Photoexcitation of the electron donor (D) within a linear, covalent donor-acceptor-acceptor molecule (D-A 1-A 2) in which A 1 = A 2 results in sub-nanosecond formation of a spin-coherent singlet radical ion pair state, 1(D +•- A 1 -•-A 2), for which the spin-spin exchange interaction is large: 2J = 79 ± 1 mT. Subsequent laser excitation of A 1 -• during the lifetime of 1(D +•-A 1 -•-A 2) rapidly produces 1(D +•-A 1-A 2 -•), which abruptly decreases 2J 3600-fold. Subsequent coherent spin evolution mixes 1(D +•-A 1-A 2 -•) with 3(D +•-A 1-A 2 -•), resulting in mixed states which display transient spin-polarized EPR transitions characteristic of a spin-correlated radical ion pair. These photodriven J-jump experiments show that it is possible to use fast laser pulses to transfer electron spin coherence between organic radical ion pairs and observe the results using an essentially background-free time-resolved EPR experiment.
ASJC Scopus subject areas
- Colloid and Surface Chemistry