Changes in the electronic structures of tetrakis(alkylthio)tetrathiafulvalenes (TTCn-TTFs) during the solid–melt transition

Abstract

The u.v. photoelectron spectra of tetrakis(alkylthio)tetrathiafulvalenes (TTC_n-TTFs) in the solid and the molten states have been measured for n= 2 and 10, where n is the number of carbon atoms in each chain. The ionisation threshold and spectral features of TTC₁₀-TTF are different in the solid and molten states, while no change is observed for TTC₂-TTF. This result proves that the low-ionisation threshold of TTC₁₀-TTF in the solid state is caused by the much closer packing of TTF moieties than that of TTC₂-TTF. The absorption spectra of these compounds have also been measured in the solid, molten and solution states. Comparison of the observed spectra reveals that the electronic structure of TTC₂-TTF in the solid state is dominated by that of an isolated molecule, while that of TTC₁₀-TTF in the solid state is strongly affected by the intermolecular interactions. The relationship between these findings on the electronic structures and the reported electric conductivities is also discussed.