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.
