Adding Spatial Control to Click Chemistry: Phototriggered Diels-Alder Surface (Bio)functionalization at Ambient Temperature

摘要

The recent years have witnessed a substantial increase of attention in the modification of materials by the highly efficient chemical methods often referred to as click chemistry. The set of reactions belonging to this class exhibit specific features such as fast reaction kinetics, high yields, orthogonal reactivity, and tolerance to a wide range of solvents. However, in some applications featuring surface patterns or three-dimensional scaffolds, these characteristics are not sufficient, because spatial control is also required. Furthermore, temporal control of chemical reactions could offer the significant advantage of triggering reactions at any time, which would be particularly interesting when a specific sequence of events is required. The use of light as a temporal and spatial trigger has very recently been applied to click methods. For instance, Bowman and co-workers reported patterns of hydrogels fabricated by azide-alkyne cycloaddi-tion cross-linking initiated by the phototriggered reduction of Cu~(II) into Cu~I, the latter being the catalyst for this reaction. However, their method presents the disadvantage of involving many species, such as the different copper species and the radical photoinitiator required to generate Cu~I. Although no such effect was reported, these species are able to diffuse in the medium and could hinder the spatially resolved character. The same applies to the widely used photoinitiated radical thiol-ene and thiol-yne reactions.