Nitrile Substituents at the Conjugated Dipyridophenazine Moiety as Infrared Redox Markers in Electrochemically Reduced Heteroleptic Ru(II) Polypyridyl Complexes.

Ruthenium(II) complexes [Ru(tap)(NN)] (tap = 1,4,5,8-tetraazaphenanthrene, NN = 11-cyano-dipyrido[3,2-:2',3'-]phenazine (11-CN-dppz) and 11,12-dicyano-dipyrido[3,2-:2',3'-]phenazine (11,12-CN-dppz)) feature the C≡N groups as infrared (IR)-active redox markers. They were studied by cyclic voltammetry, UV-vis, and IR spectroelectrochemistry (SEC), and density functional theory calculations to assign the four 1e reduction waves R1-R4 observed in dichloromethane. Generally, the NN ligands are reduced first (R1).

Ligand-Structure Effects on -Heterocyclic Carbene Rhenium Photo- and Electrocatalysts of CO Reduction.

Three novel rhenium -heterocyclic carbene complexes, [Re]-NHC-1-3 ([Re] = -Re(CO)Br), were synthesized and characterized using a range of spectroscopic techniques. Photophysical, electrochemical and spectroelectrochemical studies were carried out to probe the properties of these organometallic compounds. Re-NHC-1 and Re-NHC-2 bear a phenanthrene backbone on an imidazole (NHC) ring, coordinating to Re by both the carbene C and a pyridyl group attached to one of the imidazole nitrogen atoms.

Excitation-Wavelength-Dependent Photophysics of dd Di-isocyanide Complexes.

Binuclear Rh(I) and Ir(I) TMB (2,5-dimethyl-2,5-diisocyanohexane) and dimen (1,8-diisocyanomenthane) complexes possess dσ*pσ and dπpσ singlet and triplet excited states that can be selectively excited in the visible and UV spectral regions. Using perturbational spin-orbit TDDFT, we unraveled the detailed character and spin mixing of these electronic transitions and found that delocalization of pσ and dπ orbitals over C≡N- groups makes C≡N stretching vibrations sensitive reporters of electron density and structural changes upon electronic excitation. Picosecond time-resolved infrared spectra measured after visible light, 375 nm, and 316 nm excitation revealed excitation-wavelength-dependent deactivation cascades.

Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II).

Ruthenium(II) polypyridyl complexes [Ru(CN-Me-bpy)(bpy)] (CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, and = 1-3, abbreviated as , , and ) undergo four () or five ( and ) successive one-electron reduction steps between -1.3 and -2.75 V versus ferrocenium/ferrocene (Fc/Fc) in tetrahydrofuran.

Time-Resolved Femtosecond Stimulated Raman Spectra and DFT Anharmonic Vibrational Analysis of an Electronically Excited Rhenium Photosensitizer.

Time-resolved femtosecond stimulated Raman spectra (FSRS) of a prototypical organometallic photosensitizer/photocatalyst ReCl(CO)(2,2'-bipyridine) were measured in a broad spectral range ∼40-2000 (4000) cm at time delays from 40 fs to 4 ns after 400 nm excitation of the lowest allowed electronic transition. Theoretical ground- and excited-state Raman spectra were obtained by anharmonic vibrational analysis using second-order vibrational perturbation theory on vibrations calculated by harmonic approximation at density functional theory-optimized structures. A good match with anharmonically calculated vibrational frequencies allowed for assigning experimental Raman features to particular vibrations.

Hole Hopping Across a Protein-Protein Interface.

We have investigated photoinduced hole hopping in a Pseudomonas aeruginosa azurin mutant Re126WWCu, where two adjacent tryptophan residues (W124 and W122) are inserted between the Cu center and a Re photosensitizer coordinated to a H126 imidazole (Re = Re(H126)(CO)(dmp), dmp = 4,7-dimethyl-1,10-phenanthroline). Optical excitation of this mutant in aqueous media (≤40 μM) triggers 70 ns electron transport over 23 Å, yielding a long-lived (120 μs) Re(H126)(CO)(dmp)WWCu product. The Re126FWCu mutant (F124, W122) is not redox-active under these conditions.

A macrocyclic receptor containing two viologen species connected by conjugated terphenyl groups.

A macrocyclic receptor molecule containing two viologen species connected by conjugated terphenyl groups has been designed and synthesised. The single-crystal X-ray structure shows that the two viologen residues have a transannular NN separation of ca. 7.

Ultrafast Wiggling and Jiggling: Ir(1,8-diisocyanomenthane).

Binuclear complexes of d metals (Pt, Ir, Rh,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M-M bonding is strengthened upon dσ* → pσ excitation. We report the bridging ligand dynamics of Ir(1,8-diisocyanomenthane) (Ir(dimen)), investigated by fs-ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000-2300 cm.

Extreme Basicity of Biguanide Drugs in Aqueous Solutions: Ion Transfer Voltammetry and DFT Calculations.

Ion transfer voltammetry is used to estimate the acid dissociation constants Ka1 and Ka2 of the mono- and diprotonated forms of the biguanide drugs metformin (MF), phenformin (PF), and 1-phenylbiguanide (PB) in an aqueous solution. Measurements gave the pKa1 values for MFH(+), PFH(+), and PBH(+) characterizing the basicity of MF, PF, and PB, which are significantly higher than those reported in the literature. As a result, the monoprotonated forms of these biguanides should prevail in a considerably broader range of pH 1-15 (MFH(+), PFH(+)) and 2-13 (PBH(+)).