Heavy Atom-Enhanced Photooxidation Performance of Carbazole-Substituted BODIPY Dyes

Abstract

In this study, halogenated BODIPYs (C-Br-2-BDPY and C-I-2-BDPY) bearing a carbazole group at the meso position are synthesized and characterized using various spectroscopic techniques. Single-crystal X-ray diffraction analysis of the C-I-2-BDPY revealed that it crystallizes in a triclinic crystal system with a P-1 space group. The optical properties, singlet oxygen generation capacities, and photocatalytic activities of the BODIPY derivatives are evaluated with respect to juglone synthesis. While the nonhalogenated BODIPY (C-BDPY) exhibit negligible singlet oxygen generation (Phi(Delta) < 0.05), the iodinated (C-I-2-BDPY) and brominated (C-Br-2-BDPY) derivatives demonstrate considerably higher singlet oxygen quantum yields of 0.82 and 0.73, respectively. In the photooxidation reaction of 1,5-dihydroxynaphthalene (DHN) to juglone, these halogenated BODIPY compounds achieve conversion yields of 62.6% for C-Br-2-BDPY and 87.8% for C-I-2-BDPY within one hour. The turnover number values of the BODIPY photosensitizers show a continuous increase over time, indicating sustained product formation, whereas the turnover frequency values gradually decline, reflecting the decrease in reaction rate as the process progress. Density functional theory calculations support the experimental results by demonstrating that the presence of heavy atoms facilitates intersystem crossing and enhances the thermodynamic feasibility of the photooxidation reactions.