Big Third-order Nonlinear Optical Properties of Two Poly(3-alkylthiophene-2, 5-diyl)-(benzylidenequinomethane-2, 5-diyl) Derivatives

摘要

Two novel poly[（3-alkylthiophene-2,5-diyl）- （benzylidenequinomethane-2,5-diyl）s] derivatives, poly[（3-butylthiophene-2,5-diyl）-（p-N,N-dimethylamino）benzylidenequinomethane-2,5-diyl)]（PBTDMABQ） and poly[（3-octylthiophene2,5-diyl） -（p-N,N-dimethylamino）benzylidenequinomethane-2,5-diyl)]（POTDMABQ）, were synthesized. The band gaps of the two polymers are calculated as 1.75eV for PBTDMABQ and 1.69eV for POTDMABQ, respectively. The homogenous films of the two polymers were prepared and their third-order nonlinear optical properties were studied by the backward degenerate four-wave mixing at 532nm. By using the relative measurement technique, the third-order nonlinear optical susceptibilities of PBTDMABQ and POTDMABQ are calculated as 5.62×10-9 and 1.22×10-8ESU, respectively. It is found that substituted alky groups have strong effects on the band gap and nonlinear optical properties of the two polymers. The relatively big third-order nonlinear optical susceptibilities and small band gap of POTDMABQ resulted mainly from the longer alkyl with strong electron-donating ability can enhance the delocation degree of conjugated π electronics.