Ultraviolet absorption bands and electronic charge transfers of salicylideneanilines in singlet excited states

Abstract

Salicylideneaniline presents an electronic absorption band spectrum of complex patterns between 200 and 450 nm. However, we have successfully developed the electronic transition assignments of this molecular compound and its derivative species, substituted on the aniline ring of the salicylideneaniline structure. Thus, we have analyzed the substituent effect of the electron-acceptor groups such as -CN, -COCH3, and -NO2, as well as the electron-donor groups such as -CH3, -OCH3, and -N(CH3)(2) On the electronic transition energies of the main absorption spectral region. From a theoretical point of view, we have characterized the orbital nature of the electronic transition energies and the net charge transfer in excited electronic states by means of molecular orbital theory calculations in the AM1 and ZLNDO/S-CIS semiempirical frameworks. Our present study has permitted us to determine the three main electronic transitions localized under the broad absorption spectral band in the spectral region between 250 and 450 nm. Furthermore, we have experimentally characterized the effect of the substituents on the first three excited electronic states for every substituted salicylideneaniline compound.