The photoinduced ring opening reaction of benzo(2H)chromenes: a kinetic and thermodynamic approach

To gain more insights into the relaxation dynamics of the excited states, the Heisenberg uncertainty principle was applied to evaluate the upper limit values of the rate constants for the relaxation processes of the excited states from the widths of the vibronic peaks. The energy barriers between reactants and photoproducts were estimated by using an Arrhenius-type relationship. The low barriers that were found (∼2 kJ mol−1) satisfactorily explain the competition between the reaction path and the energy degradation processes.