Nonclassical mechanisms to modify and control organic crystal nucleation and growth

非技术总结溶液生长的单晶用作半导体、光电子和光伏器件和高能辐射探测器。这些研究得到材料研究部固态和材料化学计划的支持，填补了在理解有机材料结晶方面的空白，有机材料具有良好的光学和电学性能，可用作半导体、太阳能电池和场效应晶体管。此外，这项研究还可以提供有关结晶过程的有价值的信息，这些过程对于无数的工业、自然和生理过程是必不可少的。休斯顿大学的研究人员通过设计强大的控制策略来控制结晶，这是一项重大的基础科学挑战，这些策略依赖于了解基本的热力学和动力学机制，特别是外国化合物的作用。在工业中，与溶液或晶体-溶液界面相互作用的可溶性外来化合物被用于促进或抑制结晶。自然界通过应用控制形成的晶体的数量和生长速度的成分，实现了正在形成的晶体结构的形状、图案、成分和功能的显著多样性。从这个项目中获得的见解总体上促进了有机结晶科学的发展，特别是外来化合物对固态有机材料合成的影响。研究人员还让不同的高中生、本科生和研究生参与开展这项研究，为他们提供先进的科学和工程概念和方法方面的培训。这反过来又有助于缩小休斯敦受过教育的劳动力的需求和可获得性之间的差距，休斯敦是美国大城市中受教育程度最高的城市之一。作为该项目的一部分，由材料研究部固态和材料化学计划支持，PI和该团队设计了新的策略，以控制有机溶剂中晶体的成核和生长，这些有机溶剂使用外来化合物来调节非经典结晶行为以及成核和生长前体。公认的改性剂活性模型假定晶体成核和生长沿经典路径进行。最近的实验积累了与经典理论的显著差异。突出的非经典特征包括介观结晶前体，有序或无序，它们独立于结晶在溶液中组装，可能既促进了成核，又提供了快速的晶体生长模式。添加剂如何影响结晶前驱体的性能以促进或抑制晶体的成核和生长还没有被研究过。研究人员带来了在分子热力学和结晶动力学、晶体设计和高级表征以及分子模拟方面的互补专业知识，以追求三个具体目标：1.通过操纵参与非经典成核模式的前体来设计控制晶体成核的策略。2.利用改性剂与晶体生长前体和晶体表面阶梯束的相互作用，阐明了改性剂从生长介质中去除后仍然存在的分子和介观结晶机理。3.表征由阶跃结构和动力学介导的修饰剂对之间的相互作用，这些相互作用导致修饰剂之间的拮抗、相加或协同作用；这些相互作用被经典的抑制模型所忽视。为了涵盖一系列不同的成核和结晶行为，研究人员使用了具有良好光学和电学特性的有机晶体，可用作半导体、太阳能电池和场效应晶体管。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.