Flexible Förster resonance energy transfer-assisted optical waveguide based on elastic mixed molecular crystals

Flexible molecular crystal waveguides based on elastic molecular crystals(EMCs)are essential inflexible and compact optical materials.An increased loss coeffi-cientαdue to self-absorption is often a problem in optical waveguides(OWGs)offluorescent chemical materials waveguiding photons in active mode.Herein,the development of anthracene-based elastic mixed molecular crystals(EMMCs)is reported for Förster Resonance Energy Transfer(FRET)-assisted OWG.To yield a FRET crystal system based on elastic molecular crystals,1%–5%accep-tor doping forfluorescent molecular crystals of 9,10-dibromoanthracene 1 was successful by selecting the same regioisomer having electron-withdrawing group,9,10-diformylanthracene 2,as a dopant.In addition to conversion to the mixed system,there is a difference in the elastic modulus and hardness in EMC C1 and EMMC C2@1.However,the elastic behaviour was also shown in a few percent doping of the acceptor.Theαvalue of this EMMC,composed of 1 including 1%of 2(0.0077 dB/μm),is much lower than that of EMC composed of 1(0.1258 dB/μm)because of reducing self-absorption in the FRET system.An efficient andflexible OWG was successfully developed by selecting an appropriate acceptor molecule and its low doping rate for mixed crystal construction.This method is a practical approach in various functional andflexible crystal systems.