Solvato-chromism

Buncel E. and Rajagopal S. (1990) Solvato-chromism and Solvent Polarity Scales, Acc. Chem. Res. 23, 226—231. 

Molecular self-organization in solution depends critically on molecular structural features and on concentration. Molecular self-organization or aggregation in solution occurs at the critical saturation concentration when the solvency of the medium is reduced. This can be achieved by solvent evaporation, reduced temperature, addition of a nonsolvent, or a combination of all these factors. Solvato-chromism and thermochromism of conjugated polymers such as regioregular polythiophenes are two illustrative examples, respectively, of solubility and temperature effects [43-45]. It should therefore be possible to use these solution phenomena to pre-establish desirable molecular organization in the semiconductor materials before deposition. Our studies of the molecular self-assembly behavior of PQT-12, which leads to the preparation of structurally ordered semiconductor nanopartides [46], will be described. These PQT-12 nanopartides have consistently provided excellent FETcharacteristics for solution-processed OTFTs, irrespective of deposition methods. 

The p parameter can be obtained by determining the relative difference in solvato-chromism of 4-nitroaniline and iV,A-diethyl-4-nitroaniline ... 

Many studies have been made on the behavior of probe solutes in order to characterize the selective solvation in solvent mixtures, in particular depending on solvato-chromism. However, what is determined is the selective solvation of the probe, not of the binary solvent components with each other. It is conceivable that a spectroscopic investigation of a binary solvent mixture in the absence of a probe could be carried out if each component had a clear signal (absorption or fluorescence) at a characteristic exclusive wavelength. Such mixtures could be formamide + acetonitrile and formamide + dimethylsulfoxide, in which the C=0 bond stretching wave number of the hydrogen bond donor differs from the C=N and the S=0 bond stretching wave number of the acceptors (Alves and Santos 2007). 

To further support the formation of IL-in-oil microemulsion, we have utilized the typical polarity probe betaine 30 ( . (30) probe) [84-86]. For large negative solvato-chromism, the /Sj.(30) probe has been widely used by many groups to determine the polarity of different systems [84-90]. The absorption spectra of .j.(30) probe are shown in Rgure 15.2a, which clearly shows that the absorption maximum (2 )... 

Obviously, the difference between the solvatochromism of DMANF and FNF will cancel many of the spurious effects involved in measurements of solvent polarity. Because the envelopes of the first absorption bands for FNF and DMANF are identical (see Figure 1 in ref 15), one of the most common source of error in polarity scales is thus avoided. The polarity of a solvent on the SPP scale is given by the difference between the solvato-chromism of the probe DMANF and its homomorph FNF [Av(solvent) = Vp p - Vd anf] and can be evaluated on a fixed scale from 0 for the gas phase (i.e., the absence of solvent) to 1 for DMSO, using the following equation ... 

The fact that our scales allow solvent polarizabihty and dipolarity to be dealt with separately allowed us to revisit for the first time such interesting phenomena as dipolarity-triggered processes, which include charge transfer in biaiyl compounds and the solvato-chromism inversion in betaines. 

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