Mark R. Waterland

Symmetry breaking effects in NO3−: Raman spectra of nitrate salts and ab initio resonance Raman spectra of nitrate–water complexes

Ground-state structures and vibrational frequencies are calculated for complexes of the nitrate anion with one and two water molecules at the ab initio Hartree–Fock level with a basis set including diffuse and polarization functions. Two local minimum geometries are found for each complex. Calculations of the electronically excited states at the CIS level are then used to find the forces on each of the atoms upon vertical excitation to the two lowest-lying (near-degenerate) strongly allowed electronic transitions. These forces are converted to gradients of the excited-state potential surfaces along the ground-state normal modes and compared with the parameters obtained previously from empirical simulations of the experimental resonance Raman intensities of NO3− in dilute aqueous solution. The calculations on two-water clusters agree well with the experimental excited-state geometry changes along the totally symmetric N–O stretch. The calculations underestimate the frequency splitting of the antisymmetric ...

Exciton coupling in coordination compounds

This Perspective reviews the impact of exciton coupling on the spectroscopic properties of coordination compounds. Exciton coupling features arise in electronic absorption and circular dichroism spectra when chromophores are brought into close spatial proximity, for example by coordination to a metal centre. The analysis of these features can reveal much information such as the geometry of a complex and its absolute configuration. The extension of the exciton coupling model to polynuclear metallosupramolecular arrays is discussed.

Far-ultraviolet resonance Raman spectroscopy of nitrate ion in solution

Resonance Raman spectra are presented for the nitrate anion, NO3−, in water, ethylene glycol, methanol, and acetonitrile solution at six excitation wavelengths from 246 to 204 nm, on resonance with the lowest π→π* excitation. Absolute Raman cross sections for the CH stretches of ethylene glycol and methanol at these wavelengths are also reported. The nitrate spectra in all four solvents are dominated by fundamentals, overtones, and combination bands of the totally symmetric NO stretch (ν1) near 1043 cm−1 and the out-of-phase NO stretches (ν3) at 1340–1400 cm−1, consistent with substantial changes in NO bond length upon π-electron excitation. The intensity in ν3 and the ≈60 cm−1 splitting of this nominally degenerate vibration are indicative of pronounced breaking of the isolated molecules D3h symmetry by the local solvent environment. Intensity in the overtone of the out-of-plane mode (ν2) near 830 cm−1 suggests a change in the equilibrium geometry from planar to pyramidal upon electronic excitation. The absorption spectra and absolute Raman cross sections are simulated with a model that considers resonance with two orthogonally polarized electronic states whose degeneracy is broken by the locally asymmetric environment. Both solvent reorganization and geometry changes along the nitrate molecular vibrations make major contributions to the breadth of the absorption band. No differences between resonant and nonresonant linewidths are observed for the ν1 band.Resonance Raman spectra are presented for the nitrate anion, NO3−, in water, ethylene glycol, methanol, and acetonitrile solution at six excitation wavelengths from 246 to 204 nm, on resonance with the lowest π→π* excitation. Absolute Raman cross sections for the CH stretches of ethylene glycol and methanol at these wavelengths are also reported. The nitrate spectra in all four solvents are dominated by fundamentals, overtones, and combination bands of the totally symmetric NO stretch (ν1) near 1043 cm−1 and the out-of-phase NO stretches (ν3) at 1340–1400 cm−1, consistent with substantial changes in NO bond length upon π-electron excitation. The intensity in ν3 and the ≈60 cm−1 splitting of this nominally degenerate vibration are indicative of pronounced breaking of the isolated molecules D3h symmetry by the local solvent environment. Intensity in the overtone of the out-of-plane mode (ν2) near 830 cm−1 suggests a change in the equilibrium geometry from planar to pyramidal upon electronic excitation. The ...

Electronic absorption, resonance Raman and excited-state resonance Raman spectroscopy of rhenium(I) and copper(I) complexes, with substituted dipyrido[3,2-a : 2′,3′-c]phenazine ligands, and their electron reduced products

The electronic absorption and resonance Raman spectra of a series of rhenium(I) and copper(I) complexes with substituted dipyrido[3,2-a : 2′,3′-c]phenazine (dppz) ligands were investigated. The ligands were ben[i]dipyrido[3,2-a : 2′,3′-c]phenazine, 11,12-dimethyldipyrido[3,2-a : 2′,3′-c]phenazine, 10-methyldipy- rido[3,2-a : 2′,3′-c]phenazine and 11-methyoxydipyrido[3,2-a : 2′,3′-c]phenazine. The spectroelectrochemistry of the reduced complexes and the emission and resonance Raman spectra of the excited states are reported. Vibrational wavenumber calculations of the unsubstituted ligand suggest the presence of normal modes that are localized to various sections of the ligand structure; the resonance Raman spectra of the complexes are interpreted with reference to these calculations. The analysis of the spectra revealed that the Franck–Condon state initially formed by visible photoexcitation (450 nm) is metal-to-ligand charge-transfer in nature. Spectroelectrochemical resonance Raman and electronic absorption measurements revealed the spectral signatures for the radical anions of each of the ligands used in this study. These spectral features were used to assign the excited states formed by the complexes. Most of the complexes studied show spectral features in their excited-states that suggest that the predominant state formed within 5 ns of excitation is ligand-centred. Copyright

Sensitive determination of estriol-16-glucuronide using surface plasmon resonance sensing

For the quantitative evaluation of low levels of an estriol metabolite of estriol (estriol-16-glucuronide (E3-16G)) in liquid media, we developed a simple and highly sensitive immunoassay using a surface plasmon resonance (SPR) biosensor which did not require any time-consuming sample pretreatment steps. E3-16G was conjugated to ovalbumin (OVA) through an oligoethylene glycol (OEG) linker to form protein conjugates (E3-16G-OEG-OVA), which were then immobilized on a carboxymethyl dextran-coated sensor chip via amine coupling to develop inhibition immunoassays. A limit of detection (LOD) of 76 pg/mL was achieved using a rabbit anti-sheep primary antibody as a binding agent. The detection limit was further improved by using synthesized gold colloids (15 nm) as high mass labels conjugated to the primary antibody. In this Au nanoparticle-enhanced assay, the concentration of E3-16G in aqueous samples could be determined in 7.5 min at a level as low as 14 pg/mL. In addition, the high stability of the E3-16G-OEG-OVA surface gave no obvious drop in antibody-binding capability after more than 1000 binding/regeneration cycles which significantly lowered the research cost.

Synthesis, Structural and Nonlinear Optical Properties of 2-(3-Cyano-4-{5-[1-(2-Hydroxyethyl)- 3,3-Dimethyl-1,3-Dihydro-Indol-2-ylidene]-Penta-1,3-dienyl}-5,5-Dimethyl-5H-Furan-2-ylidene)-Malononitrile

A chromophore for nonlinear optics with extended conjugation has been synthesized, and its structure determined from X-ray diffraction data. The compound crystallizes in the monoclinic system with the space group P21/n and Z = 4. The unit cell parameters are a = 10.7826(4) Å, b = 14.5943(5) Å, c = 15.3792(5) Å and beta = 96.213(2)°. A thin film containing 5% of the chromophore in amorphous polycarbonate when poled at 180°C and 60 V/μm yields a maximum r33 value of 206 pm/V. This is seven times higher than the value found for the archetypical inorganic material, lithium niobate.

Relaxation and electron transfer dynamics in bare and DTDCI sensitized MoS2 nanoclusters

The trapping dynamics of photogenerated electrons and holes in MoS2 nanoclusters has been studied using time resolved emission polarization and absorption spectroscopies. These results are compared to absorption kinetics obtained on MoS2 nanoclusters with adsorbed DTDCI (DTDCI≡diethylthiodicarbocyanine iodide) dye. The results indicate that emission from the MoS2 band edge state is polarized, while emission from trapped electrons and holes is unpolarized. This polarization difference is used to obtain the electron and hole trapping times and values of 275 ps and 42 ps, respectively, are obtained. Decays having the same time constants are observed in the transient absorption results. The results obtained on the MoS2/DTDCI system show that electron injection occurs with a time constant of 12 ps. These kinetics also show a 225 ps decay component which is assigned to electron trapping and reverse electron transfer. The 225 ps decay time along with the 275 ps trapping time indicates that reverse electron trans...

Spectroelectrochemical studies and excited-state resonance-Raman spectroscopy of some mononuclear rhenium( I ) polypyridyl bridging ligand complexes. Crystal structure determination of tricarbonylchloro[2,3-di(2-pyridyl)quinoxaline]rhenium( I )

A number of mononuclear rhenium(I) complexes have been prepared and their physical properties and excited-state and spectroelectrochemical resonance-Raman spectra studied. These compounds have the general formula [Re(CO)3Cl(L)], where L can be 2,3-di(2-pyridyl)quinoxaline (dpq), 2-(2-pyridyl)quinoxaline (pq) or 5-methyl-2,3-di(2-pyridyl)quinoxaline (mdpq). The structure of [Re(CO)Cl(dpq)] was determined by single-crystal X-ray diffraction. The NMR data for complexes with dpq and mdpq suggest the unbound pyridyl is shielding protons on the bound pyridyl moiety. The resonance-Raman spectra of the reduced complexes show some polarisation of electron density towards the bound pyridyl ring. The excited states have very similar spectral features to those of the reduced complexes. This suggests that electrochemically prepared redox states model the metal-to-ligand charge-transfer state well, for these systems.

Determination of Estriol 16-glucuronide in human urine with surface plasmon resonance and lateral flow immunoassays

A rapid quantitative immunoassay for estriol-16-glucuronide by Surface Plasmon Resonance (SPR) sensing has been developed and applied to urine samples from non-pregnant and pregnant subjects. The assay was based on a partially-purified polyclonal antibody (pAb) raised in sheep, which showed negligible cross-reactivity with estrone-3-glucuronide and estriol-17-glucuronide. Colloidal gold coated by the pAb was used as the signal generator in the SPR-based inhibition immunoassay. An estriol-16-glucuronide-ovalbumin conjugate with an oligoethylene glycol (OEG) as linker was used to immobilize the steroid on the biosensor chip surface. The SPR assay had a limit of detection of 0.016 ng/mL, and could be performed rapidly giving results in two minutes. The assay can be carried out directly on any urine samples without complicated sample pretreatment. A one-step lateral flow strip test was also developed using the same pAb nanogold conjugates and bovine serum albumin estriol-16-glucuronide conjugates as the capture agent spotted onto a nitrocellulose membrane as the test line. A sensitive and repeatable lateral flow assay was achieved with a limit of detection of 0.49 ng/mL in time-diluted urine using a low coating concentration of the polyclonal antibody. Despite the strip sensor displaying adequate sensitivity in a standard curve generated by exposure to estriol-16-glucuronide in a spiked urine blank, the application of the strip sensors to real urine samples was not so successful due to matrix effects.

Spectroscopic and electrochemical studies of a series of copper(I) and rhenium(I) complexes with substituted dipyrido[3,2-a:2′,3′-c]phenazine ligands †

Copper(I) and rhenium(I) complexes with the ligand dipyrido[3,2,-a:2′,3′-c]phenazine (dppz) and a number of substituted analogues have been synthesized. Their spectroscopic and electrochemical properties have been studied. It is found that the lowest-energy transition for the complexes is metal-to-ligand charge transfer (MLCT) in nature. This has a low Iµ value. The resonance Raman spectra for the complexes show groups of bands that shift with substitution at the ligand and groups that remain unchanged in wavenumber. Electrochemical reduction of the complexes resulted in the formation of the ligand radical anion species for all but one system. This was confirmed by UV/VIS spectroelectrochemistry. Using resonance Raman spectroelectrochemistry marker bands have been identified for the radical anion species. The excited states of the complexes were studied by excited-state electronic absorption and time-resolved resonance Raman techniques. The former spectra are ambiguous as to the nature of the lowest excited state; however, the latter spectra confirm that this state is ligand-centred for complexes of dppz and its 11-methyl derivative. Complexes with the 11-nitro derivative appear to form excited states that are MLCT in nature.