Study On Second Harmonic Generation Of Organic Crystals And Its Enhancement Resonant To Fluorescence

In this thesis,the second harmonic generation(SHG)of organic crystals based on the central skeletons such as fluorenone and thiophene and the enhanced SHG in resonance to two-photon fluorescence(TPF)are studied.The phenylethynyl functionalized fluorenone-derived small organic molecule was designed and synthesized.The controllable self-assembly of the fluorenone-derived molecule with polymorphic crystal structures and different microstructures was studied.The linear and nonlinear optical properties of these self-assembled micro-sized organic crystals were investigated.In particular,the second-order nonlinear optics,SHG response,of the fluorenone and thiophene-based derivatives were investigated.Distinct and efficient SHG and TPF behaviors were obtained on these organic crystals.Importantly,the SHG observed in these self-assembled microstructures exhibited significant resonant enhancement in the visible spectral region.By comparing SHG intensity with pump wavelengths and fluorescence emission spectra,we find that this peculiar enhancement should be attributed to the resonance of SHG and TPF emission,which is much stronger than the resonance of SHG with absorption band that has been demonstrated before.This study clarifies the NLO response of organic crystals and its relationship with crystal structure.The nonlinear optical phenomenon of enhanced SHG in resonance to TPF is observed.These observations and findings are theoretically beneficial to modulating the NLO response of organic crystals and realizing efficient applications in optoelectronic devices of organic crystals.