Distribution of the effective conjugation length of polythiophene determined by its absorption and vertical bar chi((3))vertical bar spectra

We measured the absorption and \chi((3))\ spectra around the excitonic reso nance for Langmuir-Blodgett (LB) film of polythiophene derivative, poly(3-[ 2((S)-2-methylbutoxy)ethyl]thiophene) at 10 K and room temperature. We deri ved a theoretical distribution function for the effective conjugation lengt h taking the molecular weight distribution into consideration, and fitted t he calculated absorption and \chi((3))\ spectra to the experimental ones. F rom the fits, we estimated the average effective conjugation length to be 2 1 thiophene rings at 10 K, and 15 thiophene rings at room temperature.