Solvatochromatic

ILs are considered to be polar solvents, but can be non-coordinating (mainly depending on the IL s anion). Solvatochromatic studies indicate that ILs have polarities similar to those of short-chain alcohols and other polar, aprotic solvents... 

One of the preliminary indications which reveals the potential capacity of a material to generate second harmonics is its solvatochromatic behaviour, i.e. the ability of a material to give rise to considerable differences in its UV-visible spectrum on changing solvent. For example, the electronic absorption spectrum of cw-ferrocenyl-2-(4-nitrophenyl) ethylene in dimethylformamide shows two bands at 340 and 492 nm, respectively, whereas in heptane it displays three bands at 320, 406 and 462 nm, respectively. 

Ab initio SCRF/MO methods have been applied to the hydrolysis and methanol-ysis of methanesulfonyl chloride (334). ° The aminolysis by aromatic amines of sulfonyl and acyl chlorides has been examined in terms of solvent parameters, the former being the more solvent-dependent process.Solvent effects on the reactions of dansyl chloride (335) with substituted pyridines in MeOH-MeCN were studied using two parameters of Taft s solvatochromatic correlation and four parameters of the Kirkwood-Onsager, Parker, Marcus and Hildebrand equations. MeCN solvent molecules accelerate charge separation of the reactants and stabilize the transition... 

Carmichael, A.J., and Seddon, K.R., Polarity study of some l-alkyl-3-methyl-imidazolium ambient-temperature ionic liquids with the solvatochromatic dye, Nile Red, /. Phys. Org. Chem., 13, 591-595,2000. 

Huddleston, J. G., Broker, G. A., Willauer, H. D., Rogers, R. D., Free-energy relationships and solvatochromatic properties of l-alkyl-3-methylimidazolium ionic liquids. In Ionic Liquids, ACS Symposium Series 818, 270-288, 2002. 

The relative polarities of vanous solvents according to a new empirical solvatochromatic polarity scale [J9] are hsted in Table 8 Fluonnated compounds represent both extremes in polarity... 

While it appears that a good deal of the QEO susceptibility may be accounted for by three terms, yc, yn, and yrp, we do not intend to ignore the potential importance of other terms in Equation (9). The strategy will be to see where a reasonable cut-off of terms of Equation (9) can still lead to an adequate explanation of the structure/property trend. We are presently working on solvatochromatic and EFISH determinations of A ioi, with the aim to more fully characterize molecules with regard to yn, and have plans to experimentally determine in order to calculate yrp- There are also efforts underway to more accurately determine orientational contributions. 

Square-planar metallo(diimine)(dithiolene) complexes generally display intense, solvatochromatic absorptions in the visible region of the spectrum that are not found in the corresponding metallo-bis(dithiolene) or metallo-bis (diimine) complexes. Futhermore, the LLCT transition energy does not vary appreciably as a function of the metal ion. Extended Hiickel calculations on Ni, Pt, and Zn metallo(diimine)(dithiolene) complexes indicate that the HOMO is comprised almost entirely of dithiolene orbital character (Figure 2), while the LUMO was found to possess essentially all diimine n orbital character (112, 252, 268). In stark contrast to the spectra of square-planar Ni and Pt metallo (diimine)(dithiolene) complexes, the psuedo-tetrahedral complexes of Zn possess extremely weak LLCT transitions. Now, it is of interest to discuss the differences in LLCT intensity as a function of geometry from a MO point of view. This discussion should help to explain important orientation-dependent differences in photoinduced electron delocalization and charge separation. 

Carceroisomerism has also been observed in hemicarceplexes. Paek and coworkers have measured isomerisation energy barriers of carceroisomers in non-centrosymmetric C4v hemicarceplexes, the largest of which was found to be 15.4 Kcal mol-1 for the rotation of NMP inside the cavity [43]. It has also been claimed that the inside of carcerands and hemicarcerands can be considered as a new phase of matter. This suggestion implies effects beyond mere spatial confinement and chemical isolation, for example, a marked change in the physical bulk properties, such as the polarity or polarisability of the host cavity. Nau has obtained evidence that biacetyl included within the cavity of a hemicarcerand may experience an unusual polarisability even higher than that of di-iodomethane by using biacetyl as a solvatochromatic probe for the polarisability of the environment [44]. 

Bis Complexes. The dicyano complexes [Fe(CN)2 (diimine)2] are protonated in strong acid to give stable mono and diprotonated species. Protonation is associated with major color changes, typically dark violet to yellow, and these complexes have been used as acid-base indicators in nonaqueous titrations. They also show strong solvatochromatic charge-transfer bands. For example, the absorbance maximum of [Fe(CN)2(bipy)2] in water is 515 nm and in pyridine, 629 nm. The solvatochromism of a variety of [Fe(diimine)2(CN)2] and [Fe(diimine)(CN)4] complexes has been established, ... 

Figure 1 Compounds that exhibit large solvatochromatic shifts used to assess solvent polarity.

EXPERIMENT 9.2 INVESTIGATING SOLVATOCHROMATIC PROPERTIES OF VANADYL-d/s(2,4-PENTANEDIONE), VO(acac)2 USING VISIBLE SPECTROSCOPY... 

The terms n, a. and g are empirical solvent parameters developed by Taft and Kamlet (7). The fluoresence emission maximum of probe 1 in pure organic solvent defines the pure solvent reference line in Figure 1. When probe 1 is covalently attached to a polymer backbone which in turn is immersed in solvent, the deviation in fluorescence emission wavelength from the pure solvent correlation line reveals how the polymer perturbs the microenvironment of the probe. This microenvironment can vary from pure solvent-like to one dominated by the polymer backbone. The fluorescence emission of the probe in dry polymer is also indicated in the figure. A summary of the solvatochromatic data is discussed below. 

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