Cathodic reductions of 2,2′-bipyridine and 4,4′-bipyridine in liquid ammonia

Ground and Excited Electronic States of Quininone-Containing Re(I)-Based Rectangles: a Comprehensive Study of Their Preparation, Electrochemistry, and Photophysics

“…Therefore, the redox reactions of 1 and 2 were investigated via UV−vis−NIR spectroelectrochemical (SEC) measurements using an optically transparent thin-layer electrochemical (OTTLE) technique to establish the likely sites of electron transfer: the accessible reductions involve 4,4′-bipyridine (and quasi-reversible 3− state for quininone ligands) for the states with n = 0, 1−, and 2− (Figure and Table ). Thus, the first reduction of 1 to 1− reduces the MLCT and LMLCT band intensities, accompanied by the appearance of absorption bands at about 524, and above 840 nm, which are characteristic of the radical anion form of 4,4′-bipyridine (Figure , Top) . Nearly identical behavior was observed for 2 .…”

“…The emission peak due to the 3 MLCT state is blue-shifted to 462 nm compared to room temperature emission that can be seen in related rhenium(I) complexes. ,, Also, in the excited-state lifetime profile, 2 showed biexponential decay with a short component having a lifetime of 19 ns and a long component having 160 ns. The structured emission profile and short lifetime may be attributed to the 3 IL excited state at the high-energy region of 23.9 × 10 3 (419 nm) and 22.8 × 10 3 cm −1 (440 nm) (dual emissions indicated nonthermally equilibrated 3 LF) and the broad emission with a long lifetime may be due to the 3 MLCT and 3 LLCT state at 20.5 × 10 3 (489 nm) and 19.2 × 10 3 cm −1 (520 nm). , To confirm the presence of multiple excited states, the excitation spectrum of 2 was recorded and the uncorrected excitation spectrum is shown in Supporting Information, Figure S7. The excitation spectra of 2 showed that the emission at 440 nm is indeed due to a ligand-centered transition, and the emission at 520 nm is attributed to the MLCT transition …”

On the Structural and Electronic Properties of [Zn2(4,4′-bipyridine)(mes)4]n−(n= 0–2), a Homologous Series of Bimetallic Complexes Bridged by Neutral, Anionic, and Dianionic 4,4′-Bipyridine

“…All attempts to measure the standard potentials for the reduction of the neutral complex 1 to the radical anion, [Zn 2 (4,4′-bipy)(mes) 4 ] •– , and dianion, [Zn 2 (4,4′-bipy)(mes) 4 ] 2– , were severely hindered by the extreme air- and moisture-sensitivity of all three species. Such data would have strongly complemented our experimental observations and provide an interesting comparison with respect to the electrochemical data available for 4,4′-bipyridine. , Despite numerous attempts at recording cyclic voltammetry measurements for 1 we were unable to observe any meaningful signals because of sample decomposition. Despite extensive purging of predried solvents with dinitrogen and the transfer of solutions under an inert atmosphere, we invariably found that samples decomposed prior to the application of an electrical potential.…”

“…The redox-active behavior of 4,4′-bipyridine has been well established for over 50 years. Early electron paramagnetic resonance (EPR) studies on organic radicals in solution were the first to identify the 4,4′-bipyridyl anion (4,4′-bipy •– ) as a product of the reduction of pyridine, or 4,4′-bipyridine, with alkali metals. , Further studies on the radical anion and dianion were later conducted by several research groups employing a combination of spectroscopic, electrochemical, and computational techniques. − Electrochemical measurements on solutions of 4,4′-bipyridine reveal two consecutive chemically accessible reduction steps, highlighting the possibility of forming coordination complexes of these highly reductive species. , The use of 4,4′-bipyridine in molecular squares exhibiting ligand-centered mixed valency (LCMV) has been reported by Hupp and others, who have demonstrated that the electrochemical reduction of neutral supramolecular complexes can give rise to isostructural species where negative charges reside on bridging ligand moieties . However, despite the extensive research in this area, to the best of our knowledge there are no structural data available in the chemical literature for coordination complexes with chemically reduced forms of the 4,4′-bipyridyl ligand.…”

Order beyond a monolayer: the story of two 4,4’-bipyridine layers on the Sb(111) | ionic liquid interface

“…Therefore, it can be related to the reduction of the adsorbed 4,4'-BP to 4,4'-BP − in aprotic polar solvent 45 . The process is also visible in the measured C vs. E dependences (Figure 1b) at 210 Hz.…”