Tentative mechanism for the bistability observed during irradiation of the triphenylimidazolyl radical dimer in a CSTR

Article abstract of DOI:10.1021/ja00167a002

We previously reported on the observation of a bistability when a chloroform solution of the triphenylimidazolyl radical dimer (TPID) is irradiated in a CSTR (continuous now stirred tank reactor) (J. Phys. Chem. 1988, 92, 16). In the present paper, the photochemistry of TPID in chloroform is examined in more detail and key reactions are summarized in a 6-step mechanism. Values of relevant kinetic parameters are determined and used in numerical simulations of the TPID/CHCl₃ photochemistry in a CSTR. Multiple steady states are indeed observed when experimental values of the kinetic parameters arc used in the simulations. The bistability width and transition points are in good agreement with experimental results. It is suggested that the feedback mechanism responsible for the instability is of photometric origin. One of its key components is the screen effect that arises as the result of competitive absorption in multicomponent photochemical systems.