Photostability of Organic Glasses under Extreme Nanoconfinement*

Photodegradation is usually caused by a complex series of chemical reactions initiated by the absorption of ultra-violet light, which drastically reduces effective lifetime of advanced organic functional materials. Previous work has established capillary rise infiltration (CaRI) technique can induce extreme nanoconfinement and significantly affect the properties of materials.
Here we investigate photochemical behavior of highly confined indomethacin (IMC) in silica nanoparticles (NPs) under ultra-violet light with 254 nm and 365 nm wavelengths under anaerobic and ambient conditions with in-situ spectroscopic ellipsometry measurements. We observe that as the NP size is decreased, increasing the degree of confinement, photodegradation time is increased and IMC mass loss is decreased. The extreme nanoconfinement limits diffusion of free radicals, oxygen, and reaction products during photodegradation, enabling enhanced photostability. Given the mostly entropic nature of this process, it is expected that other molecules would also show enhanced photo/thermal stability upon increased nanoconfinement.