Dipole moments solvatochromic probes

The practical limitations in the Z-value approach can be overcome by using pyridinium A -phenolate betaine dyes such as (44) as the standard probe molecule. They exhibit a negatively solvatochromic n n absorption band with intramolecular charge-transfer character cf. discussion of this dye in Section 6.2.1, its UV/Vis spectrum in Fig. 6-2, and its dipole moment in the electronic ground and excited states mentioned in Table 6-1, dye no. 12. 

Figure 1 shows the aggregation behavior of AOT in liquid cyclohexane and supercritical fluid ethane. The systems are one-phase without added water. Surfactant aggregation is indicated by the solvatochromic probe pyridine A -oxide. Pyridine A -oxide was used because of its small size and large dipole moment (/x = 4.3 D), which allow it to partition to the center of reverse micelles instead of being trapped at the surfactant interface. This molecule is a blue shift indicator in that its U V absorption maximum shifts to lower... 

Both absorption and emission electronic transitions are acceptably described by our scales, as shown by a recent study on the solvation of a series of probes containing an intramolecular hydrogen bond, so no further comment is made here other than the following even if one is only interested in evaluating the change in dipole moment upon electronic excitation via solvatochromic analysis, a multi-parameter analysis must be conducted in order to isolate the shifts corresponding to the pure dipolar effect of the solvent. ... 

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