Solvatochromic probes structures

SCHEME 1. The structures of some of the substituted anilines used as solvatochromic probes... 

The two parts of the present volume consist of 17 chapters written by experts from 10 countries. They start with historical background, followed by chapters on the theory, structure, thermochemistry, photophysics and photochemistry and electrochemistry of anilines, on their mass spectrometry, NMR spectra and analysis and on their modern syntheses by transition metal catalysed processes. Other chapters deal with their rearrangements, their reactivity as nucleophiles, their use as solvatochromic probes, their hydrogen bonded complexes, and their versatile uses in the chemical industry, and the relevant topic of toxicity and environmental aspects. A chapter on a special group of anilines—the proton sponges—ends the book. 

UV-Vis spectroscopy can also be used to further characterize the physicochemical properties of the solution. Solution structure in SCFs has been investigated through the. use of solvatochromic probe molecules in which the n- n or electronic transition of a probe molecule responds to changes in its... 

A solvatochromic scale, based on the ultraviolet-visible, rather than the infrared, spectral band of suitable probes is that based on the Kamlet -Taft P parameter. This is again an averaged quantity, for which the wavenumber shifts of several protic indicators relative to structurally similar but aprotic homomorphs are used (Kamlet et al. 1983 Kamlet and Taft 1976). It is assumed that the nonspecific effect of a solvent on the protic probe is the same as that on the aprotic one, and that it can be expressed in terms of the n parameter for the solvent, so that the donicity of the solvent, if it is a Lewis base, causes the difference between the responses of the two probes towards the solvent. The probes originally employed were 4-nitrophenol (vs 4-nitroanisole) and 4-nitroaniline (vs 4-nitroN,N-diethylaniline), but once a n scale is known, the need for the specific aprotic homomorph values no longer exists, since the general expression ... 

The nature and magnitude of the solvent-solute interaction depend on the molecular structures of the species. However, it should be apparent that this type of interaction provides a way to assess the interaction between a solute and the solvent. This is an extremely important area of chemistry with regard to understanding the role of the solvent as it relates to effects on solubility, equilibria, spectra, and rates of reactions. As a result, several numerical scales have been devised to correlate the effects of solvent interactions, some of which are based on solvatochromic effects. However, in most cases complex dyes have been utilized as the probe solutes, but it is interesting to note that iodine also exhibits solvatochromism. 

Finally, the ambitious approach of Catalan et al. to introduce complete new comprehensive scales of solvent dipolarity/polarizabihty [SPP scale), solvent basicity SB scale), and solvent acidity SA scale) must be mentioned [296, 335-337]. These three UV/Vis spectroscopic scales are based on carefully selected positively solvatochromic and homomorphic pairs of probe dyes and include values for about 200 organic solvents for a recent review, see reference [296]. The molecular structures of the three pairs of homomorphic indicator dyes proposed are as follows ... 

The fluorescence lifetimes of the four natural DNA bases within the femtosecond range are too short to be useful as spectroscopic probes to characterize the solvation dynamics of DNA (31). The minor groove binder Hoechst 33258, the fluorescent adenine analog 2-Aminopurine (2Ap), and the base pair mimic coumarine 102-abasic site are better probes because they exhibit longer lifetimes and better solvatochromic properties. Of the two base pair analogs, the coumarine 102-abasic site base pair mimic disrupts the native DNA structure more than the adenine analog 2Ap. However, the spectroscopic characteristics of the former are superior to those of 2Ap for probing solvation dynamics. 

Pyrene derivatives are the widest used probes for qualitative solubilization [365] by virtue of the solvatochromic shifts of the absorption bands [255], the excimer formation [145,186], the polarity dependent quantum yields [197] and fluorescence life-times [185-187, 196, 197, 202, 215, 292], and the pyrene fluorescence fine structure [65, 74,78,103,112,167, 224, 363, 371] the intensity ratio of the fluorescence bands I at 372 nm and III at 383 nm is a convenient measure for the polarity of the environment of the pyrene label ( py -scale I/III values increase with polarity, cf. Fig. 27). As, however, the fluorescence of pyrene is very sensitive to the experimental set-up [372], absolute I/III values reported by different groups are difficult to compare. 

Hawker CJ, Wooley KL, Frechet JMJ (1993) Solvatochromism as a probe of the microenvironment in dendritic polyethers transition from an extended to a globular structure. J Am Chem Soc 115(10) 4375 376... 

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