CAREER: Advancing the Mechanistic Understanding of Naphthopyran Mechanochemistry

在化学系的大分子、超分子和纳米化学（MSN）和化学结构、动力学和机理-B（CSDM-B）项目的支持下，加州理工学院（Caltech）的麦克斯韦J.罗布正在推进对长链大分子或聚合物中嵌入的机械载体的化学反应性的理解。 机械载体是响应于外部机械力而经历化学转化的有机化合物。 当被引入聚合物链中时，它们可以作为传感器，并提供有关聚合物在应力下行为的有价值的信息。 机械载体的这一特性对于指导未来设计刺激响应聚合物具有重要意义，这些聚合物应用于各种领域，包括粘合剂，传感器，药物输送和可持续性。 在这项研究中，实验和计算技术将被用来系统地研究机械载体的化学，当暴露在压力下时会改变颜色。 将分析反应性并将其与机械基团的化学结构相关联，以了解和控制暴露于外部应力时的反应。 合成的分子将被纳入聚合物中，以设计独特的响应材料，在压力下改变颜色。 一些教育举措将与研究相结合，以扩大参与，并使本科生和研究生在聚合物化学，以及物理和合成有机化学的培训。 暑期研究经验将支持来自化学专业代表性不足的群体的本科生的科学发展。 此外，一个动手聚合物机械化学模块将与加州理工学院的学习，教学和外展中心合作，整合到K-12外展计划中。 这项活动每年将吸引帕萨迪纳社区的众多成员，并介绍与聚合物和材料化学相关的重要概念。 最后，将开发一个网络研讨会系列，以教育学生在化学领域的不同职业道路，以帮助建立下一代科学家。这项研究将侧重于提高对萘并吡喃机械载体机械化学反应性的机械理解。通过建立线性自由能关系，进行全面的机理和活性研究，以确定取代基对萘并吡喃的机械化学开环反应的影响。 这些研究将通过计算来补充，以提供对受力下mercury形成机制的详细见解。 此外，Robb团队将致力于开发力耦合mercury异构化的详细了解，这是萘并吡喃机械化学的关键组成部分。 在这些系统中的结构-反应性关系的改进的基本理解将有助于指导双-萘并吡喃机械基团的发展，该机械基团在聚合物中的不同机械负荷下实现不同的开环反应，从而导致具有独特耦合视觉响应的不同mercury状态。 该项目有可能推进机械化学反应性的知识，并在快速发展的聚合物机械化学领域和相关交叉学科中实现创新。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Macromolecular, Supramolecular and Nanochemistry (MSN) and Chemical Structure, Dynamics and Mechanisms-B (CSDM-B) programs in the Division of Chemistry, Maxwell J. Robb of the California Institute of Technology (Caltech) is advancing the understanding of the chemical reactivity of mechanophores embedded within long chain macromolecules or polymers. Mechanophores are organic compounds that undergo chemical transformations in response to external mechanical force. When incorporated into polymer chains, they can act as sensors and provide valuable information about the behavior of polymers under stress. This characteristic of mechanophores is important in guiding future design of stimuli-responsive polymers with applications in a variety of areas including adhesives, sensors, drug delivery, and sustainability. In this research, experimental and computational techniques will be used to systematically study the chemistry of mechanophores that change color when exposed to stress. Reactivity will be analyzed and correlated with the chemical structure of the mechanophore to understand and control response when exposed to external stress. The synthesized molecules will be incorporated into polymers to design unique responsive materials that change color under stress. Several educational initiatives will be integrated with the research to broaden participation and enable training of undergraduate and graduate students in polymer chemistry, as well as physical and synthetic organic chemistry. Summer research experiences will support the scientific development of undergraduate students from underrepresented groups majoring in chemistry. In addition, a hands-on polymer mechanochemistry module will be integrated into K-12 outreach programs in collaboration with the Center for Learning, Teaching, and Outreach at Caltech. This activity will engage numerous members of the Pasadena community each year and introduce important concepts related to polymers and materials chemistry. Lastly, a webinar series will be developed to educate students about the different career paths available in chemistry to help to build the next generation of scientists.This research will focus on the development of an improved mechanistic understanding of the mechanochemical reactivity of naphthopyran mechanophores. Comprehensive mechanistic and activity studies will be performed to determine the effect of substituents on the mechanochemical ring-opening reaction of naphthopyran by establishing linear free energy relationships. These studies will be complemented by computation to provide detailed insights into the mechanism of merocyanine formation under force. Additionally, the Robb team will work toward developing a detailed understanding of force-coupled merocyanine isomerization, which is a critical component of naphthopyran mechanochemistry. An improved fundamental understanding of structure-reactivity relationships in these systems would serve to guide the development of bis-naphthopyran mechanophores that achieve distinct ring-opening reactions under varying mechanical loads in polymers, leading to different merocyanine states with uniquely coupled visual responses. This project has the potential to advance knowledge of mechanochemical reactivity and empower innovation in the rapidly expanding field of polymer mechanochemistry and in related cross-cutting disciplines.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.