Tunable Mechanical and Optoelectronic Properties of Organic Cocrystals by Unexpected Stacking Transformation from H- To J- To X-Aggregation

Wei Ji, Bin Xue, Santu Bera, Sarah Guerin, Yanqing Liu, Hui Yuan, Qi Li, Chengqian Yuan, Linda J.W. Shimon, Qing Ma, Evan Kiely, Syed A.M. Tofail, Mingsu Si, Xuehai Yan, Yi Cao, Wei Wang, Rusen Yang, Damien Thompson, Junbai Li, Ehud Gazit*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)10704-10715
Number of pages12
JournalACS Nano
Issue number8
StatePublished - 25 Aug 2020


  • coassembly
  • mechanical property
  • molecular stacking
  • optoelectronic materials
  • organic crystals
  • supramolecular chemistry


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