Long-lived long-distance photochemically induced spin-polarized charge separation in β,β′-pyrrolic fused ferrocene-porphyrin-fullerene systemsElectronic supplementary information (ESI) available: Synthesis and molecular characterisation, data fitting and computational modelling equations,62-75 cyclic voltammograms in PhCN of related model compounds, time-resolved fluorescence studies of ZnP and 2HP, femtosecond transient absorption spectra in PhCN, studies on bimolecular charge-transfer of dyads

• Main Authors: Lee, Sai-Ho, Larsen, Allan G, Ohkubo, Kei, Cai, Zheng-Li, Reimers, Jeffrey R, Fukuzumi, Shunichi, Crossley, Maxwell J
• Format: Article
• Language: English
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c1sc00614b

The exceptionally long lived charge separation previously observed in a β,β′-pyrrolic-fused ferrocene-porphyrin-fullerene triad (lifetime 630 μ s) and related porphyrin-fullerene dyad (lifetime 260 μ s) 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 μ s-timescale process attributed to triplet recombination. Porphyrin-ferrocene conjugation enables the stabilization of long-lived triplet spin-polarized states with the individual spins separated by 23 Å.