Anthony Roberts

ORIENTATION AND SOLVATOCHROMISM OF DYES IN LIQUID CRYSTALS

The orientation and solvatochromism of some dye molecules in a liquid crystal have been investigated. Interactions with the host and the structure of the dye molecule affect the macroscopic alignment of dichroic dye molecules in a liquid crystal. It was observed that some dye molecules show a large bathochromic shift of their absorption maxima in the liquid crystal host relative to the situation in isotropic solvents. It is suggested that this is due to the occurrence of a much weaker reaction field in the anisotropic, rigid host. These dye molecules show little or no apparent order in the anisotropic host despite the observation of a reduction in the electro optic switching time when the dye is present. The highest degree of macroscopic alignment was observed for a merocyanine compound, which showed the smallest solvatochromic shift in the liquid crystal host. These results are discussed in terms of the steric, dipolar and hydrogen bond interactions between the guest and the host.

44.5L: Late-News Paper: All-organic, Transparent Up-conversion Displays with Tailored Excitation and Emission Wavelengths

In this paper we describe the Worlds first all-organic, transparent, flexible, versatile color displays based upon triplet-triplet annihilation assisted photon up-conversion. The devices work with ultra-low excitation intensities down to 10 mWcm−2 red/near-IR light. The displays are based on metallated-porphyrin sensitizers in combination with emitters in a transparent matrix and are driven by galvano-scanned laser diodes. The displays have external quantum yield as high as 3.2%. The response time can be adjusted to specific application requirements — from a few μs to few 100 μs allowing kHz-refreshment rate of the displayed information. It is possible to easily tune the optical density of the screens in order to obtain a desired transmittance for the excitation beam. We demonstrate the ability to achieve multicolor emission, using only one excitation source. There are practically no display size limitations and it is a very simple, cost-effective fabrication.