Photorefractivity in nematic liquid crystals containing electron donor-acceptor molecules that undergo intramolecular charge separation

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.