Transition energy mixture

Figure 5. Estimated transition energies of low-lying excited singlet and triplet states of the 5.35 Cl -MgP-P dimer. Si and S3 correspond to mixtures of localized states S2 and Ss correspond to iCTi and ICT2, respectively T1-T7 and Tg correspond to localized states and Ts...

Then, Dimroth and Reichardt proposed a solvent polarity parameter, Ey(30), based on transition energy for the longest-wavelength solvatochromic absorption band of the pyridynium N-phenolate betaine dye, which is dye No. 30 in a table constructed by these authors. The x(30) values have been determined for more than 360 pure organic solvents and many binary solvent mixtures. 

Mukerjee et al. [218] and Wrona et al. [219] have used the highly solvatochromic 71 transition energy of the stable 2,2,6,6-tetramethylpiperidine-l-oxide radical (TMPNO) for the development of a solvent polarity scale. So-called values, as empirical measures of solvent Lewis acidity, have been determined for 53 pure organic solvents and some binary solvent/water mixtures [219]. 

Figure 7. Transition energy of phenol blue in binary mixtures of acetone and CXDj at 35 C ( 80 bar, A 200 bar [ref. 36]).

As a final note we add that the recently reported INDO/S Cl calculations of the Cr(CO)g spectrum resulted in an intensity ratio of 1 400 for the two transitions allowed, due to the fact that with this method the interconfigurational mixing in both states is grossly overestimated. Although the calculated transition energies reported, 4.60 eV and 5.79 eV, conformed with experiment, both states were in fact calculated as an almost equal mixture of and 2lg2t. ... 

Transition energies of betaine 3 were used as the bases of the widely employed Ej (30) scale. Its negatively solvatochromic charge-transfer absorption band is shifted by ca. 360 nm on going from diphenyl ether (Xma. = 810 nm) to water (Amax = 453 nm). This high sensitivity prompted its use as a polarity indicator for over 350 pure solvents, besides a variety of solvent mixtures mieellar systems and electrolyte solutions. 

FIG. 5 The change in endothermic transition energy with time for 1 1 mixtures of drug and porous or nonporous silicon dioxide at 25A°C[0) Drug + silica 63 (porous) ( ) drug + filmed silicon dioxide M-5 (nonporous) ( ) drug+ silica 244 (porous) (A) drug + sihca 74 (porous). (From Ref 14.)... 

One of the most popular and successful scales has been developed by Dimroth and Reichardt. It is based on the pyridlnlum-N-phenoxide betaine [3], which exhibits one of the largest solvatochromic effects ever observed. The solvatochromism of this dye is negative since its ground state is considerably more polar than the excited state and is stabilized by polar solvents. Thus, in diphenylether the dye absorbs at 810 ran and appears blue-green, whereas in water the absorption is centred at 453 nm, giving an orange impression. The transition energy, expressed in kcal mol, is the so-called Ej(30) value of the solvent. Ex(30) values have been determined and tabulated for more than 270 pure solvents and many different solvent mixtures. Protonation converts the dye (Scheme 3) into a phenol as a consequence, Et(30) values cannot be measured for acidic solvents, such as carboxylic acids. 

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