We describe stable intercalation compounds of the composition xN(2)center dot WO3 (x = 0.034-0.039), formed by trapping N-2 in WO3. The incorporation of N-2 significantly reduced the absorption threshold of WO3; notably, 0.039N(2)center dot WO3 anodes exhibited photocurrent under illumination at wavelengths <= 640 nm with a faradaic efficiency for O-2 evolution in 1.0 M HClO4(aq) of nearly unity. Spectroscopic and computational results indicated that deformation of the WO3 host lattice, as well as weak electronic interactions between trapped N-2 and the WO3 matrix, contributed to the observed red shift in optical absorption. Noble-gas-intercalated WO3 materials similar to xN(2)center dot WO3 are predicted to function as photoanodes that are responsive to visible light.