title: Synthesis and excited-state photodynamics of a chlorin-bacteriochlorin dyad--through-space versus through-bond energy transfer in tetrapyrrole arrays.
abstract: Understanding energy transfer among hydroporphyrins is of fundamental interest and essential for a wide variety of photochemical applications. Toward this goal, a synthetic free base ethynylphenylchlorin has been coupled with a synthetic free base bromobacteriochlorin to give a phenylethyne-linked chlorin-bacteriochlorin dyad (FbC-pe-FbB). The chlorin and bacteriochlorin are each stable toward adventitious oxidation because of the presence of a geminal dimethyl group in each reduced pyrrole ring. A combination of static and transient optical spectroscopic studies indicate that excitation into the Qy band of the chlorin constituent (675 nm) of FbC-pe-FbB in toluene results in rapid energy transfer to the bacteriochlorin constituent with a rate of approximately (5 ps)(-1) and efficiency of >99%. The excited bacteriochlorin resulting from the energy-transfer process in FbC-pe-FbB has essentially the same fluorescence characteristics as an isolated monomeric reference compound, namely a narrow (12 nm fwhm) fluorescence emission band at 760 nm and a long-lived (5.4 ns) Qy excited state that exhibits a significant fluorescence quantum yield (Phif=0.19). Förster calculations are consistent with energy transfer in FbC-pe-FbB occurring predominantly by a through-space mechanism. The energy-transfer characteristics of FbC-pe-FbB are compared with those previously obtained for analogous phenylethyne-linked dyads consisting of two porphyrins or two oxochlorins. The comparisons among the sets of dyads are facilitated by density functional theory calculations that elucidate the molecular-orbital characteristics of the energy donor and acceptor constituents. The electron-density distributions in the frontier molecular orbitals provide insights into the through-bond electronic interactions that can also contribute to the energy-transfer process in the different types of dyads.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, NC, USA.
authors.forename: Chinnasamy
authors.initials: C
authors.lastname: Muthiah
authors.forename: Hooi Ling
authors.initials: HL
authors.lastname: Kee
authors.forename: James R
authors.initials: JR
authors.lastname: Diers
authors.forename: Dazhong
authors.initials: D
authors.lastname: Fan
authors.forename: Marcin
authors.initials: M
authors.lastname: Ptaszek
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
mesh_terms: D003198:Computer Simulation; D004735:Energy Transfer; D008027:Light; D015394:Molecular Structure; D010777:Photochemistry; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D045725:Tetrapyrroles / Q000737:chemistry*
chemical_list: D011166:Porphyrins; D045725:Tetrapyrroles; C452433:bacteriochlorin; C006969:chlorin