Exceptionally Plastic/Elastic Organic Crystals of a Naphthalidenimine-Boron Complex Show Flexible Optical Waveguide Properties.

Design of molecular compounds exhibiting flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multi-dimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine-boron complex that showed size-dependent dual mechanical bending behavior whereas its parent Schiff base was observed to be brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Further, the luminescence of the molecule was turned-on subsequent to boron complexation thereby allowing it to be explored for multi-mode optical waveguide applications. Our in-depth study of the size-dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications.