UV/Vis absorption spectroscopy

UV-Vis spectroscopy is a technique widely applicable to CyD complex formation except when the guest molecules are weakly absorbing. In principle, the method is well suited for the quantitative study of association equilibria since the measured 

Distinct polarity effects on absorption were encountered for guest molecules exhibiting polarity-dependent vibronic fine structure in their spectra, as for instance naphthalene [21], whicdi showed a marked enhancement of fine structure in the presence of 0.05-M a-CyD but not in that of 0.01-M fi-CyD (Fig. 10.3.1). In such favorable cases, the stoichiometry of inclusion could be probed using a suitably modified Benesi-HUdebrand treatment based on the absorption of a vibronic subband whose intensity is specifically enhanced by CyD inclusion. This is the case for the 290-nm transition of the La band of naphthalene which is threefold more intense in the presence of a high a-CD concentration than in neat aqueous solution 

Specific guest/host interactions, reflecting either the weak electrostatic and van der Waals forces that are responsible for complexation [22] or steric hindrance of guest motion, may influence the transition dipole moments in absorption as well as in emission. In many cases, the absorbance of the guest is found to increase upon complexation (compare Fig. 10.3.1), but the opposite trend may also be encountered, as, for example, in the system 4-hydroxybiphenyl/) -Cyd. In this latter case, steric hindrance of the exdted-state planarization of the guest has been put forward as a possible explanation [23]. 

The binuclear complexes 7b-12b exhibit an intense absorption band at 420-485 nm (e 2.6-4.5xl03 dm3 mol-1 cm-1) in acetonitrile which is ascribed to singlet [da — n ] transitions [17] (see Fig. 1). 

To correlate the intermetallic/interplanar interaction between [Pt(ClA NAN)]+ moieties with the excited state properties, comparisons between the absorption spectra of 7b and 13-15 were made. Because of longer carbon 

Molecular orbitals may be bonding ( r or tt), non-bonding (ra) or antibonding e or it ) in character. If a molecule 

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Schematic diagrams of two approaches to on-coiumn detection using UV/Vis absorption spectroscopy.

Time-resolved spectroscopic techniques are important and effective tools for mechanistic photochemical studies. The most widely used of these tools, time-resolved UV-VIS absorption spectroscopy, has been applied to a variety of problems since its introduction by Norrish and Porter almost 60 years ago. Although a great deal of information about the reactivity of organic photochemical intermediates (e.g., excited states, radicals, carbenes, and nitrenes) in solution at ambient temperatures has been amassed with this technique, only limited structural information can be extracted from... 

UV/VIS absorption spectroscopy, pioneered by Beckman (1941), is one of the oldest and most widely used instrumental techniques, despite being regarded by some analysts as obsolete. Recently there has been a renaissance in UV spectroscopy with many new techniques, instruments and data processing methods [8]. Modem highest specification UV/VIS absorption and fluores-cence/phosphorescence spectrometer instruments extend their wavelength region from the far UV (175 nm) into the NIR region (1100 nm). Small footprint UV/VIS spectrometers (200-1100 nm) are now available. Paul [9] has traced the history of UV/VIS instrumental developments. 

The interaction between 4-(4-hydroxybut-2-ynyloxy)-3-(phenylsulfonyl)-l,2,5-oxadiazole-2-oxide 16 and bovine serum albumin (BSA) was studied by spectroscopic methods including fluorescence and UV-Vis absorption spectroscopy. The results indicate that molecules 16 bind with BSA forming 1 1 complex. Thermodynamic parameters, such as AH, AG, and A.Y, were calculated. The results indicate that the binding reaction is mainly entropy driven and hydrophobic forces play a major role in this reaction <2006CHJ1050>. 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

The symmetry of the LB films was determined by polarized ultraviolet-visible (UV-Vis) absorption spectroscopy, optical rotation, and second-harmonic generation. All studies showed that the constructed LB films are anisotropic in the plane of the film and that the symmetry of the film is C2 with the twofold rotation axis perpendicular to the film plane. For example, when the SH intensity is plotted as a function of the azimuthal rotation angle (rotation around an axis perpendicular to the plane of the film), the twofold symmetry becomes evident (Figure 9.23). Isotropic films generate an SH signal independent of the azimuthal rotation angle. On the other hand, the LB... 

The ce-pyrrolidonate Pt(2.5 + )4 (19) was also found to catalyze the oxidation of benzene to phenol by hydrogen peroxide (121). By HPLC, ESR, and UV-Vis absorption spectroscopy, the main reaction pathway was confirmed to be Eq. (13). 

A number of cyano-bridged complexes are included here even though they strictly do not fall in the general family-type defined for the section. The syntheses and photophysical properties of [(NC)(bpy)2Ru(/r-NC)Cr(CN)5] and [(NC)5Cr(Ai-CI Ru(bpy)2(M-NC)Cr(CN)5] have been described. Absorption of visible light by the Ru(bpy)2 unit results in phosphorescence from the Cr(CN)g luminophore, and the results evidence fast intramolecular exchange energy transfer from the MLCT state of the Ru(bpy)2 chromophore to the doublet state of the Cr -based unit. Time-resolved resonance Raman and transient UV-vis absorption spectroscopies have been employed to investigate the MLCT excited states of [(NC)(bpy)2Ru(//-CN)Ru (bpy)2(CN)], [(NC)(bpy)2Ru(//-CN)Ru(phen)2(CN)]+, [(NC)(phen)2Ru(//-CN)Ru (bpy)2(CN)]+, [(NC)(bpy)2... 

Using ILs for the preparation of different nanoparticles is becoming popular. The latter can be easily characterized by using UV-Vis absorption spectroscopy, as it was the case with the Au nanoparticles obtained under different preparation conditions [13]. 

The photochemical and thermal stabilities of Ru complexes have been investigated in detail [8,153-156]. For example, it has been reported that the NCS ligand of the N3 dye, cri-Ru(II)(dcbpy)2(NCS)2 (dcbpy = 2,2 -bipyridyl-4,4 -dicarboxylic acid), is oxidized to produce a cyano group (—CN) under irradiation in methanol solution. It was measured by both ultraviolet-visible (UV-vis) absorption spectroscopy and nuclear magnetic resonance (NMR) [8,153]. In addition, the intensity of the infrared (IR) absorption peak attributed to the NCS ligand starts to decrease at 135°C, and decarboxylation of N3 dyes occurs at temperatures above 180°C [155]. Desorption of the dye from the 2 surface has been observed at temperatures above 200°C. 

From these results and others from UV-vis absorption spectroscopy and differential pulse polarography (data not shown), Garbin et al. (2007) concluded that HS can act as photocatalyst to pesticide photolysis in aqueous solution only for specific ranges of concentration (as seen in Figure 16.12), which in turn depended on the HS and pesticide chemical characteristics. Under ultraviolet and visible radiation, this photocatalysis is based on photogeneration of -OH radicals, and the susceptibility of pesticide molecules to -OH attacks defines the efficiency of the photocatalysis. 

NCs is indispensable. In the case of cadmium chalcogenide NCs, the concentration of a colloidal solution can be determined in good approximation by means of UV-vis absorption spectroscopy thanks to tabulated relationships between the excitonic peak, the NC size, and the molar absorption coefficient.96 An advanced approach for shell growth derived from chemical bath deposition techniques and aiming at the precise control of the shell thickness is the so-called SILAR (successive ion layer adsorption and reaction) method.97 It is based on the formation of one monolayer at a time by alternating the injections of cationic and anionic precursors and has been applied first for the synthesis of CdSe/CdS CS NCs. Monodispersity of the samples was maintained for CdS shell thicknesses of up to five monolayers on 3.5 nm core CdSe NCs, as reflected by the narrow PL linewidths obtained in the range of 23 to 26 nm FWHM. 

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