The terahertz spectra of all the formulations showed an increase in absorption with frequency and temperature (see ESI), and no discrete spectral features were present over the entire investigated range, in line with previous measurements of amorphous molecular solids . We chose the frequency of 1 THz to further investigate the relationship between the increase of absorption coefficient and temperature, as the signal-to-noise ratio of the measurement at 1 THz is high and we previously have shown that the frequency is suitable to follow the dynamics of the system .