UV Visible Spectroscopy

The UV-vis adsorption spectrum is an important characterization method for evaluation of electroluminescent/photoluminescent polymers employed in light emitting diodes, including polymer blends, to determine the overlap of the respective adsorption spectra and to design specific spectral emission under electroluminescent conditions [313]. 

Since a fulgide, its E, Z isomers, and photocyclized form exhibit different absorption spectra, electronic absorption spectra are often used to investigate the photoreaction of fulgides. The UV absorption spectra data of some aryl lulgides are listed in Table 4.1. 

In 1984, Ilge el al.30 made a careful investigation of the UV spectroscopy of a large number of fulgides and found that the changes in electronic absorption spectra resulted from changes in substituents and structural isomerizations. 

Becker et al.9 found that the absorption spectra of phenyl fulgides at - 196°C showed no characteristic difference from those at room temperature. The temperature independence of aryl fulgides was also reported by Ilge31 in 1986. 

Source Based on P. J. Darcy, R. J. Hart, and H. G. Heller, overcrowded molecules. Part 14. Photochromic systems involving (Z)-1 -methylpropylidene (diphenylmethylene)-succinic and (E)-3,5-dimethoxybenzylidene (alkyl- substituted methylene) succinic anhydrides, J. Chem. Soc., Perkin Trans. 1, 1978, 571-576. 

Both colourless and deeply coloured compounds are found among the common unsaturated heterocyclic inorganic systems. For example, borazine B3N3H6 (see Section 4.1.2.1), like benzene, is a colourless liquid which exhibits a strong absorption band in the UV region. Similarly, cyclophosphazenes (NPX2) ( = 3-6 X = halogen, alkyl, aryl, alkoxy, dialkylamino) are also 

The Synthesis and Characterisation of Inorganic Compounds, Waveland Press, Prospect Heights, IL, 1991. 

Physical Methods in Chemistry, W. B. Saunders, Philadelphia, PA, 1977. 

Ebsworth, D. W. H. Rankin and S. Cradock, Structural Methods in Inorganic Chemistry, Blackwell Scientific, Oxford, 1987. 

Chivers, A Guide to Chalcogen-Nitrogen Chemistry, World Scientific, Singapore, 2005, pp. 214-221. 

In HyperChem, you can now compute the energy difference between the ground electronic state and the first few excited electronic states of a molecular system by using the ab initio method or any of the semi-empirical methods except for the Extended Hiickel. To generate a UV-vis spectrum, you must perform a singly excited Cl method with the ab initio method or semi-empirical method you choose. 

Use the Electronic Spectrum dialog box to display and analyze the UV-vis spectrum produced by a singly excited Cl calculation. This dialog box is available only after you do a single point Cl semi-empirical calculation. Electronic Spectrum is then activated on the Compute menu. 

The energies, and Ep of the initial and final states of transitions in equations (178) and (179) are determined by the Cl eigenvalues and the transition dipole moment is obtained by using the Cl eigenvectors, that is. 

Freely mobile conduction electrons normally show a characteristic collective oscillation frequency. This plasma resonance can be observed as an absorption band in the UV-visible spectra of metal colloids. With decreasing particle size 

The most probable explanation for the lack of a plasma resonance in Auss is the damping and broadening of the resonance, as a result of size dependent, single electron 5d - 6p,6s interband transitions. Consequently, the Mie bandwidth is roughly double that of what would be predicted, that is the plasmon band is smeared out completely. [94] 

Other interpretations of the UV-visible spectroscopy experiments are less plausible as they sometimes contradict other results. Furthermore, it should be mentioned that a plasma resonance absorption has a third power dependence on the particle diameter. Thus, even if the electrons perform a collective motion in the 1 nm particle, the absorption might be too weak to be recognized above the background. 

Light absorption by a CEP causes electronic transitions from its valence band to the conduction band (n-n transitions) as well as to bands within the band gap (e.g., n-polaron transitions). The resultant UV-visible spectra are very sensitive to the 

These structures should, in principle, show LMCT transitions at two different positions. Except for TS-1, data representing these angles for other titanosilicates are not available. Such data would be useful in determining the influence of the Ti-O-Si angle on the ease of hydrolysis of the Ti-O-Si bond, which is crucially important for the stability and, hence, utility of the material in catalytic applications. 

Diffuse reflectance UV-visible data of titanosilicate samples 

Titanosilicatea Deconvoluted bands and assignments Amax, nm (relative intensity, %) 

Because of the high sensitivity of Ti-containing luminescence centers to their local environments, photoluminescence spectroscopy can be applied to discriminate between various kinds of tetrahedral or near-tetrahedral titanium sites, such as perfectly closed Ti(OSi)4 and defective open Ti(OSi)3(OH) units. Lamberti et al. (49) reported an emission spectrum of TS-1 with a dominant band at 495 nm, with a shoulder at 430 nm when the sample was excited at 250 nm. When the excitation wavelength was 300 nm, the emission spectrum was characterized by a dominant band at 430 nm with a shoulder at 495 nm. These spectra and their dependence on the excitation wavelength clearly indicate the presence of two slightly different families of luminescent Ti species, which differ in their local environments, in agreement with EXAFS measurements carried out on the same samples. 

When photoluminescence spectra were recorded for a Ti(OSi(CH3)3)4 model compound, upon excitation at 250 nm only one emission band was detected (at 500 nm), which was assigned to a perfect closed Ti(OSi)4 site. The excitation of these species is considered to be a LMCT transition, 02 Ti4+ — (0-Ti3+), and the emission is described as a radiative decay process from the charge transfer state to the ground state, O Ti3+ — 02 Ti4+. Soult et al. (94) also observed an emission band at 499 nm, which they attributed to the presence of a long-lived phosphorescent excited state. The emission band at 430 nm of TS-1 was tentatively assigned to a defective open Ti(OSi)3(OH) site (49). 

Further information might be extracted from spectrophotometric titrations if isosbestic points are observed. An isosbestic point appears when each absorption spectrum of the titration has the same absorbance at a particular wavelength, i.e. a 

Data from spectrophotometric titrations may also be used to determine the association constant (K) between the dye and DNA [25]. The data from spectrophotometric titrations, i.e. absorbance data (A0bs) at a fixed wavelength, are used to determine the concentration of bound dye (Cb), the concentration of uncomplexed dye (c), and the number of bound dye molecules per base pair (r) according to Eqs 

In additional experiments, the base selectivity of the association may be investigated by spectrophotometric titrations with synthetic polynucleotides such as 

According to the classical theory of absorption, the interaction of light with a given molecule is thought to result in the induction of dipoles through the interaction of the oscillating electric 

Since all but one of the electrons in the given molecule remain unchanged in state as a result of electronic excitation, then only the wavefunctions involved directly in the electronic transition need be considered in defining the transition dipole moment. In the case of biological macromolecules and macromolecular assemblies, relevant wavefunctions usually correlate to lone pair orbitals, n, and ttItt molecular orbitals such that only two main types of transition dipole moment need be considered, which are ( jl n ) and (tt /2 tt ) respectively. The first of these transition dipole moments is in fact zero, consequently corresponding jx electronic transitions are known as weak, symmetry forbidden transitions. The second of these transition dipole moments is always non-zero and consequently corresponding tt TT transitio ns are known as a stro ng, symmetry allowed transitions. The symmetry allowed transitions are at least 100 times more intense than symmetry forbidden transitions. 

A fall in transmittance resulting from absorption from solution in a cuvette is usually characterised in terms of absorbance, A(A,), or optical density, OD X), at the given wavelength, X, according to the Beer-Lambert law  

In general, the chromophores found typically in solutes, such as proteins, nucleic acids, carbohydrates and lipids (i.e. our biological macro molecules or macromolecular assemblies). 

In contrast with proteins and nucleic acids, carbohydrates and lipids possess few substantial inherent chromophores and so neither class of biological macro molecule has a particularly rich or useful UV-visible spectroscopic behaviour. Therefore, we shall focus the next section on structural versus functional information available from the UV-visible spectroscopy of proteins and nucleic acids only. 

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An elegant example of a system investigated by UV-visible spectroscopy is the copolymer of styrene (molecule 1) and 1-chloro-l, 3-butadiene (molecule 2). These molecules quantitatively degrade with the loss of HCl upon heating in base solution. This restores 1,3-unsaturation to the butadiene repeat unit ... 

Aromatic Radical Anions. Many aromatic hydrocarbons react with alkaU metals in polar aprotic solvents to form stable solutions of the corresponding radical anions as shown in equation 8 (3,20). These solutions can be analyzed by uv-visible spectroscopy and stored for further use. The unpaired electron is added to the lowest unoccupied molecular orbital of the aromatic hydrocarbon and a... 

In a few instances the technique of magnetic circular dichroism (MCD) spectroscopy has been used to corroborate assignments based on UV-visible spectroscopy. For example, the assignment of the intense 360 nm band for [S,N,Y to a r (2e") r (2a2") (HOMO LUMO) excitation has been confirmed by the measurement of the MCD spectrum of The MCD spectrum of [S4N3] indicates that each of the... 

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

Simultaneous with this work, Ozin and co-workers were independently investigating other bimetallic combinations. When Cr and Mo were cocondensed (133) together in Ar, using the apparatus shown in Fig. 11, a controlled pathway to CrMo was found. This molecule had previously been observed in the gas phase (30) from flash photolysis of a mixture of Cr(CO)6 and Mo(CO)g vapors. The molecule was identified (UV-visible spectroscopy) by a series of Cr/Mo/Ar concen-... 

The interaction of small, well defined, rhodium clusters, Rh and Rhs, with O2 has been investigated (220) by matrix infrared, and UV-visible, spectroscopy, coupled with metal/02 concentration studies, warm-up experiments, and isotopic oxygen studies. A number of binuclear O2 complexes were identified, with stoichiometries Rh2(02)n, n = 1-4. In addition, a trinuclear species Rhs(02)m, m = 2 or 6, was identified. The infrared data for these complexes, as well as for the mononuclear complexes Rh(02)x, = 1-2 (229), are summarized in Table XI. Metal-concentration plots that led to the determination of... 

The copper atom-acetylene matrix-reaction, monitored originally by esr spectroscopy (60) has now been investigated by IR/UV-visible spectroscopy (144), and there is general agreement on the identification of two mononuclear species, CuCCaHali.. The esr/IR/UV-visible... 

Langmuir-Blodged films have been deposited on many different substrates. The substrates used include different types of glass (such as quartz for UV-visible spectroscopy) CaF2 plates for transmission infrared spectroscopy silicon, germanium, and ZnSe plates for internal reflection infrared spectroscopy. For electrochemical applications, LB films... 

Britton, G., UV/visible spectroscopy, in Carotenoids IB Spectroscopy, Britton, G. et ah, Eds., Birkhauser Verlag, Basel, 1995, 13. 

Giusti, M.M. and Wrolstad, R.E., Characterization and measurement with UV-visible spectroscopy, in Current Protocols in Food Analytical Chemistry, Wrolstad, R.E., Ed., John Wiley Sons, New York, 2001. 

Britton, G., UV/visible spectroscopy, in Carotenoids Spectroscopy, IB, Britton, G., Liaaen-Jensen, S., and Pfander, H., Eds., Birkhanser, Basel, 1995, 13. Melendez-Martinez, A.J. et ah. Identification of isolntein (Intein epoxide) as cis-antheraxanthin in orange juice, J. Agric. Food Chem., 53, 9369, 2005. 

This paper describes the successful incorporation of molybdenum and molybdenum-nickel clusters into zeolites with 12-membered ring by aqueous ion exchange and application of the resulting materials to HDS reaction of benzothiophene. Stoichiometry of the ion exchange was examined by elemental analysis. UV-visible spectroscopy and EXAFS measurements were carried out to investigate the structure of molybdenum species loaded on zeolites. 

Further resolution of the details of oxidative dehydrogenation requires the measurement of a catalyst s degree of reduction carried out during steady state reaction. We note that UV-visible spectroscopy offers a way to perform this measurement since many of the transition metal oxides which are active as oxidation catalysts exhibit striking color changes between their oxidized and reduced states. 

T. Owen, Fundamentals of Modern UV-Visible Spectroscopy. A Primer, Hewlett-Packard Corporation, Publ. No. 12-5965-5123E (1996). 

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