Single-molecule confocal microscopy studies of electric-field induced orientation in chromophore-polymer composite materials

摘要

Chromophore-polymer composite materials for electro-optical applications are rendered active at the χ~((2)) level of susceptibility by inducing chromophore alignment through the interaction of the chromophore dipole moment with an external electric field, a process referred to as "poling". To provide insight into the molecular details of the poling process, single molecule microscopy studies of DCM (4-(dicyanomethylene)-2-memyl-6-(4-dimethylaminostyryl)-4H-pyran) and RhB (Rhodamine B) in pory(methyl acrylate) (PMA) above T_g of the polymer host are performed. Electric fields of SO V/μm are employed consistent with typical experimental conditions. The effect of environment is studied through comparative studies or RhB reorientation in oxidative and inert atmospheres. Single-molecule rotational dynamics are monitored through the time-evolution of the fluorescence anisotropy. Anisotropy correlation functions demonstrate non-exponential decay consistent with previous studies of molecular rotation dynamics in polymer melts. The rotational dynamics of DCM are found to be weakly perturbed in me presence of a 50 V/μm electric field consistent with the modest alignment potential created by the electric field relative to the amount of available thermal energy. The relevance of these findings to current models of the poling process is discussed.