Surface-Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications.

Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, we present a facile procedure to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. We obtain crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300 to 600 nm thick. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn≈0.25 and a refractive index along the slow axis of n≈1.7. We further show that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals. This article is protected by copyright. All rights reserved.