Long-lived photoinitiated charge separation in carotene-diporphyrin triad molecules

John Devens Gust, Thomas A Moore, Ana L Moore, Feng Gao, David Luttrull, Janice M. DeGraziano, Xiaochun C. Ma, Lewis R. Makings, Seung Joo Lee, Todd T. Trier, Edith Bittersmann, Gilbert R. Seely, Susanne Woodward, René V. Bensasson, Michel Rougée, Frans C. De Schryver, Mark Van Der Auweraer

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Abstract

A variety of molecular triads and dyads consisting of covalently linked carotenoid (C) and/or porphyrin (P) moieties have been prepared and studied with transient absorption and time-resolved fluorescence techniques. Diporphyrins of the type PA-PB and C-PA-PB triads demonstrate interporphyrin singlet-singlet energy transfer with rate constants ranging from 8.1 × 108 to 2.3 × 1010 s-1. The energy-transfer rates are not in accord with those predicted by the Förster dipole-dipole theory, and it is suggested that energy transfer involves a contribution from an electron-exchange mechanism. Interporphyrin photoinitiated electron transfer is observed in molecules possessing sufficient thermodynamic driving force to produce PA.+-PB.- and C-PA.+-PB.- charge-separated states. The electron-transfer rate constant increases with increasing reaction free energy change for the molecules studied, and rate constants up to 3.5 × 109 s-1 and quantum yields up to 0.68 were measured. The carotenodiporphyrin triad systems undergo a subsequent electron-transfer step to give final C.+-PA-PB.- states. These states are rather long lived (τ ≈ 250 ns), and the overall quantum yields range up to 0.32.

Original languageEnglish
Pages (from-to)3638-3647
Number of pages10
JournalJournal of the American Chemical Society
Volume113
Issue number10
Publication statusPublished - May 8 1991

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ASJC Scopus subject areas

  • Chemistry(all)

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