Symmetry Reduction of Porphycenes with Finely Tuned Optical and Electronic Properties through Oxidative Cyclization of E/Z-Mixed Dipyrroethenes

The main obstacle to the widespread application of porphycenes lies in the lack of efficient and economical methods for their production. Discovery of new synthetic methodologies for porphycene derivatives are important for fine-tuning of their optical and electrochemical properties. Herein, the preparation of a set of AABB-, ABAB-, and ABBA-type meso-tetrasubstituted unsymmetric porphycenes is reported. Their synthesis involved the acid-catalyzed oxidative coupling of AA- and BB-dipyrroethenes, or AB-type dipyrroethenes, as precursors in yields of up to 19 %. The structures were unambiguously confirmed by X-ray crystallography. The type and position of substituents in the unsymmetric porphycenes enabled fine-tuning of the optical and electronic properties, which are discussed in terms of their UV/Vis absorption, fluorescence spectroscopies, cyclic voltammetry, and density functional theory calculations.