Highly dense packing of chromophoric linkers is achieved in a novel pyrene-based metal-organic framework (MOF), [Zn(TBAPy)(1/2)(H2O)(2)], induced by an ionic liquid. This MOF displays a quick response to visible-light irradiation (photocurrent density of up to 4.492 mu A cm(-2)) and is capable of repetitive on-off photocurrent switching with a large on-off ratio (37.55).