New insight into the optical properties of thin organic films by epitaxial preparation

On the basis of the example of quaterthiophene (4T) on a Ag(111) surface, we demonstrate that epitaxial thin films can be prepared on a single crystalline substrate under suitable conditions. Optical spectra of such 4T films exhibit a highly resolved fine structure similar to that of isolated molecules. The detailed spectroscopic information thus obtained yields new insight into questions such as vibronic coupling, Stokes shift, (Davydov) line splitting and other crystalline effects.