Bathochromic shift definition

Attempts have been made to deduce the structure of the predominant form of a potentially tautomeric compound from the shifts which occur in the ultraviolet spectrum of the compound in question on passing from neutral to basic or acidic solutions. The fact that no bathochromic shifts were observed for 2- and 4-hydroxy quinoline and 1-hydroxyisoquinoline under these conditions was taken as evidence that they existed in the oxo form [similar work on substituted quinol-4-ones led to no definite conclusions ]. A knowledge of the dissociation constants is essential to studies of this type, and the conclusions can, in any case, be only very tentative. A further dif-... 

The hyper type and the hypso type may occur in mixed versions (61). The hypso type has not always been recognized as an individual spectral type by other authors, and, concomitantly, the importance of metal-to-porphyrin backbonding has been neglected (46, 48). The present scheme cannot explain why some large alkaline earth cations cause bathochromic shifts as long as a definite structural characterization of these metalloporphyrins is missing (20-22). 

Scheme 9 shows in fulgide 39, replacement of the isopropylidene group (IPD) by a dicyclopropylidene group (DCP) caused a bathochromic shift in the absorption band of the 7,7a-DHBF, owing to the partial double-bond character of the DCP group. It is obvious that the steric hindrance of R1 and R2 also affected the max of the colored form. There was not a definite role for the substituent effect on the quantum yield of photoreactions. Table 4.8 shows the absorption spectroscopic data and quantum yields of photoreactions of fulgides with different R R2 groups in toluene. 

It is difficult to bring over the same theoretical considerations from dissolved to adsorbed molecules. The unilateral interaction of an adsorbed molecule even with a smooth bare surface must be, in principle, treated rather as a binary association compound, than as a molecule half-imbedded in a continuous medium with a definite dielectric constant. A surface binary association of the polar nitrobenzene molecule with the silanol group should represent more correctly the actual situation. Actually, it has been found that a large bathochromic shift is produced by protonation of nitrobenzene in H SOi 56a). A similarly large red shift of the order of 2500 cm is displayed by the substituted nitro-benzenes, viz., -nitroanisole, nitroanile, nitrophenol, etc., when adsorbed upon a silicic acid slurry immersed in cyclohexane 46). 

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