OPTICAL ABSORBENCY OF ORIENTED THIN-FILMS

We report that the optical absorbance of oriented thin films of para-h exaphenyl (PHP), produced by vacuum deposition, shows strong anisotrop y effects. An explanation for the orientation dependence of optical ab sorption of PHP is proposed, using first principles dielectric tensor calculations. The lack of the pi-pi absorption band in the normal UV- Vis absorption spectrum is consistent with theoretical predictions for an orthorhombic thin PHP film with oligomer chains oriented near norm al to the substrate surface.