The importance of non-radiative processes in porphyrins and phthalocyanines for photocurrent generation study

Abstract
The paper deals with the singlet and triplet state properties of several organic dyes: magnesium and zinc porphyrins/phthalocyanines and lead porphyrins in dimethyl sulfoxide. The fluorescence parameters: natural fluorescence lifetime, fluorescence quantum yields were estimated. Photocurrent generation in a sandwich-like photoelectrochemical cell was also measured and it was shown that magnesium and zinc dyes are very good candidates for light energy to electric energy conversion. Otherwise, lead porphyrin is rather poor agent for organic photovoltaics due to effective transformation of absorbed energy into heat in a charge-transfer species of this dye. By means of two techniques: steady-state photoacoustics and time-resolved photothermal spectroscopy thermal properties of dyes were investigated. Thermal deactivation parameters were calculated. On the basis of Marti et al. and Rudzki-Small et al. methods the prompt and fast non-radiative interna) conversion and intersystem crossing transitions occurring in the dyes were established and the quantum yields of triplet state populations as well as the triplet lifetimes were calculated. It was shown that both singlet and triplet states participate in thermal relaxation of the dyes. This result was discussed in terms of the participation of singlet and triplet states in generation of photocurrent in a photoelectrochemical cell based on organic dyes. The energetic model of a photovoltaic cell with dyes is presented.