Local dielectric response in 1-propanol: $\alpha$-relaxation versus relaxation of mesoscale structures

TL;DR

This study compares local dielectric measurements via triplet state solvation dynamics with macroscopic dielectric and light scattering data in 1-propanol, revealing that the Debye relaxation is not prominent in local responses, and structural relaxation is consistent across methods.

Contribution

It provides the first detailed comparison between local and macroscopic dielectric responses in 1-propanol, clarifying the role of transient supramolecular structures in dielectric relaxation.

Findings

Debye process does not significantly contribute to local dielectric response.

Structural relaxation time constants are similar across measurement techniques.

Macroscopic dielectric signals are influenced by cross-correlation effects absent in local measurements.

Abstract

The dielectric Debye relaxation in monohydroxy alcohols has been subject of long-standing scientific interest and is presently believed to arise from the relaxation of transiently H-bonded supramolecular structures. Therefore, its manifestation might be expected to differ from a local dielectric probe as compared to the standard macroscopic dielectric experiment. In this work we present such local dielectric measurements obtained by triplet state solvation dynamics (TSD) and compare the results with macroscopic dielectric and light scattering data. In particular, with data from an improved TSD setup, a detailed quantitative comparison reveals that the Debye process does not significantly contribute to the local Stokes shift response function, while $\alpha$- and $\beta$-relaxations are clearly resolved. Furthermore, this comparison reveals that the structural relaxation has almost identical time constants and shape parameters in all three measurement techniques. Altogether our findings support the notion that the transiently bound chain structures lead to a strong cross-correlation contribution in macroscopic dielectric experiments, to which both light scattering and TSD are insensitive, the latter due to its local character and the former due to the molecular optical anisotropy being largely independent of the OH bonded suprastructures.