Photochemical Upconversion: Molecules, Materials, and New Frontiers
One focus of our research program involves the study of sensitized triplet fusion (TF) processes that convert low energy photons to higher energy light. Selective excitation of long-wavelength absorbing triplet sensitizers in the presence of appropriate molecular acceptors enables TF, resulting in either frequency upconverted light or the formation of desired chemical products. Various combinations of donor and acceptor have been explored and data will be presented on a number of these compositions spanning light conversions ranging from the near-UV to the near-IR. This presentation will also describe recent examples of upconversion phenomena realized in solid-state and fluidic polymeric materials along with emerging classes of sensitizers and acceptor/annihilator chromophores. Semiconductor (SC) nanocrystals are demonstrated to sensitize interfacial triplet-triplet energy transfer with molecular acceptors, providing a general paradigm for extracting triplet exciton energy from SC nanomaterials while extending their reactivity time by several orders-of-magnitude. The concept of SC nanocrystals serving as effective surrogates for molecular triplets suggests myriad of possible chemical and redox transformations relevant for fields as diverse as optoelectronics, solar energy conversion, and photobiology.