Metastable-State Photoacids and Polymers with High Photoacidity
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In recent years, metastable-state photoacids (mPAH) have been utilized to control various chemical processes using visible light and have found many applications in materials, energy, and biomedical areas. An introduction of metastable state photoacid is given in Chapter 1. In chapter 2, to clearly understand the relationship between the structures and the physicochemical properties of mPAHs, a series of mPAHs were designed and synthesized. The reversibility, stability, reverse reaction rate, and photoreaction of the mPAHs were studied in detail using UV/VIS spectroscopy. The results demonstrated that the electron-withdrawing groups on the electron-accepting moiety enhance the overall photoreaction and stability of closed-ring form, while the electron-donating group increase reversibility and decrease photoreaction. In Chapter 3, a facile synthesis of merocyanine photoacid polymers without using any protecting group is described. The polymers showed good photoactivity, high photoacidity, and were soluble in various solvents. Reversible patterning has been demonstrated using a thin film of the polymer doped with methyl orange. In Chapter 4, a novel mPAH with strong C-H acidity was described. The pKa of its photoacidic state was experimentally determined and compared to a commonly used mPAH. The photoacid showed low dark acidity and large pKa change when irradiated by visible-light. The pKa for the photoinduced C-H acidity is 4.8 units lower than that for the O-H acidity in the dark. These features together with its easy preparation make it promise for the development of photoresponsive materials based on proton transfer. Proton transfer between the photoacid and proton acceptors with different pKas in solutions and polymer films was studied. The photoacid showed superior properties in polymer films comparing to a commonly used mPAH. Photochromic films with various color changes were demonstrated as an example of potential application. In the work described in Chapter 5, a series of mPAHs were designed and synthesized, where chlorine was introduced to increase in the solubility and photoacidity of indazol mPAH. Other works for increasing the activating wavelength of the photosensitive molecules, photo release, and proton acceptors are also described in this chapter.