Solvent shift magnitude

A method for calculating the magnitude of solvent shifts on electronic transitions has been developed and applied to COF for a medium of dielectric constant equal to 80, a solvent shift of ca. 1000 cm" to higher energy (compared with the gas phase) was computed [230]. 

The emission lifetimes of Ir(ppy)2(bpy)2 + and Ir(ppyXbpy)2 + are comparable in 77 K ethanol/methanol glasses (5.0 and 6.8 /is, respectively) and in fluid room temperature methanol solutions (0.35 and 1.1 /is, respectively). The positions of the emission energies of the two complexes were found to be dependent upon the solvent medium (blue shifts in more polar solvents). The magnitude of the luminescence lifetimes and the solvent dependence of the emission spectra are indicative of 3MLCT luminescence [99]. 

If the solvent that is selected is polar (e.g., acetone, chloroform, or dimethyl sulfoxide), there are stronger dipole interactions between solvent and solute, especially if the solute molecule also contains polar bonds. The interactions between the polar solvent and a polar solute are likely to be stronger than the interactions between the solvent and tetramethylsilane (TMS, which is nonpolar), and the result is that the observed chemical shift of the molecule of interest will be shifted with respect to the observed chemical shift in a nonpolar solvent. The magnitude of this solvent-induced shift can be on the order of several tenths of a part per million in a proton spectrum. 

A general shift in the terms, mostly to lower energies (Fig. 6.5). This solvent shift is based on the interaction of the molecules within the crystal with their neighbouring molecules, i.e. on the van der Waals bonding. It is molecule-specific and has a different magnitude for different excited states. 

It is important that the occurrence of aromatic solvent shifts be recognised as the magnitude of the shifts induced in polar molecules can be large, e.g. the resonance of chloroform moves upfield 1.5 ppm when... 

The conformational preferences of 9-alkylthioxanthenes and their. S-oxides have been investigated by n.m.r. techniques, including solvent shifts. The magnitude of the chemical shifts of the 9-protons in the xanthene and thioxanthene anions indicates that their central rings are paratropic. ... 

The rehability of these analytical methods may be questionable when chemical shift differences of derivatives are of the same magnitude as variations encountered from solvent, concentration, and temperature influences. Reported fluorine chemical shift ranges for tnfluoroacetylated alcohols (1 ppm), p-fluorobenzoylated sterols (1 ppm), and p-fluorobenzoylated ammo acids (0.5 ppm) are quite narrow, and correct interpretation of the fluonne NMR spectra of these denvatized mixmres requires strict adherence to standardized sampling procedure and NMR parameters. 

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