compounds 1b and 2b
7
.79 (dd, J ¼ 8.0, 7.2 Hz, 2H). MS (ESI): m/z ¼ 515.96, 517.96, 519.95
[26,34], because change in Gibbs free energies at the process of
transferring from non-conjugated compounds 1a and 2a to con-
jugated compounds 1b and 2b were negative values based on
quantum chemistry calculation. Optical and thermodynamical
stabilities of acenaphthylene are stronger than those of cyclo-
pentadiene [38]. Therefore, two antiaromatic bisazo compounds 1b
and 2b were synthesized by an oxidation reaction of acenaph-
thoquinone bisarylhydrazones 1a and 2a with PbO . These com-
2
pounds would be useful precursors for synthesizing functional azo
polymers. Especially, the bromo groups at both ends of compound
þ
þ
2 4
H14Br N [M ]:
(
5
M ; Abundance ratio ¼ 1 : 2: 1); Calcd. for C24
15.85, 517.85, 519.85 (Abundance ratio ¼ 1 : 2: 1). Elem. Anal.
Calcd. for C24
Found: C, 55.47; H, 2.72; N,10.74. IR (KBr):
H14Br
2
N
4
(518.2): C, 55.63; H, 2.72; Br, 30.84; N, 10.81.
¼ 1581.5 (N]N),1574.0
y
ꢀ
1
and 1470.0 (C]C in Phenyl) cm
.3. Calculation methods
.
2
Based on four crystal data, nucleus-independent chemical shift
NICS) values of the compounds were calculated by time-
2b could be useful for further functionalization, for example,
p-
(
conjugation and polymerization.
dependent density functional theory (DFT) using the gauge-
invariant atomic orbital (GIAO) approach at the B3LYP/6-31G(d)
level [28,29,35]. Geometries of four compounds and they with an
accepted electron at ground and excited states were optimized by
the time-dependent density functional theory (TD-DFT) calcula-
tions using Gaussian03 software at the B3LYP/6-31G(d) level
without any constraints [30,31]. Then, output files of optimized
geometries were employed as input files for calculating harmonic
vibrational frequencies at the same level at 298.15 K and 1 atm.
Finally, enthalpies, Gibbs free energies and entropies were acquired
from output files.
3.1.2. Crystal structures
Crystal structures of the four compounds were determined by X-
ray diffraction (Fig. 1).
In crystal of 1a, bonds lengths of C1eN1 (1.396 Å) and N4eC19
(
1.397 Å) suggest that N1 and N4 connect with phenyls via single
bonds (Fig. 1ea). Bonds lengths of N1eN2 (1.341 Å) and N4eN3
1.330 Å) show that two atoms was connected by a single bond.
(
Bonds lengths of N2eC7 (1.297 Å) and C17eN3 (1.319 Å) are double
bonds. It suggests that amino groups in phenylhydrazine reacted
with carbonyl groups to form Schiff base. At the right part of mo-
ꢁ
lecular structure image, dihedral angles C3eC2eC1eN1 (179.96 ),
2
.4. UVevis absorption spectrum
ꢁ
ꢁ
C2eC1eN1eN2 (170.08 ), C1eN1eN2eC7 (174.39 ), N1eN2e-
ꢁ
ꢁ
C7eC8 (2.69 ) and N2eC7eC8eC9 (0.76 ) suggests that, in a whole,
the right phenyl ring, two nitrogen atoms and acenaphthoquinone
moiety are in a plane. At the left part of molecular structure image,
dihedral angles C23eC24eC19eN4 (175.95 ), C24eC19eN4eN3
5.53 ), C19eN4eN3eC17 (178.75 ), N4eN3eC17eC16 (179.73 )
and N3eC17eC16eC15 (1.97 ) suggests that, in a whole, the left
phenyl ring, two nitrogen atoms and acenaphthoquinone moiety
are in a plane. Therefore, in a whole, all atoms in compound 1a are
in the molecular plane. Similarly, compounds 1b, 2a and 2b are
planar molecules (Fig. 1eb, 2a and 2b). In crystal of 1b (Fig. 1eb),
bond lengths of N1eN2 (1.269 Å), N1a-N2a (1.269 Å) and C7eC7a
Compound 1a (1.8 mg), 1b (1.8 mg), 2a (2.6 mg) or 2b (2.6 mg)
was added into CH
2 2
Cl (100.0 mL) or ethanol (100.0 mL) to acquire a
ꢀ
5
ꢀ5
ꢀ5
solution of 1a (5.0 ꢂ 10 M), 1b (5.0 ꢂ 10 M), 2a (5.0 ꢂ 10 M)
ꢁ
ꢀ5
ꢀ5
or 2b (5.0 ꢂ 10 M). After the solution (5.0 ꢂ 10 M, 25 mL) of 1a,
b, 2a or 2b in ethanol was added into a measuring flask (50 mL),
O (25 mL) was added into the measuring flask to acquire a so-
ꢁ
ꢁ
ꢁ
(
1
H
ꢁ
2
ꢀ
5
lution (2.5 ꢂ 10 M) of 1a, 1b, 2a or 2b in the mixed solvent of
ethanol and water (V/V ¼ 1:1). Then, UVevis absorption spectra of
these solutions were determined by
a Shimadzu UV-3600
UVeviseNIR spectrophotometer.
(1.382 Å) suggest that two double bonds N]N were formed be-
2
.5. Cyclic voltammetry experiment
tween N1 and N2, and between N1a and N2a, moreover, a double
bonds C]C was formed between C7 and C7a, respectively. There-
fore, two phenyl rings were grafted on an acenaphthylene moiety
via two double bonds N]N to form a bisazo compound. Bond
lengths of C1eN1 (1.421 Å), N2eC7 (1.390 Å), C1a-N1a (1.421 Å)
and N2a-C7a (1.390 Å) are longer than bond length (1.334 Å) of CeN
in an aromatic compound and shorter than a single bond CeN
(1.485 Å) [20]. It suggests that two phenyl, two N]N bonds and an
acenaphthylene moiety are conjugated well. Bond length data of
At room temperature, cyclic voltammetry was performed using
an electrochemical workstation (CH instruments Inc., CHI, model
7
afluorophosphate as the supporting electrolyte. The working,
auxiliary and reference electrodes were a glassy carbon electrode, a
Pt wire and Ag/Ag , respectively. The scan rate was 100 mV s
Ferrocene was added to the sample solution at the end of the
experiment. The ferrocenium/ferrocene (Fc /Fc) redox couple was
-
1
50A) and conducted using 0.1 molL tetrabutylammonium hex-
þ
ꢀ1
.
þ
crystal 2b suggest that compound 2b would be a p-conjugated
employed as an internal potential reference. The potential was
calibrated according to the literature method [36].
molecule (Figs. 1e2b). The molecules 1a or 1b aggregated face to
face to form an H-aggregation structure and further respectively