Enhancement of Third-Order Optical Nonlinearity of Poly(aryleneethynylene)s by Introducing an Intramolecular Charge Transfer Interaction into Their π-Conjugation

Poly(aryleneethynylene) type π-conjugated polymers (PAEs) are synthesized and the third-order optical susceptibility χ(3) 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 π-electron excessive heteroaromatic rings are introduced into the π-conjugation. The χ(3) 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 π-electron delocalization caused by the CT interaction is found to be the main factor enhancing χ(3). This introduction of a CT interaction into a π-conjugation is an effective concept for the design of large χ(3) materials.