The lighter side of MOFs: structurally photoresponsive metal-organic frameworks

Metal-organic frameworks (MOFs) have emerged over the past two decades as highly promising materials in the gas storage and separation arenas, with the potential to act as rapid uptake/rapid release sorbents for CO2, CH4 and H-2 that may have significant impact in energy and sustainability technologies. However, a small but growing subset of the MOF community have been developing alternative, light-induced applications of MOFs. This review briefly outlines some of these exciting diversions from the 'traditional' applications of MOFs and focusses particularly on the design strategies of those frameworks that undergo photoinduced structural change. These strategies are classified as either (i) the imposition of photoresponsivity by a photoresponsive guest; (ii) post-synthetic modification (PSM) of frameworks to add in photoresponsive groups; (iii) synthesis of MOFs with linkers that support pendant photoresponsive groups; and, perhaps the most challenging, (iv) synthesis of MOFs from linkers that themselves have intrinsic structural photoresponsivity such that their structure is altered on illumination. Examples are given of each approach, future applications are proposed, and strategic pathways to next-generation photoresponsive frameworks are discussed.