Solvent dependence absorption

Since then, solvent-dependent absorptions of a great variety of compounds have been studied as potential reference processes for establishing empirical scales of solvent polarity. Most approaches include negatively or positively solvatochromic dyes because they are experimentally easy to handle. The use of solvatochromic dyes as solvent polarity indicators has been reviewed [1, 2, 293-296, 316], see, in particular, reference [293] only a few of these dyes can be mentioned in this Section. 

Another unusual optical property is solvatochromism (27, 28). Most inorganic complexes have small solvent-dependent absorption spectra. Pronounced solvatochromism has not been extensively characterized for inorganic complexes in solution with the exception of a recent report on the electronic spectra of a variety of dipolar dithiolene a-diimine nickel complexes (29). 

MOXTPP X = Br, Cl) in various solvents were recently examined. Both complexes exhibited dramatic shifts in the peak maxima and peak intensity (e) as compared to their unhalogenated analogs. The solvent-dependent absorption spectral features of the electron deficient metal(II) perhaloporphyrins were attributed to a coordinative interaction of the solvent with the metal ion of the porphyrin cavity. ... 

Bensasson R V, Bienvenue E, Dellinger M, Leach S and Seta P 1994 Cgg in model biological systems. A visible-UV absorption study of solvent-dependent parameters and solute aggregation J. Phys. Chem. 98 3492-5000... 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

We have also developed a method of measurement for local temperature in microspace with a fluorescence correlation technique. Using this method, the temperature elevation at the optical trapping point due to absorption of the NIR trapping beam by solvent was quantitatively evaluated the temperature at the trapping point increased linearly with increase in the incident NIR light, and the temperature elevation coefficient was mainly dependent on two physical parameters of the solvent the absorption coefficient at 1064 nm and the thermal conductivity. 

Solvatochromic pareuaeters, so called because they were Initially derived from solvent effects on UV/visible spectra, have been applied subsequently with success to a wide variety of solvent-dependent phenomena and have demonstrated good predictive ability. The B jo) scale of solvent polarity is based on the position of the intermolecular charge transfer absorption band of Reichardt s betaine dye [506]. Et(io> values are available for over 200 common solvents and have been used by Dorsey and co-%rarkers to study solvent interactions in reversed-phase liquid chromatography (section 4.5.4) [305,306]. For hydrogen-bonding solvents the... 

Spectral data of these alkaloids are presented in the review works (4,8) but do not include data for bicucullinidine (110), which was discovered in 1981 (113-116). In the IR spectra of these compounds the carbonyl region generally consists of three bands. The first one is placed at 1675-1670 cm-1 and the latter two around 1625-1590 cm-1. The amino acid nature of these compounds is demonstrated by the presence of an NH band (2350 cm-1) found in the IR spectrum of bicucullinine (108) (117), as well as by the solvent-dependent position of the N(CH3)2 group in the H-NMR spectra. For instance, in the spectrum of bicucullinine (108) run in basic aqueous solution it can be found at <52.08 (118), in DMSO-d6 at <52.69 (113,116), and in CFjCOOD at <53.13 (117,119). Moreover, in H-NMR spectra the influence of the C-l carbonyl group on the chemical shift of H-8 can be observed. This proton falls in its deshielding zone and is shifted downfield around 1 ppm compared to the absorption of H-8 in spectra of monoketo acids. 

In contrast, the diphenyl analogue of 182/192 and other triafulvenes5 showed marked solvent dependence of UV absorption, whereas the diphenyl analogue of 194 does not (see above). The origin of this complex behavior is still an open question. 

Gaines (15) has previously described the use of merocyanine dyes as a nonaqueous means of determining Bronstcd acid concentration. Merocyanine dyes are protonated by strong acids to produce protonated dye which has a distinct visible absorption (Figure 1). The unprotonated dye form (3) has a solvent dependent visible absorption maxima. The present studies were performed in acetonitrile or dichloromcthane solvent where absorption maxima were at 576 nm and 610 nm respectively. The absorbance of the protonated form (4) is relatively unaffected by choice of solvent and is clearly separable from the absorbance of the free dye. The extinction coefficient of the free dye is quite large (71,000 in dichloromethane) which allows determination of small amounts of acid such as 10 6 mmol with an average error of less than 10%. 

If an organic solvent is used to dissolve the chemical, water should be added to reduce the dehydrating effect of the solvent within the gut lumen. The volume of water or solvent-water mixture used to dissolve the chemical should be kept low, since excess quantities may distend the stomach and cause rapid gastric emptying. In addition, large volumes of water may carry the chemical through membrane pores and increase the rate of absorption. Thus, if dose- dependent absorption is suspected, it is important that the different doses are given in the same volume of solution. 

In the case of benzotriazole compounds which display both absorption bands, the observed spectrum consists of the superposition of the individual spectra that correspond to the two distinct ground-state species. The absorption spectrum of TIN in methanol/dimethylsulfoxide (DMSO) solvent mixtures varies with the composition of the solvent (Figure 5) in a manner which suggests that the proportion of planar and non-planar forms of TIN is solvent dependent. 

The reprecipitation strategy lies in the conversion of the products dissolved in a suitable organic solvent into nanodispersed systems in a different medium by a precipitation/condensation procedure. On the other hand, the ion-association strategy can produce ion-based dye nanoparticles in pure aqueous media by utilizing a water-insoluble ion-pair formation reaction. The following example shows the size-dependent absorption properties for the cation-based pseudoisocyanine (PIC see the chemical structure in Fig. 4) dye nanoparticles. 

Attention should be paid to the additional hydrogen bonding effect in protic solvents like alcohols. It has indeed been observed that correlations of solvent-dependent properties (especially positions and intensities of absorption and emission bands) with the fcT(30) scale often follow two distinct lines, one for non-protic solvents and one for protic solvents. 

The commonest modern method for determining the degree of hydration is to measure the intensity of the broad n- carbonyl absorption band at about 280 m/x, which disappears on hydration. Early measurements (Schou, 1926, 1929 Harold and Wolf, 1929, 1931) show considerable discrepancies, but the results of later workers are in reasonable agreement. The main uncertainty lies in the value to be assigned to the maximum extinction coefficient of the unhydrated carbonyl compound, which varies between 12 and 80 for different compounds. This is commonly taken as the value measured in a non-hydroxylic solvent such as hexane or cyclohexane, but this is not strictly valid, since the intensities of n-n- transitionsvary somewhat with the solvent (see e.g. Dertooz and Nasielki, 1961) moreover, since the shape of the band and the value of e are also solvent-dependent it may make some difference whether the extinction coefficients are compared at the same wavelength, at the respective maxima, or in terms of the band area. Special difficulties arise... 

The infra-red spectra of the trimethyl, dimethyl- and dimethylethyl-carbonium salts in excess antimony pentaduoride are shown in Figs. 4a, b, and c. The IRTRAN cells used are not transparent below 770 cm , thus obscuring the 650 cm SblY absorption which would, however, be overlapped by the solvent SbFs absorption. The broad, intense absorption band which appears in all the spectra near 1550 cm is present in the solvent spectrum. It was found to be dependent on the purity of the SbFs, but the nature of the impurity was not established. It should also be mentioned that Deno found an intense absorption at 1533 cm in cyclohexenyl cations thus, secondary carbonium ions formed from the reaction with olefins (which arise from deprotonation) could add to this broad absorption. 

One aspect of the research will examine equilibrium aspects of solvation at hydro-phobic and hydrophilic interfaces. In these experiments, solvent dependent shifts in chromophore absorption spectra will be used to infer interfacial polarity. Preliminary results from these studies are presented. The polarity of solid-liquid interfaces arises from a complicated balance of anisotropic, intermolecular forces. It is hoped that results from these studies can aid in developing a general, predictive understanding of dielectric properties in inhomogeneous environments. 

Tables 3-2 and 3-3 summarize the infrared and proton-NMR (nuclear magnetic resonance) spectroscopic properties of alcohols and ethers. In the proton NMR, the oxygen atom is deshielding. Phenols and alcohols rapidly exchange protons so their NMR spectra are solvent dependant. The alcohol and ether groups don t have any characteristics absorptions in UV-vis spectra.

Anhydro-1,2-dimethyl-3,5-diphenyl-4-hydroxy-1,2-diazolium hydroxide (373, R = R = Me, R = R = ph) shows a band (1546 cm" in dimethyl sulfoxide), which has been assigned as a carbonyl band. This absorption band, which is much lower than, for example, the sydnones (1) (vco 1750-1770 cm ) has been briefly considered in relation to the electronic characteristics of type A and type B meso-ionic heterocycles. However, the significance of this spectral difference must surely await more extensive comparison betweeen corresponding type A and type B heterocycles. The compound (373, R = R = Me, R = R = Ph) also shows a striking solvent dependence of its ul-traviolet/visible spectrum (Ama CjHg 447 McjSO 421 CHClj 410 Bu,OH 370 MeOH 345 Hp 325 nm). °... 

As mentioned in sections 1.2.2.2 and 1.2.3.2, the photochromic reactions of spirobenzopyran and spironaphthoxazines show a marked solvent dependency and this is also the case with benzo and naphthopyrans. Consequently, spectral data collected from the literature is only comparable within any one study or where the same solvent has been used. This accounts for any discrepancies between one set of results and any other one listed in this and related sections of this chapter. The data normally quoted when discussing the properties of photochromic materials relate to the absorption maximum (2. ) of the coloured state, the change in optical density (absorbance) on exposure to the xenon light source (AOD) and the fade rate which is the time in seconds for the AOD to return to half of its equilibrium value. 

Examination of the optical spectrum of the filtered purple solution gave a structured absorption band with maxima at 514 and 543 nm. This position is remarkably close (566 nm) to the n-n electronic transition predicted by Davis and Goddard for the parent system H2N=N. As expected for an n-n transition, the position of the absorption maximum is solvent dependent. In dichloromethane solution, A,i ax is 541 nm, in 2-propanol it is 526 nm. The blue shift of 15 nm is completely consistent with the n-n absorptions of isoelectronic carbonyl compounds. 

A subsequent picosecond electronic absorption spectroscopic study of TPE excited with 266- or 355-nm, 30-ps laser pulses in cyclohexane found what was reported previously. However, in addition to the nonpolar solvent cyclohexane, more polar solvents such as THF, methylene chloride, acetonitrile, and methanol were employed. Importantly, the lifetime of S lp becomes shorter as the polarity is increased this was taken to be evidence of the zwitterionic, polar nature of TPE S lp and the stabilization of S lp relative to what is considered to be a nonpolar Sop, namely, the transition state structure for the thermal cis-trans isomerization. Although perhaps counterinmitive to the role of a solvent in the stabilization of a polar species, the decrease in the S lp lifetime with an increase in solvent polarity is understood in terms of internal conversion from to So, which should increase in rate as the S -So energy gap decreases with increasing solvent polarity. Along with the solvent-dependent hfetime of S lp, it was noted that the TPE 5ip absorption band near 425 nm is located where the two subchromophores— the diphenylmethyl cation and the diphenylmethyl anion—of a zwitterionic 5ip should be expected to absorb hght. A picosecond transient absorption study on TPE in supercritical fluids with cosolvents provided additional evidence for charge separation in 5ip. 

A third example can be taken from analytical chemistry. Absorption and resonance Raman spectra of phenol blue were measured in liquid and supercritical solvents to determine the solvent dependence of absorption bandwidth and spectral shifts. Good correlation between absorption peak shift and resonance Raman bands and between Raman bands and bandwidth of C-N stretching mode were observed while anomalous solvent effect on the absorption bandwidth occnrred in liquid solvents. Large band-widths of absorption and resonance Raman spectra were seen in supercritical solvents as compared to liquid solvents. This was dne to the small refractive indices of the supercritical solvents. The large refractive index of the liqnid solvents only make the absorption peak shifts withont broadening the absorption spectra (Yamaguchi et al., 1997). 

Complexes of rhenium(bipyridine)(tricarbonyl)(picoline) units linked covalently to magnesium tetraphenylporphyrins via an amide bond between the bipyridine and one phenyl substituent of the porphyrin 19 exhibited no signs of electronic interaction between the Re(CO)3(bpy) nnits and the metalloporphyrin units in their gronnd states. However, emission spectroscopy revealed a solvent-dependent quenching of porphyrin emission upon irradiation into the long-wavelength absorption bands localized on the porphyrin. 

Benzo[c]furan (4) exhibits a long-wave absorption band of medium intensity in the region of 340 nm. Lack of solvent dependence together with mirror relationship to the fluorescence spectrum signifies a tt-ti band a rotational analysis of the vapor phase spectrum led to an assignment as 82 <- Ap 1,3-Diaryl-substituted benzo[c]furans show a strong absorption band in the region of 415 nm in sterically hindered compounds, this... 

The steady-state spectra obtained for different alcohols are depicted in fig. 1. While the absorption spectra red shift with increasing solvent polarisability (from methanol to octanol), the fluorescence shows a red-shift when going from octanol to methanol. The total Stokes shifts are very large 7.900 100 cm 1 for PSBR/MeOH and 6.870 100 cm 1 for octanol. Another striking observation is the 30 % smaller width of the fluorescence spectrum of methanol (AE = 3.420 cm 1) compared with other alcohols. While the widths of the fluorescence spectra are solvent-dependent, the absorption spectra have a FWHM of -5.100 cm"1, irrespective of the solvent. As we will substantiate in the following, this behavior indicates that the potential energy surface around the fluorescent point is different than near the Franck-Condon zone probed by absorption, as suggested by quantum chemistry calculations [7]. 

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