ENHANCEMENT OF 3RD-ORDER OPTICAL NONLINEARITY OF POLY(ARYLENEETHYNYLENE)S BY INTRODUCING AN INTRAMOLECULAR CHARGE-TRANSFER INTERACTION INTO THEIR PI-CONJUGATION

Poly(aryleneethynylene) type pi-conjugated polymers (PAEs) are synthesized and the third-order optical susceptibility ((3)(chi)) of their thin films is evaluated. There is a red-shift in the electronic absorption of the PAE caused by an intramolecular charge transfer (CT) interaction when pi-electron excessive heteroaromatic rings are introduced into the pi-conjugation. The ((3)(chi)) value of the PAEs is enhanced by increasing the CT interaction and reaches more than 10(-11) esu in the near resonant region. The increase in the pi-electron delocalization caused by the CT interaction is found to be the main factor enhancing ((3)(chi)). This introduction of a CT interaction into a pi-conjugation is an effective concept for the design of large ((3)(chi)) materials.