Liu Shasha, Wang Wei
State Key Laboratory of Analytical Chemistry for Life Science, Chemistry and Biomedicine Innovation Center, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
Shenzhen Research Institute of Nanjing University, Shenzhen 518000, China.
Proc Natl Acad Sci U S A. 2024 Nov 19;121(47):e2415379121. doi: 10.1073/pnas.2415379121. Epub 2024 Nov 13.
Cooperative spin crossover (SCO) compounds are one of the most promising molecular bistable solids due to their intriguing thermal hysteresis phenomena around room temperature. It is well known that hysteresis is an essential kinetic effect, however, accurate assessment of the spin transition kinetics of SCO nanomaterials remains scarce. Herein, we developed a thermal-optical methodology to image the thermally induced spin transition kinetics of single SCO nanoparticles in a quantitative, repeatable, and high-throughput manner. Single-particle measurement revealed an intrinsic nucleation-dominated spin transition mechanism, where a highly stochastic nucleation process was clearly observed during the repeatable measurements. By quantifying the dependence of nucleation time on temperature, the activation energy barriers for nucleation were further extracted at a single particle level. Based on this foundation, the high throughput of the optical imaging not only contributed to uncovering the significant nanoparticle-to-nanoparticle heterogeneity, with implications for a negative correlation between apparent activation energy barriers for nucleation and size of the SCO nanoparticles, but also facilitated identifying a minority with high activation energy at least twice the average value. The extraordinary performance was then attributed to the fewer defects within their structures, as confirmed by further results from the in situ creation of defects by thermal ablation, thereby setting the lower limit for the intrinsic activation energy of ideal SCO crystals and promising their potential for future applications in high-performance molecular devices.
合作自旋交叉（SCO）化合物是最有前途的分子双稳态固体之一，因为它们在室温附近具有引人入胜的热滞现象。众所周知，滞后是一种基本的动力学效应，然而，对SCO纳米材料自旋转变动力学的准确评估仍然很少。在此，我们开发了一种热光学方法，以定量、可重复和高通量的方式对单个SCO纳米颗粒的热诱导自旋转变动力学进行成像。单颗粒测量揭示了一种内在的成核主导自旋转变机制，在重复测量过程中清楚地观察到了高度随机的成核过程。通过量化成核时间对温度的依赖性，在单颗粒水平上进一步提取了成核的活化能垒。在此基础上，光学成像的高通量不仅有助于揭示显著的纳米颗粒间异质性，这意味着SCO纳米颗粒的成核表观活化能垒与尺寸之间存在负相关，而且有助于识别出少数活化能至少是平均值两倍的高活化能颗粒。这种非凡的性能随后归因于其结构中较少的缺陷，热烧蚀原位产生缺陷的进一步结果证实了这一点，从而设定了理想SCO晶体固有活化能的下限，并有望其在高性能分子器件中的未来应用潜力。
