Orientational and Vibrational Relaxation Dynamics of Perylene in the Cyclohexane–Ethanol Binary Solvent System

Abstract

The rotational dynamics and vibrational population relaxation of the nonpolar probe molecule perylene have been studied in a series of ethanol-cyclohexane binary solvent mixtures, with the goal of relating solvent system composition to local organization. Steady-state spectroscopic data show that there is a discontinuous dependence of the spectroscopic origin on binary solvent system composition for perylene. Both rotational diffusion and vibrational population relaxation time constants show a clear discontinuity between 5% and 7.5% (v/v) ethanol in cyclohexane, suggesting a discontinuous change on molecular scale rearrangement in the chromophore local environment. We interpret these results in the context of the chromophore residing in an environment that is not homogeneous on the molecular scale and changes in its average conformation with binary solvent system composition.

A Comparison of Energy Flow in Micelle and Vesicle Structures

“…Vibrational population relaxation measurements were carried out using a picosecond pump–probe instrument that has been described in detail elsewhere . We provide a brief synopsis of the salient features of the instrument.…”

“…Vibrational population relaxation measurements were carried out using a picosecond pump−probe instrument that has been described in detail elsewhere. 8 We provide a brief synopsis of the salient features of the instrument. The source laser is a passively mode-locked Nd:YVO 4 laser (Spectra Physics Vanguard) that produces 13 ps pulses with a 12 ns interpulse spacing.…”

“…We focus here on intermolecular vibrational energy transfer (IVET) in the solution phase. There have been a number of simulations and experimental examinations of IVET in liquids, − but more remains to be understood. In this work we focus on how the conformation of the local environment of a molecule influences initial vibrational energy transfer efficiency as well as longer-term dissipation.…”

“…The decanoic acid/decanoate conjugate base system is capable of forming either micelles or vesicles, depending on solution pH and amphiphile concentration. We have chosen to use the chromophore perylene (Figure b) as a probe because of its well understood spectroscopic properties and its insolubility in water. ,,, Perylene partitions selectively into solution regions dominated by amphiphile aliphatic chains. The local environment of perylene formed by micelles is relatively confined and of nominally spherical symmetry.…”

Liquid–Liquid Equilibrium Data for Cyclohexane–Ethanol–Solvent Ternary Systems and Their Correlation with the Nonrandom Two-Liquid Model

“…The solvent composition was found to affect the spectral responses of CMOH in a mixture containing Cy and EtOH. 7 Since the Cy−EtOH solvent system is suitable for dilution crystallization, Guo et al 8 used a mixture of Cy and EtOH to purify clopidogrel hydrogen sulfate (form II) [CHS (II)] and measured the solubility of CHS (II) in the binary solvent system in the temperature range of 283.35−333.75 K. Qiu and Blanchard 9 selected perylene as a nonpolar probe molecule and investigated its rotational diffusion and vibrational relaxation dynamics in a series of Cy−EtOH mixed solutions. A clear discontinuous change was observed in the chromophore environment for EtOH concentrations ranging from 5 to 7.5% (v/v).…”