Advent and features of pyriporphyrinoids: an overview of a pyridine-based porphyrin analogue.

Pyriporphyrinoids have recently attracted a significant proliferation of attention due to their versatile characters, which stem from structural motifs in which the pyridine moiety is involved. The evolution of pyriporphyrin chemistry revealed the subtle modifications of the macrocyclic core that tweak the electronic structure as compared to the parental macrocycle. The amendment of π-electronic organization inside the core manifests exceptional photophysical and coordination properties that cover a vast range of seemingly contradictory fields. In fundamental chemistry, the pyridine unit acts as a modulator of π-conjugated porphyrinoid systems, resulting in aromaticity swapping. From the applied chemistry perspective, these macrocycles are primarily utilized as (i) sensors, (ii) NIR absorbing photoacoustic dyes, (iii) electrochemical catalysts, (iv) singlet biradicaloid generation and (v) contributors to generate metal complexes with intriguing binding modes. Surprisingly, despite their prominence, pyriporphyrinoids are inadequately investigated, while pyridine unit-embedded calixphyrin, calixpyridinopyrrole and calixpyridine are barely reported. This review article illustrates the controlled formation of specific porphyrinic scaffolds with pyridine unit(s) and diverse functionalized heterocyclic and/or carbocyclic building block(s), and demonstrates a substantial influence on the macrocyclic properties.