Photoisomerization in dendrimers by harvesting of low-energy photons

摘要

Infrared radiation can induce low-frequency molecular vibrations, but, with the exception of hydrogen-bond reorganization, the excitation energy tends to be dissipated rapidly through molecular collisions rather than inducing photochemical changes. Here we show that in a macromolecular system that is designed to be insulated against collisional energy scattering, infrared absorption can excite photoisomerization by multi-photon intramolecular energy transfer. We have prepared highly branched dendrimers from aryl ethers with a photoisomeriz-able azobenzene core, in which infrared excitation of the aromatic units is apparently followed by a channelling of the absorbed energy to the core while the dendrimer matrix protects against collisional de-excitation. These findings suggest a strategy for harvesting low-energy photons to effect chemical transformations.