The title cluster is luminescent at 77 K and exhibits an unsaturated site for binding anions when the counter ion is PF6−. A series of five non-luminescent metalloporphyrins exhibiting carboxylate anchoring groups were synthesized and characterized. These are the sodium salts of the 5-carboxyphenyl-tri-10,15,20-tolyl-, trans-di-5,10-carboxyphenyl-di-15,20-tolyl-, and tetra-5,10,15,20-carboxyphenyl(metallo)porphyrin (metallo = chloroiron(III), nickel(II)) anions. Evidence for supramolecular assemblies between the carboxylates and the cluster is provided by 31P NMR and UV–vis spectroscopy. The binding constant, K1n, extracted from the UV–vis data via Benesi-Hildebrand, Scott and Scatchard plots are approximately 21,000 ± 5,000 M−1 for the nickel(II) species, in agreement with the previously reported zinc(II) ones (K11 = 20,000 ± 2,000 M−1), but those for the chloroiron(III) are measured to be lower (12,500 ± 3,500 M−1). This association is accompanied by a complete quenching of the luminescence of the cluster which can only be due to an efficient energy transfer to the d–d states of the chloroiron(III) and nickel(II) species but an electron transfer from the nickel(II)-containing chromophore to the cluster is also possible. This work demonstrates the profound effect that supramolecular interactions may have on the photophysical properties despite the long donor–acceptor separation.
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This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), le Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT), the Centre d’Etudes des Matériaux Optiques et Photoniques de l’Université de Sherbrooke (CEMOPUS), and the Agence National de la Recherche (ANR) for a grant of a Research Chair of Excellence. PDH thanks Prof. C. Reber for the Université de Montréal for the measurement of the solid state emission spectra of the title cluster.
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