Pseudolocal phonons in p-terphenyl: pentacene single crystals

The structural nature of the phonon sidebands in the fluorescence and excitation spectra of pentacene guests in p-terphenyl crystals at 4.2 K are investigated using site-selective spectroscopy. The distinct features in the phonon sideband structure were observed to depend significantly on the guest site configuration of pentacene occupying four inequivalent sites in the triclinic p-terphenyl lattice. The sharp peaks dominating the phonon sideband structure are assumed to arise from the pseudolocal phonons. The eigenvalues and eigenvectors of the pseudolocal phonons are calculated carrying out a modified normal mode analysis on the distinct pentacene site configurations including the contribution of all intermolecular atom-pair interactions.