In numerous bio-organisms template-assisted crystallization of purine and pterin derivatives yield crystal morphologies having unique optical properties, such as extreme birefringence: a high refractive index for light polarized within the network plane (in the range n~1.8-2.0), and a low refractive index (~1.4) perpendicular to it. Extreme birefringence has been shown in the past years to give rise to highly efficient light reflecting and light scattering systems greatly exceeding those achievable by amorphous materials. Notably, the birefringence of these organic crystals significantly exceeds even that of the most birefringent inorganic counterparts used in optical systems today, such as calcite (Δn~0.16, ~10%).

Although there have been significant advance in the research and development of heterogeneous and surface guided organic crystallization, most of the past scientific effort has been invested in the research of crystals built from aromatic conjugated macrocyclic molecules rather than dielectric crystals constructed from small aromatic molecules, despite their promising potential as functional components in various optical elements. This is due to the difficulty in tuning the crystallization process of small aromatic molecules to yield a desired morphology.

Here we present surface guided crystallization of bio-inspired birefringent purine derivatives, theophylline, and etofylline, using single crystal quartz substrate as the growth template, by simple solution processing. The resulting macrocrystals are quasi 2D crystalline sheets that are typically in the range of millimeters in length, hundreds of microns in width while having an extremely uniform thickness in the hundreds of nanometers range. Control of the growth direction via epitaxy results in high optical anisotropy in the plane with a refractive index difference of Δn~0.25 and a refractive index along the slow axis nslow~1.7. We use lithographic methods to pattern these crystalline arrays into a metamaterial with polarization-dependent optical properties, demonstrating the potential utility of these structures in optical applications. To the best of our knowledge, this is the first optical metasurface constructed from organic crystalline dielectrics, opening the door to the fabrication of various optical devices from organic dielectric crystals-based platform.