Extending Photoinduced Charge Separation Lifetimes by Using Supramolecular Design: Guanine–Perylenediimide G‑Quadruplex

We report here a potassium-induced guanine quadruplex as a supramolecular platform for controlled assembly of electron donor–acceptor systems. A monodisperse, C₄-symmetric octamer of a guanine–perylene-3,4,9,10-bis­(dicarboximide) conjugate (GPDI) was prepared in tetrahydrofuran. The two layers of cyclic guanine tetramers have the same direction of rotation, and the PDI moiety between the layers adopts a nearly eclipsed relationship (H-aggregation), as revealed by small- and wide-angle X-ray scattering, NMR spectroscopy, and steady-state UV/vis absorption. Following photoexcitation of the PDI moiety in the quadruplex, charge separation occurs in τ_CS = 98 ± 12 ps to give G^+•-PDI^–• that recombines in τ_CR = 1.2 ± 0.2 ns, which is >100 times longer than that in the monomeric GPDI dyad. The transient absorption spectrum of G^+•-PDI^–• within the GPDI quadruplex suggests the formation of a radical anion delocalized over the neighboring PDI units, and this result is consistent with the more favorable electrochemical reduction potential for PDIs in the quadruplex relative to the monomer.