The tunable third-order optical nonlinearities of a diarylethene-zinc phthalocyanine hybrid

The diarylethene-zinc phthalocyanine hybrid T-ZnPc showed both solvent-dependent and photo-controllable J-aggregation behavior, thus afforded multiple possibilities for tuning the third-order nonlinearities of T-ZnPc by external stimuli. The cubic hyperpolarizability (γ) values of T-ZnPc were found to increase in J-aggregates, which was further enhanced by UV-irradiation. The γ value of molecularly dispersed T-ZnPc in 20:1 chloroform-ethyl acetate mixture was measured as 1.2 × 10^-3°esu. Under the illumination of UV light, this value increased to 2.8 × 10^-3°esu due to formation of strong J-aggregates, suggesting a 2.3-fold enhancement. Besides, it was found that both the nonlinear absorption and the nonlinear refraction contributed significantly to the large γ values of T-ZnPc, while for most of our previous studied Pcs, the nonlinear refraction always plays a predominant role. This observation further demonstrated that the incorporation of thiophene rings into Pcs could significantly increase their multi-photon absorption cross-sections.