Liquid crystalline semiconductors for organic electronics

This research is based on the synthesis and evaluation of novel liquid crystalline materials with light-emitting and or charge-transporting properties. Some of the liquid crystals (LCs) synthesised incorporate photopolymerisable diene or methacrylate end groups, situated at the peripheries of the molecular core. These photoreactive liquid crystalline monomers are often termed reactive mesogens. The generation of linearly and circularly polarised light emission have been observed and a White-Light Organic Light-Emitting Diode (WOLED) fabricated from binary mixtures of LCs. A series of fluorene-containing LCs have been synthesised for use as hole-transport, electron-transport and electroluminescent materials. Many of these materials exhibit nematic phases, which is beneficial for alignment due to the lower viscosity present in the nematic phase compared to the smectic phase. Columnar LCs with low melting points were synthesised by variation of the aliphatic groups at the 3,4,9,10-positions of a perylene tetracarboxylate. A fluorene-containing material with perfluorinated chains at the 9-position of the fluorene was synthesised, although the required LC phase was not observed. High electron-affinity nitrogen-containing smectic LCs have been synthesised with relatively low LC transition temperatures. These materials may prove useful as electron-transport materials. An electroluminescent chiral nematic LC was synthesised, which leads to the possibility of circularly polarised light. The possibility of a full-colour LC-Organic Light-Emitting Diode (OLED) has been demonstrated with the synthesis of a red-emitting material, a green-emitting material and a blue-emitting material. All three materials are LCs with high glass transition temperatures, which is important for device stability as these materials are not reactive mesogens. A White-Light OLED has been demonstrated by the mixing of two LCs. This nematic binary mixture when used as the emissive layer in an OLED emits white-light that is voltage independent and not due to Förster energy transfer. Consequently this mixture can be aligned and linearly polarised light emission has been generated with a 9:1 ratio. A series of perylene-containing LCs have been synthesised for use as electron-transport materials in OLEDs or electron-acceptors in organic photovoltaics