Selective photoexcitation of the donor in an electron donor-acceptor1-acceptor2 (D-A1-A2) molecule, in which D = perylene and both A1 and A2 = naphthalene-1,8:4,5-bis(dicarboximide), results in sub-nanosecond formation of a spin-correlated singlet radical pair 1(D+•-A1-•-A2) having a large electron spin-spin exchange interaction, 2J, which precludes its observation by transient EPR spectroscopy. Subsequent selective photoexcitation of A1-• rapidly produces 1(D+•-A1-A2-•), resulting in a dramatic decrease in 2J, which allows coherent spin evolution to mix the singlet (S) radical pair state 1(D+•-A1-A2-•) with the T0 triplet sublevel of 3(D+•-A1-A2-•) in an applied magnetic field, where B 蠑 2J. A spin-polarized transient EPR spectrum characteristic of the spin-correlated radical pair D+•-A1-A2-• is then observed. The time delay between the two laser pulses was incremented to measure the rate of decoherence in 1(D+•-A1-•-A2) in toluene at 295 K, which was found to be 8.1 × 107 s-1. Deuteration of the perylene donor or the toluene solvent decreases the decoherence rate constant of 1(D+•-A1-•-A2) to 4.3 × 107 s-1 and 4.6 × 107 s-1, respectively, while deuteration of both the perylene donor and the toluene solvent reduced the decoherence rate constant by more than half to 3.4 × 107 s-1. The data show that decreasing electron-nuclear hyperfine interactions significantly increases the zero quantum coherence lifetime of the spin-correlated radical pair.
ASJC Scopus subject areas
- Materials Chemistry