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Phenol derivatives are interesting molecules for theoretical studies due to their relatively small size and similarity to organic species. 2,6-dibromo-4-nitrophenol was investigated by using density functional theory (DFT). XRD data and optimized DFT studies are found to be in good correspondence with each other. Analysis of title compound was obtained by B3LYP/6-31 + G(d,p) level of theory to explain the vertical transactions. Calculated FT-IR and FT-Raman results are found to be in good agreement with experimental FT-IR and FT-Raman findings. Natural bond theory (NBO) study was also performed using B3LYP/6-31 + G(d,p) method. Correlations between the proton and carbon-13 experimental chemical shifts and the GIAO NMR calculations are in good agreement and these values have been used for the definitive signal assignments to the corresponding structures. Electronic absorption spectra of DBNP has been calculated by using CIS-DFT method based on the B3LYP/6-311++G (d,p) level of the optimized structure in gas phase. [ABSTRACT FROM AUTHOR]

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 time-dependent 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. [ABSTRACT FROM AUTHOR]