My ACS Macro Letters paper where I, along with Malar Azagarsamy, characterized the gelation and degradation behavior of a PEG hydrogel containing a photodegradable coumarin moiety in the crosslinker. We found the coumarin molecule enables extremely rapid degradation at both visible and ultraviolet wavelengths behaves very nicely in accordance with established theories. Have a read at http://pubs.acs.org/doi/abs/10.1021/mz500230p. The abstract is pasted below:

The design, synthesis, and characterization of a new class of coumarin-based photodegradable hydrogels are reported. Hydrogel formation was achieved rapidly and efficiently under aqueous conditions using copper-catalyzed click chemistry, which afforded excellent control over the rate of network formation. Rapid photodegradation, to the point of reverse gelation, was observed using both 365 and 405 nm light, and micrometer-scale features were eroded using two-photon irradiation at wavelengths as long as 860 nm.