Electron transfer (ET) reactions in a series of donor-acceptor (D-A) molecules (2, 2ʹ-bipyridine)2Ru(4-CH3-2,ʹ-bipyridine-4ʹ)-(CH2)n-(4, 4ʹ-bipyridinium-CH3)4+ (n = 2-5, 7, 8) exchanged onto the surface of large-pore zeolites (Y, L, and mordenite) were studied in suspensions by nanosecond flash photolysis/transient diffuse reflectance techniques. From solid state CP-MAS spectra of 13C-labeled compounds, it was established that the D-A molecules occupy surface sites in which the A end is occluded by the zeolite channels, while the size-excluded D end is exposed. The rate of forward ET reactions from photoexcited D to A decreases with increasing spacer length. The back ET reaction is approximately 105 times slower for D—A diads on the zeolite surface than in solution. Slowing of the back ET rate and a maximum in charge separation quantum yields at n = 4, 5 are attributed to lateral charge transfer diffusion on the zeolite surface to form an intermolecular charge-separated state. Addition of size-or charge-excluded electron donors (Dʹ) to the suspension gives a Dʹ-D-A triad, in which the initial ET reaction can be between D and A, or Dʹ and D, depending on energetics and the spacer length n. In both cases a long-lived charge-separated state is formed between Dʹ and A.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry