Enhanced NH⋯π and CH⋯π nonclassical hydrogen bonds induce the phase transition of N,N´-diphenyl-1,4-phenylenediamine under high pressure
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Updated: Jul 17, 2026

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Published on: June 29, 2021
Mingting Li1, Lili Zhang2, Kai Wang3
1Department of Materials Physics and Chemistry, School of Materials Science and Engineering, Northeastern University, NO. 3-11, Wenhua Road, Heping District, Shenyang, 110819, China.
Abstract:
The crystal structural stability and optical properties of N,N´-diphenyl-1,4-phenylenediamine (C18H16N2, B3) under high pressure are investigated using in situ high-pressure Infrared (IR) absorption spectroscopy, synchrotron angular-dispersive X-ray diffraction (ADXRD), photoluminescence (PL) spectroscopy, and Ultraviolet-visible (UV-vis) absorption spectroscopy. The results show that enhanced N-H···π and C-H···π nonclassical hydrogen bonds under high pressure induce a Phase I (orthorhombic) to Phase II (triclinic) transition in B3 crystals, initiating at approximately 1.8 GPa and completing around 5.9 GPa, accompanied by a ∼2.00% collapse in the normalized unit cell volume. Moreover, the continuous enhancement of intermolecular interactions results in a red shift and eventual quenching of the PL emission throughout the compression process. This study provides a spectroscopic and structural basis for understanding how weak N-H···π and C-H···π interactions drive phase transitions and modulate the optical properties of organic supramolecular polymorphs under high pressure.
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