Mechanisms of chromophore reorientation probed with in-situ, pressure second harmonic generation

Research to determine the mechanisms which tie chromophore reorientation to polymer relaxation is crucial to the development of thermally stable NLO polymers.1 Most of the work to date has been performed above or near the glass transition temperature where the decay of the NLO properties of the material is tied to the glass transition and the α-motion of the polymer backbone. Devices which rely upon permanently poled polymer films for their NLO characteristics are not designed to operate near or above the glass transition because their nonlinear properties would quickly dissipate. A study of the coupling between polymer motion and chromophore reorientation below the glass transition temperature is necessary to gain insight into the reorientional dynamics of the chromophores at common device temperatures. Using the results of elevated temperature studies to predict the behavior of the NLO properties below T g may not be accurate if the mechanisms responsible for chromophore reorientation are not the same in both regimes.