Electronic structure of novel phthalocyanine analogues containing the 1,2,4-triazole unit

Summary form only given. Although symmetrical phthalocyanines are well documented, there are few reports on asymmetric phthalocyanines (Pc´s) due to their preparative difficulties. Low symmetrical Pc´s are particularly attracting as materials for nonlinear optics. Other effects such as the modulation of the intensity and the wavelength of the absorption bands are also of great relevance. In this contribution, we present a theoretical investigation of the electronic properties of a novel type of non-centrosymmetric phthalocyanine analogues where one isoindole unit has been replaced by a 1,2,4-triazole moiety. The effects of this unit on the molecular and electronic structure of phthalocyanine are analyzed by performing geometry optimizations at the semiempirical and ab initio levels. By comparison to phthalocyanines, the theoretical calculations predict the following main differences: i) The HOMO is mainly localized on the triazole ring and is significantly lower in energy dueto the contribution of nitrogen atoms. Higher oxidation potentials could therefore be expected for these compounds. ii) The lowest energy electronic transition (Q band) is shifted to the blue and appears bellow 500 nm. iii) The extension of the isoindole units by annelation of benzene rings does not affect the energy of the HOMO and produces and additional shift to higher energies of the visible Q band.