Ru Monoimines with Extended Excited-State Lifetimes and Geometrical Modulation of Photoinduced Mixed-Valence Interactions

RAMÍREZ-WIERZBICKI, IVANA; PIESLINGER, GERMAN E.; ARAMBURU-TRO?ELJ, BRUNO M.; ABATE, PEDRO O.; CADRANEL, ALEJANDRO

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2023

0020-1669

The photophysical properties of monodentate-imineruthenium complexes do not usually fulfil the requirements forsupramolecular solar energy conversion schemes. Their shortexcited-state lifetimes, like the 5.2 ps metal-to-ligand charge transfer(MLCT) lifetime of [Ru(py)4Cl(L)]+ with L = pz (pyrazine),preclude bimolecular or long-range photoinduced energy orelectron transfer reactions. Here, we explore two strategies toextend the excited-state lifetime, based on the chemicalmodification of the distal N atom of pyrazine. On one hand, weused L = pzH+, where protonation stabilized MLCT states,rendering thermal population of MC states less favorable. On theother hand, we prepared a symmetric bimetallic arrangement inwhich L = {(μ-pz)Ru(py)4Cl} to enable hole delocalization via photoinduced mixed-valence interactions. A lifetime extension of 2orders of magnitude is accomplished, with charge transfer excited states living 580 ps and 1.6 ns, respectively, reaching compatibilitywith bimolecular or long-range photoinduced reactivity. These results are similar to those obtained with Ru pentaammine analogues,suggesting that the strategy employed is of general applicability. In this context, the photoinduced mixed-valence properties of thecharge transfer excited states are analyzed and compared with those of different analogues of the Creutz−Taube ion, demonstrating ageometrical modulation of the photoinduced mixed-valence properties.