Third-order optical nonlinearities in a regioregular head-to-tail poly(3-(4-dodecylphenyl)thiophene)

Optical properties of conjugated polymers have been studied extensively and they have been recognized as important nonlinear optical materials because of their high potentials, such as large nonresonant third-order optical susceptibility, χ⁽³⁾, and femtosecond response time derived from π-electron delocalization. The effective conjugation length of the polymer is an important factor for expanding optical nonlinearities. Recently, contrasting nonlinear optical properties between regioregular and irregular poly(3-dodecylthiophene) thin films with different effective conjugation lengths was reported. In the paper, we present the nonresonant third-order optical nonlinearities in a regioregular (Head to Tail) and irregular poly(3-(4-dodecylphenyl)-thiophene) thin films. A large χ⁽³⁾ and an ultrafast response were obtained from experimental results of the transient four-wave mixing (FWM) and the z-scan method. The χ ⁽³⁾ value of the regioregular polymer was about 1.5 times larger than the irregular one