Relationship between chemical reactivity and photochromism using 1,2-dithienylethene-based molecular switches

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(Thesis) Ph.D.
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Molecular systems with integrated chemical reactivity and photochromic functions are potentially beneficial for the development of novel functional materials. Rationally designed photoresponsive compounds can be used to regulate chemical reactivity using light, and such systems could significantly influence both synthesis and drug delivery by increasing efficiency and decreasing undesired side-reactions or side effects. Chemical reactivity can also be employed to control the photochromic behaviour of photoswitches, providing a locking mechanism and enabling chemical detection through facile monitoring. Dithienylethene-based molecular switches are particularly well-suited to the development of functional systems with integrated chemical reactivity functions since they can be toggled between two thermally stable and structurally unique isomers when irradiated with light of the appropriate wavelengths. Dithienylethene derivatives exhibit significant differences between their ring-open and ring-closed forms, which can influence their reactivity. Alternatively, multiple strategies permit the regulation of their photochromic properties through chemical reactions or interactions. The research presented in this thesis focuses on the development of novel approaches to integrate photochromism and chemical reactivity. First, the concept of reactivity-gated photochromism is introduced and demonstrated using a spontaneous and mild chemical reaction. Results show that non photoswitchable molecules can be rendered photoactive by creating the dithienylethene architecture using the Diels-Alder cycloaddition. The use of the dithienylethene architecture as a photocleavable group that combines reactivity-gated photochromism and photogated reactivity is then presented. This approach is based on the Diels-Alder reaction between photostable dienes and dienophiles to generate photoswitchable dithienylethene derivatives. The photoresponsive unit is employed to regulate the reverse cycloaddition, enabling selective and sequential photorelease of the small dienophile auxiliary. Finally, the Lewis acidity of a boron-containing dithienylethene derivative is photomodulated. Upon exposure to light of the appropriate wavelengths, the isomerisation of the dithienylethene backbone causes a bond rearrangement of the 1,3,2-dioxaborole unit, directly affecting the electron density of the boron centre and changing the Lewis acidity of the atom.
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