Tetrathiafulvalene-based materials for organic field effect transistors. Inspection of their semiconductor properties by means of molecular spectroscopy and quantum chemistry

The absorption and emission electronic and vibrational Raman spectra of a series of tetrathiafulvalene compounds have been recorded, assigned with the guide of density functional theory calculations, and interpreted according to their chemical nature of the introduced modifications of the tetrathiafulvalene unit. It turns out that the highest occupied molecular orbital energy can be stabilized while the lowest unoccupied molecular orbital energy is much less affected by substitution of TTF. Importantly, the substitution of tetrathiafulvalene leads to organic materials more resistant to oxidation and operational degradation. The vibrational Raman spectra have been also compared with that of the tetrathiafulvalene unit mainly focusing on the molecular structures. A vibrational splitting in the main lines of the spectra of these derivatives has been recognized and interpreted. The most prominent Raman lines of the spectra combined with the geometrical neutral -> cation evolution have been related with the vibrational reorganization energy. These vibrational reorganization energies have been calculated and the trend identified with the behavior of the main Raman lines of the solid-state spectra. Relationships between the strongest Raman lines, the modes with the highest Frank-Condon activities and the vibrational modes with the main contributions to the inner-sphere reorganization energy (i.e., molecular mechanism for relaxing or dissipating energy excess or excitations) have been established. The realization of the connection among these magnitudes supposes a novelty in the field.