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Efficient heterogeneous photosensitizing materials require both large accessible surface areas and excitons of suitable energies and with well‐defined spin structures. Confinement of the tetracationic cyclophane (ExBox⁴⁺) within a nonporous anionic polystyrene sulfonate (PSS) matrix leads to a surface area increase of up to 225 m²g⁻¹in ExBox•PSS. Efficient intersystem crossing is achieved by combining the spin‐orbit coupling associated to Br heavy atoms in 1,3,5,8‐tetrabromopyrene (TBP), and the photoinduced electron transfer in a TBP⊂ExBox⁴⁺supramolecular dyad. The TBP⊂ExBox⁴⁺complex displays a charge transfer band at 450 nm and an exciplex emission at 520 nm, indicating the formation of new mixed‐electronic states. The lowest triplet state (T₁, 1.89 eV) is localized on the TBP and is close in energy with the charge separated state (CT, 2.14 eV). The homogeneous and heterogeneous photocatalytic activities of the TBP⊂ExBox⁴⁺, for the elimination of a sulfur mustard simulant, has proved to be significantly more efficient than TBP and ExBox⁺⁴, confirming the importance of the newly formed excited‐state manifold in TBP⊂ExBox⁴⁺for the population of the low‐lying T₁state. The high stability, facile preparation, and high performance of the TBP⊂ExBox•PSS nanocomposites augur well for the future development of new supramolecular heterogeneous photosensitizers using host–guest chemistry.

 

Coherent interactions are prevalent in numerous photodriven processes, ranging from photosynthetic energy transfer to superexchange-mediated electron transfer, resulting in numerous studies aimed towards identifying and understanding these interactions. A key motivator of this interest is the non-statistical scaling laws that result from coherently traversing multiple pathways due to quantum interference. To that end, we employed ultrafast transient absorption spectroscopy to measure electron transfer in two donor-acceptor molecular systems comprising a p-(9-anthryl)-N,N-dimethylaniline chromophore/electron donor and either one or two equivalent naphthalene-1,8:4,5-bis(dicarboximide) electron acceptors at both ambient and cryogenic temperatures. The two-acceptor compound shows a statistical factor of 2.1  0.2 rate enhancement at room temperature and a non-statistical factor of 2.6  0.2 rate enhancement at cryogenic temperatures, suggesting correlated interactions between the two acceptors with the donor and with the bath modes. Comparing the charge recombination rates indicates that the electron is delocalized over both acceptors at low temperature but localized on a single acceptor at room temperature. These results highlight the importance of shielding the system from bath fluctuations to preserve and ultimately exploit the coherent interactions. 

Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor–bridge–acceptor (D–B–A) systems as well as competitive reaction pathways in acceptor–donor–acceptor (A–D–A) and acceptor–donor–acceptor′ (A–D–A′) systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV 2+ ) and dipyridylthiazolothiazole (TTz 2+ ) electron acceptors doubly-linked by means of two p -xylylene linkers (TTzExVBox 4+ ), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox 4+ ) to establish an A–D–A′ system, in which the ExV 2+ and TTz 2+ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz + ˙–Per + ˙–ExV 2+ and TTz 2+ –Per + ˙–ExV + ˙ in <1 ps, while back electron transfer in TTz 2+ –Per + ˙–ExV + ˙ proceeds via the unusual sequence TTz 2+ –Per + ˙–ExV + ˙ → TTz + ˙–Per + ˙–ExV 2+ → TTz 2+ –Per–ExV 2+ . In addition, selective chemical reduction of TTz 2+ gives Per ⊂ TTzExVBox 3+ ˙, turning the complex into a D–B–A system in which photoexcitation of TTz + ˙ results in the reaction sequence 2 *TTz + ˙–Per–ExV 2+ → TTz 2+ –Per–ExV + ˙ → TTz + ˙–Per–ExV 2+ . Both reactions TTz 2+ –Per + ˙–ExV + ˙ → TTz + ˙–Per + ˙–ExV 2+ and TTz 2+ –Per–ExV + ˙ → TTz + ˙–Per–ExV 2+ occur with a (16 ± 1 ps) −1 rate constant irrespective of whether the bridge molecule is Per + ˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D–B–A systems.