PHOTOISOMERIZATION IN DENDRIMERS BY HARVESTING OF LOW-ENERGY PHOTONS

Infrared radiation can induce low-frequency molecular vibrations, but, with the exception of hydrogen-bond reorganization(1-3), the excitati on energy tends to be dissipated rapidly through molecular collisions rather than inducing photochemical changes. Here we show that in a mac romolecular system that is designed to be insulated against collisiona l energy scattering, infrared absorption can excite photoisomerization by multiphoton intramolecular energy transfer. We have prepared highl y branched dendrimers(4-6) from aryl ethers with a photoisomerizable a zobenzene core, in which infrared excitation of the aromatic units is apparently followed by a channelling of the absorbed energy to the cor e while the dendrimer matrix protects against collisional de-excitatio n. These findings suggest a strategy for harvesting low-energy photons to effect chemical transformations.