Surface light-induced changes in thin polymer films

Abstract

With the sensitivity of photothermal deflection spectroscopy (PDS), it is possible to detect features that cannot be observed by other means, such as singlet-triplet transitions, weak charge-transfer bands, and weak photo-chemical changes at the surface. The films studied were those commonly used as charge transport materials in organic photoconductors, and are comprised of a small organic molecule and a polymer binder. The PDS spectra indicate the formation of charge transfer complexes between the two components in the solid state. The strength depends on the various combinations and can be correlated to relative energy level offsets between the IIOMO of the small molecule and the LUMO of the polymer binder. Reversible photochemistry resulting from UV exposure can also be detected at the surface.