As we prepare to perform pump-pump-probe experiments on excited radical ions, we continue to look for the best experimental conditions to photochemically generate these elusive species in a (single) pump-probe experiment.
Here, we investigate the generation of the radical anion of naphthalene diimide (NDI) via reductive quenching of its T1 excited state by an electron donor in acetonitrile. Upon excitation of NDI at 355 nm, a fast intersystem crossing occurs from the populated S1 state to a T4 triplet manifold. This process has been reported to take place with a 2 ps time constant and is evidenced by the transients centered at 600 and 460 nm, resulting in a mixing of S1 and T4 spectral features seen in spectrum B obtained from a global analysis assuming a sequential model. Later, relaxation to T1 state occurs, resulting in the typical triplet features observed in spectrum C. Finally, the T1 state is quenched by the electron donor, generating the radical anion (NDI•−, spectrum D) that is visible at 1.7 ns and is therefore ready to be re-excited in a two-color experiment.
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Eric Vauthey
Physical Chemistry Department - Sciences II - 玉美人传媒
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