Optical nonlinearities and transient dynamics of 2-(2′-hydroxyphenyl)benzoxazole studied by single-beam and time-resolved two-color Z-scan techniques

Optical nonlinearities (including nonlinear absorption and nonlinear refraction) and the temporal properties of the nonlinear refraction of 2-($2^{\prime }$-hydroxyphenyl)benzoxazole (HBO) based on excited-state intramolecular proton transfer in its two-photon absorption (TPA) range have been investigated, for the first time to our knowledge, by single-beam and time-resolved two-color Z-scan techniques. By establishing the kinetic model of HBO that is due to the TPA, we obtained the TPA coefficient, the molecular hyperpolarizability of the ground state of the enol tautomer of HBO, and the nonlinear refraction, represented by ${\sigma }_r,$ of the excited state of the keto tautomer of HBO. The theoretical results are in good agreement with the experimental ones, which shows that, on the one hand, the excited-state intramolecular proton transfer of HBO can be achieved through the excitation in its TPA range and that, on the other hand, the optical nonlinearities of HBO are closely related to the dynamics of HBO that are involved in the excited-state intramolecular proton transfer.