Shift, bathochromic

A bathochromic shift of about 5 nm results for the 320-nm band when a methyl substituent is introduced either in the 4- or 5-posiiion, The reverse is observed when the methyl is attached to nitrogen (56). Solvent effects on this 320-nm band suggest that in the first excited state A-4-thiazoline-2-thione is less basic than in the ground state (61). Ultraviolet spectra of a large series of A-4-thiazoline-2-thiones have been reported (60. 73). 

This bathochromic shift is typical of 77 —> tt transitions. The behavior of the water solution when acidified was attributed by Albert (175) absorption by the thiazolium cation, by analogy with pyridine. However, allowance is made for the very weak basicity of thiazole (pK = 2.52) compared with that of pyridine (pK = 5.2), Ellis and Griffiths (176) consider the differences between the spectrum of thiazole in water and in 

A large bathochromic shift is observed in the blue-green dye (126) [65605-46-1] (89) prepared from the dia2o component 3 - amino - 5-nitr o - 2,1-b en2is o thia2 ole. 

Table 11 Bathochromic Shift caused by Substituents on Isothiazole (Isothiazole Ama = 244nm,

In every case a bathochromic shift that is greater for asymmetrical than for symmetrical dyes has only been observed. 

A further strong bathochromic shift is observed as the basicity of the primary amines is increased by A/-alkylation, eg, malachite green [569-64-2] Cl Basic Green 4, =621 nm (5). 

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 

However, benzylidene derivatives show a strong bathochromic shift in comparison with alkylidene derivatives. Thus absorption is a result of the whole conjugated system that is comparable to that of the quinoid dyes. The color of this type of compound is sensitive to acids and bases. 

In general, electron-releasing substituents cause a bathochromic shift of the n band 

Phenylation of tfie piimaiy amino groups also produces an increased bathochromic shift in the wavelength of absorption with increasing degree of phenylation. Only monophenylation of each amino group is possible, eg, as in (6) and (7). 

As in the case of pyridine (185), the quaternization of thiazole induces a bathochromic shift of the ultraviolet absorption spectrum in ethanol the long wavelength maximum at 232.3 nm (3900) for thiazole moves to 240 nm (4200) for 3-methylthiazolium tosylate (186) (Table 1-19). 

A 2-methylthio substituent decreases the basicity of thiazole pK = 2.52) by 0.6 pK unit (269). The usual bathochromic shift associated with this substituent in other heterocycles is also found for the thiazole ring (41 nm) (56). The ring protons of thiazole are shielded by this substituent the NMR spectrum of 2-methylthiothiazole is (internal TMS, solvent acetone) 3.32 (S-Me) 7.3 (C -H) 6.95 (Cj-H) (56, 270). Typical NMR spectra of 2-thioalkylthiazoles are given in Ref. 266. 

As in the case of the free bases, the substitution of a nuclear hydrogen atom by a methyl group induces a bathochromic shift that decreases in the order of the position substituted 4->5->2- Ferre et al. (187) have proposed a theoretical model based on the PPP (tt) method using the fractional core charge approximation that reproduces quite correctly this Order of decreasing perturbation. 

Whatever their nature may be, phenyl or alkyl, the substituents of the thiazole ring in position 4 or 5 give a bathochromic shift (110, 111) of the absorption of a symmetrical trimethine thiazolocyanine compared to an unsubslituted dye. For a given substituent, this shift is greater for position 5 than for 4 (112). 

An alkyl group in the chain of a monoraethine thiazolocyanine prevents the molecule from being planar. It gives a bathochromic shift of 40 nm and a decrease of the oscillator strength (26), as is the case for other methine dyes. 

Steric overcrowding associated with the interaction betw een the thiocarbonyl group and a bulky alkyl group gives a bathochromic shift. This has been interpretated as evidence for a smaller thiocarbonyl group" in the first excited state (73). 

Any electron-attracting group, -NO2, -CN, -Ac, or -COjEt, on the a-carbon of the methine chain of a thiazole dye gives a bathochromic shift (120). A reverse effect is observed for an alkoxy group. 

Comparison of the ultraviolet spectra of analogous sulfur and selenium compounds shows that there is very little difference in the absorption curves, except for a slight bathochromic shift in the case of the selenium derivatives- 

The absorption maximum of a disubstituted anthraquinone gready depends on the substituents and their positions (Table 2). The 1,4-disubstituted compound shows a remarkable bathochromic shift. The effects of P-substituents on 1,4-dianainoanthraquinones (14) are shown in Table 3. Larger bathochromic shifts are observed with increasing electron-withdrawing abiUty of P-substituents. 

Electron-donating or -withdrawing properties of a substituent on the 4 and 5 positions have also been used in order to modulate the basicity in the hope to observe either hypsochromic or bathochromic shift (110). 

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 

Electronic absolution spectra of metals sorbed on NH -S surfaces in the presence of BPR have a maximum in the field of 19000 cm -18000 cm adding of DPC to the solution leads to forming complexes, which is characterized by bathochromic shift to the range of 17000-16000 cm f Thus the absolution maximum is shifted bathochromically by 50-70 nm. 

Until now, no final conclusion seems to have been reached as to the origin and amplitude of the phenomenon. The nature of the alkyl group fixed on the nitrogen atoms does not influence the position of but substituents of different kinds produce, for trimethine thiazolocyanine as well as styryl derivatives (116), a bathochromic shift in the order  

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