A Change of Pace: Record\nPhotoresponse through Spirooxazine\nConfinement in a Metal–Organic Matrix

Modern and upcoming high-speed optoelectronics\nas well\nas secure\ndata storage or solar energy harvesting technologies integrating stimuli-responsive\nmaterials fully rely on the fundamental concept of rapid transitions\nbetween discrete states possessing different properties. Relatively\nslow transition kinetics between those states for commonly used classes\nof photochromic compounds in solution or bulk solids severely restrict\nthe applicability of stimuli-responsive materials for device development.\nHerein, we report a multivariate strategy based on a photochromic\nspirooxazine derivative, coordinatively integrated in the solvent-free\nconfined space of a solid-state matrix, such as a metal–organic\nframework (MOF), for the first time, resulting in the fastest photoresponse\nreported for any solid-state material to date. The photoisomerization\nrate for the developed photochromic material was estimated to be 126\ns<sup>–1</sup>, surpassing any literature reports to the best\nof our knowledge. We also shed light on the fundamentals of the correlation\nbetween framework topology, the nature of organic linkers, and the\npresence/absence of organic solvent within the scaffold voids on the\nmaterial photoresponse using a series of isoreticular frameworks.\nOverall, the presented conceptual approach allows for tailoring the\nisomerization kinetics of photochromic molecules in the solid state\nover a range of 4 orders of magnitude–an unprecedented span\nthat provides a pathway for addressing challenges associated with\nthe response rate and photoisomerization, which are key criteria in\nstimuli-responsive material development.