Comparison of third-order nonlinear optical properties of benzothiazolium salt and neutral benzothiazole derivative: Broadband absorption response and transient dynamic analysis.

Two benzothiazole derivatives, neutral benzothiazole derivative and the corresponding benzothiazolium salt, were designed and synthesized. Broadband reverse saturable absorption (RSA) were observed for both compounds in different solvents under femtosecond Z-scan, and the range of RSA of benzothiazolium salt showed larger redshift compared with that of the neutral benzothiazole. However the variations of absorption properties of these samples in femtosecond and picosecond time regimes were different. The transient absorption spectrum reveal the conversion process from the initial local excited (LE) state to the charge transfer (CT) state and the nonlinear optical response of two compounds in different time regimes were analysed. • The benzothiazole derivatives containing pyrene have large nonlinear responses. • Substitution of benzothiazole by benzothiazolium results in large redshift in linear absorption and two-photon absorption. • Conversion from the local excited state to the charge transfer state was present in both samples. • The benzothiazolium is more affected by different time regimes and solvents than the neutral benzothiazole. [ABSTRACT FROM AUTHOR]