title: Excited-state energy-transfer dynamics in self-assembled triads composed of two porphyrins and an intervening Bis(dipyrrinato)metal complex.
abstract: The synthesis and characterization of various triads composed of a linear array of two zinc porphyrins joined via an intervening bis(dipyrrinato)metal(II) complex are reported. The preparation exploits the facile complexation of dipyrrins with divalent metal ions to give bis(dipyrrinato)metal(II) complexes [abbreviated (dp)(2)M]. Copper(II) and palladium(II) chelates of dipyrrins (available by oxidation of dipyrromethanes) were prepared in 50-80% yield. A one-flask synthesis of bis(dipyrrinato)zinc(II) complexes was developed by oxidation of a dipyrromethane with DDQ or p-chloranil in the presence of Zn(OAc)(2).2H(2)O in THF ( approximately 80% yield). Three routes were developed for preparing porphyrin-dipyrrins: (1). Suzuki coupling of a boronate-substituted zinc porphyrin (ZnP) and bis[5-(4-iodophenyl)dipyrrinato]Pd(II) to give the (ZnP-dp)(2)Pd triad (50% yield), followed by selective demetalation of the (dp)(2)Pd unit by treatment with 1,4-dithiothreitol under neutral conditions (71% yield); (2). oxidation of a porphyrin-dipyrromethane with p-chloranil in the presence of Zn(OAc)(2).2H(2)O followed by chromatography on silica gel (71% yield); and (3). condensation of a dipyrrin-dipyrromethane and a dipyrromethane-dicarbinol under InCl(3) catalysis followed by oxidation with DDQ (10-16% yield). Four triads of form (ZnP-dp)(2)Zn were prepared in 83-97% yield by treatment of a porphyrin-dipyrrin with Zn(OAc)(2).2H(2)O at room temperature. Free base dipyrrins typically absorb at 430-440 nm, while the bis(dipyrrinato)metal complexes absorb at 460-490 nm. The fluorescence spectra/yields and excited-state lifetimes of the (ZnP-dp)(2)Zn triad in toluene show (1). efficient energy transfer from the bis(dipyrrinato)zinc(II) chromophore to the zinc porphyrins (98.5% yield), and (2). little or no quenching of the resulting excited zinc porphyrin relative to the isolated chromophore. Taken together, these results indicate that bis(dipyrrinato)zinc(II) complexes can serve as self-assembling linkers that further function as secondary light-collection elements in porphyrin-based light-harvesting arrays.
authors.affiliation: Departments of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
authors.forename: Lianhe
authors.initials: L
authors.lastname: Yu
authors.forename: Kannan
authors.initials: K
authors.lastname: Muthukumaran
authors.forename: Igor V
authors.initials: IV
authors.lastname: Sazanovich
authors.forename: Christine
authors.initials: C
authors.lastname: Kirmaier
authors.forename: Eve
authors.initials: E
authors.lastname: Hindin
authors.forename: James R
authors.initials: JR
authors.lastname: Diers
authors.forename: Paul D
authors.initials: PD
authors.lastname: Boyle
authors.forename: David F
authors.initials: DF
authors.lastname: Bocian
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey