Resonant Raman spectroscopy of organic semiconductors

Epitaxial films of a prototype organic semiconductor, 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) are investigated with resonant Raman spectroscopy and density functional calculations. It is shown that the resonant Raman spectra are mainly determined by the vibrational properties of an isolated molecule, and the pronounced subbands in the absorption spectra of dissolved PTCDA molecules can be related to elongations of the Raman-active breathing modes between the ground state and the relaxed excited state.