Photophysical properties of peripherally charged dendrimers designed for two-photon excited fluorescence imaging

Water soluble dendritic structures with significant two-photon absorption (TPA) properties in the biological spectral window (700-1100 nm) are of particular interest for several biomedical applications [1]. As fluorescent probes for bioimaging, in particular, dendrimeric nano-objects with high two-photon brilliance (?2?) are required. The one-photon photophysical characterization of newly designed organic dots is thus important to determine their emissive properties and to disentangle their dependence on environmental aspects such as solvent polarity and aggregation induced effects. We report here on the one-photon characterization of a series of newly designed dendrimers based on a phosphorous based scaffold linked to TPA active fluorophores, decorated with cationic groups on the periphery in order to achieve hydrophilicity. Dendrimers of generation 2 up to 3 containing two different fluorophores have been studied. The number of peripheral charges varies between 24 and 48 (Figure 1). Detailed steady-state and time-resolved spectroscopic studies have been performed in solvents of different polarity, with reference to monomer fluorophores chosen as models. The photophysical properties of the dendrimers are discussed on the basis of thermodynamic grounds and on the analysis of aggregation effects, where both intra-molecular and inter-molecular interactions are taken into consideration. The European Community's Seventh Framework Programme under TOPBIO project - grant agreement n. 264362 - is gratefully acknowledged. [1] Mongin, O.; Rouxel, C.; Vabre, J.-M.; Mir, Y.; Pla-Quintana, A.; Wei, Y.; Caminade, A.-M.; Majoral, J.-P.; Blanchard-Desce, M. Proc. SPIE-Int. Soc. Opt. Eng. 2009, 7403, 740303/1-740303/12.