β-Pyrrole functionalized porphyrins: Synthesis, electronic properties, and applications in sensing and DSSC

Abstract

Porphyrin is a class of tetrapyrrole compound with both natural and synthetic occurrence and its derivatives perform a significant role as light harvesting antenna in the natural photosynthetic process. The functionalized porphyrin derivatives are well studied in the light-harvesting process which include energy-transfer and electron-transfer processes. The porphyrin-based D–A systems have been explored for its tunable optical and electronic properties, which can be attained by controlled modification of the substituents at the meso and β-pyrrolic positions. The β-functionalized porphyrins remain much unexplored as compared to the meso-functionalized porphyrins. The porphyrin macrocycle with substituents at the β-pyrrolic positions such as bromo, formyl, vinyl, ethynyl, nitro and amino group are versatile building blocks for the preparation of different porphyrin analogues. These porphyrin analogues can be utilized to mimic the natural photosynthetic systems and to investigate the intramolecular excitation energy transfer. Tuning of optical and electronic properties of the porphyrin macrocycle have been investigated over the years to improve the efficacy of a wide range of applications including organic light emitting diodes, photodynamic therapy, nonlinear optics, dye sensitized solar cells, single molecule switches and many more. Dye Sensitized Solar Cells (DSSCs) has emerged as a cutting-edge technology in the field of photovoltaics (PV) due to the low production cost and high-power conversion efficiency. The porphyrin based push–pull systems show good performance in DSSC applications with a improved power conversion efficiencies up to 13% for meso-substituted porphyrin and 7.4% for the β-substituted porphyrin dyes. The β-substituted porphyrins are much unexplored in DSSC due to synthetic difficulty. This review focus on the synthetic aspects of the β-functionalized porphyrins, which further helps in better understanding about their electronic properties, sensing ability and device performances in dye sensitized solar cells (DSSCs).