Photochemical [2+4]-Dimerization Reaction from the Excited State.

Aryl-maleimides undergo a novel [2+4]-photodimerization instead of the expected [2+2]-photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl-maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non-bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions.

Modulating Photochemical Properties to Enhance the Stability of Electronically Dimmable Eye Protection Devices†.

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole-based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers.

Towards Upcycling Biomass-Derived Crosslinked Polymers with Light.

Photodegradable, recyclable, and renewable, crosslinked polymers from bioresources show promise towards developing a sustainable strategy to address the issue of plastics degradability and recyclability. Photo processes are not widely exploited for upcycling polymers in spite of the potential to have spatial and temporal control of the degradation in addition to being a green process. In this report we highlight a methodology in which biomass-derived crosslinked polymers can be programmed to degrade at ≈300 nm with ≈60 % recovery of the monomer. The recovered monomer was recycled back to the crosslinked polymer.

Manipulating excited state reactivity and selectivity through hydrogen bonding - from solid state reactivity to Brønsted acid photocatalysis.

Hydrogen bonding mediated control of photochemical reactions is highlighted with an eye towards the development of Brønsted acid mediated photocatalysis.

A phototunable anion receptor for C-HX interactions with benzoate anions.

A supramolecular receptor consisting of two anthracene moieties with binding motifs for binding of benzoate anions is reported here. NMR studies indicate that the binding involves π-π interactions and CHX interactions. Upon exposure to >350 nm light, the receptor undergoes a [4 + 4] photoelectrocyclization restricting the access to the binding site for benzoate. The reverse reaction works in the presence of the dual stimuli of 254 nm light and the benzoate anions. The work thus demonstrates a light mediated dynamic control of the binding pocket of a supramolecular anion receptor.