Umpolung Photoinduced Charge Separation in an Anion-bound Supramolecular Complex

摘要

A new supramolecular system, consisting of an expanded porphyrin, cyclo[8]pyrrole (>C8) and a pyrene carboxylate (>Py) is capable not only of electron transfer upon photoexcitation, but results in “umpolung” or a reversal of the predicted charge-separation behavior in that the higher energy radical ion pair, >C8^•+–Py^•− (2.58 eV) is formed as opposed to >C8^•−–Py^•+ (1.31 eV). This observation is rationalized in terms of the latter radical ion pair, >C8^•−–Py^•+ being in the Marcus inverted region. Transient absorption spectral studies reveal a charge-separated lifetime of 300 µs, which decays to the triplet state of cyclo[8]pyrrole, also an exceedingly long-lived species. The novel features of this non-covalent dyad highlight the potential utility of anion binding in the construction of supramolecular electron transfer systems.