Phenyl rings chromophores

First, it is possible to excite a chromophore corresponding to the active site, and detennine which modes interact with it. Second, by using UV excitation, the amino acids with phenyl rings (tryptophan and tyrosine, and a small contribution from phenylalanine) can be selectively excited [4], The frequency shifts in the resonance Raman spectrum associated with them provide infomiation on their enviromnent. 

Electronic (UV-Vis) spectroscopy has not been utilized in a routine manner. This is perhaps due to the fact that the nature of heterocycles is rather difficult to correlate correctly, with the chromophoric absorption. The UV-Vis absorption spectra of 23b (Table 2) have been studied in detail with R = H, C6H13, CgH17, C20H21, C4H9, and 4-( I, 11. With the exception of 23 (R = 4-C6Hi3C6H4) and which contains conjugated A -phenyl ring, the... 

Intermolecular hydrogen bonding between neighbouring NH- and CO-groups -comparable with the crystal structure of quinacridone pigments (see p. 461) - and tt- tt interactions between the chromophore planes and the planes of the phenyl rings make for the excellent solvent and migration resistance of this rather small molecule [5]. 

As an example, for spiro-oligophenyls in the series 35a-d with 4, 6, 8, and 10 phenyl rings in the chromophore, the absorption maxima are 332, 342, 344, and 344 nm in dichloromethane, respectively. The first fluorescence maxima increase... 

Instead of the phenyl ring, a fluorescent chromophore has been attached to N(4) (85) and this compound has then been used for detecting Vitamin D metabolites and retinoic acid <94TL1917>. 

One feature that is of immense benefit for flavonoid analysis is the presence of the phenyl ring. This excellent chromophore is, of course, UV active and provides the reason why flavonoids are so easy to detect. Their UV spectra are particularly informative, providing considerable structural information that can distinguish the type of phenol and the oxidation pattern. 

For those complexes where the chromophore is not coordinated to the metal center directly, the orientation of the chromophore is important to ensure efficient energy transfer. The series of ligands L29-L32 were investigated for correlations between structural parameters found in the solid state (see, for example, Fig. 12) and solution (by NMR spectroscopy) and photophysical properties (69,70). It was found that both chromophore-metal separation and the angle of orientation have a direct influence on the quantum yield of the europium complexes. For example, the difference in quantum yield between [Eu(L29)]3+ and [Eu(L30)]3+ (0.06 and 0.02, respectively) cannot be attributed solely to the chromophore-metal separation, so may also depend on the better orientation of the chromophore in the L29 system as measured by the angle a between the metal center, the amide nitrogen atom, and the center of the phenyl ring. 

The ketone group is a useful model for other types of chromophores because it can be selectively excited in the presence of other groups in polymer chains such as the phenyl rings in polystyrene and so the locus of excitation is well defined. Furthermore there is a great deal known about the photochemistry of aromatic and aliphatic ketones and one can draw on this information in interpreting the results. A further advantage of the ketone chromophore is that it exhibits at least three photochemical processes from the same excited state and thus one has a probe of the effects of the polymer matrix on these different processes by determination of the quantum yields for the following photophysical or photochemical steps l) fluorescence,... 

Under this heading are collected solvatochromic probes which have an amino group attached to a phenyl ring that in turn is bonded by more than one bond to other moieties (Schemes 2 and 3). All these groups are generally further substituted in order to produce chromophores that have a wide solvatochromic amplitude. 

---