Synthesis and Studies of Phenothiazine Bridged 3‐Pyrrolyl BODIPY Dyads

Two phenothiazine‐bridged 3‐pyrrolyl BODIPY dyads, 1 and 2 , were synthesized through Sonogashira coupling of 3,7‐diethynyl‐ N ‐methylphenothiazine with meso ‐( p ‐iodophenyl) and α ‐bromo 3‐pyrrolyl BODIPY, respectively. Although both molecules contain identical donor and acceptor units, their linkage modes differ: Compound 1 connects through the meso ‐phenyl ring of 3‐pyrrolyl BODIPY unit, whereas compound 2 connects through the α ‐position of the appended pyrrole of 3‐pyrrolyl BODIPY unit. 1D and 2D NMR analyses confirmed that this topological change modifies the donor–acceptor conjugation pathway. Consequently, 2 exhibits strongly redshifted absorption and emission bands relative to 1 (638 vs. 587 nm and 685 vs. 618 nm, respectively), along with a larger Stokes shift. Both dyads show irreversible, oxidation‐dominated electrochemical responses, but 2 oxidizes at a lower potential, consistent with enhanced conjugation. DFT and TD‐DFT calculations attribute these differences to the smaller donor–acceptor dihedral angle and greater HOMO delocalization in 2 . Overall, the NMR, optical, electrochemical, and computational results consistently support a linkage‐site‐dependent structure–property relationship, in which the α‐pyrrolyl connection enhances donor–acceptor communication within these molecular frameworks.