Electronic Structure of Schiff Bases—2-(Salicylideneamino)phenol, 2-(Salicylideneamino)aniline and 2-(Salicylideneamino)benzenethiol—

Abstract

The electronic absorption spectra of 2-(salicylideneamino)phenol (SAP), 2-(salicylideneamino)aniline (SAA) and 2-(salicylideneamino)benzenethiol (SABT) have been measured in various media. Their polarization spectra have been also obtained by the use of the stretched polymer film technique. From the spectral data in conjunction with ab initio and semiempirical MO calculations, the molecular and electronic structure and the nature of the electronic transitions of the above compounds have been clarified. SAP, SAA and SABT are considered to have twisted molecular structures: the salicylideneamino groups are tilted against the phenyl groups by 29, 37 and 34° for SAP, SAA and SABT, respectively. The first electronic transition (357 nm band) of SAP (SAA, 382 nm or SABT, 352 nm) is polarized along the longer-molecular axis, to which charge transfer transition from 2-hydroxyphenyl(2-aminophenyl or 2-mercaptophenyl) to azomethine group is considerably contributed.