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

Abstract

AbstractFlexible molecular crystal waveguides based on elastic molecular crystals (EMCs) are essential in flexible and compact optical materials. An increased loss coefficient α due to self‐absorption is often a problem in optical waveguides (OWGs) of fluorescent 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% acceptor doping for fluorescent 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. The α value 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 and flexible 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 and flexible crystal systems.