Optical transitions in oligoihiophenes: a semi-empirical study

Contrary to recent literature reports high level multi-reference determinant configuration interaction techniques do not accurately reproduce the s0-s1 transition energies in oligothiophenes. For a series of oligomers containing between 2 and 11 rings, accurate energies (within 0.1 eV of experiment) can be obtained using ZINDO/S coupled with configuration interaction involving only single excitations (SCI). Calculations are carried out on the basis of geometries optimised using MNDO, AM1 or PM3 semi-empirical methods.