UC Santa Barbara

In this work, I explore new design strategies for the development of stimuli-responsive materials—specifically, light-responsive liquid crystal elastomers (LCEs)with the goal of creating bio-inspired smart responses rather than optimizing traditional performance metrics. LCEs are molecularly ordered soft materials capable of undergoing reversible phase transitions between nematic (ordered) and isotropic (disordered) states. This molecular transition induces macroscopic contractions. By embedding photoresponsive molecules into the LCE matrix, one can exploit light as a remote, tunable, and spatially resolved stimulus to drive these phase transitions. While most work in the field has focused on maximizing actuation metrics such as speed, amplitude, or efficiency, the central goal of this thesis is to shift perspective: to draw inspiration from biological systems and explore how synthetic materials might interact with light in ways that resemble living matter—through feedback, regulation, and resilience. To do this, development of new light-responsive liquid crystalline systems, where photochemistry and material sciences converge, needs to be realized.The first three chapters of this work focus on expanding the chemical landscape of photoswitches in LCEs. Photoswitches are molecules that undergo reversible structural changes between a ground and a metastable state in response to specific wavelengths of light. These molecules are key to imparting dynamic, light-responsive behavior to materials, mirroring how biological systems adapt to fluctuating light environments. However, by 2022, the number of photoswitches successfully integrated into LCEs remained limited. The first chapter of this thesis describes this gap, offering a historical perspective on how various classes of photoswitches have been utilized in LCEs, particularly in the context of soft robotics and programmable matter.The second chapter turns toward synthetic limitations. Many photo-responsive molecules are chemically sensitive and cannot withstand the harsh conditions often required for LCE polymerization. To address this, I developed a new, mild-condition polymerization chemistry that allows the integration of sensitive molecular switches. Recognizing, however, that widespread adoption of new chemistries can be challenging for non-specialists, the third chapter introduces a modular post-functionalization strategy based on siloxane chemistry. Here, LCEs are synthesized with a latent chemical handle that can undergo click chemistry post-polymerization. This platform allows the introduction of photoswitches via simple soaking procedures, decoupling material synthesis from molecular design, and enabling the creation of a diverse library of functional LCEs. This strategy was further extended to incorporate donor–acceptor Stenhouse adducts (DASAs)—a class of negative photochromes—into the LCE matrix in the fourth chapter of this work. In this system, I show that DASAs enable deep photoactivation using white light, allowing optical responses in films up to several millimeters thick. This is, to my knowledge, the first demonstration of bulk actuation in LCEs triggered by broadband visible light, highlighting the promise of DASAs as ideal candidates for solar-responsive materials. Given that white light is abundant, low-energy, and non-hazardous, this work positions DASAs as a gateway to more accessible and deployable photomechanical systems, including applications in underwater (chapter 6) actuation without reliance on high-intensity lasers or UV radiation. In the final part of the thesis, I introduce the concept of self-protective materials through energy intake suppression, again taking cues from living organisms. Under high light intensities and mechanical constraints, LCEs, particularly those lacking feedback, can undergo both chemical degradation and mechanical failure. I show that DASA-based materials, due to their negative photochromism, can self-limit optical energy intake, limiting overstimulation and protecting their own structural and functional integrity. This built-in photoprotection extends the operational range and lifetime of the material, both chemically and mechanically. Importantly, I demonstrate that collective performance, such as overall contraction or work output, is superior in self-regulating collectives compared to their non-regulating counterparts. This shift in design logic, from maximizing performance to preserving function over time, suggests a new paradigm for responsive materials: one focused on longevity, adaptability, and resilience, echoing the principles of living systems that thrive by surviving, not just by specific-metric performance.