Triggering proton-coupled electron-transfer (PCET) reactions with light in a nanoconfined host environment would bring about temporal control on the reactive pathways via kinetic stabilization of intermediates. Using a water-soluble octahedral Pd(6)L4 molecular cage as a host, we show that optical pumping of hostguest charge transfer (CT) states lead to generation of kinetically stable phenoxyl radical of the incarcerated 4-hydroxy-diphenylamine (1-OH). Femtosecond broadband transient absorption studies reveal that CT excitation initiates the proton movement from the 1-OH radical cation to a solvent water molecule in similar to 890 fs, faster than the time scale for bulk solvation. Our work illustrates that optical hostguest CT excitations can drive solvent-coupled ultrafast PCET reactions inside nanocages and if optimally tuned should provide a novel paradigm for visible-light photocatalysis.