Date of Award

6-26-2026

Date Published

August 2026

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Xiaoran Hu

Keywords

Atropisomer;Diarylethene;Mechanochemistry;Mechanophore

Subject Categories

Chemistry | Physical Sciences and Mathematics

Abstract

Stimuli-responsive organic structures are advanced, intelligent platforms that dynamically adjust their physical or chemical properties—such solubility, or color—in response to external stimuli including light, heat, pH, redox conditions, mechanical force, or magnetic fields. Among these structures, mechanophores represent an important class that is specifically responsive to mechanical force. Synthetic mechanophores can be rationally engineered to exhibit tunable mechanosensitivity as well as tailored chemical and physical properties. In this work, we designed and synthesized a type of atropisomeric mechanophores based on sterically congested diarylethene photoswitches, and systematically investigated their mechanical and photochemical properties. Chapter 1 Chapter 1 provides a general introduction to mechanophores. Mechanophores are broadly classified into two categories: covalent and non-covalent systems. Furthermore, diarylethene-based configurational mechanophores are presented as a unique class that combines two key advantages: permanent readout and high mechanosensitivity. Chapter 1 also presents a general overview of diarylethene derivatives, including their synthesis, spectroscopic properties, and applications. Particular emphasis is placed on atropisomerism and photochromism. The chapter describes the light-induced 6π electrocyclization process in diarylethenes and the stereoselectivity between different isomers. Finally, the applications of diarylethenes as light-responsive molecular systems are discussed. Chapter 2 Chapter 2 examines another structure–mechanical activity relationship, namely the lever-arm effect, in benzobisthiadiazole-based diarylethene mechanophores. As in Chapter 3, the polymer anchoring site is a key determinant of mechanical sensitivity. Three mechanophores sharing a similar diarylethene core but bearing rigid polymer-anchoring arms of different lengths were designed and analyzed using DFT calculations. Mechanophore-containing polymers were again subjected to solution-phase ultrasonication to assess mechanochemical reactivity. In addition, single-molecule force spectroscopy was employed to directly measure the force threshold. Notably, one mechanophore exhibited an exceptional force threshold of 131 pN. Chapter 3 Chapter 3 investigates the structure–mechanical activity relationship, focusing on the regiochemical effect in benzobisthiadiazole-based diarylethene mechanophores. The force-coupling angle plays a critical role in determining mechanochemical sensitivity. To explore this effect, three regioisomers of the same diarylethene core were designed, differing only in their polymer anchoring sites. Density functional theory (DFT) calculations were used to predict their mechanochemical activity. Polymers incorporating these mechanophores were subjected to solution-phase ultrasonication to evaluate their mechanical activity experimentally. Chapter 4 Chapter 4 introduces a distinct class of diarylethene derivatives based on a dithienylphenanthrene framework. In this work, we developed and investigated a new family of dithienylphenanthrene-based configurational mechanophores and systematically evaluated their mechanochemical and photochemical behavior. Our initial mechanophore design exhibited mechanical inactivity and limited photochemical stability. To address these challenges, we established a systematic synthetic and structural modification strategy to access functionalized dithienylphenanthrene derivatives. Through rational structural tuning, we were able to modulate both mechanical responsiveness and photochemical performance. As a result, optimized dithienylphenanthrene mechanophores with significantly enhanced mechanosensitivity and improved photostability were successfully developed.

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Open Access

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