Ruthenium Assemblies for CO2 Reduction and H2 Generation: Time Resolved Infrared Spectroscopy, Spectroelectrochemistry and a Photocatalysis Study in Solution and on NiO

Two novel supramolecular complexes RuRe ([Ru(dceb)2(bpt)Re(CO)3Cl](PF6)) and RuPt ([Ru(dceb)2(bpt)PtI(H2O)](PF6)2) [dceb = diethyl(2,2′-bipyridine)-4,4′-dicarboxylate, bpt = 3,5-di(pyridine-2-yl)-1,2,4-triazolate] were synthesized as new catalysts for photocatalytic CO2 reduction and H2 evolution, respectively. The influence of the catalytic metal for successful catalysis in solution and on a NiO semiconductor was examined. IR-active handles in the form of carbonyl groups on the peripheral ligand on the photosensitiser were used to study the excited states populated, as well as the one-electron reduced intermediate species using infrared and UV-Vis spectroelectrochemistry, and time resolved infrared spectroscopy. Inclusion of ethyl-ester moieties led to a reduction in the LUMO energies on the peripheral bipyridine ligand, resulting in localization of the 3MLCT excited state on these peripheral ligands following excitation. RuPt generated hydrogen in solution and when immobilized on NiO in a photoelectrochemical (PEC) cell. RuRe was inactive as a CO2 reduction catalyst in solution, and produced only trace amounts of CO when the photocatalyst was immobilized on NiO in a PEC cell saturated with CO2.

Surface Enhanced Infrared Spectroelectrochemistry using a Microband Electrode

The successful use of a microband electrode printed on a silicon internal reflection element to perform time resolved infrared spectroscopy is described. Decreasing the critical dimension of the microband electrode to several hundred micrometers provides a sub-microsecond time constant in a Kretschmann configured spectroelectrochemical cell. The high brilliance of synchrotron sourced infrared radiation has been combined with a specially designed horizontal attenuated total reflectance (ATR) microscope to focus the infrared beam on the microband electrode. The first use of a sub-microsecond time constant working electrode for ATR surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) is reported. Measurements show that the advantage afforded by the high brilliance of the synchrotron source is at least partially offset by increased noise from the experimental floor. The test system was the potential induced desorption of an adsorbed monolayer of 4-methoxypyridine as measured using step-scan interferometry. Based on diffusion considerations alone, the expected time scale of the process was less than 10 microseconds but was experimentally measured to be three orders of magnitude slower. A defect-mediated dissolution of the condensed film is speculated to be the underlying cause of the unexpected slow kinetics.

Helmet Phthalocyaninato Iron Complex as a Primary Drier for Alkyd Paints

This study describes the catalytic performance of an iron(III) complex bearing a phthalocyaninato-like ligand in two solvent-borne and two high-solid alkyd binders. Standardized mechanical tests revealed strong activity, which appeared in particular cases at concentrations about one order of magnitude lower than in the case of cobalt(II) 2-ethylhexanoate, widespread used in paint-producing industry. The effect of the iron(III) compound on autoxidation process, responsible for alkyd curing, was quantified by kinetic measurements by time-resolved infrared spectroscopy and compared with several primary driers. Effect of the drier concentration on coloration of transparent coatings was determined by UV–Vis spectroscopy.

Characterization of Excited States in a Multiple-Resonance-Type Thermally Activated Delayed Fluorescence Molecule Using Time-resolved Infrared Spectroscopy

We have investigated the correlation between the photophysical properties and the excited-state detailed characteristics in a multiple-resonance-type thermally activated delayed fluorescence (TADF) molecule, DABNA-1, using time-resolved infrared vibrational spectroscopy. In comparison of the distinctive vibrational spectra in the fingerprint region, 1000 - 1700 cm^-1, to the simulated spectra by density functional theory calculations, we found the best calculation condition. On the basis of the calculations, we determined the excited-state geometries and molecular orbitals of the lowest excited singlet (S₁) and triplet (T₁) states as well as the ground state (S₀). We revealed that the similarity of the potential surfaces between T₁ and S₀ suppresses the nonradiative decay and causes the high fluorescence quantum yield via TADF process.

Characterization of Excited States in a Multiple-Resonance-Type Thermally Activated Delayed Fluorescence Molecule Using Time-resolved Infrared Spectroscopy

We have investigated the correlation between the photophysical properties and the excited-state detailed characteristics in a multiple-resonance-type thermally activated delayed fluorescence (TADF) molecule, DABNA-1, using time-resolved infrared vibrational spectroscopy. In comparison of the distinctive vibrational spectra in the fingerprint region, 1000 - 1700 cm^-1, to the simulated spectra by density functional theory calculations, we found the best calculation condition. On the basis of the calculations, we determined the excited-state geometries and molecular orbitals of the lowest excited singlet (S₁) and triplet (T₁) states as well as the ground state (S₀). We revealed that the similarity of the potential surfaces between T₁ and S₀ suppresses the nonradiative decay and causes the high fluorescence quantum yield via TADF process.

Determining Excited-State Structures and Photophysical Properties in Phenylphosphine Rhenium(I) Diimine Biscarbonyl Complexes Using Time-Resolved Infrared and X-ray Absorption Spectroscopies

We have explored the structural factors on the photophysical properties in two rhenium(I) diimine complexes in acetonitrile solution, cis,trans-[Re(dmb)(CO)₂(PPh₂Et)₂]+ (Et(2,2)) and cis,trans-[Re(dmb)(CO)₂(PPh₃)₂]+ ((3,3)) (dmb = 4,4'-dimethyl-2,2'-bipyridine, Ph = phenyl, Et = ethyl) using the combination method of time-resolved infrared spectroscopy, time-resolved extended X-ray absorption fine structure, and quantum chemical calculations. The difference between these complexes is the number of phenyl groups in the phosphine ligand, and this only indirectly affects the central Re(I). Despite this minor difference, the complexes exhibit large differences in emission wavelength and excited-state lifetime. Upon photoexcitation, the bond length of Re-P and angle of P-Re-P are significantly changed in both complexes, while the phenyl groups are largely rotated by ~20º only in (3,3). We concluded that the instability from steric effects of phenyl groups and diimine leads to the smaller Stokes shift of the lowest excited triplet state (T₁) in (3,3). The large structural change between the ground and excited states causes the longer lifetime of T₁ in (3,3).

Determining Excited-State Structures and Photophysical Properties in Phenylphosphine Rhenium(I) Diimine Biscarbonyl Complexes Using Time-Resolved Infrared and X-ray Absorption Spectroscopies

We have explored the structural factors on the photophysical properties in two rhenium(I) diimine complexes in acetonitrile solution, cis,trans-[Re(dmb)(CO)₂(PPh₂Et)₂]+ (Et(2,2)) and cis,trans-[Re(dmb)(CO)₂(PPh₃)₂]+ ((3,3)) (dmb = 4,4'-dimethyl-2,2'-bipyridine, Ph = phenyl, Et = ethyl) using the combination method of time-resolved infrared spectroscopy, time-resolved extended X-ray absorption fine structure, and quantum chemical calculations. The difference between these complexes is the number of phenyl groups in the phosphine ligand, and this only indirectly affects the central Re(I). Despite this minor difference, the complexes exhibit large differences in emission wavelength and excited-state lifetime. Upon photoexcitation, the bond length of Re-P and angle of P-Re-P are significantly changed in both complexes, while the phenyl groups are largely rotated by ~20º only in (3,3). We concluded that the instability from steric effects of phenyl groups and diimine leads to the smaller Stokes shift of the lowest excited triplet state (T₁) in (3,3). The large structural change between the ground and excited states causes the longer lifetime of T₁ in (3,3).

EMI Series Mechanistic Investigation of a Visible Light Mediated Dehalogenation/Cyclisation Reaction using Iron(III), Iridium(III) and Ruthenium(II) Photosensitizers

The mechanism of a visible light-driven dehalogenation/cyclization reaction was investigated using ruthenium(II), iridium(III) and iron(III) photosensitizers by means of steady-state photoluminescence, time-resolved infrared spectroscopy, and nanosecond/femtosecond transient absorption spectroscopy. The...