Bathochromic shifts substituent effect

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. 

Unconjugated 1,3,4-thiadiazoles have no selective absorption above 220 nm. Substituents with lone pairs cause bathochromic shifts the effect of an alkylthio group is greater than... 

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). 

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. 

PPP calculations reproduce the nitro substituent effect and heterocyclic effect on the /,max. For example, the bathochromic shift by substitution of a nitro group is calculated (ca.20nm). It is in good agreement with the experimental value determined (A,max = 598 nm) in toluene. PPP calculation exactly predicts the bathochromic shift by benzo-annelation of the indoline and benzopyran residues (Table 2). In the neutral quinoid form, the calculated charge densities for the ground and first excited states by PPP... 

Substituent effects on the Vax of the colored form in these series are interesting and are dependent on the pyran component. For compound 20, substitutions at position 3, 6, or 8 (or 3, 6, 8 ) affects the X substantially, i.e., the absorption band lies in a wide range 475-609nm. The 7,7 -, 8,8 -, or 10,10 -dinitro-substituted compounds 21 reveal a somewhat hypso-chromic shift, relative to unsubstituted derivative, whereas the bathochromic shift (1(M0 nm) is observed with dinitro substitution at the same position in compound 22. For compound 23, the pronounced shift is also observed with 8-nitro substitution. Many other spectral data are collected in Ref. 1. 

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. 

On the other hand, the introduction of halide substituents at the C-2 and C-6 position decreases fluorescence quantum yields and gives a bathochromic shift of emission maxima. For example, bromine at the C-2 and C-6 position in compound 14b deteriorates fluorescence quantum yields from 0.95 (14a) to 0.45 and the emission maximum is red-shifted by 42 nm. Moreover, iodine at the C-2,6 position in compound 14d gives the similar bathochromic shift to bromine (14b, 44 nm) and more dramatic reduction in quantum yields (almost nonfluorescent, photophysical properties were interpreted as the heavy atom effect of halides on a BODIPY core skeleton. The bathochromic shift of BODIPY dyes without dramatic decrease in quantum yield was observed by the introduction of vinyl substituents at the C-2 and C-6 position. The extension of conjugation... 

The x-band in malachite green arises from an NBMO—>n transition, so that 3- and 4-substituents affect the energy of the excited state only and bring about spectral shifts of the first absorption band which vary linearly with the appropriate Hammett substituent constants. Thus, electron-withdrawing groups cause bathochromic shifts of the x-band whereas donor substituents cause hypsochromic shifts (Table 6.6) [64,67]. The 3-band arises from a n—>n transition [68] so that substituent effects are less predictable. As the donor strength of the 4-substituent increases, however, the 3-band moves bathochromically and eventually coalesces with the x-band - at 589 nm in the case of crystal violet (6.164), which possesses two NBMOs that are necessarily degenerate [69]. 

With durene an orange coloration develops and a clear bright red solution results from hexamethylbenzene. The quantitative effects of the dramatic colour changes are manifested in the spectral shifts of the electronic absorption bands that accompany the variations in aromatic conjugation and substituents. The progressive bathochromic shift parallels the decrease in the arene ionization potentials (IP) in the order benzene 9.23 eV, naphthalene 8.12eV, and anthracene 7.55 eV, much in the same manner as that observed with the tropylium acceptor (Takahashi et al.,... 

The ultraviolet spectra may be of use in determining the position of further substitution of 1-aryltriazoles 4-Substituents produce a bathochromic shift whereas 5-substituents, probably for steric reasons, have the opposite effect. Thus 5-methyl-1-phenyltriazole absorbs at 230 nm (log e 3.84), and the hindered 5-benzhydryl-l-p-bromophenyl-triazole has an absorption maximum at 210 nm (log e 5.60). ... 

A shift (also known as a red shift ) in a substance s electronic absorption spectrum toward longer wavelengths, as a consequence of a substituent, solvent, environment, or other effect. The opposite of a bathochromic shift is referred to as a hypsochromic shift. 

An effect observed in the spectrum of a chemical species in which a substituent, solvent, change in environment, or other effect causes the electronic absorption spectrum to shift to shorter wavelengths. The opposite effect is referred to as a bathochromic shift. The hypsochromic shift is also known as the blue shift. 

Some generalizations have been made about the effect of various substituents on the absorption maxima and molar absorptivities (165). As expected, the absorption band around 280 nm is displaced to lower wavelengths when two methoxyls are replaced by a methylenedioxy group. The UV spectra of pavines are slightly affected by protonation on nitrogen (755). Similarly, quaternary species furnish UV spectra which closely resemble those of their tertiary counterparts (153). In some pavine bases such as norargemonine (13), the expected bathochromic shift on addition of alkali has not been observed (702). 

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