Saturation effects in the nonlinear optical response of regioregular, highly conjugated poly(3-alkyl-thiophene) thin films

Abstract Third harmonic generation measurements on highly conjugated regioregular poly(3-dodecylthiophene) thin films using a fundamental wavelength of 1907 nm give an absolute value of χ (3) (-3ω;ω,ω,ω) = 4×10 −11 esu. This value is the nonlinear susceptibility of the most highly conjugated polythiophene film reported to date (λ max = 555 nm). Comparison to less conjugated samples reveals a saturation in the dependence of χ (3) the effective conjugation length.