Photoinduced electron transfer in a charge-transfer complex formed between corannulene and Li+@C60by concave-convex π-π interactions

Mihoko Yamada, Kei Ohkubo, Mitsuhiko Shionoya, Shunichi Fukuzumi

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Abstract

A charge-transfer (CT) complex was formed between corannulene (C20H10) and lithium ion-encapsulated [60]fullerene (Li+@C60) with the binding constant KG = 1.9 × 10 M-1 by concave-convex π-π CT interactions in benzonitrile at 298 K, exhibiting a broad CT absorption extended to the NIR region. Femotosecond laser excitation of the C20H10/Li+@C60 CT complex resulted in the singlet chargeseparated (CS) state, 1(C20H10•+/Li+@C60•-), which decayed with the lifetime of 1.4 ns. Nanosecond laser excitation of Li+@C60 resulted in intermolecular electron transfer (ET) from C20H10 to the triplet excited state of Li+@C60 [3(Li+@C60)∗] to produce the triplet CS state 3(C20H10•+/Li+@C60•-). The distance between two electron spins in the triplet CS state was estimated to be 10 Å from the zero-field splitting pattern observed by EPR measurements at 4 K. The triplet CS state decayed to the ground state via intramolecular back electron transfer (BET). The CS lifetime was determined to be 240 μs in benzonitrile at 298 K. The temperature dependence of the rate constant of BET afforded the reorganization energy (λ = 1.04 eV) and the electronic coupling term (V = 0.0080 cm-1). The long lifetime of triplet CS state results from the spin-forbidden BET process and a small V value.

Original languageEnglish
Pages (from-to)13240-13248
Number of pages9
JournalJournal of the American Chemical Society
Volume136
Issue number38
DOIs
StatePublished - 24 Sep 2014

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© 2014 American Chemical Society.

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