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Tunable mechanical and optoelectronic properties of organic cocrystals by unexpected stacking transformation from H- to J- and X-aggregation

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journal contribution
posted on 2022-10-06, 08:28 authored by Wei Ji, Bin Xue, Santu Bera, Sarah GuerinSarah Guerin, Yanqing Liu, Hui Yuan, Qi Li, Chengqian Yuan, Linda J. W. Shimon, Qing Ma, Evan Kiely, SYED ANSAR TOFAILSYED ANSAR TOFAIL, Mingsu Si, Xuehai Yan, Yi Cao, Wei Wang, Rusen Yang, DAMIEN THOMPSONDAMIEN THOMPSON, Junbai Li, Ehud Gazit
Molecular stacking modes, generally classified as H-, J-, and X-aggregation, play a key role in determining the optoelectronic properties of organic crystals. However, the control of stacking transformation of a specific molecule is an unmet challenge, and a priori prediction of the performance in different stacking modes is extraordinarily difficult to achieve. In particular, the existence of hybrid stacking modes and their combined effect on physicochemical properties of molecular crystals are not fully understood. Herein, unexpected stacking transformation from H- to J- and X-aggregation is observed in the crystal structure of a small heterocyclic molecule, 4,4'-bipyridine (4,4'-Bpy), upon coassembly with N-acetyl-l-alanine (AcA), a nonaromatic amino acid derivative. This structural transformation into hybrid stacking mode improves physicochemical properties of the cocrystals, including a large red-shifted emission, enhanced supramolecular chirality, improved thermal stability, and higher mechanical properties. While a single crystal of 4,4'-Bpy shows good optical waveguiding and piezoelectric properties due to the uniform elongated needles and low symmetry of crystal packing, the significantly lower band gap and resistance of the cocrystal indicate improved conductivity. This study not only demonstrates cocrystallization-induced packing transformation between H-, J-, and X-aggregations in the solid state, leading to tunable mechanical and optoelectronic properties, but also will inspire future molecular design of organic functional materials by the coassembly strategy.


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ACS Nano;14 (8), pp. 10704-10715


American Chemical Society



Other Funding information

ERC, SFI, Irish Centre for High-End Computing (ICHEC), National Natural Science Foundation of China, Natural Science Foundation of Jiangsu province


© 2020 ACS This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see



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