超分子结构中的共价键力化学

Several energy sources are used to drive chemical reactions in small molecules. Commonly, we use heat, photons or electrons to bypass high-energy transition states. Although grinding mixtures with mortar and pestle is at the very beginning of chemistry, the use of mechanical energy is not the go-to methodology for today’s chemists. When mechanical potential is included in a chemical reaction, the reaction thermodynamic space is changed due to the directionality of the applied force. This remarkable effect has been used in the past to develop new organic transformations, such as making thermally forbidden pericyclic reactions the main mechanism at room temperature. Yet, to transmit the force to a specific bond, a polymer handle is typically necessary. In polymer mechanochemistry, the parameters leading to bond scission are quite well understood; yet, in classical mechanochemistry, which is dominated by non-covalent interactions, the required parameters for a successful reaction is still quite vague. In addition, these new mechanochemical transformations shown in polymers can be very useful in small molecule synthesis if the polymer handle could be dispensed of..Here we propose to bridge these two “mechanochemistries” by introducing strong directional non-covalent interactions which are well understood to make supramolecular networks in which the sum of the non-covalent interactions could overcome the energy of a single covalent bond. By systematically increasing the non-covalent interaction energy, we will measure the limit in which covalent bonds start to be activated even at low molecular weights. Focusing on the synergetic and competitive relationships between non-covalent interaction and covalent bonds, this research will make covalent mechanochemistry a useful methodology to modern organic synthesis, and, in addition, will provide fundamental understanding on the oldest chemistry, the grinding of molecules in the solid state.

化学反应通常通过光、热、电、辐射等外界刺激作用于分子引发，而机械力作为广泛存在的能量传递方式，因其固有的宏观属性和复杂的相互作用而较少被应用。目前在聚合物力化学中，影响化学键断裂的因素已经较为清楚，将力传递到特定化学键上通常需要聚合物链作为传导介质。但在传统力化学中，非共价相互作用是重要因素，因而用力来进行有效化学反应的条件尚不明确。若可以不依赖于聚合物的存在，则力化学中的转变就能应用于小分子合成中。因此，本项目致力于考察以超分子结构为介质的力化学中非共价作用和共价键既相互促进又相互竞争的关系，设计、合成小分子形成的超分子聚合物和网络，在强的超分子作用存在下实现共价键的机械力活化；构建多种超分子结构，结合聚合物和传统力化学，通过系统增加非共价作用的强度，研究在低分子量体系中力诱导共价键活化的阈值。这一研究旨在推动共价力化学在现代有机合成中应用，并帮助理解传统力化学中固态研磨发生转变的机理。

化学反应通常通过光、热、电、辐射等外界刺激作用于分子引发，而机械力作为广泛存在的能量传递方式，因其固有的宏观属性和复杂的相互作用而较少被应用。机械力在化学反应中不仅影响反应进行的机理，有效地改变反应的优先路径，同时，机械能向化学能的转变具有清洁、高效的优势，所以研究机械能向化学能的这一新维度能量转变非常重要。目前在聚合物力化学中，影响化学键断裂的因素已经较为清楚，将力传递到特定化学键上通常需要聚合物链作为传导介质。但在传统力化学中，非共价相互作用是重要因素，因而用力来进行有效化学反应的条件尚不明确。若可以不依赖于聚合物的存在，则力化学中的转变就能应用于小分子合成中。因此，本项目致力于考察以超分子结构为介质的力化学中非共价作用和共价键既相互促进又相互竞争的关系，设计、合成小分子形成的超分子聚合物和网络，在强的超分子作用存在下实现共价键的机械力活化；构建多种超分子结构，研究在超分子体系中力诱导共价键活化的阈值，实现小分子晶体中力诱导化学键的形成和断裂；详细研究溶液和固体状态下的结构和光物理性质，阐明了其中的共价键形成和断裂的具体机理；系统探究了分子结构、堆积方式对力致变色行为的影响，实现了力的大小、作用方式对响应行为的多维度调控。这一研究旨在解决力化学和材料科学中的一些基本问题，发展力作为能量传递的一种方式进行小分子的化学反应，推动共价力化学在现代有机合成、力响应功能性材料等领域的应用。