Monodisperse glassy-nematic conjugated oligomers with chemically tunable polarized light emission

A novel series of monodisperse conjugated oligomers were synthesized by inserting varied segments into blue-emitting oligofluorenes to complete the color gamut of light emission. Quantum mechanical calculations revealed that the electron transition dipoles lie largely parallel to the long molecular axes of the central segments responsible for light emission. The orientational order parameter characterizing molecular alignment in thermally processed glassy-nematic films was evaluated at 0.77 to 0.87 by UV-vis absorption dichroism. With an emission dichroic ratio ranging from 9.4 to 13.7, polarized photoluminescence provided further evidence that the long molecular axes are aligned with the nematic director. Polarized organic light-emitting diodes (OLEDs) comprising selected materials resulted in red and yellowish green light emission with dichroic ratios of 14.4 and 18.0 and luminance yields of 0.51 and 5.91 cd/A, respectively. These two sets of data represent the best performance to date of red and green polarized OLEDs.