Bathochromic effect shifts

Bathochromic effect = Shift of absorbed light to longer wavelength... 

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). 

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. 

For less polar compounds, the solvent effect is weak. However, if the dipole moment of the chromophore increases during the transition, the final state will be more solvated. This is the case for n — n transitions in ethylenic hydrocarbons with a slightly polar double bond. A polar solvent has the effect of stabilising the excited state, which favours the transition. A shift towards greater wavelengths is observed unlike the spectrum obtained in a nonpolar solvent. This is the bathochromic effect. 

Bainbridge, 292 Bandwidth, 282 Bar spectrum, 290 Baseline correction (UV), 212 Bathochromic effect, 196 Beer-Lambert s law, 205, 220 Biosensor, 365 Bloch s theory, 130 Blue-shift, 195 Boltzmann distribution, 131 Bonded silica, 53 Bragg s law, 245 BSA, 336 Burner (AAS), 261... 

Thalictrum minus L. var. microphyllum (Ranunculaceae) was the source of the amorphous base (+)-uskudaramine (358), C39H44N208, [a] 5 +84° (c 0.15, MeOH). The structure proof of uskudaramine was simplified by comparison of its properties with those of the isomeric (+)-istanbulamine (173, Section II,C,47), isolated from the same source. Notably, the NMR spectrum of 358 lacks the H-8 (8 6.84) singlet of 173, and its UV spectrum shows not only a bathochromic base shift but also a hyperchromic effect, characteristic of a 3- or 9-hydroxyaporphine. 

The introduction of an alkoxy group into the central benzene ring causes a distinct shift toward orange. A similar bathochromic effect is obtained by replacing this benzene with naphthalene. 

The bathochromic effect of methyl groups is small (about 2 nm). An additional band in the region 305-345 nm (log e 3.48-3.76) was found in the spectra of the [b]-series and the benzo derivative. Only the thieno[b]tro-pylium salts exhibit a third band at 338-346 nm (log s 3.57-3.78). Dichloro-dimethyl compound 337b, compared with the tetramethyl derivative 337a, shows a bathochromic shift of about 10 nm (67JOC1610). 

Consequently the absorption curves of compounds I and II do not contain maxima but only shoulders (Fig. 40). They are shifted towards longer wavelength (bathochromic effect) as compared with the original nitroparaftlns. 

Bathochromic shift (Effect) Shift of a spectral band to lower frequencies (longer wavelengths) owing to the influence of substitution or a change in environment... 

---