Monodisperse Oligofluorenes Forming Glassy-Nematic Films for Polarized Blue Emission

Abstract

The first series of monodisperse glass-forming, nematic oligofluorenes was synthesized following a divergent−convergent approach. Both chain length and pendant structure were found to affect solid morphology and phase transition temperatures. With optimized structural parameters, a Tg close to 150 °C and a Tc beyond 375 °C were achieved. This material class is characterized by its ability to form monodomain glassy nematic films via spin-coating, thermal annealing at 10 to 20 °C above Tg for 15−30 min, and cooling to room temperature without encountering crystallization. The absorption and emission dichroic ratios of 80−90-nm-thick films increase from 7 to 17 with an increasing molecular aspect ratio, while the photoluminescence quantum yield varies erratically from 43 to 60%. Superior stability of emissive color and of emission dichroic ratio and that against thermally activated crystallization were also demonstrated through prolonged heating of a film at 10 °C above Tg under argon.