1754 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J. Am. Chem. SOC. zyxwvutsr 1995,117, 1754-1758 Aggregation in Fluid Solution of Dendritic Supermolecules made of Ruthenium(I1) zyxw - and Osmium(I1)-Polypyridine Building Blocks Sebastiano Campagna,*@ Antonino Giannetto? Scolastica Serroni? Gianfranco Denti,lb Sebastiano Truss0,1C Francesco Mallamace,ld and Norbert0 Micali*JC Contribution from the Dipartimento di Chimica Inorganica, Analitica e Struttura Molecolare dell ’Universith, via Sperone 31, I-98166 Vill. zyxw S. Agata, Messina, Italy, Laboratorio di Chimica Inorganica, Istituto di Chimica Agraria dell’Universitic, via S. Michele degli Scalzi 2, I-50124 Pisa, Italy, Dipartimento di Fisica dell’Universitii, via Sperone 31, 1-98166 Vill. S. Agata, Messina, Italy, and Istituto di Tecniche Spettroscopiche del CNR, via Sperone 31, I-98166 Vill. S. Agata, Messina, Italy Received June 14, I994@ Abstract: Elastic and quasi-elastic light scattering and conductivity experiments have been performed on the supramolecular species [Ru{ zyxwvuts @-2,3-dpp)Ru[@-2,3-dpp)R~(bpy)~1~}31(PF6)~0,1, and [Os{ @-2,3-dpp)Ru[@-2,3-dpp)- Ru(bpy)2]2}3](PF6)20, zyxwvutsr 2, in dilute fluid solution at room temperature (bpy = 2,2’-bipyridine; 2,3-dpp = 2,3-bis(2- pyridy1)pyrazine). Aggregation phenomena occur in fluid solution for 1 and 2 even at concentrations as low as M. The dimension of the aggregates at 298 K in a M acetonitrile solution is about 100 nm. The effects of ionic strength and solvent polarity on the aggregation are discussed. Intermolecular attractive interactions between the hydrophobic aromatic moieties of the supermolecules are likely at the basis of the aggregation process. The results obtained indicate that the nanometer-sized hyperbranched supermolecules investigated here zyx can be considered as colloidal systems as far as the aggregation properties are concerned. Introduction Design and synthesis of ultralarge supramolecular species (nanostructures) capable of exhibiting specific functions is an important challenge now facing chemistry.2 Well-defined na- nometric species can be obtained by the “cascade a p p r ~ a c h ” ~ (hyperbranched molecules, also called cascade molecules, dendrimers, or arborols) and can be considered as a bridge between molecular and material science^.^ Properties and new applications of these species are only beginning to be expl~red.~~~~*~-~ On the other hand, it is known that various nanometer-sized species, such as microemulsion, micelles, silica particles, and biological macromolecules, can organize themselves in semi- @ Abstract published in Advance ACS Abstracts, January 1, 1995. (1) (a) Dipartimento di Chimica Inorganica, Universith zyxwvuts di Messina. (b) Istituto di Chimica Agraria, Universita di Pisa. (c) ITS-CNR, Messina. (d) Dipartimento di Fisica, Universita di Messina. (2) (a) Lehn, J.-M. Angew. Chem., zyxwvutsrqpo Znt. Ed. Engl. 1988,27, 89. (b) Molecular Electronic Devices; Carter, F. L., Siatkowski, R. E., Woltjen, H., Eds.; North Holland Amsterdam, 1988. (c) Lehn, J.-M. Angew. Chem., Znt. Ed. Engl. 1990, 29, 1304. (d) Whitesides, G. M.; Mathias, J. P.; Seto, C. T. Science 1991, 254, 1312. (e) Ball, P.; Garwin, L. Nature 1992,355, 761. (3) (a) Buchlein, E.; Wehner, W.; Vogtle, F. Synthesis 1978, 155. (b) Newkome, G. R.; Baker, G. R.; Saunders, M. J.; Russo, P. S.; Gupta, V. K.; Yao, Z.; Miller, J. E.; Bouillon, K. J. Chem. Soc., Chem. Commun. 1986,752. (c) Tomalia, D. A.; Naylor, A. M.; Goddard, W. G., Ill Angew. Chem., In?. Ed. Engl. 1990,29, 138. (d) Serroni, S.; Denti, G.; Campagna, S.; Juris, A.; Ciaho, M.; Balzani, V. Angew. Chem., Znt. Ed. Engl. 1992, 31, 1493. (e) Miller, T. M.; Neenan, T. X.; Zayas, R.; Blair, H. E. J. Am. Chem. SOC. 1993, 115, 356. (f) Mourey, T. H.; Turner, S. R.; Rubinstein, M.; Frkchet, J. M. J.; Hawker, C. J.; Wooley, K. L. Macromolecules 1992, 25, 2401. (4) (a) Mekelburger, H.-B.; Jaworek, W.; Vogtle, F. Angew. Chem., Znt. Ed. Engl. 1992, 31, 1571. (b) Kim, Y. H. Adv. Mater. 1992, 4, 764. (c) Hodge, P. Nature 1993,362, 18. (d) Dagani, R. Chem. Eng. News 1993, 71 (4), 28. (e) Frbchet, J. M. J. Science 1994, 263, 1710. macroscopic edifices in s ~ l u t i o n . ~ . ~ For example, latex particles of 80 nm diameter at a volume fraction of in water and a salt concentration of M give rise to formation of clusters in which the internal structure is self-similar (fractal dimension, 2.1) and the dynamics are governed by reaction limit aggrega- ti or^.^^^ For temary microemulsions (decane/water/dodecyl sulfoxysuccinate),the growth of percolation clusters with fractal dimension 2.5 is observed as a function of temperature. The size of the clusters can reach a fraction of a micrometer, while the dimensions of the droplets are on the order of 10 nm.5’6 Biological macromolecules in water solution (e.g., lysozima, BSA, DNA) show aggregation phenomena, and the structure exhibits a diffusion-limited cluster-cluster aggregation (fractal dimension, 1.75).536 Some of us have recently prepared nanometer-sized hyper- branched supermolecules made of Ru(II) and Os(II) building blocks which exhibit quite interesting photophysical and electrochemical Here, we report the aggregation properties in acetonitrile at very low concentrations of two representative species of this family of compounds, studied by laser light scattering and conductivity experiments. The reported investigation concems the decanuclear species [Ru{@-2,3-dpp)- (5) (a) Mallamace, F.; Micali, N. Croat. Chem. Acta 1992,65, 379. (b) Magazil, zyxwvu S.; Maisano, G.; Mallamace, F.; Micali, N. Phys. Rev. A 1989, 39, 4195. (c) Mallamace, F.; Micali, N. Long-Range Order in Disperse Systems; La Rivista del Nuovo Cimento, Societa Italiana di Fisica: Bologna, 1992. (6) (a) Majolino, D.; Mallamace, F.; Migliardo, P.; Micali, N.; Vasi, C. Phys. Rev. A 1989, 40, 4665. (b) Bolle, G.; Cametti, C.; Codastefano, P.; Tartaglia, P. Phys. Rev. A 1987, 35, 837. (c) Cametti, C.; Codastefano, P.; Tartaglia, P. Phys. Rev. A 1987,36, 4916. (7) (a) Serroni, S.; Denti, G.; Campagna, S.; Ciano, M.; Balzani, V. J. Chem. Soc., Chem. Commun. 1991, 944. (b) Denti, G.; Campagna, S.; Serroni, S.; Ciano, M.; Balzani, V. J. Am. Chem. SOC. 1992,114, 2944, and references therein. 0002-7863/95/1517-1754$09.00/0 0 1995 American Chemical Society