Azobenzene-functionalized cascade molecules: Photoswitchable supramolecular systems

Cascade molecules bearing up to 32 azobenzene groups in the periphery have been prepared from poly(propylene imine) dendrimers and N-hydroxysuccinimide esters. The dendritic azobenzene species show similar isomerization properties as the corresponding azobenzene monomers. The all-E azobenzene dendrimer units can be reversibly switched to the Z form by light of the appropriate wavelength and can be converted back to the E form by either irradiation or by heating. That the photoisomerization quantum yield of each photoactive unit is not dependent on the number of such units present in the species shows there is so far no effective steric constraint towards photoisomerism on increasing dimension (generation) of the dendrimer, The first attempts to use dendrimers for holography materials are described: It is shown that holographic gratings with diffraction efficiencies up to about 20 % can be optically recorded in thin films of azobenzene dendrimers.