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

Salicylideneaniline presents an electronic absorption band spectrum of comp lex patterns between 200 and 450 nm. However, we have successfully develope d the electronic transition assignments of this molecular compound and its derivative species, substituted on the aniline ring of the salicylideneanil ine structure. Thus, we have analyzed the substituent effect of the electro n-acceptor groups such as -CN, -COCH3, and -NO2, as well as the electron-do nor 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 transit ion energies and the net charge transfer in excited electronic states by me ans of molecular orbital theory calculations in the AM1 and ZLNDO/S-CIS sem iempirical frameworks. Our present study has permitted us to determine the three main electronic transitions localized under the broad absorption spec tral band in the spectral region between 250 and 450 nm. Furthermore, we ha ve experimentally characterized the effect of the substituents on the first three excited electronic states for every substituted salicylideneaniline compound.