(4ba) Molecular Mobility in Non-Linear Optical Glassy Chromophores

Organic second-order nonlinear optical (NLO) materials are being actively pursued for applications in photonic devices such as high-speed electro-optic (EO) modulators, optical switches, and frequency converters. For practical applications, NLO materials must have both high macroscopic EO activity and thermal stability within the operating temperature range. High macroscopic EO activity can be achieved by acentrically ordering a system containing a high density of high dipole chromophores via electric field poling at elevated temperatures. Thermal stability requires the system to have internal constraints to prevent collapse of the acentric order at operating temperatures. Recent efforts for achieving both requirements have focused on dendrons capable of self-assembly through various 'soft' non-covalent interactions within self-assembling molecular glassy chromophores (SAMGCs). An example of these 'soft' interactions are arene-perfluoroarene (e.g. phenyl-pentafluorophenyl) quadrupolar interactions, which provide excellent EO activity and good thermal stability. In this study, experimental (novel scanning probe microscopy techniques) and theoretical techniques (molecular dynamics simulation) were used to determine the energetics of the underlying molecular mobility within SAMGCs incorporating phenyl-, naphthyl- or anthryl-pentafluorophenyl interactions. Further, the energetics of these mobilities are tied to their thermal relaxation behavior. Insights gained are being used to guide synthesis of next-generation organic NLO materials.