Cf. Chapman et al., MEASUREMENTS OF THE SOLUTE DEPENDENCE OF SOLVATION DYNAMICS IN 1-PROPANOL - THE ROLE OF SPECIFIC HYDROGEN-BONDING INTERACTIONS, Journal of physical chemistry, 99(13), 1995, pp. 4811-4819
Time-resolved Stokes shift measurements (similar to 20 ps effective re
solution) are used to measure the solvation times of 16 different prob
e solutes in a single solvent, 1-propanol (253 K). The solutes were ch
osen so as to provide a wide range of chemical structures and physical
properties consistent with the requirements of strong fluorescence an
d high solvent sensitivity. Rather than exhibiting a continuous range
of solvation times, the dynamics observed with these solutes indicated
a division into two distinct classes. The majority (11) of the solute
s were observed to fall into a ''normal'' category. The solvation time
s of these solutes span a relatively narrow range, 0.14-0.22 ns, times
consistent with expectations based on nonspecific theories of solvati
on dynamics. The remaining five solutes, all simple aromatic amines, f
orm a distinct group whose solvation dynamics is at least 2-fold faste
r than those of the ''normal'' solutes. The difference between these t
wo classes of solutes appears to reflect differences in the nature of
their hydrogen-bonding interactions with the solvent.