Organic Polarized Light-Emitting Diodes via FoErster Energy Transfer Using Monodisperse Conjugated Oligomers

摘要

Conjugated polymers are promising for electronic and photonic applications, such as thin-film transistors, light-emitting diodes, photovoltaics, and sensors. In particular, blue organic light-emitting diodes (OLEDs) have been demonstrated using polyfluorenes. Emission of green and red light has also been demonstrated via modulation of electronic energy levels through copolymerization. Linearly polarized OLEDs are potentially useful as an efficient light source for liquid-crystal displays (which account for the bulk of flat-panel displays today), for electroluminescent displays with reduced glare and increased contrast, for projection displays, and for stereoscopic imaging systems. The concept of linearly polarized electroluminescence, except in the case of white light, has been demonstrated by taking advantage of the thermotropic nematic mesomorphism exhibited by polyfluor-enes and other conjugated polymers. The idea is to preserve uniaxial molecular alignment in a solid film upon thermal annealing, with subsequent cooling through the glass-transition temperature without encountering crystallization. From the materials perspective, monodisperse conjugated oligomers offer numerous advantages over polydisperse conjugated polymers. Monodisperse conjugated oligomers are characterized by a well-defined and uniform molecular structure as well as superior chemical purity via recrystallization or column chromatography.