Study on third-order two-photon fluorescence property of DAST

Abstract

With the extended π-electronic delocalization, organic 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) exhibits excellent third-order saturation absorption and optical limiting properties, but rare results about its third-order nonlinear emission have been previously reported. In this work, a flexible DAST−polyvinyl alcohol composite film was prepared, and its nonlinear emission properties were systematically characterized. Results reveal that besides a distinct second harmonic generation signal originating from the non-centrosymmetric macroscopic packing of the DAST chromophores, a strong third-order two-photon excited fluorescence signal was also measured from the composite, as experimentally confirmed by a quadratic dependence of the emission intensity on the pumped intensity. These nonlinear emission behaviors reveal that ionic organic DAST molecules hold great potential applications in laser frequency conversion and optical imaging.