Modulating Photochemical Properties to Enhance the Stability of Electronically Dimmable Eye Protection Devices.

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole-based stabilizers were evaluated for stabilizing the liquid crystals.

Quantification of photoinduced order increase in liquid crystals with naphthopyran guests.

Photoinduced order-increasing phase transitions can occur in dye-liquid crystal mixtures when the photoproduct of the excitation of the dye molecules is more compatible with the liquid crystalline medium than the initial dye species. A detailed investigation of the photoinduced changes of the phase behavior and optical properties of mixtures of liquid crystals with naphthopyran guests upon exposure to light at 365 nm is presented here. In these guest-host systems, the nematic-to-isotropic phase transition temperature is increased upon irradiation.

Light-induced liquid crystallinity.

Liquid crystals are traditionally classified as thermotropic, lyotropic or polymeric, based on the stimulus that governs the organization and order of the molecular system. The most widely known and applied class of liquid crystals are a subset of thermotropic liquid crystals known as calamitic, in which adding heat can result in phase transitions from or into the nematic, cholesteric and smectic mesophases. Photoresponsive liquid-crystal materials and mixtures can undergo isothermal phase transitions if light affects the order parameter of the system within a mesophase sufficiently.

Electronic interactions in a branched chromophore investigated by nonlinear optical and time-resolved spectroscopy.

The third order nonlinear optical properties of a trimer branched chromophore system and its linear molecule analog are investigated. Two-photon absorption and degenerate four wave mixing measurements were carried out on both systems. An enhancement in the nonlinear optical effect is observed for the branched trimer molecule in comparison to the linear chromophore system.

Coherent effects in energy transport in model dendritic structures investigated by ultrafast fluorescence anisotropy spectroscopy.

Measurements of ultrafast fluorescence anisotropy decay in model branched dendritic molecules of different symmetry are reported. These molecules contain the fundamental branching center units of larger dendrimer macromolecules with either three (C(3))- or four (T(d), tetrahedral)-fold symmetry. The anisotropy for a tetrahedral system is found to decay on a subpicosecond time scale (880 fs).