Femtosecond charge transfer in assemblies of discotic liquid crystals

The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material.