Long-lived long-distance photochemically induced spin-polarized charge separation in β,β′-pyrrolic fused ferrocene-porphyrin-fullerene systems

Sai Ho Lee, Allan G. Larsen, Kei Ohkubo, Zheng Li Cai, Jeffrey R. Reimers, Shunichi Fukuzumi, Maxwell J. Crossley

Research output: Contribution to journalArticlepeer-review

83 Scopus citations

Abstract

The exceptionally long lived charge separation previously observed in a β,β′-pyrrolic-fused ferrocene-porphyrin-fullerene triad (lifetime 630 μs) and related porphyrin-fullerene dyad (lifetime 260 μs) is attributed to the production of triplet charge-separated states. Such molecular excited-state spin polarization maintained over distances of up to 23 Å is unprecedented and offers many technological applications. Electronic absorption and emission spectra, femtosecond and nanosecond time-resolved transient absorption spectra, and cyclic voltammograms of two triads and four dyads are measured and analyzed to yield rate constants, donor-acceptor couplings, free-energy changes, and reorganization energies for charge-separation and charge-recombination processes. Production of long-lived intramolecular triplet states is confirmed by electron-paramagnetic resonance spectra at 77-223 K, as is retention of spin polarization in π-conjugated ferrocenium ions. The observed rate constants were either first predicted (singlet manifold) or later confirmed (triplet manifold) by a priori semiclassical kinetics calculations for all conceivable photochemical processes, parameterized using density-functional theory and complete-active-space self-consistent-field calculations. Identified are both a ps-timescale process attributed to singlet recombination and a μs-timescale process attributed to triplet recombination.

Original languageEnglish
Pages (from-to)257-269
Number of pages13
JournalChemical Science
Volume3
Issue number1
DOIs
StatePublished - Jan 2012

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