Unravelling the ultrafast dynamics of a N-BODIPY compound

Although the photophysics of BODIPY compounds has been widely investigated in the last few years, their analogues N-BODIPY, with nitrogen substitution at the boron center, did not receive comparable attention. In this work we report the synthesis and photochemical characterization of a substituted N-BODIPY compound, by means of a combined theoretical and spectroscopic approach. Compared to a standard BODIPY, the compound under investigation presents a lower fluorescence quantum yield (QY) in the visible region. The excited state relaxation dynamics of the dye was studied in different solvents, showing further fluorescence quenching in polar solvents, and excited state decay rates strongly dependent on the environment polarity. The role of the pendant moieties and the involvement of charge transfer states in the excited state dynamics was experimentally addressed by transient absorption spectroscopy, and further analyzed with TD-DFT calculations, which allowed precise assignment of the transient signals to the correspondent electronic configuration. The complete picture of the N-BODIPY behavior shows the presence of both charge transfer and localized states, influencing the observed photophysics to different amounts, depending on the excitation conditions and the surrounding environment.