Third‐harmonic generation from regio‐regular and regio‐irregular poly(3‐dodecylthiophenes). Dependence of χ(3) on conjugation length

The third‐order nonlinear optical susceptibility of regio‐regular poly(3‐dodecylthiophenes) is observed to be enhanced by a factor of 10 as compared to that of regio‐irregular poly(3‐dodecylthiophenes) when pumped at 1907 nm. The increase in the effective conjugation length from regio‐irregular to regio‐regular poly(3‐dodecylthiophene) is estimated from linear absorption data and the reported absolute value measured at 1907 nm represents the nonlinear susceptibility of the most highly conjugated regio‐regular polythiophene film measured to date.