Journal of Physical Chemistry A, Vol.108, No.29, 6090-6095, 2004
Rotational dynamics of nondipolar probes in butanols: Correlation of reorientation times with solute-solvent interaction strengths
Rotational relaxation of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been examined in four isomeric butanols as a function of temperature in order to find out how the rotation of the solute molecules is influenced by the solute-solvent interaction strength. It has been observed that the hydrogen bonding interactions with the butanols do not influence the rotation of DMDPP. On the other hand, the rotation of DPP is affected by its interactions with the solvents, and as a result the reorientation times of DPP have been found to be over a factor of 2 longer than that of DMDPP. Two sets of reorientation times have been obtained, one corresponding to DMDPP and the other to DPP, when the reorientation times of both probes were normalized by the solvent viscosities. The observed pattern is a consequence of almost identical interaction Strengths between the four isomeric butanols and the given probes. These results indicate that the relative differences in the hydrogen bond donating abilities of the butanols do not manifest in the measured reorientation times of the solute molecules.