Nonclassical mechanisms to modify and control organic crystal nucleation and growth

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NON-TECHNICAL SUMMARYSolution-grown single crystals serve as semiconductor, optoelectronic, and photovoltaic devices and detectors for high-energy radiation. These studies, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, fill a gap in understanding crystallization of organic materials that carry promising optical and electronic properties for use as semiconductors, solar cells, and field-effect transistors. Additionally, the research can provide valuable information about crystallization processes, which are essential for a myriad of industrial, natural, and physiological processes. Researchers at the University of Houston take on the grand fundamental science challenge to control crystallization by designing robust control strategies that rest on understanding the fundamental thermodynamic and kinetic mechanisms, and in particular the role of foreign compounds. In industry, soluble foreign compounds that interact with the solution or the crystal-solution interface are deployed to promote or inhibit crystallization. Nature achieves remarkable diversity of shapes, patterns, compositions, and functions of the arising crystalline structures by applying ingredients that control the number of formed crystals and their rates of growth. Insights gained from this project advance the science of organic crystallization in general, and the influence of foreign compounds on the synthesis of solid state organic materials in particular. The researchers also involve a diverse cohort of high school, undergraduate, and graduate students in carrying out this research, which provides them with training in advanced science and engineering concepts and methods. This in turn contributes to narrowing the gap between the demand and availability of educated workforce in Houston, which is among the widest in large U.S. cities.TECHNICAL SUMMARYAs part of this project, which is supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, the PI and this team design novel strategies to control the nucleation and growth of crystals from organic solvents that employ foreign compounds to regulate nonclassical crystallization behaviors and the nucleation and growth precursors. The accepted models of modifier activity presume that crystal nucleation and growth advance along classical pathways. Recent experiments have accumulated significant discrepancies with the classical theories. The highlighted nonclassical features involve mesoscopic crystallization precursors, ordered or disordered, which assemble in the solution independently of crystallization and may both facilitate nucleation and feed a fast mode of crystal growth. How additives impact the properties of the crystallization precursors to enhance or suppress crystal nucleation and growth has not been examined. The researchers bring complementary expertise in molecular thermodynamics and kinetics of crystallization, crystal design and advanced characterization, and molecular simulations to pursue three specific aims: 1. Design strategies to control crystal nucleation by manipulating precursors involved in nonclassical nucleation modes. 2. Elucidate molecular and mesoscopic crystallization mechanisms that persist after removal of the modifier from the growth medium by exploiting the interactions of modifiers with crystal growth precursors and with step bunches on the crystal surface. 3. Characterize interactions between pairs of modifiers mediated by the step structures and dynamics that lead to antagonistic, additive, or synergistic cooperativities between modifiers; these interactions have been disregarded by classical inhibition models. To cover a diverse array of nucleation and crystallization behaviors, the researchers employ organic crystals that carry promising optical and electronic properties for use as semiconductors, solar cells, and field-effect transistors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.