Photophysical properties of pheophorbide-a-substituted diaminobutane poly-propylene-imine dendrimer

Dendrimers are very promising molecules as hosts for guest embedding as wel l as for multiple covalent coupling of dye molecules to their peripheral gr oups. The use of such dendrimer-dye conjugates as part of a modular carrier system for photodynamic therapy has recently been discussed. Using covalen t coupling we accomplished an average loading of 12-13 molecules of pheopho rbide a to one diaminobutane poly-propylene-imine dendrimer molecule of the third generation (DAB dendrimer) having a total number of 16 binding sites . This was confirmed with various photophysical measurements and MALDI-mass spectrometry. As long as the dye molecules are covalently bound to the dendrimer, their p hotosensitized generation of singlet oxygen is reduced dramatically due to interactions between different dye molecules. The main interaction is suppo sed to be a Forster-energy transfer along the surface of the dendrimer-dye complex. Nevertheless the remaining photo-physical generated singlet oxygen leads to a destruction of the dendrimer backbone under illumination. The p hotophysical properties of the covalently linked dye-dendrimer complexes an d especially the remarkable influence of illumination on these properties a re presented in this paper. (C) 2001 Elsevier Science B.V. All rights reser ved.