Using the sensitive absorption technique of Photothermal Deflection Spectroscopy (PI1S) it is possible to detect subtle spectral features in the absorption spectra of polymeric thin films that cannot be detected by other means. This paper describes observations of weak charge-transfer complex (CIC) formation and also light-induced changes in various organic films. The filns studied were those commonly used as charge transport materials in organic photoconductors, comprised of a small transport molecule and a polymer binder. The optically measured CTC bands can be used to establish single electron energy levels of the constituents. Reproducible photo-induced changes are manifest both in the strong UV transitions as well as in the “sub-gap” absorption and appear to be correlated with the photo-chemical stability of the constituents. The light-fatigue has both a reversible as well as irreversible component.