Emerging Classes of Smart Materials: Organic Single Crystals to Biological Nano Particles
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Stimuli responsive materials, also known as “smart” materials, are capable of altering their properties in a controllable fashion in response to external stimuli. While most reported smart materials are based on synthetic polymeric systems, there exists a need to develop a novel class of smart materials with properties better suited for commercial settings. In this dissertation, we investigate two emerging classes of smart materials—organic single crystals and viral nanoparticles. First, we report novel class of thermo-responsive single crystalline compounds known as naphthalene diimides (NDIs). The single crystalline butoxyphenyl N-substituted NDI (BNDI), a derivative of NDI, exhibits thermo-mechanical and thermochromic behavior. The monoclinic phase of BNDI can be thermally transformed to its triclinic polymorph and the stress accumulated due to this phase transition can be released in the form of mechanical energy. In fact, we demonstrated that the energy associated with this phase transition could be utilized to lift a metal ball ~100 times heavier than the single crystal itself. Furthermore, BNDI exhibits colossal anisotropic thermal expansion with highest positive expansion coefficient reported for an organic compound so far. Next, we investigated the thermochromic and thermo-salient behavior of alkoxyphenyl Nsubstituted NDI (ANDIs). It was clear that the thermo-salient behavior of ANDIs can be tuned by changing the alkyl substituents over a wide range of temperatures. Thermochromic ANDIs can be incorporated to commercially available polymers and we show that ANDI polymer composites also exhibit reversible thermochromism. The reasoning behind thermochromism in BNDI was further investigated using both experimental data and computational simulations. The developments in nanotechnology have also produced smart materials that can respond to external stimuli in a controllable fashion. Viral nanoparticles—particularly symmetrical, polyvalent biological macromolecules are very attractive in nanomaterial-based research. Among viral nanoparticles, tobacco mosaic virus (TMV) is one of the most extensively-studied plant viruses, particularly known for its rod-shaped structure and stability in extreme conditions. Herein, we report proton relaxation properties and redox responsiveness of organic radical contrast agents (ORCAs) conjugated to TMV nano-particles. The ORCA-TMV particles show enhanced T1 contrast at low fields and T2 contrast at high fields compare to ORCA small molecules. Furthermore, we created a quenchless bimodal probe for fluorescence/MR imaging by conjugating a fluorescence dye to the interior and ORCAs to the exterior surfaces of TMV. We have also shown that the reduced from of ORCA-TMV can respond to enzymatically produced superoxides. Biomimetic mineralization is another promising area of research as this process can significantly increase the stability of biological macromolecules such as enzymes, proteins, and viral nanoparticles. Previous reports show that TMV can act as a template for ZIF-8 growth, resulting in core shell bio nanoparticles (CSBNs). Finally, we investigate the responsiveness for biomimetics mineralization by TMV when its surface is modified with charged molecules. The formation of CSBN was not prevented by the surface charge of the viral nano particle. However, we show that higher loading of positive charge on the surface of TMV will reduce the encapsulation efficiency of biomimetics mineralization process.