Comparative spectral diffusion studies in the millikelvin range between a protein and a glass point to a strong shielding of the chromophore from the strain and/or electric fields of the host and to quite specific features of the energy landscape.
We measured the pressure shift of spectral holes for four probe molecules, which differed in size, polarity, and charge, as a function of burn frequency. The solvent was in all cases the same, namely, ethanol/methanol glass. We found that the pressure shift depends in a linear fashion on burn frequency and that the associated slope is uniform despite the variation in the solute-solvent interaction. It seems to be a property of the solvent, solely. These findings can be well understood by assuming that the pressure-induced line shift is proportional to the solvent shift. In this case, the compressibility of the host glass follows directly from the slope of the pressure shift vs frequency data.
The broadening of spectral holes burnt into the J-band of molecular aggregates of the pseudoisocyaninetype under isotropic pressure conditions is measured and compared with the respective behavior of holes burnt into the monomer absorption. From the ratio of the pressure broadening the coherence length of the exciton on the aggregate chain can be determined. 120 and 101 monomer units for the two dyes investigated are found.') D-95440 Bayreuth, Federal Republic of Germany.
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