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SUBSTITUENT EFFECTS ON THE ABSORPTION AND VIBRATIONAL SPECTRA OF SOME 2-HYDROXY SCHIFF BASES: DFT/TDDFT, NATURAL BOND ORBITAL AND EXPERIMENTAL STUDY

The electronic structure of salicylideneaniline (SA) and some of its derivatives are investigated both experimentally and theoretically. The equilibrium geometric structures of the studied compounds are determined at the B3LYP/6-311++G** level of theory. A set of 12 substituted SA derivatives is considered in the present work. The choice of these substituents aims to create a push-pull system on the SA basic structure which would shade light onto its photo physics. The electronic absorption spectra of SA are recorded in the UV-VIS region, in both polar and nonpolar solvents. Assignments of the observed electronic transitions are facilitated via timedependent density functional theory (TDDFT) computations at the same level of theory. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The extent of delocalization and intramolecular charge transfer are estimated and discussed in terms of natural bond orbitals (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. Solvent effects on the electronic absorption spectra are discussed in terms of the difference in polarizabilities of the ground and excited states. FTIR spectra of SA and its derivatives are measured in KBr platelets. Detailed vibrational assignments are given based on the calculated potential energy distributions. ″IR marker bands″ that characterize the SA framework are identified. The effect of substituents, the nature of the characteristic ″marker bands″, and intensity quenching of some bands are discussed.

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Том 56, 3 UDC 541.65:548.737 SUBSTITUENT EFFECTS ON THE ABSORPTION AND VIBRATIONAL SPECTRA OF SOME 2-HYDROXY SCHIFF BASES: DFT/TDDFT, NATURAL BOND ORBITAL AND EXPERIMENTAL STUDY S.A. Elroby1,3, S. Aboud1, S.G. Aziz1, R. Hilal1,2 1Chemistry Department, Faculty of Science, King abdullaziz University, Jeddah, Saudi Arabia 2 E-mail: rhilal@kau.edu.sa 3Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt Chemistry Department, Faculty of Science, Benisuef University, Benisuef, Egypt Received March, 5, 2014 The electronic structure of salicylideneaniline (SA) and some of its derivatives are investigated both experimentally and theoretically. <...> The equilibrium geometric structures of the studied compounds are determined at the B3LYP/6-311++G** level of theory. <...> The choice of these substituents aims to create a push-pull system on the SA basic structure which would shade light onto its photo physics. <...> The extent of delocalization and intramolecular charge transfer are estimated and discussed in terms of natural bond orbitals (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. <...> Detailed vibrational assignments are given based on the calculated potential energy distributions. ″IR marker bands″ that characterize the SA framework are identified. <...> DOI: 10.15372/JSC20150303 Keywords: electronic spectra, vibrational spectra, DFT/TDDFT, solvent and substituent effects, NBO analysis, 2-hydroxy Schiff bases. <...> Numerous experimental studies [25— 28 ] on SA have been devoted to the analysis of the mechanism and dynamics of the proton transfer Elroby S.A., Aboud S., Aziz S.G., Hilal R., 2015 ЖУРНАЛ СТРУКТУРНОЙ ХИМИИ Май – июнь С. 444 – 456 ЖУРНАЛ СТРУКТУРНОЙ ХИМИИ. 2015. <...> The absorption spectrum of SA shows a quite prominent band at 300—400 nm attributed to the photoexcitation to a ππ* excited state [ 29 ]. <...> This transient has a long lifetime of the order of milliseconds and a maximum absorption band at 474 nm [24 ]. <...> The origin of each absorption band is identified and the contributing configurations and MOs are characterized. <...> An attempt is made to identify and assign the ″IR marker bands″ for SA. <...> NBO theory [ 35, 36 ] proved to be extremely useful in analyzing hyper conjugative [ 37 ] interactions through the second-order perturbation energy <...>
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