Study On Optical Nonlinearity Of Pyrene Derivatives

Pyrene is considered a building block for the construction of ?-conjugated derivatives,the ?-conjugated system has significant modulation effects on the optical nonlinearity of the materials,pyrene derivatives possesses an abundance of ? electrons,endowing it with high optical transmittance characteristics in the visible region.In addition,pyrene derivatives with appropriate design have been extensively utilized in many fields as biological probes,laser dyes,organic light-emitting diodes and optical limiting,thus being favored by researchers.In this paper,the nonlinear optical properties and ultrafast dynamics of two novel conjugated pyrene derivatives(C1 and C2)with D-?-A structure were investigated.The nonlinear absorption properties of two pyrene derivatives under femtosecond(515-700 nm),picosecond(532 nm)and nanosecond(532 nm)time regions were systematically investigated by Z-scan measurements.It was found that the C1 and C2 realized reverse saturable absorption(RSA)under different pulse widths excitation resulting from twophoton absorption and excited-state absorption(ESA).In addition,both compounds realized broadband RSA under femtosecond excitation.Quantum chemical calculations indicated that two mechanisms for the HOMO-LUMO excitation of the two molecules exist simultaneously: intramolecular charge transfer(which is considered to trigger the nonlinear optical response)and ?-?* transition.It was found that the ?-?* transition localized in the pyrene group can contribute to the increase in the nonlinear absorption of pyrene derivatives.In addition,the ultrafast dynamics processes of C1 and C2 were studied by femtosecond transient absorption spectra,which showed that the ESA of C1 and C2 does not originate in the same excited state.Through numerical fitting of the dynamics curves,we determined the decay parameters of the four processes and provided the dynamics information about the locally excited singlet state and the charge-transfer state.C1 and C2 showed ultrafast broadband RSA and can respond to multiple excitation pulses(fs,ps and ns),suggests these pyrene derivatives as important candidates for optoelectronic and optical limiting applications.This study analyzes the ultrafast dynamics processes of the both derivatives and reveals the influence of ?-?* transition on nonlinear optical properties of these derivatives,provides theoretical support for design high performance conjugated molecules and research the photophysical processes of organic materials in the future.