The Use of Light to Control Photo-thermoresponsive Systems

Integration of light and chemical reactivity is potentially beneficial for developing new materials with chemical and physical properties that can be regulated by light. Molecular switches based on the 1,2-dithienylethene (DTE) architecture are a class of photochromic molecules that can integrate light and chemical reactivity, providing a platform to develop these new materials. Photochromic dithienylethene derivatives can toggle between two electronically and structurally unique isomers when irradiated with light of an appropriate wavelength. The electronic and structural changes of dithienylethene derivatives can be employed to regulate chemical reactivity using light, which makes them very attractive for many applications such as controlled drug delivery, catalysis and imaging. Alternatively, chemical reactivity can be used to regulate the photochromic properties of dithienylethenes, making them useful in applications such as monitoring and detection. This thesis describes the success in integrating light and chemical reactivity to develop new thermoresponsive materials having the ability to respond to changes in temperature that also can be controlled by light. In a first study (Chapter 2), the concept of the reactivity-gated photochromism is expanded using the Diels-Alder reaction between a series of photoswitchable dienes and dienophiles. It is shown that the electronic changes that occur during the isomerization of a cleavable dithienylethene derivative “gates” the reversibility of the Diels-Alder reaction. An external heat source can only trigger the reverse Diels-Alder reaction when the molecule is first irradiated with light of an appropriate wavelength. In a second study (Chapter 3), a new thermally self-healing polymer is developed by the Diels-Alder reaction between dithienylfuran (DTF) and maleimide monomers to generate a photoresponsive dithienylethene. Results show that UV and visible light “gate” the reversibility of the Diels-Alder reaction and turn the self-healing properties of the polymer ‘off’ and ‘on’, respectively. The thermoresponsive polymer developed in this chapter requires an external heat source to trigger the reverse Diels-Alder reaction. In a third study (Chapter 4), a thermoresponsive anthracene endoperoxide ligand is anchored on the surface of gold nanoparticles. Results show that the indirect heat generated during the photothermal effect of gold nanoparticles triggers the bond-breaking reaction and releases singlet oxygen. In a fourth study (Chapter 5), a new strategy to control the photothermal release of small molecules from the surface of SiO2−Au core-shell nanoparticles is presented. It is shown that irradiation of the nanosystem with visible light triggers the ring-opening reaction of a dithienylethene chromophore then the indirect heat generated by the NIR light induces the reverse Diels-Alder reaction and releases small molecules. Similar to AND logic gate, this system requires both inputs (NIR and visible light) to be present to achieve the desired output (bond-breaking and release).