Ala H. R. Al-Obaidi

Time-resolved resonance Raman spectroscopy of triplet-state metallated and free-base tetraarylporphyrins

Resonance Raman spectra of the T1 excited states of Zn and free-base tetra-4-sulfonatophenylporphyrin (TPPS) have been recorded at room temperature in aqueous solution using two-colour time-resolved methods. The spectra of both sulfonated molecules are very similar to their tetraphenylporphyrin (TPP) analogues, which have been recorded in THF solution using the same pump–probe conditions, but they have higher signal-to-noise ratios because interference from strong solvent bands is reduced. Although two different T1 spectra of Zn(TPP) have been reported these spectra differ slightly from each other and from the spectrum reported here, which has band positions very close (±6 cm–1) to those of Zn(TPPS). The high S/N ratios obtainable for the water-soluble porphyrins have allowed reliable polarization data to be recorded for their S0 and T1 states. This data set allows a realistic comparison of the changes in bonding associated with excitation of both free-base and Zn tetraarylporphyrins to the T1 state.Semi-empirical (AM1) calculations of the bond-length changes associated with excitation of free-base TPP and the simpler model tetra-4-fluorophenylporphyrin (TFP) to their T1 states follow qualitative predictions based on the orbital coefficients of the HOMO and LUMO involved in the transition. These structural changes accord satisfactorily with the observed changes in frequency on excitation of the vibrational modes of free-base TPP and TPPS. The calculated bond-length changes are strikingly close to those previously calculated for Zn(TFP), where Jahn–Teller effects are expected. The primary effect of the Jahn–Teller distortion in the molecular orbital calculations is to lift the degeneracy of the eg LUMO pair of the Zn complexes. Once this degeneracy is lifted the calculated geometry changes for both free-base and Zn complexes converge because they arise from a HOMO to LUMO excitation between two orbitals which have similar coefficients in both. The observation that the directions of the shifts of most of the vibrational modes in the T1 states of the free-base and Zn porphyrins are the same, supports this general conclusion. The only band which displays significantly different behaviour between the metallated and free-base systems is ν11 which is a B1g mode. This suggests that the Jahn–Teller distortion that lifts degeneracy of the LUMO in the T1 states of the Zn complexes occurs along a B1g coordinate.

Raman spectroelectrochemical studies and crystal structure of a binuclear copper(I) complex with a bridging diimine ligand

Raman spectroelectrochemical and X-ray crystallographic studies have been made for the binuclear copper(I) complex, [(Ph3P)2Cu(dpq)Cu(PPh3)2][BF4]2, where dpq is the bridging ligand 2,3-di(2-pyridyl)quinoxaline. The X-ray data show that the pyridine rings are twisted out of plane with respect to the quinoxaline ring which is itself non-planar. The UV/VIS spectra of the metal-to-ligand charge-transfer excited state and those of the electrochemically reduced complex are similar. The resonance-Raman spectrum of the latter species exhibits little change in the frequency of the pyridinylquinoxaline inter-ring C–C bond stretching mode, compared to the ground elecronic state. This suggests minimum change in the inter-ring C–C bond order in the electrochemically or charge-transfer generated radical anion. Semiempirical molecular-orbital calculations on both the neutral dpq and radical anion show two near-degenerate lowest unoccupied orbitals in the neutral species. One is strongly bonding across the inter-ring C–C bond while the other is almost non-bonding. The Raman data suggest that it is this latter orbital which is populated in the transient and electrochemical experiments.

Laser profiling for subsea hydrocarbon production systems

The correct alignment and setting of the components inside subsea wellheads is critical to ensure that all seals perform at the high pressures found in subsea hydrocarbon production systems. Of particular importance is the alignment of the tubing hanger and how it engages with the subsea trees or wellhead. The tubing hanger supports the production tubing string with carries the hydrocarbon from the reservoir and experiences pressures up to 15 kPsi. Full and correct engagement of the locking and sealing mechanisms of the tubing hanger is critical in containing the production fluids. Here we present the results of a trial of a laser profiler to assess the interior surfaces of a wellhead. The scanner has been shown to be capable of effectively inspecting the interior surface of the wellhead for damage and measuring the interior structures to allow the tubing hanger to be installed correctly.

A Fraction Distortion Model for Accurate Camera Calibration and Correction

While camera calibration is a fundamental yet challenging problem for 3D measurement, it has attracted intensive attention from 3D vision community. In this paper, we propose a new model to characterise camera distortion in the process of the camera calibration. This model attempts to blindly characterise the overall camera distortion without taking the specific radial, decentring, or thin prism distortion into account. To estimate the parameters of interest, the well-known Levernburg-Marquardt algorithm is applied. To initialise the Levernburg-Marquardt algorithm, the results from the classical Tsai algorithm are estimated. After both the camera intrinsic and distortion parameters have been estimated, the distorted image points are corrected using again the Levernburg-Marquardt algorithm initialised by these distorted image points themselves. The performance of algorithms is measured as absolute and relative correction errors and collinear fitting errors. The experimental results based on both synthetic data and real images show that the proposed algorithm often successfully characterises the camera overall distortion, producing encouraging results for camera calibration and correction.

Surface second harmonic generation of oligonucleotides on surfaces

Laser induced surface second harmonic generation (SSHG) has been applied to study the nature of oligonucletides on glass surfaces. A very strong SSH signal from most of the investigated oligonucletides was observed. The oligonucleotides were found to be resistant to damage from the incident laser radiation, up to peak pulse powers 8MW. The surface second harmonic signal intensity has been shown to be strongly dependent on the angle of the incident laser beam with respect to the sample surface. The study of both angle and polarization dependencies of glass surfaces coated with 12 mer oligonucletide AAAAAATTTTTT and fluorescein fTTTTTTTTTTTT labelled 12 mer oligonucletide is reported. The SSHG technique has been used for quantitative measurements to determine the surface concentration of several oligonucletide samples. The measured surface concentration dependence offers the potential for the development of oligonucleotide assays based on surface second harmonic generation.

Time-resolved Raman spectroscopy of excited-state porphyrins

Time-resolved resonance Raman spectroscopy has been used to probe the lowest excited singlet and triplet states of free-base meso-tetraarylporphyrins. Both single-color and two-color time-resolved techniques have been used to probe the excited singlet states, while the triplet spectra were obtained in two-color experiments with a time-delay between pump and probe lasers of 30 ns. Marker bands for each of these three states have been identified. The information which qualitative analysis of the Raman spectra can give on the structural differences between these excited states is discussed.

Observation of biphasic kinetics in light-induced spin-state crossover in an iron(II) complex in solution

Relaxation of the 1A1 [graphic omitted] 5T2 spin equilibrium in acetonitrile of the complex of FeII with the multidentate pyridyl macrocyclic ligand N,N′,N″-tris(2-pyridylmethyl)-1,4,7-triazacyclodecane (tp[10]aneN3) after perturbation by a pulsed laser provides the first example of biphasic kinetics for spin crossover in solution with a fast (τ < 30 ns) temperature-independent process coupled to a slower, temperature-dependent step; barrierless spin change is so far unique among spin equilibrium systems.