title: A molecular clip throws new light on the complexes formed by a family of cyclam-cored dendrimers with Zn(II) ions. Efficient energy transfer in the heteroleptic complexes.
abstract: Complexation of Zn(II) ions by cyclam cored dendrimers appended with four (G0), eight (G1) and 16 naphthyl chromophores (G2) at the periphery have been investigated in CH₃CN-CH₂Cl₂ 1 : 1 (v/v) solution by absorption and emission, ESI-mass and ¹H NMR spectroscopy. The results obtained can be interpreted by the formation of complexes of 2 : 1 dendrimer to metal stoichiometry, at low metal ion concentration, and 1 : 1 complexes upon further addition of Zn(II) ions, for all the dendrimer generations. Upon addition of a molecular clip C²⁻ consisting of two anthracene sidewalls bridged by a benzene group with two sulfate substituents in the para positions, heteroleptic complexes of general formula [GnZnC] are formed. Interestingly, in these complexes, a very efficient quenching (practically 100%) of the dendrimer naphthyl luminescence and sensitization (ca. 90%) of the clip anthracene emission take place. The complex [G2ZnC] exhibits a very high molar absorption coefficient in the UV spectral region owing to the 16 naphthyl chromophores of the dendrimer and the two anthracene units of the clip (ε = 1.7 × 10⁵ M⁻¹ cm⁻¹ at 263 nm). Furthermore, the excitation energy absorbed by the naphthyl chromophores is efficiently funneled to the two anthracene units of the clip, which emits in the blue spectral region.
authors.affiliation: Dipartimento di Chimica G. Ciamician and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare, Università di Bologna, via Selmi 2, I-40126, Bologna, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Branchi
authors.forename: Giacomo
authors.initials: G
authors.lastname: Bergamini
authors.forename: Luca
authors.initials: L
authors.lastname: Fiandro
authors.forename: Paola
authors.initials: P
authors.lastname: Ceroni
authors.forename: Antonello
authors.initials: A
authors.lastname: Alvino
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Doddi
authors.forename: Fritz
authors.initials: F
authors.lastname: Vögtle
authors.forename: Frank-Gerrit
authors.initials: FG
authors.lastname: Klärner
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D004735:Energy Transfer; D006571:Heterocyclic Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D021241:Spectrometry, Mass, Electrospray Ionization; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D050091:Dendrimers; D006571:Heterocyclic Compounds; C024560:cyclam; D015032:Zinc