Liquid crystalline composite materials have been prepared that are strongly photorefractive. Nematic liquid crystals were doped with both electron donor and electron acceptor molecules that undergo facile, photoinduced, electron transfer reactions to yield mobile ions. A photorefractive gain ratio of 1.88 was observed. This gain ratio was achieved with low applied electric fields (0.4 kilovolts per centimeter) requiring only a 1.5-volt battery and low light intensities (100 milliwatts per square centimeter) in samples 37 to 88 micrometers thick that showed no loss in gain over a 6-month period.

No abstract

We report photorefractivity in nematic liquid crystals doped with electron donor−acceptor molecules that undergo intramolecular photoinduced charge separation. We show that subsequent intermolecular electron transfer from the intramolecular ion pairs to neutral donor−acceptor molecules is responsible for the charge migration over macroscopic distances that is required to produce photorefractivity. The results are compared to nematic liquid crystals doped with identical unlinked donors and acceptors that can achieve charge separation only through intermolecular electron transfer. We find that the liquid crystals doped with molecules that first undergo intramolecular charge separation exhibit superior photorefractivity when compared to the same liquid crystals doped with unlinked donors and acceptors. The differing mechanisms for charge generation and charge transport in these liquid crystal composites are analyzed.

The first observation of photorefractivity in ferroelectric liquid crystals (FLCs) is reported here. Dopant chromophores chosen to optimize production of mobile ions and careful control of the wavevector and light polarization are believed to play a decisive role in the observed behavior. The Figure is a schematic illustration of the experimental geometry used.