Doping-induced polaron formation and solid-state polymerization in benzoporphyrin–oligothiophene conjugated systems

Benzoporphyrins and their derivatives are of high interest in organic semiconductor technology due to their peculiar physical properties valuable for optoelectronic applications. Following our previous work successfully developing meso-thienyl- or meso-bithiophenyl-substituted zinc benzoporphyrins as efficient ternary components for bulk heterojunction solar cells, we describe herein detailed spectroscopic studies on doping of solid films of these benzoporphyrins under iodine atmosphere. Solid-state doping and oxidative polymerization are investigated by Raman and Fourier transform infrared spectroscopy. Structural and vibrational changes upon doping are explored with supporting data from density functional theory calculations. Furthermore, the optical and spectroscopic characteristics of the films of these materials are also monitored during the doping, and the polaron formation as evidenced by in situ attenuated total reflection Fourier transform infrared and UV–vis spectroscopy is observed. These results suggest that the target zinc benzoporphyrins, both in monomeric and in polymeric forms, should be good candidates in several other optoelectronic applications.