Synthesis, Structures, and Properties of Highly Brominated Phenyl‐Bridged bis(3‐pyrrolyl BODIPY)s

ABSTRACT

Two highly brominated phenyl‐bridged bis(3‐pyrrolyl BODIPY)s, namely dodecabrominated derivative 2 and tetradecabrominated derivative 3 , were synthesized by treating the parent bis(3‐pyrrolyl BODIPY) 1 with excess Br ₂ in 1,2‐dichloroethane at room temperature for 10–20 min, followed by chromatographic purification. Compound 2 was obtained in low yield and exhibited poor solubility, whereas compound 3 was isolated in good yield. Both derivatives were structurally characterized by x‐ray crystallography, with additional NMR characterization. The crystal structures revealed significant distortion of the 3‐pyrrolyl BODIPY framework upon extensive bromination, with compound 3 displaying greater distortion owing to increased steric congestion caused by the additional bromine substituents. Bromination also substantially altered the optical and electrochemical properties of the bis(BODIPY) framework. The absorption spectrum of 2 retained a profile similar to that of 1 , but its absorption bands underwent pronounced bathochromic shifts. In contrast, 3 exhibited a broad absorption profile with a hypsochromic shift relative to 2 . Both brominated derivatives showed bathochromically shifted fluorescence accompanied by reduced fluorescence quantum yields. The electron‐withdrawing bromine substituents facilitated reduction at low potentials. Notably, tetradecabrominated derivative 3 exhibited highly efficient singlet oxygen generation. DFT/TD‐DFT studies were in agreement with the experimental observations.