Department of Chemistry, Universitat de les Illes Balears, Cra. Valldemossa, Km. 7.5, 07122, Palma de Mallorca, Spain.
Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, C/Catedrático José Beltrán, 2, 46980, Paterna, Spain.
Angew Chem Int Ed Engl. 2022 Nov 21;61(47):e202213345. doi: 10.1002/anie.202213345. Epub 2022 Oct 25.
Hydrogen-bonded squaramide (SQ) supramolecular polymers exhibit uncommon thermoreversible polymorph transitions between particle- and fiber-like nanostructures. SQs 1-3, with different steric bulk, self-assemble in solution into particles (AggI) upon cooling to 298 K, and SQs 1 and 2, with only one dendronic group, show a reversible transformation into fibers (AggII) by further decreasing the temperature to 288 K. Nano-DSC and UV/Vis studies on SQ 1 reveal a concentration-dependent transition temperature and ΔH for the AggI-to-AggII conversion, while the kinetic studies on SQ 2 indicate the on-pathway nature of the polymorph transition. Spectroscopic and theoretical studies reveal that these transitions are triggered by the molecular reorganization of the SQ units changing from slipped to head-to-tail hydrogen bonding patterns. This work unveils the thermodynamic and kinetic aspects of reversible polymorph transitions that are of interest to develop stimuli-responsive systems.
氢键型 squaramide（SQ）超分子聚合物在粒子状和纤维状纳米结构之间表现出不常见的热可逆多晶型转变。具有不同空间位阻的 SQs 1-3 在冷却至 298 K 时在溶液中自组装成颗粒（AggI），而只有一个树枝状基团的 SQs 1 和 2 通过进一步降低温度至 288 K 显示出可逆转变为纤维（AggII）。对 SQ 1 的纳米 DSC 和 UV/Vis 研究揭示了 AggI 到 AggII 转化的浓度依赖性转变温度和 ΔH，而对 SQ 2 的动力学研究表明多晶型转变的途径性质。光谱和理论研究表明，这些转变是由 SQ 单元的分子重排触发的，从交错氢键模式转变为头到尾氢键模式。这项工作揭示了可逆多晶型转变的热力学和动力学方面，这对于开发刺激响应系统很有意义。
