Unveiling Distinct Ferroelectric Behaviour of Polar Polymorphic Forms of an Organic Molecular Crystal via Quantum Crystallography
- Yogita Gupta
- Talk
- May 1, 2025
Yogita Gupta, Sanjay Dutta, Anil Kumar and Parthapratim Munshi*
Multifunctional Molecular Materials Laboratory, Department of Chemistry, School of Natural Sciences, Shiv Nadar Institution of Eminence, Delhi-NCR, Uttar Pradesh-201314, India.
e-mail: parthapratim.munshi@snu.edu.in
Polymorphism, i.e., the ability of a molecule to possess diverse spatial arrangements in crystalline form [1], can lead to the exhibition of distinct properties [2]. However, a strategic design of multifunctional materials with targeted applications necessitates a deeper understanding of the structure-property relationships, which is achievable via a quantum crystallography approach [3]. Organic molecules comprising keto-enol and enamine-imine are known to exhibit ferroelectricity (FE) in their crystalline form through a cooperative proton tautomerism mechanism (PTM) [2,4].
Illustration of proton tautomerism pathway in polar forms of 1
Recently, some of us have explored FE in the polymorphic crystal of an enamine-imine-based organic compound, 2-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole(1), which exhibits trimorphs [5]. While two forms crystallize in a polar space group (P41 and Pca21) (Figure 1), the third form crystallizes in a centrosymmetric space group (I41/a). The P41 form exhibits notable FE at room temperature, but the Pca21 form fails to exhibit notable FE. Here, we employed multipolar analysis [6] of electron densities derived using high-resolution X-ray diffraction data and periodic calculation-based dynamic structure factors to understand the variation of electronic distributions between the two polar forms. Further, we estimated the energy barrier for the proton hopping in both forms based on first-principles calculations. Furthermore, we calculated sublattice polarisations to support the mechanism behind their distinct FE properties. Our study demonstrates that the quantum crystallographic approach can not only provide deeper insights into the role of molecular packing and intermolecular interactions in dictating physical properties, but it is also a useful tool for designing futuristic materials.
References:
[1] Bernstein, J. Oxoford University Press Inc., New York 2002.
[2] Dutta, S. et al., Chem. Commun., 55 (2019), 9610-9613.
[3] Genoni, A. et al, Chem. Eur. J., 24 (2018), 10881-10905.
[4] Horiuchi, S. et al, Nat. Commun., 8 (2017),14426.
[5] Dutta, S. et al., ACS Appl. Electron., Mater. 3 (2021), 3633-3640.