Electronic structure, absorption spectra, and hyperpolarisabilities of some novel push-pull zinc porphyrins. A DFT/TDDFT study

DFT/TDDFT calculations have been performed on some novel push-pull zinc porphyrins (denoted ZnPor 1, ZnPor 2, and ZnPor 3). This theoretical work aims to investigate the electronic structure, absorption spectra, and hyperpolarisabilities of these molecules. To examine the effects of the peripheral substituents on the molecular properties, zinc porphine (ZnP) and zinc tetraphenylporphine (ZnTPP) were also included in the study. The orbital energy level patterns of the substituted zinc porphyrins are indeed rather different from those of ZnP and ZnTPP. The peripheral substitution breaks the molecular D-4h symmetry of the porphyrin, thereby leading to the splitting of the absorption Q band. On the other hand, the B band in the spectra may not arise only from a single excited state; instead, it could be made up of several states that are close in energy. The calculated hyperpolarisabilities (beta(vec)) increase strongly from ZnPor 1 to ZnPor 2 to ZnPor3. The latter two molecules were predicted to have a large beta(vec) value and thus may have potential application in the development of nonlinear optical (NLO) materials.