We are developing photoswitches to modulate structure-function relationships in molecules and materials. Our chromophores interconvert between two isomers when exposed to two different colours of light, each isomer having unique electronic and structural properties. We use them to:

control reactivity,
unlock potential therapeutics and catalysts,
act as convenient visual detectors for toxic agents,
release small molecules ‘on-demand’,
reversibly turn ‘on’ and ‘off’ paralysis in living organisms,
act as a photoresponsive mimic of the enzyme cofactor pyridoxal phosphate,
control dry-adhesives based on the microstructures found in the natural wall-crawlers such as geckos,
‘lock’ and ‘unlock’ thermal reactions such as the Diels-Alder cycloaddition, and
control the strength of polymer adhesives.

We take advantage of the fact that gold nanoparticles absorb green or red light and convert it to heat to break bonds in small molecules and release them from the surface of the nanoparticles. Our original studies focused on releasing fluorescent dyes and single-strands of DNA, and we have demonstrated this in live cells. We are using light to heat nanoparticles and release singlet oxygen (a known therapeutic), which has the advantage over traditional photodynamic therapy that the system brings the oxygen along with the nano-assembly and one does not have to rely on the presence and collision of molecular oxygen with the sensitizer. We are combining our photoswitches with our nanoparticles to show that two colors of light are needed to break bonds and release small molecules from the surface of the nanoparticles, providing (much like a ‘logic gate’) a heightened level of control over release processes.

We use lanthanide-doped upconverting nanoparticles (UCNPs) to convert multiple near infrared photons into UV and visible light to trigger photochemistry on and near the surface of the nano-systems. This approach is very general and can be used to “uncage” sequestered molecules, to trigger the dissociation of block copolymer micelles and release biomacromolecules from hydrogels. Our systems are also potentially useful as optical probes when combined with some of our photoswitches. The emission from the UCNPs can be turned on and off depending on which isomeric form the switch is in and this is effective in live organisms where the organic ligands reversibly quench the emission from the nanoparticles as a new motif for imaging technologies. We are developing advanced nano-systems where based on the power of the NIR light, either UV or visible light can be generated, which can be used for two-way photoswitching. This an illustrative example where only one nanoparticle and only one type of light are needed to induce selective photochemistry.

We are developing UCNPs that are water compatible but still allow organic photochemistry to take place. We achieve this by wrapping our UCNPs in amphiphilic polymer shells that provide nano-environments for organic species to be sequestered. This ‘plug-and-play’ strategy represents a relatively universal method to synthesize complex systems for use in imaging applications, where many photoreactions of organic compounds are suppressed (or the chromophore is simply not soluble in water).

Other materials we have investigated are:

the materials in kidney stones,
self-assembling structures made up of hydrogen bonds, and
self-assembling structures made up of coordination chemistry.