Ultrafast Broad-Band Optical Limiting in Simple Hydrazone Derivatives with a Π-Conjugated System: Effect of Two-Photon-Induced Singlet-State Absorption

Abstract

Two simple hydrazone derivatives (A1 and A2) linked with different Π-conjugated systems are designed and synthesized to reach ultrafast broad-band optical limiting (OL) under different pulse widths. To exploit various virtues of two-photon absorption (TPA)-induced excited-state absorption (TPA–ESA), ESA is successfully established on a singlet state. Both compounds show a broad-band ESA range from 556 to 750 nm and a relatively long ESA lifetime. A1 displays a larger broad-band reverse saturable absorption than A2 in the multiwavelength Z-scan experiments. Furthermore, superior OL performance in A1 is shown from 515 to 800 nm under both femtoseconds and picoseconds. The thresholds (2.07 × 10–3 J/cm2 at 532 nm under 190 fs) are lower than those of most of the OL materials reported previously. Our results indicate that singlet-based TPA–ESA is a feasible method to achieve OL with high linear transmittance and broad-band and ultrafast response. Simple molecules with proper design display superior OL performance, which offers us a practical way to achieve ultrafast broad-band OL in low-cost organic materials.