Optical transitions in oligothiophenes : a semi-empirical study

Contrary to recent literature reports high level multi-reference determinan t configuration interaction techniques do not accurately reproduce the S-0- S-1 transition energies in oligothiophenes. For a series of oligomers conta ining between 2 and 11 rings, accurate energies (within 0.1 eV of experimen t) can be obtained using ZINDO/S coupled with configuration interaction inv olving only single excitations (SCI). Calculations are carried out on the b asis of geometries optimised using MNDO, AM1 or PM3 semi-empirical methods.