When exposed to UV (365 nm, 2 mW) radiation, the bulk crystals of a two-dimensional metal–organic framework [Hphen]₂[(UO₂)₂(ox)₃] (1,phen = 1,10-phenanthroline, ox = oxalate) are exfoliated into thin sheets (2 μm) and its photoluminescence can be quenched in an incredibly sensitive manner, setting 1 as a superior UV-detection material. When upgrading the UV source into a 300 W xenon light source, the crystals of 1 can be further exfoliated into monolayer nanosheets (0.92 nm).