title: Porphyrins fused with strongly electron-donating 1,3-dithiol-2-ylidene moieties: redox control by metal cation complexation and anion binding.
abstract: A new class of redox-active free base and metalloporphyrins fused with the 1,3-dithiol-2-ylidene subunits present in tetrathiafulvalene, termed MTTFP (M = H2, Cu, Ni, Zn), have been prepared and characterized. The strong electron-donating properties of MTTFP were probed by electrochemical measurement and demonstrated that oxidation potentials can be tuned by metalation of the free base form, H2TTFP. X-ray crystal structures of H2TTFP, ZnTTFP, and CuTTFP revealed that a severe saddle-shape distortion was observed with the dithiole rings bent out of the plane toward one another in the neutral form. In contrast, the structure of the two-electron oxidized species (CuTFFP(2+)) is planar, corresponding to a change from a nonaromatic to aromatic structure upon oxidation. A relatively large two-photon absorption (TPA) cross-section value of H2TTFP(2+) (1200 GM) was obtained for the free base compound, a value that is much higher than those typically seen for porphyrins (<100 GM). Augmented TPA values for the metal complexes were also seen. The strong electron-donating ability of ZnTTFP was further enhanced by binding of Cl(-) and Br(-) as revealed by thermal electron-transfer between ZnTTFP and Li(+)-encapsulated C60 (Li(+)@C60) in benzonitrile, which was "switched on" by the addition of either Cl(-) or Br(-) (as the tetrabutylammonium salts). The X-ray crystal structure of Cl(-)-bound ZnTTFP was determined and provided support for the strong binding between the Cl(-) anion and the Zn(2+) cation present in ZnTTFP.
authors.affiliation: Department of Chemistry and Biochemistry, University Station-A5300, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Nathan L
authors.initials: NL
authors.lastname: Bill
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.forename: Steffen
authors.initials: S
authors.lastname: Bähring
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Lim
authors.forename: Sangsu
authors.initials: S
authors.lastname: Lee
authors.forename: Christina M
authors.initials: CM
authors.lastname: Davis
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Kent A
authors.initials: KA
authors.lastname: Nielsen
authors.forename: Jan O
authors.initials: JO
authors.lastname: Jeppesen
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
mesh_terms: D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry; D018360:Crystallography, X-Ray; D004583:Electrons; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D014050:Toluene / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D000838:Anions; D002412:Cations; D056831:Coordination Complexes; D006571:Heterocyclic Compounds; D008665:Metalloporphyrins; D014050:Toluene; C063887:tetrathiafulvalene; C004848:dithiol