Supramolecular Chemistry DOI: 10.1002/ange.200801334 Self-AssemblyofaLight-HarvestingAntennaFormedbyaDendrimer, aRu II Complex,andaNd III Ion** CarloGiansante,PaolaCeroni,*VincenzoBalzani,andFritzVögtle Self-assembly of molecular components by weak, non-cova- lent interactions is widespread in nature)s forms and func- tions [1] and is attracting increasing interest in artificial systems. [2] The study of light-induced processes in artificial molecular assemblies is a very promising approach to control mechanical movements, process information, and harvest sunlight. [3] Lanthanide metal ions exhibit long-lived and line-like luminescence, but direct excitation of lanthanide metal ions is inefficient because of the forbidden nature of their electronic transitions. Therefore, coordinating organic or inorganic chromophores are usually exploited to sensitize the lumines- cence of the ions (antenna effect). [4] A particularly interesting class of ligands are dendrimers because they can collect excitation light and encapsulate chemical species in prede- termined sites. [5] We report herein on a three-component self- assembled light-harvesting antenna formed by a dendrimer, a Ru II complex, and a luminescent Nd III ion. Dendrimer D (Scheme 1), consisting of a 1,4,8,11-tetra- azacyclotetradecane (cyclam) core with appended 12 dime- thoxybenzene and 16 naphthyl units [6] encapsulates Nd III ions, but, when photoexcited, it is unable to transfer energy to the metal ion. [7] We have now found that when Nd III is added, as trifluoromethanesulfonate salt, to a CH 3 CN:CH 2 Cl 2 solution containing D and [Ru(bpy) 2 (CN) 2 ] in a 1:1 molar ratio, self- assembly leads to a three-component system, {D·Nd III ·[Ru- (bpy) 2 (CN) 2 ]}, in which the luminescence of both D and [Ru(bpy) 2 (CN) 2 ] is quenched and the luminescence of Nd III is sensitized. In this three-component system excitation of the dendrimer in the UV and of the Ru II complex in the Vis and UV spectral regions is indeed followed by efficient energy transfer to the lanthanide metal ion which emits NIR light, and plays the role of a light harvesting unit. For comparison purposes, we have also investigated the systems in which Gd III replaces Nd III . Dendrimer D has a single and strongly coordinating site, thatis,itscyclamcore.InCH 3 CN:CH 2 Cl 2 1:1(v/v)solution, D forms stable D 2 M complexes, [8] where M = Nd III , Eu III , Gd III , Tb III , Dy III (see Supporting Information). Complexes of Ru II containing 2,2’-bipyridine (bpy) and cyanide ligands, [Ru(bpy) 2 (CN) 2 ] and [Ru(bpy)(CN) 4 ] 2À , are particularly interesting because they are luminescent and can play the role of ligands giving rise to supercomplexes. [9,10] In particular, [Ru(bpy) 2 (CN) 2 ] has low-energy absorption bands and a luminescence band in the visible region which are related to metal-to-ligand (bpy) charge-transfer (MLCT) excited states (spin-allowed states for the absorption bands; the lowest spin-forbidden state for the emission band). [9b,c,11] The energies of these excited states are strongly dependent on the interaction of the cyanide ligands with solvent mole- cules, [9,11] proton, [12] or metal ions. [13] In particular, the lowest energy band maximum shifts toward the blue when cyanide ligands are linked to a cation because of the lower electron Scheme 1. Formulae of dendrimer D and the [Ru(bpy) 2 (CN) 2 ] complex. [*] C. Giansante, Prof. Dr. P. Ceroni, Prof.Dr. V. Balzani Dipartimento di Chimica “G. Ciamician” Università di Bologna Via Selmi 2, 40126 Bologna (Italy) Fax: (+ 39)051-209-9456 E-mail: paola.ceroni@unibo.it Prof. Dr. F. Vögtle KekulØ-Institut für Organische Chemie und Biochemie Universität Bonn Gerhrad-Domagk Strasse 1, 53121 Bonn (Germany) [**] This work has been supported in Italy by MIUR (PRIN 2006034123_003). Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Zuschriften 5502 # 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2008, 120, 5502 –5505