Energy dissipation and relaxation processes in deoxy myoglobin after photoexcitation in the Soret region Original Research Article

The kinetics of the spectral evolution of myoglobin (Mb) following the Soret band (S) excitation (405 nm) were measured in the Q-band (450–630 nm) and band-III (730–900 nm) regions. There are two ultrafast electronic relaxation steps, one less than 100 fs and another of a few 100 fs that bring Mb to the ground electronic state (S0). The anisotropy reaches 0.1 by ≈400 fs and then remains constant as the system approaches equilibrium. Further relaxation involves a biphasic decay dominated by a few ps component in addition to a smaller 15 ps component. These processes are ascribed to vibrational cooling in the ground electronic state. The distinctive shapes of the transient spectra are consistent with predictions of the differences between the spectra of hot and colder S0 molecules.