Specific features of UV-vis absorption spectra of cis- and trans-polythiophenes.

UV-vis optical spectra of several polythiophene with number of dimers n=1, 5, 10, 15 for cis- and trans-forms were investigated. The study was done theoretically using semi-empirical AM1 (Austin Model 1) and PM3 (Parametric Method 3) methods with the appropriate molecular geometry optimization. The experimental UV-vis absorption spectra were used for verification of the both semi-empirical theoretical models. With the increasing number of dimers a red shift of the absorption edge was observed. Solvent does not play a crucial role on behavior of the absorption spectrum. A comparison of the both semi-empirical methods with the observed experimental absorption spectra is performed. Role of state dipole moments of the investigated polythiophenes in the behavior of the observed UV-vis spectra is discussed. Particular role of pi-conjugated bonds is demonstrated.