Bathochromic effects

Methoxythiazole has been prepared by the Williamson reaction. The methoxy group exerts a bathochromic effect on the 233-nm band of the thiazole and shields both C-2H and C-5 H (0.67 and 0.89 ppm) (289). 

A rigidized molecule obtained when the two a-carbons of the trimethine chain are linked by a dimethylene bridge cannot be planar. According to the resonance concept, its stability increases as a bathochromic effect of 41 nm is observed (122). The of the bistyryl dye obtained by the substitution of the -proton in the chain of a styryl dye by a dialkylamino group is nearly the same as for the parent styryl dye (123). 

There is a wide variety of dyes unique to the field of hair coloring. Successive N-alkylation of the nitrophenylenediamines has an additive bathochromic effect on the visible absorption to the extent that violet-blue dyes can be formed. Since the simple A/-alkyl derivatives do not have good dyeing properties, patent activity has concentrated on the superior A/-hydroxyalkyl derivatives of nitrophenylenediamines (29,30), some of which have commercial use (31). Other substituents have been used (32). A series of patents also have been issued on substituted water-soluble azo and anthraquinone dyes bearing quaternary ammonium groups (33). 

The direction of the long-wavelength maximum shift caused by the heterosubstitution or the introduction of substituents is deterrnined by the Forster-Dewar-Knott rule (40—42). Spatial hindrances within the symmetrical PMDs cause bathochromic effects (39,43), whereas the introduction of an acetylenic bond is accompanied by the maximum shift to the short-wavelength spectral region (44). 

In Table 29 the u(C=0) and other characteristic bands are given for some saturated five-membered heterocycles, and compared with the corresponding absorption frequencies for cyclopentanone. Adjacent NH groups and sulfur atoms have the expected bathochromic effect on r (C=0), whereas an adjacent oxygen atom acts in the reverse direction. The CHa vibrations of cyclopentanone are repeated to a considerable extent in the heterocyclic analogs. 

Table 30 reports u C=0) for a variety of azolinones containing ring double bonds. The hypsochromic effect of an oxygen atom or CRa group versus the bathochromic effect of NR, S or C=C can readily be traced. 

Tile ultraviolet spectrum of 3-iiitro-l,8-iiaphthyridiiie in methanol A ax [m/A](log e) = 206 (4.06), 238 (4.47), 311 (3.68), and 323 (3.65) showed bathochromic effect of the long-wavelength bands of 10 and 5 m/A with respect to the parent 1,8-naphthyridine (87MI2). Tlie bathochromic effect of 3-nitro group in 1,8-naphthyridine was compared with the effects of some other substituents. 

The introduction of a substituent, especially a free or methylated hydroxyl group, determines a bathochromic shift of band II in the visible region. The 1,4-naphthoquinone absorption bands are at 245, 257, and 335 nm and the bands are at 243, 263, 332, and 405 nm for anthaqninone. The introduction of a substituent (especially a hydroxyl group) in the aromatic ring of a naphthoquinone determines a strong bathochromic effect (up to 100 nm) and some UV bands are shifted into the visible (vis) region. 

Hypochromic and bathochromic effects of the absorption spectrum of berberine on binding of all B-form DNAs (Fig. 6a). 

An electron-donating group in the 4-position of the pyrazoline ring has a slight hypsochromic effect, but an electron-withdrawing group has a bathochromic effect. 

If the bathochromic effect of geminal dicyano substitution is assumed to be in the same range as found for ethylenic reference compounds79, from the positions of maxima in 182 and 193 the absorption of the parent triafiilvene can be estimated to appear in the region of 205—215 nm. This is in qualitative agreement with MO prediction172 that the rr -> 77 transition for methylene cyclopropene will fall near 200 nm. 

Generally, the transparency of a molecular x electron system narrows with increasing conjugation (bathochromic effect) while its nonlinear efficiency increases. The urea molecule is a small conjugated molecule transparent up to 2000 A with a low (3 value 1.3 10-3 e.s.u. (10). For 4-nitro 4 -dimethylaminostilbene the... 

Of the various anthracenedione isomers, only the 9,10-compound is used for the synthesis of dyes it is usually referred to simply as anthraquinone (6.1). The parent compound is pale yellow in colour, having a weak absorption band in the visible region (n—>tt transition). The presence of one or more electron-donating substituents leads to significant bathochromic effects so that relatively simple derivatives are of commercial importance as dyes. The colour of such compounds, which usually contain amino or hydroxy groups, can be attributed to the existence of a charge-transfer absorption band [1]. 

Alkylation of aminotriphenylmethane dyes has a bathochromic effect, which is even more pronounced on arylation, as illustrated in Table 6.5. 

Heteroatom-containing derivatives of pentalene and azulene are 8- and 10-jr-electron systems, respectively, and have been extensively studied by Hafner and co-workers.301-304 A few examples are presented in Schemes 30, 47, and 86. Electron-rich azapentalenes 247—249305 306 and various aza-azu-lenes 250—252300-302 have intense colors and are stable but oxygen-sensitive compounds. Azulenes with nitrogen heteroatoms placed in positions with high electron density, such as position 5, or positions 5 and 7, present a hypsochromic effect, while a heteroatom in position 6, with low electron density, exerts a bathochromic effect. When both types of positions are substituted by heteroatoms, their effect is canceled out.307 The bond lengths in 252 (Scheme 86), as determined by X-ray, indicate delocalization as in 252a and 252b.308 309... 

In several examples including nitroanilines, the effect of twisting the chromophore from planarity decreases the absorption intensities. The reasons for the bathochromic effect as the angles of twist in the 4-aniline series increase is subject to discussion. When considering this (as well as in all attempts to obtain definitions of polarity of solvents by quantitative parameters) it is important to exclude or minimize the presence of hydrogen bonding overlapping158 other interactions. 

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