Chromophores phenyl

Another example for an application of computed sector maps is the OR of phenylalanine, as far as contributions from the phenyl group are concerned [155]. Sector maps for benzene were computed as shown in Fig. 25. The findings of [155] were in agreement with a revised sector rule for the phenyl chromophore by Pescitelli et al. who investigated a set of chiral molecules with phenyl substituents (PhCH(Me)R, with R = Et, "Pr, Pr, and Bu) [265],... 

The specific absorption of the pure phenyl chromophore is quite low for R type compounds e 200 (in methanol). If the molecule has 2 or 3 phenyl radicals, e increases to about 400 or 600. Thus the E 1%/lcm for many drugs is around 5-20, i. e. measurements should be taken in concentrations of about 20-50 mg/100 ml. 

Die spezifische Absorption des reinen Phenyl-Chromophors ist recht niedrig Fur Verbindungen... 

The absolute configurations of chiral 1-0-arylglycerols and related compounds have been assigned on the basis of their chiroptical properties in Cupra A solution, " and chiroptical data have been reported for a series of 2-phenyl-l,3-dioxolan, -dioxan, and -dioxepan (i.e. 0-benzylidene) derivatives of glycerol and D-mannitol. In the latter study, the signs of the Cotton effects of and L transitions of the phenyl chromophore were rationalized in terms of recently proposed sector rules for these transitions. 

The excimer fluorescence of polystyrene (PS) solution has been widely studied since early sixties, predominately for intrachain excimer formation between adjacent pendant phenyl chromophores on the chain in dilute solutions, c < 5.10 g/dl. As the excimer interaction is a very short range interaction between an excited state and a ground state qhromophore at a parallel planar configuration of 0.33-0.35 nm apart, it should be useful to probe the molecular aggregation processes. For the present discussion only the concentration dependence of the intensity ratio < = of the excimer to monomer (isolated excited chromophore) fluorescence will be of interest. Typical fluorescence spectrum of PS in solution is shown in Fig. 2. The overlap between the monomer fluorescence peak (X = 285 nm) and the excimer fluorescence peak (X = 330 nm) is not severe so that simple peak intensity ratio is adequate for the evaluation of < within usual experimental errors. Results of first such investigation by Roots and Nystrom to show a sharp turn at the overlap concentration c (c [n] = 1) were not confirmed. Extensive studies carried out in the author s laboratory showed a peculiar concentration... 

The CD observed in the conformational model arises from the perturbation of a single phenyl chromophore by a chiral centre directly bound to it and may provide an idea of the optical activity due to the local site symmetry in the copolymers examined. 

Stationary state measurements (Longworth and Bovey, 1966, Bokobza et al., 1977) as well as measurements of the transient behavior of the excited states (De Schryver et al., 1982a) were reported. Longworth and Bovey (1966) published the uncorrected fluorescence spectra of meso Al and racemic Al at 298 and 77 K. At 77 K the spectra are, within experimental error, identical and resemble the spectrum of toluene at 77 K. At 298 K excimer emission is detected for meso Al and racemic Al. The ratio of the intensity of the excimer emission (Id, at 313 nm) over the intensity of the locally excited state emission (Im, at 283 nm) equals 2.45 for meso Al and 0.74 for racemic Al. The difference in excimer forming capacity is explained based on the NMR data reported above (Bovey et al., 1965). The meso isomer starting from the TG/GT form reaches the TT conformation via an easy bond rotation, leading to a full overlap of the phenyl chromophores. The racemic isomer is predominantly TT (75%) with about 25% of GG present at room temperature. 

The rotations to TG/GT (also full overlap of the phenyl chromophores) are less favourable leading to less excimer species within the radiative lifetime of the excited phenyl groups. At 77 K, however, the time required for bond rotation to the appropriate conformation exceeds the radiative lifetime and therefore no excimer emission is observed. 

Ultraviolet Spectra.—Interaction between the chromophores in phenylsulphonyl-guanidines through an empty c/-orbital on S, and between the sulphone w-system and the guanidine chromophore, is indicated by u.v. spectra, while related studies show the lack of homoconjugation (through-space conjugation) in aryl benzyl sulphides. U.v. fluorescence and phosphorescence data indicate exciton interaction between the phenyl chromophores in diphenyl sulphide. ... 

In addition, the circular dichrosim spectrum of diselenobis(benzoyl)-bridged bis(P-CD) 2 exhibits two positive Cotton effect peaks for the Lb and La transitions of phenyl group and a positive Cotton effect peak for the Se-Se transition. Therefore, we can deduce that the linker group in 2 is located at the exterior of CD cavity, where both the La and Lb transitions of phenyl chromophore are nearly perpendicular to the CD axis, resulting in the positive Cotton effect peaks. On the other hand, the Se-Se moiety is situated between the two narrow rims of dual CD cavities (Fig. 3). Hence, the transition moment of Se-Se bond is perpendicular to the CD axis, which consequently results in the positive Cotton effect [9]. 

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