Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA.
Davidson School of Chemical Engineering, Purdue University, 480 W Stadium Ave, West Lafayette, IN, 47907, USA.
Nat Commun. 2023 Mar 21;14(1):1304. doi: 10.1038/s41467-023-36871-9.
Cooperativity is used by living systems to circumvent energetic and entropic barriers to yield highly efficient molecular processes. Cooperative structural transitions involve the concerted displacement of molecules in a crystalline material, as opposed to typical molecule-by-molecule nucleation and growth mechanisms which often break single crystallinity. Cooperative transitions have acquired much attention for low transition barriers, ultrafast kinetics, and structural reversibility. However, cooperative transitions are rare in molecular crystals and their origin is poorly understood. Crystals of 2-dimensional quinoidal terthiophene (2DQTT-o-B), a high-performance n-type organic semiconductor, demonstrate two distinct thermally activated phase transitions following these mechanisms. Here we show reorientation of the alkyl side chains triggers cooperative behavior, tilting the molecules like dominos. Whereas, nucleation and growth transition is coincident with increasing alkyl chain disorder and driven by forming a biradical state. We establish alkyl chain engineering as integral to rationally controlling these polymorphic behaviors for novel electronic applications.
协同作用被生命系统用于规避能量和熵障碍，以产生高效的分子过程。协同结构转变涉及晶体材料中分子的协同位移，而不是典型的逐个分子成核和生长机制，后者通常会破坏单晶性。协同转变因其低转变势垒、超快动力学和结构可逆性而备受关注。然而，协同转变在分子晶体中很少见，其起源尚不清楚。二维醌式噻吩（2DQTT-o-B）的晶体是一种高性能的 n 型有机半导体，遵循这些机制表现出两种截然不同的热激活相转变。在这里，我们表明烷基侧链的重排引发协同行为，使分子像多米诺骨牌一样倾斜。然而，成核和生长转变与烷基链无序度的增加同时发生，并由形成双自由基态驱动。我们确定烷基链工程对于合理控制这些用于新型电子应用的多晶型行为是不可或缺的。
