Stokes red shift

Flere the index m has values 0 for the 532-nm measmements, +1 for the first anti-Stokes (blue-shifted) line, and -1,-2 for the first, second Stokes (red-shifted) lines, etc. n is the diffraction order (0, 1, 2) and o is the groove spacing of the grating, supplied by the... 

A surprising finding is that for 16 of the 19 Trps, protein contributes a red shift to the steady state Stokes shift, a result that is statistically very improbable. The extreme bias toward red shifts for the protein contributions suggests that protein electric fields relative to the modest ground-state dipole of the Trp residue may be important in the evolution of the protein folds. 

Emission of d-f type in the divalent lanthanides is usually quenched by multiphonon relaxation from the 5d level to levels of the 4/ configuration. There are a few exceptions. When the red shift and Stokes shift place the 5d level of Sm " near to or below the Dq state (Fig. 5.3) - df emission may occur. The same applies for Eu when the level is shifted to near to or below 7/2. When for Tm the 5d level is not shifted too much towards the F j2 level, df emis-... 

Indole in cyclohexane and ethanol is excited at 270 nm populating a mixture of the La and Lb states. The La and Lb states differ in their spectral structure (Fig. la)) and Stokes shifts [3]. The unstructured spectrum of the La state shows a large Stokes shift due to the large change of the dipole moment upon electronic excitation. The dipole moment of the Lb state is similar to the ground state value. In nonpolar solvents like cyclohexane, the Lb state is energetically below the La state and its emission spectrum exhibits vibronic structure. In the polar solvent ethanol state reversal occurs after the electronic excitation and the La state becomes responsible for the more red shifted fluorescence [4],... 

The steady-state spectra obtained for different alcohols are depicted in fig. 1. While the absorption spectra red shift with increasing solvent polarisability (from methanol to octanol), the fluorescence shows a red-shift when going from octanol to methanol. The total Stokes shifts are very large 7.900 100 cm 1 for PSBR/MeOH and 6.870 100 cm 1 for octanol. Another striking observation is the 30 % smaller width of the fluorescence spectrum of methanol (AE = 3.420 cm 1) compared with other alcohols. While the widths of the fluorescence spectra are solvent-dependent, the absorption spectra have a FWHM of -5.100 cm"1, irrespective of the solvent. As we will substantiate in the following, this behavior indicates that the potential energy surface around the fluorescent point is different than near the Franck-Condon zone probed by absorption, as suggested by quantum chemistry calculations [7]. 

There is another artefact that can arise with concentrated samples, and this is the reabsorption of emission light by the sample itself. Light which is emitted at the centre of the cell must travel through a pathlength of a few mm of the sample, and absorption will take place in the wavelength region of overlap of the emission and absorption spectra. This problem can be serious when the Stoke s shift of these spectra is small. Reabsorption then results in an apparent red shift of the emission maximum with increasing concentration. 

All the emission spectra in solution showed a maximum peak with a shoulder on the red side. It was observed that the photoluminescence A.max in dilute THF solution red shifted from 470 to 474. They also exhibited similar Stokes shifts (about 66 nm) due to their similar backbone. The fluorescence quantum yields ( F) of these molecular wires in dilute THF solution were measured to be 0.25 for 470,0.22 for 471,0.20 for 472,0.20 for 473, and 0.18 for 474, respectively. The excited-state lifetime for OTEs was found to be single-exponential within a few hundred picoseconds. However, in THF solution (10 17 M), the decay of the emission maximum band for these molecular wires was found to be biexponential with two excited-state lifetimes yielding a c2 of <1.2. One excited-state lifetime ranged from 0.42 to 0.30 ns, which was in agreement with that in OTEs. Another one exhibited a... 

In Table 5 absorption and emission gaps are reported the red-shift of the emission gap with respect to the absorption is less evident for the case of the cluster with the double-bonded O (see the Stokes shift values) the same... 

---