Supramolecular click chemistry for the self-assembly of a stable Zn( II)–porphyrin–C 60 conjugate{ Ali Trabolsi, a Mourad Elhabiri, a Maxence Urbani, bc Juan Luis Delgado de la Cruz, c Fettah Ajamaa, c Nathalie Solladie ´,* b Anne-Marie Albrecht-Gary* a and Jean-Franc ¸ois Nierengarten* c Received (in Cambridge, UK) 28th July 2005, Accepted 21st September 2005 First published as an Advance Article on the web 28th October 2005 DOI: 10.1039/b510782b Owing to the complementarity between a bis-Zn(II)–porphyrin receptor and a fullerene ligand bearing two pyridine substi- tuents, the substrate can be clicked onto the ditopic receptor, thus leading to a stable non-covalent macrocyclic 1 : 1 complex. The use of non-covalent interactions to assemble molecular building blocks in a controlled manner is an attractive strategy to produce advanced functional materials with new optoelectronic properties. 1 However, self-assembled systems are not always very stable in solution, and the design of supramolecular ensembles with high binding constants remains an important challenge. As part of this research, we have recently developed the supramolecular click chemistry principle 2,3 as a new and powerful concept for the preparation of stable macrocyclic non-covalent arrays. Specifically, a supramolecular complex has been obtained from a bis-crown ether receptor and a bis-ammonium fullerene ligand. Owing to the complementarity of the two components, the bis-cationic substrate can be clicked onto the ditopic crown ether derivative, thus leading to a stable macrocyclic 1 : 1 complex. This new approach appears to be easily applicable to a wide range of functional groups for the preparation of new supramolecular architectures with tunable structural and electronic properties. In this paper, we now show that supramolecular click chemistry is perfectly suited for the preparation of a stable non-covalent fullerene–porphyrin hybrid system. Indeed, C 60 –porphyrin dyads are interesting molecular devices in which photoinduced intramolecular processes such as electron and energy transfer are evident. 4 Furthermore, photo- voltaic devices prepared from porphyrin–fullerene systems have shown promising energy conversion efficiencies. 5 Non-covalent C 60 –porphyrin derivatives can be easily obtained from C 60 derivatives bearing a pyridine moiety and metallopor- phyrins through coordination to the metal ion. 6 The binding constants are however rather low. 6 In order to improve the stability of such systems we have decided to apply the supramolecular click concept. The bis-Zn(II)–phorphyrinic recep- tor L 2 Zn has been selected as a platform containing two equivalent Zn binding sites separated by about 20 s. Substrate 2, bearing two pyridine sub-units, has been designed to allow the assembly of a macrocyclic clicked edifice with the L 2 Zn receptor. For the sake of comparison, binding studies have also been carried out with the reference compounds 1, pyridine (Py) and L 1 Zn. Compounds L 1 Zn and L 2 Zn have been prepared according to previously reported procedures. 7 The syntheses of compounds 1 and 2 are depicted in Scheme 1. The C s -symmetrical fullerene bis-adduct precursor 3 was obtained in eight steps as already described. 8 Reaction of dicarboxylic acid 3 with an excess of alcohol 4 in CH 2 Cl 2 under esterification conditions using N,N9-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) gave 2 in 60% yield. Compound 1 was prepared in two steps from alcohol 4. Esterification with acid 5 8 (DCC, DMAP) followed by reaction of the resulting malonate with C 60 ,I 2 and diazabicyclo[5.4.0]undec-7- ene (DBU) under Bingel conditions 9 afforded methanofullerene 1. The 1 H- and 13 C-NMR spectra of both 1 and 2 were in full agreement with their C s -symmetrical structures. Compounds 1 and 2 were also characterized by FAB mass spectrometry. In both cases, the expected molecular ion peak was observed (1: m/z 5 1400.3 [M+ H] + , calc. for C 102 H 66 NO 6 5 1400.49; 2: m/z 5 2436.1 [M + H] + , calc. for C 163 H 147 N 2 O 19 5 2436.06). The ability of bis-porphyrin L 2 Zn to form a supramolecular complex with bis-pyridine 2 was first evidenced by 1 H-NMR a Laboratoire de Physico-Chimie Bioinorganique, UMR 7509 du CNRS, ECPM, ULP, 25 rue Becquerel, 67200, Strasbourg, France. E-mail: amalbre@chimie.u-strasbg.fr; Fax: +33 (0) 3 90 24 26 39; Tel: +33 (0) 3 90 24 26 38 b Groupe de Synthe `se de Syste `mes Porphyriniques, Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077, Toulouse Cedex 4, France. E-mail: solladie@lcc-toulouse.fr; Fax: +33 (0) 5 61 55 30 03; Tel: +33 (0) 5 61 33 31 00 c Groupe de Chimie des Fullere `nes et des Syste `mes Conjugue ´s, Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077, Toulouse Cedex 4, France. E-mail: jfnierengarten@lcc-toulouse.fr; Fax: +33 (0) 5 61 55 30 03; Tel: +33 (0) 5 61 33 31 00 { Electronic supplementary information (ESI) available: UV-vis and luminescence spectrophotometric titration of L 1 Zn and L 2 Zn; F 0 /F at 600 nm vs. concentration of 1 plot. See DOI: 10.1039/b510782b COMMUNICATION www.rsc.org/chemcomm | ChemComm 5736 | Chem. Commun., 2005, 5736–5738 This journal is ß The Royal Society of Chemistry 2005