Luminescent Anthracene-based Elastic Mixed Molecular Crystals for Flexible and FRET-Assisted Optical Waveguides

Abstract Optical waveguides based on elastic molecular crystals are of interest as flexible and compact optical communication materials. Low emission efficiency is often a problem in terms of communication signal strength, and an increase in the loss factor α due to fluorescence reabsorption in the crystal reduces the photon transport efficiency. Here, we report the development and improvement of Förster resonance energy transfer (FRET)-assisted optical waveguides using anthracene-based elastic mixed molecular crystals. 9,10-Dicyanoanthracene was selected as the dopant for solution-grown crystallization of 9,10-dibromoanthracene. 1H NMR measurements of the obtained crystals showed that the acceptor doping to be 1% to 5%. Elastic behavior was observed even when doped with a few percent of the acceptor. The quantum efficiency was 0.016, a dramatic improvement over the previous luminescent elastic mixed molecular crystals (0.004). The α value (92 dB/cm) of this crystal containing 1%-doped 9,10-dicyanoanthracene is much lower than that of the crystal consisting of only 9,10-dibromoanthracene (1258 dB/cm) due to the reduced reabsorption in the FRET system. We have demonstrated a practical approach toward developing improved fluorescent, highly efficient, and flexible optical waveguides by constructing the mixed crystal structure by selecting appropriate acceptor molecules and their low doping ratios.