UV-visible studies

Further evidence came from in situ UV-visible studies by Breikss and Abruna (1986), apparently using external reflectance from a Pt electrode. Figure 3.58(A) shows the absorption spectrum for the rhenium complex in solution in the absence of C02 prior to electrolysis. The potential of the working electrode was then slowly ramped to more cathodic values until it reached —1.7 V, whereupon a reddish material formed with a spectrum labelled B in Figure 3.58, having a Am = 512nm. The potential was then... 

UV-visible studies were done that showed that the switching times and stability toward multiple cycling was excellent for this material. In the context of the reports by Hammond discussed above, it is interesting that the oxidation process described in Equation 4.3 did not lead to film dissolution, since the net charge of the formula unit for CuPB in its oxidized form should (at least formally) be zero. This suggests that the... 

The fluoride-selective chromogenic and fluorescent sensor 14 containing naphthalene ureas was synthesized by Lee and coworkers [22]. From UV-visible studies, the sensor 14 showed a characteristic band at 325 nm. Upon addition of F", a new peak at 379 nm occurred in MeCN DMSO (9 1 v/v). Furthermore, Aem of 14 at 379 nm was shifted to 445 nm upon addition of F" (Ka= 14,200 M"1). 

In UV-visible studies of metal-14 anions showed bathochromic shifts of their absorption maxima in comparison with those of the precursor organogermanes. This absorption band (Table 5) can be explained in terms of a transition from the non-bonding orbital of the metal (HOMO) to the lowest anti-bonding orbital (LUMO) of the metal-carbon bonds for alkyl metal-14 anions or of the phenyl groups in the aryl series . Moreover, the bathochromic shifts on going from hthium to potassium are indicative of CIP (Contact Ion Pair) formation for the aryl group-14 anions with an electron localization at the metal. 

A temperature-dependent UV-visible study on [Eu(D03A)(H20) ] shows the existence of a hydration equilibrium with = 1, 2, strongly weighted towards [Eu(D03A)(H20)2]. Extrapolation to the Gd analogue indicated a water exchange rate in [Gd(D03A)(H20) ] to be twice as fast as in... 

Olivier D, Richard M, Che M, Bozon-Verduraz F and Clarkson R B (1980), EPR, ENDOR, and UV-visible study of the nickel-hydrogen interactions in a NiCa-X zeolite , J Phys Chem, 84, 420. 

The mechanism for this reaction has been determined by Halpem on the basis of NMR and UV-visible studies. A radical chain process is initiated by an equilibrium between the hydride Rh(OEP)H and the dimer [Rh(OEP)]2. The different steps of the process are summarized in Scheme 6. 

Porphyrins were first introduced into clays in 1977 by the physical absorption of porphyrin molecules into montmor-illonite in aqueous solutions." The most common examples are the binding of tetracationic M(TMPyP) porphyrins, M = Co(II), Mn(III), Fe(III), into montmor-illonite clays. Co(TMPyP) was the first porphyrin to be intercalated into montmorillonite by ion exchange in acid solution. The interlayer distance expanded from 27 to 37 A upon intercalation. UV-visible studies revealed the retention of cobalt ions in the porphyrin molecules. Mansuy and coworkers have extended this approach and prepared the Mn-porphyrin intercalated materials. These solids are efficient alkene epoxidation and alkane hydroxylation catalysts." Additionally, the catalyst exhibited a marked shape selectivity in favor of small linear alkanes when compared to more bulky substrates. It was also shown that... 

The data in Table I were measured for a number of representative NLO azo containing chromophores by the application of our thermal protocol (6). Also included in the table (column 6) are the temperatures for which 10% of the chromophore decomposition exotherm is lost after 30 minutes of heating in a sealed capillary. These data were determined by Goldfarb et al. (7), and we thank these authors for the use of these data prior to publication. The limited data provided in the last column were determined by variable temperature UV-visible studies of the decrease in absorbance at the long wavelength Amax of the chromophore when it was incorporated into a polyimide via a thermally stable flexible tether (vide infra) 6b). While there is some scatter in the data, it is obvious that the thermal protocol has predictive utility in assessing the utility of NLO chromophores for high temperature poled polymer applications. 

El Mouahid, O., A. Rakotondrainibe, P. Crouigneau, J.M. Leger, and C. Lamy (1998). A UV-visible study of the electropolymerization of CoTAPP at vitreous carbon and investigation of its catalytic activity towards the electroreduction of dioxygen. J. Electroanal. Chem. 455, 209-222. 

An unresolved problem with these polyethylene-bound ruthenium clusters is their thermal decomposition. This decomposition, which was noted by Drago, was confirmed by UV-visible studies of solutions of these polyethylene-bound catalysts and is the principle limit to catalyst recyclability in the case of this cluster catalyst. 

Table 2.6 Initiation rates for Hoveyda-type complexes (at 298 K in DCM), as determined by UV/visible studies with EVE as substrate (25-200 mmol...

The material from which the cold window is made is chosen to suit the spectroscopic techniques to be employed. For IR studies, CsBr or Csl are preferred. These are softer and less prone to cracking than NaCl or KBr and can better withstand repeated cooling and warming cycles. Although also transparent in the UV and visible regions of the spectrum, CsBr and Csl tend to deform and become scratched, which results in scattering of the shorter wavelengths. For this reason, CaFj or sapphire windows are often preferred for UV-visible studies. The external windows of the vacuum chamber do not have to be cooled, so KBr, which is inexpensive, is a popular choice for both IR and UV-visible experiments. 

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