Lattice vibrations of {\gamma}- and \b{eta}-coronene from Raman and theory

TL;DR

This study combines Raman microscopy and advanced DFT calculations to analyze how lattice vibrations in coronene change across phase transitions, revealing detailed atomic motions and mode assignments.

Contribution

It provides the first combined experimental and theoretical analysis of polymorph-dependent lattice vibrations in coronene, clarifying mode evolution across phases.

Findings

Raman frequencies agree within 4 cm-1 between experiment and theory

Distinct vibrational modes identified for {b3}- and beta;-coronene

Mode analysis explains differences in Raman spectra between phases

Abstract

We combine polarization-resolved low frequency Raman microscopy and dispersion-corrected density-functional calculations (DFT-D3) to study polymorph-dependent lattice vibrations in coronene, a model molecular system for nanographenes and disc-like organic semiconductors that exhibits two crystalline structures with distinct electronic and optical properties. Changes in low energy Raman-active lattice phonons are followed across the {\gamma}- to \b{eta}-phase transition at 150 K. Raman frequencies calculated using DFT-D3 agree to within 4 cm-1, and on the basis of polarisation dependence of peak positions and intensities we achieve a clear mode assignment. Studies of the associated atomic motions show how the pure librational and rotational modes of {\gamma}-coronene change into mixed roto-librations in the \b{eta}-phase, explaining the remarkable differences in Raman spectra of the two phases.