The tension activated C–C bond: physical organic models and functional organic materials

Carbon–carbon (C–C) bond is widely acknowledged for its strength, yet its scission is surprisingly common in a diverse array of selective mechanochemical transformations under tension. Polymer mechanochemistry employs polymer chains to direct and transduce tensile force, setting an ideal stage for investigating the tension activated C–C bond in both mechanochemical reactions and mechano-responsive materials. Whereas C–C bond scission under tensile force has been known since middle 20th century, the scope of reactions initiated from tensioned C–C bond remains limited, involving mostly retro-pericyclic reactions. In addition, the vectorial nature of force results in intricate coupling with reaction trajectories, making it challenging to understand and predict structure-reactivity relationships under tension using conventional chemical intuitions. To tackle these two challenges, this thesis will be focusing on developing new mechanochemical reactions using tension activated C–C bond and applying them in mechano-responsive materials, as well as developing a physical organic model to build an intuitive picture of reactivity under tension. In the second chapter of this thesis, I detail the development of an unprecedented mechanochemical mechanism based on the tension activated C–C bond, named diradical elimination cascade. This strategy enables the design and synthesis of a bifunctional mechanosensitive motif (i.e., mechanophore) built from norborn-2-en-7-one (NEO) that not only releases carbon monoxide (CO) as a gaseous signaling molecule (GSM), but also turns on the aggregation-induced emission upon mechanochemical activation. The third chapter explores the further generalization of the diradical elimination cascade strategy to release sulfur dioxide (SO2) as another GSM with therapeutic potential. A thermally stable but mechanochemically labile mechanophore was designed based on an 8-thiabicyclo[3.2.1]octane 8,8-dioxide (TBO) motif. We quantified the mechanochemical reactivity of TBO by single molecule force spectroscopy and resolved its single-event activation. The mechanism of TBO activation was also investigated using ab initio steered molecular dynamic simulations. The fourth chapter discusses the development of an intuitive physical organic model to understand and predict the reactivity of C–C bond under tensile force, by leveraging two key molecular features: the effective force constant (keff) and reaction energy (ΔE). Through a comprehensive experimental and computational investigation with four norborn-2-en-7-one (NEO) mechanophores, we establish the relationship between these features and the force-dependent energetic changes along the reaction pathways. A multivariate linear model was then established to predict the transition force (f*) of more than 30 C–C bonds in various mechanophores. In the fifth chapter, a new NEO mechanophore scaffold was designed and synthesized to achieve mechano-activatable multi-color photoluminescence and white emission in aggregated states. The new NEO derivates were examined in both solution ultrasonication and solid-state grinding. Energy transfer between nascent and activated states was observed in NEOs bearing strong electron-donating groups. The energy transfer process was further regulated by tuning mechanophore activation and incorporation, enabling the development of force-controlled multicolor fluorescence and white emission. Finally, chapter six will outline future opportunities for the tension-activated C–C bond and the diradical elimination cascade strategy.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Sun, Yunyan

Contributors dc:contributor

• Moore, Jeffrey Scott
• Chan, Jefferson
• Suslick, Kenneth
• Guironnet, Damien

• Mechanochemistry
• Mechanophore
• Carbon–carbon Bond Activation
• Reactivity

Statement dc:rights

• © 2024 by Yunyan Sun. All rights reserved.

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127423

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127423