The geometry of tetrathiotetracene as a donor in charge transfer complexes: an ab initio theoretical investigation

Ab initio STO-3G calculations are performed on both tetracene (T) and tetrathiotetracene (TTT), and their respective radical-cations. Mulliken populations indices and nodal structure of the HOMO explain the geometry changes of these compounds upon ionization. The strong relaxation energy calculated for tetrathiotetracene, and its low first ionization potential, are related to the grafting of the two disulfide bridges and largely justify the peculiar behavior of TTT upon charge transfer