Stability of NLO chromophores in doped polymer films during electric field poling

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Abstract
Thin films of organic polymers doped with specific chromophores may be used to exhibit substantial and useful second-order nonlinear optical phenomena. Such films must be subjected to DC electric field poling to eliminate the inherent inversion symmetry. In principle such poling processes may be monitored using UV absorption spectroscopy, but there are many factors which lead to ambiguity in any interpretation. In particular the authors show that the electric field poling can result in ionic-current-induced chemical transformation of the NLO chromophore to a NLO inactive moiety. They consider the stability of azo-based chromophores which are a common class of NLO chromophores. This electric field induced modification could lead to serious overestimation of any poling effects using UV spectroscopy and places limitations on potential technological applications. Such degradation does not occur in materials prepared from polymers which contain chemically linked chromophores.