UC Riverside

Stimulus-response chemical systems have been pushed to the forefront of research since the 2016 Nobel prize was awarded for molecular machines. Photoreactive systems represent one of the most promising of all stimulus-response systems. These systems can rapidly overcome large energy barriers to create useful effects like motion and adhesion. Furthermore, light is easily tunable, and can be rapidly delivered to the location necessary to generate the reaction leaving the surroundings unaffected. While many photoreactive systems have been found there exist many ways to improve their effectiveness or elicit more useful properties from them. This dissertation focuses on three photoreactive systems generating adhesion, photomechanical motion, and spin stabilization in a crystal. Adhesion can be enabled by light through a variety of methods. Photocrosslinking, photoinduced phase changes, and mechanical bonding between surfaces have all been previously explored methods for photoadhesives. Reversible adhesion has been more elusive though. By focusing on noncovalent adhesion this experiment was able to generate a photoreversible adhesive using a polar substrate, a nonpolar glue, and spiropyran, a photochrome that changed color and polarity when exposed to light. The shear strength was increased by a factor of 5 between the reacted and unreacted state and the entire system was reversible to within 10% of its initial values. Photomechanical systems can be used to do work in place of electronic motors. 9-anthracene carboxylic acid (9AC) is a well-known thermal backreaction photomechanical system. By looking at the fluorescence recovery after photobleaching combined with calculations of the energetics of isolated molecules and those in the crystal lattice we were able to develop a deeper understanding of the crystal system. Calculations showed an energetic threshold of 80-90 kJ per mole was the limiting energy for the dimerization reaction, due primarily to the steric interactions of molecules. The absence of hydrogen fluorine intermolecular bond formation along with the energy differences was able to explain much of the observed differences in mechanical reset times. The crystal kinetics were much more complicated though as a strong concentration dependence of the dimer was observed. Two state systems have many potential applications in quantum information systems. Crystal defects are one such two state system that has seen success as a qubit candidate. 4-azidobenzoic acid generates a stable nitrene biradical when reacted in a crystal. By fluorinating the 4-azidobenzoic acid changes to the crystal structure as well as the reduced ability for the radical to form side products stabilized the nitrene for weeks at room temperature and produced the characteristic signal of a nitrene biradical at 6700 G. Both nitrenes fluoresces in the visible spectrum allowing for readouts of quantum information. The foundation of a nitrene based quantum information system has been laid but further investigation is needed to make it a reality.