Photochromic 2D Metal-Organic Framework Nanosheets (MONs): Design, Synthesis, and Functional MON-Ormosil Composite

of layered porous metal-organic frameworks (MOFs) in a top-down fashion constitutes a successful approach to 2D metal-organic nanosheets (MONs), the analogs of graphene. The planned synthesis of layered MOFs is a challenging crystal-engineering exercise. Development of photochromic MONs that respond to light is a much bigger challenge; indeed, photochromic MONs are heretofore unknown. Here, we demonstrate engineering of layered MOFs and access to photochromic MONs. The strategy entails the use of programmed photochromic organic linkers characterized by a bulged core and metal-mediated self-assembly that occurs only in two dimensions, leading to layered MOFs. MONs exfoliated from such MOFs exhibit brilliant photochromism perceptible to the naked eye. We show that the MONs can be entrapped in an ormosil matrix for the development of polymer composites that display uncomplicated thermal bleaching kinetics. Thus, immobilization of photochromic 2D MONs containing void spaces in a polymer matrix for ophthalmic lens and other applications is compellingly demonstrated.