Single-crystal-to-single-crystal [2+2] photodimerizations: from discovery to design

The purpose of this review is to address fundamentals and applications of single-crystal-to-single-crystal (SCSC) reactions, based on the [2+2] photodimerization. An overview of SCSC [2+2] photodimerizations, which comprise single- and multi-component solids, will be given. We reveal that materials that exhibit SCSC reactivity can be considered to have been achieved via either discovery or design. We suggest that SCSC [2+2] photodimerizations, if generally achieved, could provide new avenues to control bulk physical properties of solid-state materials.