**1. Introduction**

In the natural photosynthesis process, chlorophyll converts incident light into chemical energy with nearly 100% quantum yield through many complex steps. This excellent phenomenon inspired many scientists to study porphyrin derivatives and their metallated forms exten‐ sively for many decades and continue to be so. Substantial information has been gathered on the synthesis, structural characterization, and dependence of their property on the structure and applications of porphyrins [1]. Porphyrins can be tailored by modifying the aromatic

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ring at the β and *meso* positions of the pyrrole and by metallating the tetradentate core of the porphyrin ring with almost all the transition metal ions. Thereby electronic properties of the porphyrins such as redox process, light absorption property, energy, and electron transfer capabilities can be amended [2]. Hence, porphyrins have witnessed their participation in the wide range of applications in various fields such as photovoltaics, artificial photosynthesis, photodynamic therapy, catalysis, and enzymatic systems.

As mentioned above, crafting the redox potentials of the porphyrins by modifying the periph‐ ery or the core of the aromatic ring remains the key strategy behind its multifunctional behav‐ ior. Most of such compounds are electroactive, exhibit multiple redox couples, and have been investigated for their electrochemical properties, generally, in nonaqueous solvents. Various factors such as a type of metal ion and its oxidation state present at the core, nature of the macrocyclic aromatic ring, and an axial ligand attached to the metal ion will affect the electro‐ chemistry of the molecule.

Porphyrins exhibit outstanding absorption of electromagnetic radiation in the visible region. Upon light illumination, electrons present in the HOMO will get excited to LUMO of the por‐ phyrin. Photoexcitation followed by various relaxation processes and charge separation is shown in **Figure 1**. Long‐lived radical ion pairs of porphyrins can be observed by stabilizing the charge separated states. Generally, the basic electrochemistry of the porphyrins is related to its electron donating or accepting behavior in the ground state. Electrochemistry of porphyrins under condi‐ tions similar to that of photovoltaic devices, artificial photosynthetic systems involves the other states depicted in **Figure 1**. In the following sections, we discuss the fundamental and applied electrochemistry of the porphyrins and its derivatives. Without going for the exhaustive citation of all the reported literature, representative examples have been chosen to support our discussion.

**Figure 1.** Representation of the molecular structure (a), HOMO and LUMO (b) of zinc tetraphenylporphyrin (ZnTPP) and the photoexcitation process followed by various relaxation events (c). Reprinted with permission from Ref. [65]. Copyright 2015 Elsevier Ltd.
