Light-Emitting Organic Materials with Variable Charge Injection and Transport Properties

Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron- or hole-conducting core were designed for tunable charge injection and transport properties. Representative glassy-isotropic and glassy-liquid-crystalline (i.e., noncrystalline solid) materials were synthesized and characterized; they were found to exhibit a glass transition temperature and a clearing point close to 140 and 250 °C, respectively; an orientational order parameter of 0.75; a photoluminescence quantum yield up to 51%; and HOMO and LUMO energy levels intermediate between those of blue-emitting oligofluorenes and the ITO and Mg/Ag electrodes commonly used in organic light-emitting diodes, OLEDs. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.