CEO/semiempirical calculations of UV–visible spectra in conjugated molecules

The collective electronic oscillators (CEO) approach based on the TDHF approximation is combined with INDO/S, MNDO, AM1, and PM3 semiempirical Hamiltonians. This technique is applied to compute and analyze the electronic structure of acceptor-substituted oligomers and conjugated polymers. Calculated excited-state energies and oscillator strengths agree well with the experimental data and with each other. In particular, the results using the Hamiltonians parameterized for ground-state calculations such as AM1 and PM3 agree well with the INDO/S results. In addition, a two-dimensional analysis of the corresponding transition density matrices provides an efficient way for tracing the origin of various optical transitions by identifying the underlying changes in charge densities and bond-orders.