On the complexity of the 1,3-dithiole-2-thione chromophore. UV-Vis polarization spectroscopy and theoretical calculations

The electronic transitions of 1,3-dithiole-2-thione (DTT) are investigated by Linear Dichroism (LD) spectroscopy in the near-UV and visible regions and by quantum chemical calculations. The LD experiments are performed in the spectral region 46,000-20,000 cm-1 (217 - 500 nm) using stretched polyethylene (PE) as an anisotropic solvent. The observed spectral features are compared with electronic transitions calculated by Time-Dependent Density Functional Theory (TD-DFT) considering different functionals and a variety of basis sets. The DTT chromophore is complex and a full elucidation may require the application of more advanced theoretical models with consideration of multiply excited electronic configurations and evaluation of multi-state vibronic couplings.