Weber’s Red-Edge Effect that Changed the Paradigm in Photophysics and Photochemistry

Excitons in Carbonic Nanostructures

“…Essentially, as it is seen in Figure 13, the emission band remained very broad and strongly Stokes-shifted from the excitation band. This behavior does not depend on the excitation wavelength which suggests the absence of inhomogeneous broadening contributions to the spectra [181]. One may notice that, on deep cooling, the spectra remaining with temperature-independent intensity are even more highly shifted to longer wavelengths compared to the room-temperature spectra.…”

“…If it is, then the effects of inhomogeneous broadening should not be seen (the dynamics will average the sub-states with different excitation energies). In contrast, in the case of ground-state heterogeneity, variable species in ensemble will respond to solvent in a more or less similar way, generating the total solvent effect [181]. In reported cases, the solvent-dependent fluorescence spectra were not affected by modulation of excitation wavelength [164,188], indicating that the polarity effects and wavelength tunability were uncoupled.…”

“…Its relation to the red edge effects [175,180] seems to be incorrect. Since the spectral selection can be observed also on the "blue edge" of the excitation band (see Figure 5) and the excitation spectra also shift as a function of emission wavelength, the most probable is the interpretation in terms of the ground-state heterogeneity [100,181].…”

“…Inhomogeneous broadening is different. It is caused by static disorder in the population of fluorophores due to the fact of their distribution on interaction energies with the environment [181]. It can be both static and dynamic, and the transition from dynamic to static mode can be seen in cryogenic studies as a dramatic reduction in the line width and Stokes shifts, the appearance of zero-phonon lines, etc.…”

Origin of Excitation Dependent Fluorescence in Carbon Nanodots

“…The extent of excitation dependent spectral shift (>100 nm) for CNDs is way beyond the generally observed shift of ∼10 nm due to incomplete solvation or red-edge effect in very high viscosity solvents, polymers, organized assemblies, etc., as reported with regular fluorophore . Red edge effect is observed only in the case of slow relaxation from distributed excited states, and this effect is not resolved from author’s experiments. − Moreover, ground state heterogeneity, as reported in other cases, is also expected to result in excitation dependent spectral shift and needs to be duly considered. , Therefore, despite several promises, slower solvent relaxation leading to multicolor fluorescence in CNDs fails to explain the observed discrete energy levels at different excitation wavelengths (Figures 2 and 3 in ref ). Second, reorientation of solute, i.e., anisotropy decay time, is independent of excited state energy relaxation by solvation.…”