All-Organic Composite Films for High Flexibility and Giant Nonlinear Optical Limiting Responses.

Given the substantial π-electron delocalization observed in 4--dimethylamino-4--methyl-stilbazolium tosylate (DAST), a high third-order nonlinear optical response can be expected that might manifest itself in various ways for potential applications. To probe the possibility and assess its potential, all-organic DAST-polymethyl methacrylate (PMMA) composite films were prepared by a simple solution casting method, and their nonlinear absorption performances were measured by an open-aperture Z-scan system. The results reveal that under irradiation by a 380 fs laser pulse at 520 nm or a 6 ns laser pulse at 532 nm, the DAST-PMMA composite films with a DAST concentration of 0.125 wt % exhibit similar giant optical limiting (OL) responses with OL threshold of 7.84 or 0.37 GW cm, both superior to those of most organic and inorganic OL materials measured under similar conditions. These all-organic composite films show high flexibility, and interestingly, their OL responses can remain stable even after exposure to air for 3 months. The superior OL behaviors of such materials in the femtosecond and nanosecond regimes are attributed to the two-photon absorption and the combination of two-photon absorption and excited-state absorption, respectively. The simple preparation, high flexibility, giant OL responses, and excellent environmental stability suggest that such novel all-organic composite films hold great potential for applications in flexible OL devices.