Hypsochromic shifts

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). 

The meso carbon atom should present a carbenium structure with a low TT electron density in the ground state, in the excited state this carbon possesses the carbeniate structure (C ) with a high tt electron density (119). An electron-donating group in such a position should stabilize the ground state and rise the excited state to the highest level hypsochromic shift results as a whole. 

The shade may be varied by choosing amines. For aromatic amines, the steric effect of substituents in the ortho position reduces the conjugation of the anibno group with the anthraquinone moiety, and the result is a hypsochromic shift and brighter shade. Thus Cl Acid Blue 129 (120) has a more reddish and brighter shade than Cl Acid Blue 25 (118). Cycloalkylamines have a similat effect on the shade. Cl Acid Blue 62 [5617-28-7] (125) Cl 62045) is an example. 

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... 

Substituents in positions 3 and 4 produce bathochromic shifts whereas substituents in position 5 produce hypsochromic shifts, which become more pronounced as the bulk of... 

Hypoxanthine, 2-trifluoromethyl-synthesis, 5, 587 Hypoxanthine, trimethylsilyl-glycosylation, 5, 536 Hypoxanthinium nitrate, 1,3,7-trimethyl-thiation, 5, 540 Hypsochromic shift, 1, 344... 

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... 

He found that the UV maximum exhibits a hypsochromic shift in an alkaline medium. In the IR spectra he found maxima in the carbonyl... 

In the UV spectrum of the protonation products there is a hypsochromic shift of the absorption maximum of enyne system compared to the bases (74DIS) this agrees with the data of the protonation of simple enamines and dienic amines (69MI1). 

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). 

The hypsochromic shift indicates, however, that the excited state (Sj) of Ar —NJ is destabilized relative to S0 in the complex as a consequence of the charge shift (Skrabal, 1994). 

Very large hypsochromic shifts of — 20 to — 87 nm in the electronic spectra of the diazonium salt 4.19 in the presence of 15-crown-5, and even 12-crown-4, were found by Walkow (1988). Obviously they cannot be due to insertion complexes. 

The Amax of bridged dyes such as thiazoloindole symmetrical and unsymmetrical trimethine dyes are shifted toward shorter wavelength compared to the corresponding N-phenylthiazolocyanine. This hypsochromic shift corresponds to an electron-donating substituent in the opposition of the chain when steric hindrance is absent (121). 

ABP = 2-amino-5-bromophenyl(pyridin-2-yl)methanone 226,227 Absorbance, determination of 31 Absorption, measurement of 9,17,31 molar coefficient 36, 40 quantitative relationship 35, 36 recording of spectra 30, 31 -bathochromic/hypsochromic shift 31 -comparison to spectra of solutions 31 scanning curves 17,31,32 ACB = 2-amino-5-chlorobenzophenone 227... 

To qualify the environment into which the colorant molecule is embedded, the actual fluorescence spectrum is compared with the one under standard conditions. If the fluorescence emission spectrum is shifted to longer wavelengths (bathochromic shift), it can be concluded that the molecular enviromnent is of a more polar nature or is polarized by the excited fluorophore. Conversely, a fluorescence shift to shorter wavelengths (hypsochromic shift) indicates a transfer of the fluorophore from a polar... 

In addition, dehydrogenated structures were found to cause a hypsochromic shift. Since, with the exception of neobetanin, these betacyanin degradation products were found not to be native to betalain crops, it is suggested that these peculiar structures may be used as heat indicators to assess the thermal loads of the respective products have undergone during production. 

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