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