Vinylruthenium-triarylamine conjugates as electroswitchable polyelectrochromic NIR dyes

Abstract

We here report on triarylamine-derived styryl ruthenium complexes 1–3 where one (1), two (2) or three (3) vinyl ruthenium moieties are appended to a triphenylamine core. The near equivalency of the styryl ruthenium and the triarylamine redox systems leads to strong interactions between these moieties and strong mixing of the respective frontier orbitals. This results, inter alia, in the observation of two to four consecutive, reversible one-electron redox couples with potential splittings of 185–435 mV. The associated radical cations and higher oxidized forms show strong absorptions whose positions vary from deep in the near-infrared (NIR) to the border region between the Vis and NIR regimes as a function of the oxidation state. Extinction coefficients and oscillator strengths reach rather impressive values of up to 90 000 l mol-1 cm-1 and ≥1.0. Complexes 1–3 thus constitute polyelectrochromic dyes with two to three addressable and distinguishable states that can be reversibly interconverted by application of an appropriate potential. The electronic transitions underlying the intense low energy absorptions are assigned with the aid of time dependent-density functional theory (TD-DFT) and involve strongly delocalized molecular orbitals (MOs). Charge and spin delocalization in the (radical) cations are probed by electron paramagnetic resonance spectroscopy (EPR) and infrared (IR) spectroelectrochemistry.