Trinaphthyl-triazines: towards persistent room temperature columnar mesomorphic matrices

Abstract

Although organic light emitting devices (OLEDs) are widely used today, they still suffer from significantly low efficiency, leaving substantial room for further development. For this purpose, alignable anisotropic columnar and nematic liquid crystals made of disk-shaped molecules hold great potential for OLEDs, as aligning emitter dipoles relative to device surfaces can significantly reduce losses caused by inefficient light outcoupling. Triazine derivatives have previously been identified as a suitable large-T₁-energy core with threefold symmetry to allow the elaboration of liquid crystalline moieties, and carboxylic alkyl ester groups have proven to be appropriate substituents to induce high viscosity. Trinaphthyl-triazines thus appear as convenient aryl moieties, and therefore we have elaborated various trinaphthyltriazine tri- and hexaesters to combine adjusted phase behavior with good optoelectronic characteristics. These compounds presented persistent hexagonal columnar and nematic mesomorphism, even at room temperature. Their photophysical behavior was evaluated through experimental (both at 300 and 60 K) and computational (TD-DFT) investigations to assess the applicability in aligned display technologies. All series exhibited a large S₀–S₁ energy gap, and a somewhat shorter S₀–T₁ energy gap. Such band gaps, combined with room-temperature mesophase alignment, make these materials promising fluorescent host matrices for aligned display technologies.