Synthesis and photochemical behavior of phosphorus dendrimers containing azobenzene units within the branches and/or on the surface

We describe the synthesis of three series of phosphorus-containing dendrimers having azobenzene derivatives specifically placed at some generations in the interior and/or on the surface. The largest compound obtained possesses 48 azobenzene groups on the surface. Irradiation at 350 nm induces isomerization of the azobenzene groups from the E form to the Z form, whatever their location. The thermal back-isomerization to the E form in the dark at room temperature was observed in all cases. The kinetics of this Z-->E back-isomerization was studied in several cases; the rate is not dependent on the number of azobenzene units or of the generation, when the azobenzene groups are linked to the surface of the dendrimer. A different behavior was observed when the azobenzene groups were located within the framework of the dendrimer.