The synthesis and photochemical characterization of meso-tetra-thienyl porphyrins

A series of meso-thienyl porphyrins were synthesized through Lindsey's procedure and characterized. Compared with H2TPP (tetraphenylporphyrin), the absorption and fluorescence spectra of thienyl porphyrins have red shift obviously which show that thienyl substituents at meso-position change the electronic structure of tetrapyrrole ring. With protonation using CF3COOH, the absorption bands of thienyl porphyrins are further red shifted. The absorption bands of meso-thienyl porphyrins change correspondingly with the variation of solvents' properties, however the maxima emission wavelengths corresponding to Q* have little relation with solvents. And the fluorescence lifetime become so less even to 1.1 ns. The half-wave redox potential shows cathodic shift relative to H2TPP. These changes above are all ascribed to the introduction of thienyl group at meso-position and the possibility of more planarity of meso-thienyl porphyrins for the small size of thienyl group which is helpful to the extending π-delocalization of thienyl groups to the tetrapyrrole ring.