α ‐Pyrrole Functionalized BODIPYs: Photophysical, Electrochemical, Spectroelectrochemical, Nanosecond Transient Absorption and Time‐Resolved Spectroscopic Studies

Abstract

4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives have gained significant attention for various optoelectronic and biomedical applications due to their tunable photophysical and electrochemical properties. Herein, we report three phenothiazine‐functionalized meso ‐anisyl BODIPYs ( BDPZ1 – BDPZ3 ), synthesized via Suzuki cross‐coupling reactions, incorporating phenothiazine ( BDPZ1 ), formyl‐substituted phenothiazine ( BDPZ2 ), and cyano‐substituted phenothiazine ( BDPZ3 ) at the α ‐positions of the BODIPY unit. These α ‐substituted BODIPYs exhibit strong absorption in the visible region, with absorption onset extending toward longer wavelengths. The presence of electron‐withdrawing groups on the phenothiazine units results in blueshifted absorption maxima for BDPZ2 and BDPZ3 compared to BDPZ1 . The electrochemical studies reveal multiple redox processes, with BDPZ2 and BDPZ3 exhibiting anodically shifted first‐ and second‐oxidation potentials relative to BDPZ1 , consistent with the reduced donor strength of the substituted phenothiazines. Spectroelectrochemical analysis reveals the emergence of new NIR absorption peaks upon oxidation. Notably, BDPZ1 – BDPZ3 do not exhibit intrinsic triplet states; instead, their triplet states are accessed via intermolecular photosensitization with 2,6‐diiodoBodipy, giving triplet lifetimes of 60–118 μs as determined by nanosecond transient absorption spectroscopy. This study highlights how variations in the phenothiazine substituents influence the photophysical and electrochemical properties and excited‐state behavior of the BODIPYs, providing valuable insights for designing BODIPY‐based materials for optoelectronic applications.