Red shift effect

The red-shifting effect of ester oxygen atom is weak and strongly dependent on substitution, possibly because the competition between the aforanentioned stereoelectronic effects is closely balanced. The carbonyl stretch in amides is very sensitive to substitution and its analysis is further complicated by the presence of combination bands (only the blue-shifled of the two bands is shown in Figure 12.6). 

Poly(l,4-naphthylenevinylene) (106) is accessible via the Wessling polymerization procedure. Lenz, Karasz, Wegner et al. have published the synthesis of PNV 106, starting from l,4-bis(chloromethyl)naphthalene [127, 128]. The poly(l,4-naphthylenevinylene) (106) displays an optical absorption energy of 2.05 eV, slightly red-shifted by about 0,3 eV relative to the parent PPV 60-system, due to the electronic effect of the annelated benzene ring. 

The microenvironment in water-containing AOT-reversed micelles has a marked effect on the spectral properties of flnorescein. The absorption peaks are red-shifted by about 10 nm from the corresponding positions in aqueous solution, the absorption extinction coefficient increases with R, and the fluorescence is more effectively quenched in AOT-reversed micelles than in aqueous solution [149],... 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

Che and coworkers have studied the effect of halide ions on the emission. Initial addition of a small amount of [NBu4]Y to [Au2(dcpm)2](CF3S03)2 in acetonitrile led to enhancement of the emission intensity and red-shifted emission Xmax, from 508 to 510 (Cl ), 514 (Br ) and 530 (F) nm. Further addition of [NBu4]Y resulted in a decrease in emission intensity. It is reasonable to assign the absorption band... 

In addition to the photoluminescence red shifts, broadening of photoluminescence spectra and decrease in the photoluminescence quantum efficiency are reported with increasing temperature. The spectral broadening is due to scattering by coupling of excitons with acoustic and LO phonons [22]. The decrease in the photoluminescence quantum efficiency is due to non-radiative relaxation from the thermally activated state. The Stark effect also produces photoluminescence spectral shifts in CdSe quantum dots [23]. Large red shifts up to 75 meV are reported in the photoluminescence spectra of CdSe quantum dots under an applied electric field of 350 kVcm . Here, the applied electric field decreases or cancels a component in the excited state dipole that is parallel to the applied field the excited state dipole is contributed by the charge carriers present on the surface of the quantum dots. 

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