title: Phosphorus(V) Porphyrin-Manganese(II) Terpyridine Conjugates: Synthesis, Spectroscopy, and Photo-Oxidation Studies on a SnO2Surface.
abstract: A major challenge in designing artificial photosynthetic systems is to find a suitable mimic of the highly oxidizing photoactive species P680in photosystem II. High-potential phosphorus(V) porphyrins have many attractive properties for such a mimic but have not been widely studied. Here, we report the synthesis and photophysical characterization of a novel phosphorus(V) octaethylporphyrin-oxyphenyl-terpyridine conjugate (PPor-OPh-tpy, 1) and its corresponding manganese(II) complex (PPor-OPh-Mn(tpy)Cl2, 2). The X-ray structure of 2 shows that the Mn(II) and P(V) centers are 11.783 Å apart and that the phenoxy linker is not fully conjugated with the terpyridine ligand. The porphyrin fluorescence in 1 and 2 is strongly quenched and has a shorter lifetime compared to a reference compound without the terpyridine ligand. This suggests that electron transfer from tpy or Mn(tpy) to the excited singlet state of the PPor may be occurring. However, femtosecond transient absorbance data show that the rate of relaxation to the ground state in 1 and 2 is comparable to the fluorescence lifetimes. Thus, if charge separation is occurring, its lifetime is short. Because both 1 and 2 are positively charged, they can be electrostatically deposited onto the surface of negatively charged SnO2nanoparticles. Freeze-trapping EPR studies of 2 electrostatically bound to SnO2suggest that excitation of the porphyrin results in electron injection from1PPor* into the conduction band of SnO2and that the resulting PPor•+species acquires enough potential to photo-oxidize the axially bound Mn(II) (tpy) moiety to Mn(III) (tpy).
authors: Department of Chemistry, Brock University , 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada.
authors: Prashanth K
authors: PK
authors: Poddutoori
authors: Department of Chemistry, University of North Texas , 11555 Union Circle, 305070, Denton, Texas 76203-5017, United States.
authors: Gary N
authors: GN
authors: Lim
authors: Department of Chemistry, Brock University , 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada.
authors: Melanie
authors: M
authors: Pilkington
authors: Department of Chemistry, University of North Texas , 11555 Union Circle, 305070, Denton, Texas 76203-5017, United States.
authors: Francis
authors: F
authors: D'Souza
authors: Department of Chemistry, Brock University , 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada.
authors: Art
authors: A
authors: van der Est