Oriented assembly of metal-organic frameworks and deficient TiO2 nanowires directed by lattice matching for efficient photoreversible color switching

The photoreversible color switching system (PCSS) is attracting increasing attention for use in alleviating energy crisis and environmental problems. We report a robust PCSS in which lattice matching enables bottom-up oriented assembly between metal-organic frameworks (MOFs) and inorganic nanocrystals (INCs), two distinct entities that differ drastically in structure and function. Specifically, cubic-phase Prussian blue (PB) of a framework backbone is spontaneously attached to rutile TiO2 nanowires in a defined orientation triggered by the lattice matching between the (001) plane of TiO2 and the (222) plane of PB. Ultraviolet light irradiation accelerates the photoelectron transport within the oriented TiO2/PB system and enables fast photo switching. The derived TiO2/PB paper can be ranked as one of the best light-printing papers in literature because of its high resolution (∼ µm) and capability to be repeatedly written for >100 times without significant loss of contrast. The ultrathin TiO2 nanowires are rich in oxygen and Ti vacancies, which allow visible- and sunlight-light printing. Density functional theory calculations suggest that the [Fe(CN)6]4− ligand from the PB attaches preferentially to the (110) surface of TiO2 to give the ordered TiO2/PB assembly. The findings demonstrate the strong versatility of particles-mediated assembly in advanced materials design.