title: Photoinduced long-lived charge separation in a tetrathiafulvalene-porphyrin-fullerene triad detected by time-resolved electron paramagnetic resonance.
abstract: Photoinduced electron transfer has been observed in a molecular triad, consisting of a porphyrin (P) covalently linked to a tetrathiafulvalene (TTF) and a fullerene derivative (C(60)), in the different phases of the liquid crystal E-7 and in a glass of 2-methyltetrahydrofuran (2-MeTHF) by means of time-resolved electron paramagnetic resonance (EPR) spectroscopy. In both solvents, an EPR signal observed immediately after excitation has been assigned to the radical pair TTF(*+)-P-C(60)(*-), based on its magnetic interaction parameters and spin polarization pattern. In the 2-MeTHF glass and the crystalline phase of E-7, the TTF(*+)-P-C(60)(*-) state is formed from the TTF-(1)P-C(60) singlet state via an initial TTF-P(*+)-C(60)(*-) charge-separated state. Long-lived charge separation ( approximately 8 mus) for the singlet-born radical pair is observed in the 2-MeTHF glass at cryogenic temperatures. In the nematic phase of E-7, a high degree of ordering in the liquid crystal is achieved by the molecular triad. In this phase, both singlet- and triplet-initiated electron transfer routes are concurrently active. At room temperature in the presence of the external magnetic field, the triplet-born radical pair (T)(TTF(*+)-P-C(60)(*-)) has a lifetime of approximately 7 mus, while that of the singlet-born radical pair (S)(TTF(*+)-P-C(60)(*-)) is much shorter (<1 mus). The difference in lifetimes is ascribed to spin dynamic effects in the magnetic field.
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Di Valentin
authors.forename: Arianna
authors.initials: A
authors.lastname: Bisol
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Agostini
authors.forename: Paul A
authors.initials: PA
authors.lastname: Liddell
authors.forename: Gerdenis
authors.initials: G
authors.lastname: Kodis
authors.forename: Ana L
authors.initials: AL
authors.lastname: Moore
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Moore
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
authors.forename: Donatella
authors.initials: D
authors.lastname: Carbonera