Synthesis and investigation of photophysical properties of porphyrin-embedded polythiophene

Abstract

In this research, trans-A2B2-porphyrins and trans-A2B2-benzoporphyrins bearing phenyl and thiophene-based meso-substituents were synthesized and characterized by nuclear magnetic resonance spectroscopy and mass spectrophotometry. The photophysical properties of both solutions and films of the target compounds were also investigated by UV-visible and fluorescence spectrophotometry. Comparative studies of these compounds revealed that the replacement of phenyl with thiophene meso-substituents, the introduction of the additional thiophene ring and the extension of the porphyrin π-conjugated system significantly affected their photophysical and electrochemical properties. Energy levels of their highest occupied molecular orbital and lowest unoccupied molecular orbital, and their energy gap were estimated and found to be in a range of –5.79 to –5.55, –4.05 to –3.87 and 1.5 to 1.9 eV, respectively. The electropolymerization through the bithiophenyl units of the target compounds gave desirable porphyrin-embedded polythiophenes, the formation of which was confirmed by cyclic voltammetry and UV-visible spectrophotometry. Their absorption properties of the resulting polymers were consistent with those of the monomers with broader typically occurred for the porphyrinic polymers.