title: Photoswitched singlet energy transfer in a porphyrin-spiropyran dyad.
abstract: A photochromic nitrospiropyran moiety (Sp) has been covalently linked to a zinc (PZn) and to a free-base (P(H2)) porphyrin. In the resulting dyads (P(Zn)-Sp(c) and P(H2)-Sp(c)), the porphyrin first excited singlet states are unperturbed by the closed form of the attached spiropyran. Excitation of the spiropyran moiety of either dyad in the near-UV region results in ring opening to a merocyanine form (P-Sp(o)) that absorbs at 600 nm. The open form re-closes thermally in 2-methyltetrahydrofuran with a time constant of 20 s, or following irradiation into the 600 nm band. Excitation of the zinc porphyrin moiety in the merocyanine form of the dyad yields 1PZn-Sp(o). The lifetime of the zinc porphyrin excited state is reduced from its usual value of 1.8 ns to 130 ps by singlet-singlet energy transfer to the merocyanine moiety to give PZn-1Sp(o). The quantum yield of energy transfer is 0.93. Quenching is also observed in the free base dyad, where 1P(H2)-Sp(o) and P(H2)-1Sp(o) exchange singlet excitation energy. This photoswitchable quenching phenomenon provides light-activated control of the porphyrin excited states, and consequently control of any subsequent energy or electron-transfer processes that might be initiated by these excited states in more complex molecular photonic or optoelectronic devices.
authors.affiliation: Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Bahr
authors.forename: G
authors.initials: G
authors.lastname: Kodis
authors.forename: L
authors.initials: L
authors.lastname: de la Garza
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: A L
authors.initials: AL
authors.lastname: Moore
authors.forename: T A
authors.initials: TA
authors.lastname: Moore
authors.forename: D
authors.initials: D
authors.lastname: Gust
mesh_terms: D001578:Benzopyrans / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D004735:Energy Transfer / Q000528:radiation effects*; D007211:Indoles; D008027:Light; D008958:Models, Molecular; D009574:Nitro Compounds; D010788:Photosynthesis; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D013057:Spectrum Analysis; D015032:Zinc / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D007211:Indoles; D009574:Nitro Compounds; D011166:Porphyrins; C088184:spiropyran; D015032:Zinc