Discovery of Non-linear Optical Materials by Function-Based Screening of Multi-component Solids

Non-centrosymmetric arrangement in the solid state is a prerequisite for a molecule to exhibit second harmonic generation (SHG), yet the majority of achiral molecules crystallize in centrosymmetric lattices. Despite advances in circumventing the molecular preference for centrosymmetric structures, current screening methods of discovering SHG active materials need large quantities of parent material. Here, we present a function-based screening method that is designed to consume small quantities of parent material for screening a large pool of coformers that enhance the probability of discovering SHG active materials. With this method, ∼30 mg of a non-linear optical (NLO) chromophore, N-(2-aminoethyl)-4-nitro-2-ansidine (1), was sufficient for screening 50 coformers, resulting in five SHG active compounds. Crystal-structure analysis revealed that non-covalent interactions influence the disposition of NLO-phore dipoles and thus affect the bulk SHG properties. Quantum chemical calculations highlighted the coformer contribution toward the second-order susceptibility coefficients, providing a deeper understanding of the structure-property relationships in these SHG materials. Addressing the increasing demand for efficient non-linear optical (NLO) materials for technologically relevant applications is a challenge because of the current unsustainable models of discovery. The ineffectiveness of these methods in accelerating the discovery of materials with the requisite non-centrosymmetry and ideal chromophore alignment for high performance in applications such as second harmonic generation (SHG) is now recognized as a challenge for the field. In order to optimize this discovery process, we present a high-throughput screening experimental approach. Unlike current experimental methods, this approach is neither sample nor labor intensive and selects hits on the basis of a functional assay. We have successfully demonstrated the practical utility of this method by using an organic NLO chromophore, which resulted in five SHG active salts. Testing the adaptability of this technique with other NLO chromophores will establish whether this becomes the frontline experimental method for discovering NLO materials. Current experimental methods for discovering non-linear optical (NLO) materials are sample intensive, resulting in a slow pace of discovering new materials with large bulk SHG activity. Matzger and colleagues demonstrate a simple, functionally guided high-throughput screening approach that consumes a very small amount of parent NLO-phore to screen large numbers of coformers, maximizing the chances of finding efficient SHG active materials. They successfully discovered five new NLO active salts with only ∼30 mg of parent compound.