EFFECTS OF SUBPHASE ADDITIONS ON OPTICAL NONLINEARITY OF HEMICYANINE DERIVATIVE LANGMUIR-BLODGETT MONOLAYERS

UV-visible absorption spectroscopy and second-harmonic generation were used to examine the effects of potassium iodide (KI) in the subphase on the optical and structural properties of pure and mixed hemicyanine derivative (DAEP) monolayers. It was found that with increasing KI co ncentration in the subphase, an enhancement of the effective molecular hyperpolarizability beta was always associated with a red shift of th e absorption peak in both pure and mixed DAEP monolayers. Three mechan isms (''spacer'' effect, charge distribution change and structural imp rovement) were responsible for the observed beta enhancement. The firs t two contributions were comparable and explained by a 2 omega resonan ce effect.