Synthesis and Photophysical Characterizations of Benzimidazole Functionalized BODIPY Dyes

Herein, a series of new BODIPY dyes substituted by 2-phenyl benzimidazole units at the meso (C8) position including methyl/ethyl, phenyl, or p-methoxyphenyl moieties at the distal and proximal positions of the BODIPY core have been successfully synthesized and their photophysical characteristics were analyzed. Experimentally investigating absorption and fluorescence profiles in the THF media was followed by density functional theory (DFT) calculations to clarify photophysical features. Theoretical analyses have revealed that upon excitation, both electrons and holes are confined solely within the BODIPY core. The energy levels of the frontier molecular orbitals converge depending on the presence of the phenyl and p-methoxyphenyl substituents. The orbital distributions of both electron and hole were in the -3 and -5 positions, which demonstrates a continuous conjugation with the BODIPY core at these sites. However, the electron density present on the phenyl rings located at the -1, -7, and -8 (meso) positions was found to be negligible. The benzimidazole-BODIPYs exhibited photodynamic activity (Φ_∆) ranging from ~ 7% to ~ 11%, determined by a comparative method. Moreover, the compounds have shown to maintain their stability thermally in a non-reactive/inert environment up to temperatures surpassing 300 °C, exhibiting primarily a two-phase decomposition process. These compounds have the potential to function as antibacterial and anti-biofilm agents when used in concentrations ranging from 0.5 to 2.0 mg/mL. The results provide a basis for evaluating heterocyclic benzimidazole units on photophysical processes containing BODIPY chromophores.