Deep UV Initiated Excited State Dynamics of Flavins

Abstract

Flavins are redox-active chromophores in blue light activated enzymes and hence play crucial roles in several photobiological processes. Photophysics of flavin compounds has been the subject of intense research due to the involvement of its electronic excited states in those photochemical and photobiological processes. In majority of the published literature, the excited states corresponding to absorption at 450 and 375 nm of flavins have been investigated to deduce the underlying molecular mechanism of these photoinduced processes. However, the photodynamics in the excited state associated with 266 nm absorption band has not been investigated. These highly absorbing singlet excited states are important because solar flux contains a considerable amount of UV light along with low energetic visible photons. Through a comprehensive resonance Raman experiments, theoretical calculations and classical wave-packet dynamics simulations, we have determined the sub-100 femtosecond structural dynamics of flavins upon photoexcitation to their 266 nm excited state. We have also determined the modespecific reorganization energies along each observed vibrational modes. Our simulation method can partition the total spectral broadening into homogeneous and inhomogeneous broadening components contributing to both absorption and Raman line shapes. We find upon excitation, the first solvation shell inertially responds with an ultrafast timescale of ~ 30 fs for all of the flavins. Initial excited state parameters obtained from our simulation will impact studies on flavin containing proteins that utilize flavin as a probe of protein dynamics.