Theoretical study of 2-phenylbenzoxazole derivatives and derived phenolic Schiff compounds in gas and solution phases: Electronic structures and optical properties

Theoretical investigation has been carried out for the electronic structures, optical properties and electron transition mechanism of R-substituted 2-phenylbenzoxazole complexes (nb) and derived phenolic Schiff bases (na) (n = 1, R = CH₃; n = 2, R = N(CH₃)₂; n = 3, R = Cl; n = 4, R = NO₂). In the gas phase, the ground and excited states were fully optimized at the B3LYP/cc-pVDZ, HF/cc-pVDZ and CIS/cc-pVDZ, respectively. For each derivative, two conformations are available, one with a downward hydrogen (H2) and the other with an upward hydrogen, and the former one is more stable than the latter one. Absorption and emission spectra of all species were calculated by the time-dependent density functional theory (TD-DFT) based on the ground and excited states geometries. The absorption and emission spectra were consistently blue shifted in going from na to nb. The solvent effects on molecular geometries and optical properties were characterized in several solvents from B3LYP/cc-pVDZ and HF/cc-pVDZ calculations employing the Onsager model within the framework of the self-consistent reaction field (SCRF) theory. The SCRF calculations provide reliable information regarding the solvent effects on the geometries and optical properties of the conjugate compounds.