Through-Space Ultrafast Photoinduced Electron Transfer Dynamics of a C-Encapsulated Bisporphyrin Covalent Organic Polyhedron in a Low-Dielectric Medium

Ultrafast photoinduced electron transfer (PIET) dynamics of a C-encapsulated bisporphyrin covalent organic polyhedron hybrid (C@COP-5) is studied in a nonpolar toluene medium with fluorescence and transient absorption spectroscopies. This structurally rigid donor (D)-acceptor (A) molecular hybrid offers a new platform featuring conformationally predetermined cofacial D-A orientation with a fixed edge-to-edge separation, R (2.8 Å), without the aid of covalent bonds. Sub-picosecond PIET (τ ≤ 0.4 ps) and very slow charge recombination (τ ≈ 600 ps) dynamics are observed. The origin of these dynamics is discussed in terms of enhanced D-A coupling (V = 675 cm) and extremely small reorganization energy (λ ≈ 0.18 eV), induced by the intrinsic structural rigidity of the C@COP-5 complex.