A. Kanaani et al. / Journal of Molecular Structure 1063 (2014) 30–44
31
photochromic reaction of AAQs involves photoinduced reversible
aryl group migration process. The ‘‘trans’’ quinone isomer under-
goes photochemical rearrangement of the p-bond system to form
There has been growing interest in using organic materials for
nonlinear optical (NLO) devices, functioning as second harmonic
generators, frequency converters, electro-optical modulators, etc.
Since the second order electric susceptibility is related to first
hyperpolarizability, the search for organic chromophores with
large first hyperpolarizability is fully justified. The organic com-
pounds showing high hyperpolarizability are those containing an
electron donating or withdrawing group interacting through con-
jugated double bonds. Consequently, the present work thought
interesting to examine the potential energy surface (PES) at the
DFT level of theory in order to obtain the kinetic and thermody-
namic parameters as well as reasonable understanding the conver-
sion of ‘‘trans’’ and ‘‘ana’’ forms in gas phase.
the ‘‘ana’’-quinone isomer upon irradiation with UV light
(Scheme 1) [5–7]. It was found that this process is photochemically
and thermally reversible, as well as represents a new type of pho-
tochromic reaction of substituted AQs [8–10]. Also, photochemical
migration of hydrogen, or acyl groups from trans-quinoid to the
ana-quinoid structure was investigated [9–10]. Stability of ‘‘ana’’
and ‘‘trans’’ forms at ambient temperature is required for technical
application of aryloxyquinones [11,12]. Natural and synthetic 9,10-
AQs show a wide spectrum of biological activities [13–16].
The theoretical ab initio and normal coordinate analysis give
information regarding to the nature of the electronic structure,
the functional groups, orbital interactions and mixing of skeletal
frequencies. The structural characteristics and vibrational spectro-
scopic analysis of title compound by the quantum mechanical
ab initio and DFT methods have not been studied. Thus, extensive
experimental and theoretical studies were carried out on ‘‘trans’’
and ‘‘ana’’ forms to obtain a complete, reliable and accurate vibra-
tional assignments and structural characteristics of the compound.
Ab initio quantum mechanical method is widely used for simulat-
ing IR spectrum [17,18]. Time-dependent DFT (TD-DFT) calcula-
tions have also been used for the analysis of the electronic
spectrum and spectroscopic properties. The energies, degrees of
hybridization, populations of the lone electron pairs of nitrogen,
energies of their interaction with the anti-bonding pꢁ orbitals,
electron density (ED) distributions and E(2) energies have been cal-
culated by NBO analysis using DFT method to give clear evidence of
stabilization originating from the hyperconjugation of various
intra-molecular interactions. In this work, IR, 1H, 13C NMR param-
eters and UV–Vis spectrum of ‘‘trans’’ and ‘‘ana’’ forms are reported
experimentally and theoretically.
2. Experimental
The mid-IR spectra were recorded in the 4000–400 cmꢂ1 region
with spectral resolution of 2 cmꢂ1 by averaging the results of 16
scans on a Perkin–Elmer RXI Fourier Transform spectrophotometer
using KBr pellet technique (solid phase). The ultraviolet absorption
spectrum was examined in the range of 200–800 nm using Perkin–
Elmer lambda 25 recording spectrophotometer. The photoinduced
(rans) form was formed upon UV irradiation (Hg lamp DRSh-260+
UV-transmitting glass filters). Cyclic voltammetry measurements
were performed by means of AUTOLAB PGSTAT20 potentiostat–
galvanostat (EcoChemie, Netherlands). The electrochemical prop-
erties of title compound (c = 2 ꢃ 10ꢂ3 M) was investigated by cyclic
voltammetry with CH2Cl2 as the solvent in the presence of 0.1 M
Bu4NBF4 as the supporting electrolyte using Pt working and coun-
ter electrodes and Ag/AgCl as reference electrode at ambient tem-
perature [21]. Prior to the measurements the solution was purged
with argon to remove residual oxygen. The NMR spectra were re-
corded for trans form at ambient temperature on a Brucker
AVANCE DRX 400 MHz using CDCl3 as solvent. Melting point was
measured on a Buchi 510 melting point apparatus and is uncor-
rected. Chemicals were obtained from Merck and Fluka and used
without further purification. The development of reaction was
monitored by thin layer chromatography (TLC) analysis on silica
gel 60 GF254 aluminum sheets, using ethyl acetate:petroleum ether
(1:3) as mobile phase. The spots were exposed by UV light and io-
dine vapor.
Theoretically calculated HOMO and LUMO energies are closely
associated to oxidation potentials and reduction potentials of mol-
ecules. As stated by Koopman’s theorem [19], ionization energy is
equal to the HOMO energy of a molecule, but of opposite sign, with
the consequence that oxidation potentials may be related to HOMO
energies. The electron located in the HOMO orbital is removed dur-
ing oxidation. In a similar way LUMO energy is related to reduction
potentials. Both HOMO and LUMO energies may readily be calcu-
lated, i.e. by means of DFT and other computational methods, as
extensively discussed elsewhere [20].
2.1. Synthesis of 4-((9,10-dioxo-9,10-dihydroanthracen-1-yl)oxy)
benzaldehyde (3) (Scheme 2)
The starting 1-dichloroanthraquinone 1 (2.77 g, 10 mmol) and
4-hydroxybenzaldehyde 2 (2.8 g, 11 mmol) were dissolved in
30 mL of dry N,N-dimethylformamide (DMF) in round bottom flask,
followed by addition of dry K2CO3 (6.9 g, 49.9 mmol) while the
solution was stirred at reflux. Stirring was continued for 36 h at re-
flux conditions. After completion of the reaction, it was monitored
by TLC, solvent was evaporated under vacuum and water added to
CHO
O
CHO
O
O
O
O
hv1
hv2
H
O
H
O
O
Cl
O
K2CO3, DMF, Reflux
+
O
O
O
OH
1
2
O
3
"trans"-form
"ana"-form
Scheme 2. Synthesis of 4-((9,10-dioxo-9,10-dihydroanthracen-1-yl)oxy)benzalde-
Scheme 1. Photochromic reaction of aryloxyanthraquinones (AAQs).
hyde (3).
Kanaani
