Electronic structure of Schiff bases - 2-(salicylideneamino) phenol, 2-(salicylideneamino) aniline and 2-(salicylideneamino)benzenethiol

The electronic absorption spectra of 2-(salicylideneamino) phenol (SAP), 2- (salicylideneamino)aniline (SAA) and 2-(salicylideneamino) benzenethiol (SA BT) have been measured in various media. Their polarization spectra have be en also obtained by the use of the stretched polymer film technique. From t he spectral data in conjunction with ab initio and semiempirical MO calcula tions, the molecular and electronic structure and the nature of the electro nic transitions of the above compounds have been clarified. SAP, SAA and SA BT are considered to have twisted molecular structures: the salicylideneami no groups are tilted against the phenyl groups by 29, 37 and 34 degrees for SAP, SAA and SABT, respectively. The first electronic transition (357 nm b and) of SAP (SAA, 382 nm or SABT, 352 nm) is polarized along the longer-mol ecular axis, to which charge transfer transition from 2-hydroxyphenyl (2-am inophenyl or 2-mercaptophenyl) to azomethine group is considerably contribu ted.