We report on the rotational diffusion and vibrational population relaxation dynamics of perylene and
1-methylperylene in the primary normal alcohols methanol through n-decanol. The rotational diffusion dynamics
of the two chromophores are the same to within the experimental uncertainty for n-propanol through n-decanol.
We observe a double exponential decay of the induced orientational anisotropy for 1-methylperylene in all
of the alcohols and for perylene in n-propanol through n-decanol. These data are consistent with previous
literature reports on perylene in high-viscosity solvents and on 1-methylperylene in n-alkanes longer than
n-octane. These data also reveal a substantial difference in the behavior of perylene in n-alkanes and n-alkanols.
Both chromophores reorient as oblate rotors in the n-alkanols, with the aspect ratio of the oblate ellipsoid
describing their motion depending on the solvent aliphatic chain length. The vibrational population relaxation
dynamics of the two probe molecules differ significantly, not only because of the difference in the nature of
the solvent−solute coupling but also because of subtle differences in the organization of the solvent around
the two chromophores. These data reflect the importance of solvent self-association in determining the local
environments of these two chromophores.
Complex formation and dissociation rate constants have been independently determined for solvated nickel(II) ion reacting with eight macrocyclic tetrathiaether ligands and one acyclic analogue in acetonitrile at 25 degrees C, mu = 0.15 M. The macrocyclic ligands include 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) and seven derivatives in which one or both ethylene bridges have been substituted by cis- or trans-1,2-cyclohexane, while the acyclic ligand is 2,5,9,12-tetrathiatridecane (Me2-2,3,2-S4). In contrast to similar complex formation kinetic studies on Ni(II) reacting with corresponding macrocyclic tetramines in acetonitrile and N,N-dimethylformamide (DMF), the kinetics of complex formation with the macrocyclic tetrathiaethers show no evidence of slow conformational changes following the initial coordination process. The differing behavior is ascribed to the fact that such conformational changes require donor atom inversion, which is readily accommodated by thiaether sulfurs but requires abstraction of a hydrogen from a nitrogen (to form a temporary amide). The latter process is not facilitated in solvents of low protophilicity. The rate-determining step in the formation reactions appears to be at the point of first-bond formation for the acyclic tetrathiaether but shifts to the point of chelate ring closure (i.e., second-bond formation) for the macrocyclic tetrathiaether complexes. The formation rate constants for Ni(II) with the macrocyclic tetrathiaethers parallel those previously obtained for Cu(II) reacting with the same ligands in 80% methanol-20% water (w/w). By contrast, the Ni(II) dissociation rate constants show significant variations from the trends in the Cu(II) behavior. Crystal structures are reported for the Ni(II) complexes formed with all five dicyclohexanediyl-substituted macrocyclic tetrathiaethers. All but one are low-spin species.
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