Polymorphism in $\alpha$-sexithiophene crystals: Relative stability and transition path

TL;DR

This study combines theoretical calculations and experimental data to analyze the stability, transition pathways, and electronic properties of different polymorphs of $ ext{α}$-sexithiophene crystals, revealing the low-temperature phase's higher stability.

Contribution

It provides a detailed theoretical and experimental investigation of polymorphism in $ ext{α}$-sexithiophene, including stability comparison and transition path estimation.

Findings

Low-temperature phase is more stable by about 50 meV/molecule.

Transition path with an energy barrier of approximately 1 eV/molecule.

Electronic properties of different crystal structures are characterized.

Abstract

We present a joint theoretical and experimental study to investigate polymorphism in $\alpha$-sexithiophene (6T) crystals. By means of density-functional theory calculations, we clarify that the low-temperature phase is favorable over the high-temperature one, with higher relative stability by about 50 meV/molecule. This result is in agreement with our thermal desorption measurements. We also propose a transition path between the high- and low-temperature 6T polymorphs, estimating an upper bound for the energy barrier of about 1 eV/molecule. The analysis of the electronic properties of the investigated 6T crystal structures complements our study.