Electronic excitation of sulfur-organic compounds - performance of time-dependent density functional theory

To define the scope and limitations of the time-dependent density functiona l theory (TDDFT) method, spectral absorption data of a series of about 100 neutral or charged sulfur-organic compounds with up to 24 non-hydrogen atom s and up to four sulfur atoms were calculated in the near-UV, visible and I R regions. although the theoretical vertical transition energies correspond only approximately to experimental absorption band maxima, the mean absolu te deviation was calculated to be 0.21 eV (1600 cm(-1)). The main absorptio n features of various compounds with monocoordinated or dicoordinated sulfu r atoms are well reproduced. As far as possible TDDFT results were compared with those of semiempirical Zerner's intermediate neglect of differential overlap (ZINDO/S) and of Pariser-Parr-Pople (PPP) calculations. TDDFT also works well in cases where the semiempirical methods fail. Limitations of TD DFT were encountered with calculations of spectral absorptions of dye molec ules. The "vinylene shift" of polymethine dyes is not reproduced by TDDFT. Whereas electronic excitation energies delocalized polar and betainic chrom ophores are reasonably well reproduced, excitation energies of charge-trans fer-type and charge-resonance-type transitions of weakly interacting compos ite chromophores are significantly underestimated.