Long-Lived Long-Distance Photochemically Induced Spin-Polarized Charge Separation In Beta,Beta '-Pyrrolic Fused Ferrocene-Porphyrin-Fullerene Systems

Publisher:
Royal Soc Chemistry
Publication Type:
Journal Article
Citation:
Chemical Science, 2012, 3 (1), pp. 257 - 269
Issue Date:
2012-01
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The exceptionally long lived charge separation previously observed in a b,b'-pyrrolic-fused ferrocene-porphyrin-fullerene triad (lifetime 630 mu s) and related porphyrin-fullerene dyad (lifetime 260 mu s) is attributed to the production of triplet charge-separated states. Such molecular excited-state spin polarization maintained over distances of up to 23 angstrom 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 p-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 mu s-timescale process attributed to triplet recombination.
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