Hypsochromic band shift

Overall, the band shifts experimentally observed for all kinds of absorptions are the net results of three, partly counteracting contributions electrostatic (dipole/dipole dipole/induced dipole blue shift), dispersion ( red shift), and specific hydrogen-bonding blue shift). Which of these solute/solvent interactions are dominant for the solute under study depends on the solvents used. For example, the results obtained for pyridazine, as shown in Fig. 6-5, clearly implicate hydrogen-bonding as the principle cause of the observed hypsochromic band shift that occurs when the HBD solvent ethanol is added to solutions of pyridazine in nonpolar -hexane [98]. The intensity of n n absorption bands is usually very low because they correspond to symmetry-forbidden transitions, which are made weakly allowed by vibronic interactions cf. Fig. 6-5). 

Lil, Bal2, Ca(SCN)2, and Mg(C104)2 to solutions of (44) in acetonitrile leads to a differential hypsochromic band shift which increases with this ionophore order, i.e. with increasing charge density of the cation [211], Obviously, salts act similarly to other polar compounds (solvents) when added to solutions of (44). The polarity of binary iono-phore/solvent mixtures as a function of composition can be quantitatively described in a manner similar to other binary solvent/solvent mixtures [197, 213],... 

The direct determination of SA values for more acidic solvents was not possible because in such solvents the indicator dyes (52) and (53) are protonated at the carbonyl oxygen atom. For such acidic solvents, 3,6-diethyl-l,2,4,5-tetrazine (DETZ) was introduced as a third probe dye [337b]. This aromatic tetrazine exhibits a solvent-dependent n n absorption in the visible region a change from methylcyclohexane = 550 nm) to hexafluoro-2-propanol (Imax = 517 nm) leads to a hypsochromic band shift of A2 = —33 nm (Av = +1160 cm ), mainly due to the HBD acidity of the... 

Another UV/Vis spectroscopic method for the determination of water in organic solvents involves the use of solvatochromic dyes (such as the pyridinium A-phenolate betaine dye (44) m Chapter 7.4), and is based on the observation that water has a very high polarity compared with most organic solvents [142-145]. Even small amounts of water cause a strong hypsochromic band shift of the dissolved solvatochromic dye, which can be related to the water content by a cahbration curve. A typical detection hmit of this method is of the order of 1 mg water in 1 mL solvent for routine spectrophotometers [142], An analogous solvatochromic method has been developed for the determination of aqueous ethanol mixtures [146],... 

While 9b (n = 2) revealed a small but significant selective coloration with Nal, cation-induced hypsochromic band shifts were observed with Li+, Na+, K+, Rb+, and Cs+, decreasing in that order these were explained satisfactorily in terms of the electrostatic interactions between the complexed cations and the p-nitrophenolate dipole of the merocyanine. Conversely, the hypsochromic band... 

Steric hindrance due to alkyl substituents increases the torsion angle between phenylene units, which results in an additional (unwanted) increase of the band gap. The emission band shifts into the violet region of the spectrum (APL 400 nm) [583]. The hypsochromic shift... 

Phthalocyanine metal complexes in the multicomponent systems can be in three states [5] in the form of a monomer with narrow absorption band in the 665-675 nm [11-14], H-aggregates with their absorption band shifted relative to the monomer hypsochromically to -630 nm, and J-aggregates with an absorption band batho-chromically shifted relative to the monomer to wavelengths of 730-850 nm. H- and... 

As shown in Figure 7, n n - and n - 7t -transitions often behave differently. If cyclohexane (b) is replaced by methanol (a) as the solvent, the polarity increases considerably, so that the 71 - It band is shifted by 10-20 nm towards the red (bathochromic) and the n -> 7u -band by 10 nm towards the blue (hypsochromic). This shift gives an indication of the effect not only of the solvent polarity on the behavior of the bands, but also of the structure of the system. A change in intensity of the absorption band is described as hyperchromic (intensity increase) or hypochromic (intensity decrease) [5], [31]. 

For BZP adsorbed from water onto Cl2-1500 modified cellulose, the ground-state absorption curves appear now as broad bands, shifted hypsochromically when compared with BZP/C12-1700 ethanol case, where the vibronic absorption bands of the carbonyl group can be seen (Figure 1). These hypsochromic shifts are quite characteristic of the n 7t transition with increasing polarity of the surface... 

Solvatochromism Solvent-induced shift of the UVA is/NIR absorption band (and change in intensity) of light-absorbing solute. A hypsochromic (blue) shift with increasing solvent polarity is called negative solvatochromism, a corresponding bathochromic (red) shift is called positive solvatochromism. 

The auto-association of A-4-thiazoline-2-thione is clearly indicated b the hypsOchromic shift (5 nm) of the 315-nm band when the spectrum is first recorded at 50°C and then at —25°C (10 M in cyclohexane). In the same temperature range the spectrum of 3-methyl-A-4-thiazoline-2-thione remains unchanged (61). 

Their physical properties closely resemble those of pterin, which has a basic pKt, of 2.20 and an acidic one of 7.86 associated with N-1 protonation and a hypsochromic shift of the long-wavelength absorption band in the UV spectrum, and N-3 deprotonation effecting a bathochromic shift respectively (Table 4). The xanthopterin (4) and isoxanthopterin types... 

A hypsochromic shift of 20-50 cm is observed in the double-bond stretching region, when the enamines are converted to the corresponding iminium salts by the electrophilic addition of a proton at the /3-carbon atom. The shift is accompanied by an enhancement in the intensity of the band. Leonard and co-workers (68,71-74) have used this absorption shift as a diagnostic tool for the determination of the position of the double bond... 

In the UV spectral range complexation with 18-crown-6 causes a hypsochromic shift of the band with the longest wavelength in various solvents (Bartsch et al., 1976 Hashida and Matsui 1980). Gokel and Cram (1973) reported that complexation with binaphtho-20-crown-6 (11.2) produces a yellow to red color. This phenomenon is very likely to be due to a charge-transfer band between a naphthalene ring as donor (7i-base) and the arenediazonium ion as acceptor (7i-acid). 

Kuokkanen (1986, 1987 a, 1991) supported the proposal of Nakazumi et al. (1983) based on kinetic and spectrophotometric comparisons of arenediazonium salt solutions in the presence of 18-crown-6 and pentaglyme. He also extended the systematic work on complex formation of benzenediazonium salts, substituted in the 2-position, and in the presence of 15-crown-5 (Kuokkanen, 1990 Kuokkanen et al, 1991). He discovered a useful way to differentiate between the two types of complexes in Scheme 11-2. Increasing the relative concentration of the host compound shifts the ultraviolet absorption band of both types of complex hypsochromically, whereas the NN stretching frequencies are significantly increased only in the case of insertion complexes. ... 

Geometrical cis-trans isomers — The UV-Vis spectra of most cis isomers are similar to those of the corresponding dll-trans isomer. However, a few consistent differences can be found in the spectra of cis isomers as compared to those from the corresponding a -trans compound a hypsochromic shift (2 to 6 nm for mono-dY through 34 nm for tetra-c ), a decrease in absorbance, a reduction of the spectral fine structure, and tlie appearance of a new absorption band known as a cis peak. For example, in a study in which the structures were confirmed by NMR, the isomers... 

The of 33 shows a bathochromic shift, compared to that of the corresponding spironaphthopyran [ max 531, 558(s) nm in toluene].78 The substituent effect in 2, 5, 6 - and 5-position of 33 on the absorption band of the colored form has been examined.72,77,7s The donor substituent group in 6 -position, such as piperidino group, gives a hypsochromic shift by 35 nm, but 5 -carbomethoxy substitution results in a bathochromic shift by 20 nm. This may be due to interaction between oxygen atom of the phenolate and methoxy group. 

---