Ultrafast Broad-band Optical Limiting And Photophysical Mechanism Of Hydrazone Derivatives

This paper is contributed on the investigation of optical limiting(OL)materials,two simple hydrazone derivatives A1((E)-2-(2-(pyren-1-ylmethylene)hydrazinyl)benzo[d]thiazole)and A2((E)-2-(2-(2,4-dimethoxybenzylidene)hydrazinyl)benzo[d]thiazole)are designed and synthesized based on the photophysical mechanism of singlet-based two-photon absorption(TPA)induced excited state absorption(TPA-ESA)to achieve ultrafast broad-band optical limiting materials which can satisfy different laser pulse width.The nonlinear optical(NLO)property of the molecule is modulated by linking with different ?-conjugated systems in the peripheral substituent.The character of ESA and the magnitude of NLO response of A1 and A2 were respectively studied by the transient absorption spectra and Z-scan experiment.It finds that molecule A1 with larger ?-conjugated structure shows superior NLO property.The photophysical mechanism is confirmed to be singlet-based TPA-ESA in the degenerate pump-probe measurement.A simple three-energy-level model and the corresponding rate equation are established to explain the dynamics.Meantime,with the help of the frontier molecular orbital analysis,the correlation of molecular structure and property is revealed:the NLO property of these asymmetric organic molecules will be promoted by enhancing the intramolecular charge transfer,as well as,expanding the molecular ?-conjugationIn the OL experiments,A1 displays remarkable ultrafast OL from 515 nm to 800 nm under femtoseconds,picoseconds and nanoseconds.The thresholds(2.07×10-3 J/cm2,under 190 fs at 532 nm)are lower than those of most of the optical limiting materials reported previously.Our results indicate that singlet-based TPA-ESA is a feasible method to achieve excellent optical limiting materials with high linear transmittance and broad-band and ultrafast response.Simple molecules with proper design will display superior optical limiting performance,which offers us a practical way to achieve excellent optical limiting materials.