Expanding Dendrons. The Photoisomerism of Folded Azobenzene Dendrons

Irradiation of a folded azobenzene dendron system triggers a large, reversible structural expansion. The dendrons adopt a compact helical conformation in the stable E form owing to the E geometry of azo linkage and the syn-syn preference of the dendritic branch points. E --> Z photoisomerization disrupts this folded conformation in a manner that decreases the packing efficiency and results in an expansion in hydrodynamic volume.