ИСТИНА

Here we discuss the origin and photophysics of fluorophores responsible for NIR fluorescence in biotissues. Despite significant differences in molecular composition, the optical properties of these fluorophores are remarkably similar, and the reason for this remains largely unknown. We employed fluorescence spectroscopy with (sub)picosecond resolution to elucidate the role of electronic interactions within heterogeneous systems of fluorophores, which form as a result of oxidation processes in living organisms. We revealed an ultrafast decay component with characteristic decay lifetime of 0.5–1.5 ps and spectral diffusion originating from excitation energy transfer (EET) in the system. The rate of EET was positively correlated to the fraction of aromatic species and tightness of aromatic species packing. Diminishing the number of EET donor acceptor pairs resulted in a lower impact of the ultrafast component to fluorescence decay. Our results uncover the role of electronic coupling among fluorophores responsible for NIR optical properties formation in biosystems and provide a framework for studying photophysical processes in heterogeneous systems of natural fluorophores.