Spectral evidence for different phases exhibiting the Shpolskii effect in concentrated solutions of pyrene and dibenzofuran in frozen n-alkanes

Ab initio simulation of pyrene spectra in water matrices

“…Similarly to the absorption spectrum in ice, the broadening is caused by the low-frequency modes with Huang-Rhys factors of 1-6 corresponding to librations of pyrene in the solvent cage. Similar broad bands were observed in such polar matrices as silica gel or inorganic glasses, 9,[11][12][13] where the effect was attributed to the inhomogeneous broadening.…”

“…However, the comparison of the calculated spectra with broad-band spectra of pyrene in solutions, 7,35,[41][42][43][44][49][50][51] Shpolskii spectra, [9][10][11][12][13][14]17,52,53 site-selective, 71 or jet-cooled 26 spectra shows that both Franck-Condon and Herzberg-Teller active modes are observed in the experimental spectra with comparable intensities. Therefore, nonadiabatic intensity borrowing that lis the symmetry restriction for the FC active modes is extremely important in the case of isolated pyrene molecule.…”

“…9,10 Narrow quasi-line spectra are obtained in Shpolskii matrices (frozen alkanes), 9,10 while the spectra obtained on pure silica gel or in silica glass matrices exhibit inhomogeneous broadening. 9,[11][12][13] The relative intensities of individual emission peaks of pyrene and, therefore, the overall emission bandshape also depend on the environment. [14][15][16][17][18][19] This dependence made it possible to use pyrene as an environment polarity probe.…”