Inhomogeneous and single molecule line broadening of terrylene in a series of crystalline n-alkanes

We present a study of single molecule linewidth broadening of terrylene in dodecane, tetradecane, and hexadecane matrices. The Shpolskii bulk absorption spectra exhibit increase of the bandwidths and site complexity with increasing n-alkane chain length. Single molecule lines are broadened above the lifetime limit even at 1.6 K in all three solvents. The linewidth distributions suggest the existence of relaxing two-level systems coupled to the molecular transitions. Spectral diffusion was observed in the forms of spontaneous and photoinduced frequency jumps. Temperature dependencies of the single molecule linewidths show a wide range of power-law dependencies below 3 K and, in some cases, exponentially activated behavior above 3 K. Possible origins of the line broadening are discussed.