M. Belsley

Quantitative investigations of quantum coherence for a light-harvesting protein at conditions simulating photosynthesis

Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the initial dynamic response of photosynthetic proteins can involve quantum coherence. We show how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of PC645 at increasing levels of acidity to determine if the change in pH affects the quantum coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change.

2-Arylthienyl-Substituted 1,3-Benzothiazoles as New Nonlinear Optical Chromophores

A series of nonlinear optical chromophores 6 containing a substituted benzothiazole ring have been synthesized and characterized. 1,3-Benzothiazoles 6 were prepared by treating various formyl derivatives of thienyl compounds withortho-aminobenzenethiol in fair to excellent yields. These in turn were prepared by Suzuki coupling between aryl and thienyl precursors. The electronic interactions between donor and acceptor end groups in the conjugated 1,3-benzothiazoles 6 are revealed by the intense and markedly solvatochromic CT transitions. The solvatochromic behaviour of compounds 6 was determined by linear regression analyses of absorption maxima in several solvents, where benzothiazole 6f was found to be a very appropriate indicator dye whose absorption wavenumbers (Δmax = 1590 cm–1) in aliphatic and dipolar aprotic and in aromatic and chlorinated solvents correlated excellently with the π* values defined by Kamlet and Taft. Hyper-Rayleigh scattering was used to measure the first hyperpolarizabilities β of the aforementioned compounds. Thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that good nonlinearity and thermal stability are well balanced for chromophores 6, making them good candidates for device applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, properties and photochromism of novel charge transfer compounds with Keggin anions and protonated 2,2′-biquinoline

Abstract Several novel compounds with protonated 2,2′-biquinoline (biqui) and Keggin polyoxoanions (α-isomers), having the general formula (Hbiqui) m [XM 12 O 40 ]· n solv, X=P ( m =3), Si ( m =4); M=Mo, W; n =0, 3; solv=H 2 O, N , N -dimethylformamide (dmf), were synthesized and characterized by analytical, spectroscopic and X-ray diffraction techniques. Electronic spectroscopy (visible/UV) indicated the presence of intermolecular charge transfer between the organic and inorganic moieties in the solid state. Evidence for the existence of intermolecular electronic interaction in solution was found for compounds with the [SiW 12 O 40 ] 4− anion, a fact quite uncommon for charge transfer compounds based on Keggin anions. A single crystal X-ray diffraction study could be performed on (Hbiqui) 4 [SiW 12 O 40 ]·3dmf crystals, but the refinements revealed the presence of highly disordered 2,2′-biquinoline molecules and α-[SiW 12 O 40 ] 4− anions. Photosensitivity to sunlight and to W-lamp visible light was assessed for all compounds. Photochromic properties were found for solids with [XMo 12 O 40 ] m − Keggin anions. Reduction of these anions upon irradiation was observed by diffuse reflectance and EPR spectroscopy. After a minimum of 5 h under sunlight, the extent of anion reduction followed the order (Hbiqui) 3 [PMo 12 O 40 ]·3dmf>(Hbiqui) 4 [SiMo 12 O 40 ]·3dmf>(Hbiqui) 3 [PMo 12 O 40 ]>(Hbiqui) 4 [SiMo 12 O 40 ]·4H 2 O. The Kurtz powder test was used to evaluate the second-order non-linear optical properties of the prepared compounds. (Hbiqui) 4 [SiW 12 O 40 ]·3H 2 O originated a second harmonic generation signal with intensity about 15% that of urea for 1064 nm radiation.

Crystal growth and characterization of a new nonlinear optical material: Urea L-Malic acid

A new nonlinear optical organic crystal, viz. Urea L-Malic acid, has been grown from aqueous solution employing the techniques of solvent evaporation and slow cooling. The grown crystals were found to be transparent in the visible region. The complete morphology of the crystal has been worked out and its hardness was evaluated using Vickers indentation method. The grown crystals were characterized employing several techniques such as micro-carbon-hydrogen-nitrogen analysis, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV-VIS-IR spectroscopy and refractive index measurement. Preliminary measurements indicate that the second harmonic generation efficiency at a fundamental wavelength of 1064 nm is roughly three times that of KDP.

Yarn Diameter Measurements Using Coherent Optical Signal Processing

A method to measure variations in yarn diameter using coherent optical signal processing based on a single photodiode plus additional electronics is described. The approach enables us to quantify yarn irregularities associated with diameter variations which are linearly correlated with yarn mass variations. A robust method of system auto-calibration, eliminating the need for a temperature and humidity controlled environment, is also demonstrated. Two yarns that span the diameter ranges commonly used in the textile industry were used to verify the system linearity and ascertain its resolution. The results obtained have been verified using image analysis. Moreover, a diameter characterization was performed under real-world conditions for three types of yarns and a correlation with capacitive measurements is also presented. The system with sensitivity of 0.034 V/mm2 is able to detect minute variations of yarn diameter and characterize irregularities starting at very low thresholds (commercial systems generally characterize variations of 30% or greater relative to the average value).

Growth and characterisation of cadmium sulphide nanocrystals embedded in silicon dioxide films

Abstract In this communication we report on the growth and the optical characterisation of CdS quantum dots in the diameter range of 4–10 nm embedded in silicon dioxide glass films grown by magnetron rf-sputtering technique with post-deposition annealing. Optical transmission measurements display a marked blue shift of the absorption band edge due to the quantum confinement of the electrons and holes in the CdS nanocrystals. The mean diameter of the nanocrystals was estimated from absorption spectra using a standard theoretical model. A study of the effect of the nanocrystal size on the Raman spectra has been made from an analysis of the first order LO mode lineshape. The increase in the linewidth observed with decreasing crystal size is in agreement with the results of a calculation based on the phonon confinement model. The asymmetric lineshape is well reproduced by the model, but they fail to reproduce the large low-frequency tail. The origin of this tail is discussed considering several possible sources proposed in the literature and is under study. Room temperature infrared reflectance measurements have also been obtained showing a diffuse band at about 230–300 cm−1, which closely corresponds to CdS optical polar phonons observed in the bulk crystals. However, we are unable to fit the observed spectra by assuming just this contribution. Instead, by including an additional contribution due to CdO we are able to well simulate the experimental spectra using a model based on the Maxwell-Garnet theory.

Oriented single-crystal-like molecular arrangement of optically nonlinear 2- methyl-4-nitroaniline in electrospun nanofibers

In-plane aligned nanofibers of organic 2-methyl-4-nitroaniline (MNA) were produced by the electrospinning technique using a 1:1 weight ratio with poly(l-lactic acid). The fibers are capable of enormous efficient optical second harmonic generation as strong as pure MNA crystals in powder form. Structural, spectroscopic, and second harmonic generation polarimetry studies show that the MNA crystallizes within the fibers in an orientation in which the aromatic rings of MNA are predominantly orientated edge-on with respect to the plane of the fiber array and with their dipole moments aligned with the fiber axis. The results show that the electrospinning technique is an effective method to fabricate all-organic molecular functional devices based on polymer nanofibers with guest molecules possessing strong nonlinear optical and/or polar properties.

Optical Yarn Hairiness Measurement System

This paper presents a system developed for measuring yarn hairiness using a coherent optical signal processing technique, in steps of 1 mm. The system hardware is divided into two main parts: optical, for establishing an image regarding yarn hairiness and electronic, which converts the optical signal to a proportional voltage signal. Additionally, software using LabVIEWTM was also designed to acquire the output voltage with a data acquisition board (DAQ) and to perform the corresponding data processing. This system is able to quantify the traditional commercial hairniness parameters, as sH (%), CVH (%), H and spectral analysis based on FFT. In addition several other parameters, novel in textile characterization, such as DRH (%), IDRH (%), UH (%) and spectral analysis based on FWHT and FDFI are readily available. The results obtained using this system to characterize a 4.20 g/Km cotton yarn are presented.

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.

Development of a Yarn Evenness Measurement and Hairiness Analysis System

This paper presents an automatic yarn characterization system, based on capacitive sensors for evenness measurement and on optical sensors for hairiness analysis. This approach enables direct yarn mass determination in 1 mm range for evenness, an increase by a factor of eight over the most common commercial solutions (8 mm), and will also enable hairiness measurement up to 1 mm with high accuracy. This system determines all parameters commonly used in textile industry, for different sensitivity values defined by the operator. It also presents new parameters, not measured by commercial equipments (integral deviation rate-IDR, different signal processing techniques to detect error patterns (fast Walsh-Hadamard transform-FWHT) and other adapted parameters (deviation rate-DR, spectrograms (fast Fourier transform-FFT), coefficient of variation-CV, mean deviation-U, number and length of faults)