Mechanochromic Luminescent Tetrathiazolylthiophenes: Evaluating the Role of Intermolecular Interactions through Pressure and Temperature-Dependent Raman Spectroscopy

The Raman spectrum of the mechanochromic luminescent tetrathiazolylthiophene has been investigated as a function of pressure and temperature. This study verifies the sensitivity of the Raman spectroscopy as a technique to characterize and understand the structural effects causing any mechanochromic changes. Continuous and evident Raman shifts and changes in intensities of the strongest lines in the spectra occur while increasing pressure or lowering temperature. These spectral changes are related to the modulation of intermolecular C-H···N hydrogen bonding previously identified for this system. The Raman bands involved are assigned to collective normal modes associated to the CC bond stretching of the rings and reveal that the modulation of local hydrogen bonding interaction has indeed an effect that has an impact on the whole conjugated structure of the molecule. Pressure-dependent Raman spectra have been also computed by means of periodic density functional theory calculations of the crystal, giving an accurate prediction of the experimental trends.