Computational insights into the photophysical behavior of BODIPY dyes: The impact of substituents on radiative and nonradiative decay pathways

This study provides computational insights into the photophysical behavior of a series of BODIPY derivatives (BDPA:P1–P4) with phenyl, naphthyl, anthryl, and pyrenyl substituents. By employing density functional theory (DFT) and spin-flip time-dependent DFT (SF-TDDFT), we systematically investigated how these substituents modulate the electronic structure, absorption/emission characteristics, and charge transfer processes. Our results reveal that although the BODIPY core predominantly determines the frontier orbital distributions, the nature of the substituents induces systematic shifts in HOMO and LUMO energies, alters charge transfer lengths, and significantly influences the radiative and nonradiative recombination dynamics. Radiative recombination rates correlate strongly with the transition dipole moments, with values ranging from 0.82 × 10⁸ s⁻¹ for BDPA:P3 to 3.81 × 10⁸ s⁻¹ for BDPA:P1. In contrast, nonradiative decay occurs through two competing channels: conical intersections provide an efficient decay pathway for BDPA:P1, BDPA:P2, and BDPA:P3 (with activation barriers between 27.6 and 32.2 kJ/mol leading to decay rates on the order of 10⁷ s⁻¹), whereas internal conversion becomes more pronounced in BDPA:P4. These findings underscore the potential of substituent engineering to tune the photophysical properties of BODIPY dyes for applications in organic light-emitting diodes (OLEDs) and dye-sensitized solar cells (DSSCs).