Third-order nonlinear optical spectroscopy in charge-transfer type conjugated polymers

摘要

We have investigated the linear and third-order nonlinear optical properties in a charge-transfer (CT) type conjugated copolymer, PThQx, which is composed of an electron-donating molecule, thiophene (Th), and electron-accepting one, quinoxaline (Qx), by using the linear absorption, two-photon absorption (TPA), and third-harmonic generation (THG) spectroscopies. In comparison with a homopolymer, polythiophene, the absorption coefficient alpha of PThQx is significantly reduced, while its third-order nonlinear susceptibility (chi((3))) is unchanged. This indicates that the figure of merit for the nonlinear optical materials, defined as chi((3))alpha, is enhanced in PThQx. This enhancement comes from the CT character of the excited states in PThQx, in which a hole and an electron are created on different molecules.