Wave-function symmetry control of electron-transfer pathways within a charge-transfer chromophore

ARAMBURU-TRO?ELJ, BRUNO M.; RAMÍREZ-WIERZBICKI, IVANA; SCARCASALE, FRANCO; OVIEDO, PAOLA S.; BARALDO, LUIS M.; CADRANEL, ALEJANDRO

Journal of Physical Chemistry Letters

American Chemical Society

Año: 2020 vol. 11 p. 8399 - 8405

Despite a diverse manifold of excited states available, it is generally accepted that the photoinduced reactivity of charge-transfer chromophores involves only the lowest-energy excited state. Shining a visible-light laser pulse on an aqueous solution of the chromophorequencher [Ru(tpy)(bpy)(μNC)OsIII(CN)5]- assembly (tpy = 2,2´;6,2´´-terpyridine and bpy = 2,2´-bipyridine), we prepared a mixture of two charge-transfer excited states with different wavefunction symmetry. We were able to follow, in real time, how these states undergo separate electron-transfer reaction pathways. As a consequence, their lifetimes differ in 3 orders of magnitude. Implicit are energy barriers high enough to prevent internal conversion within early excited-state populations, shaping isolated electron-transfer channels in the excited-state potential energy surface. This is relevant not only for supramolecular donor/acceptor chemistry with restricted donor/acceptor relative orientations. These energy barriers provide a means to avoid chemical potential dissipation upon light absorption in any molecular energy conversion scheme, and our observations invite to explore wave-function symmetry-based strategies to engineer these barriers.