Unraveling the Correlation between Crystallographic Structure and Charge Transport in Metal Poly(heptazine imides)
Xiaocong Liang, Sikang Xue, Min Shen, Yan Ye, Hangyu Zhuzhang, Wandong Xing, Can Yang, Zhiyang Yu, Guigang Zhang, Xinchen Wang
Abstract
Charge transfer, which is closely related to the molecular structure and packing order of polymer semiconductors, plays a critical role in determining their photocatalytic performance. Metal poly(heptazine imides) (M-PHI), with visible-light absorption capacity, represent a promising class of photocatalysts for energy and environmental applications. A precise understanding of the configuration of their building units and the resulting structure–function relationship is essential to the rational design of advanced polymer materials. In this study, advanced characterization techniques, including the iDPC-STEM, combined with density functional theory (DFT) calculations, are employed to reveal the local molecular structures of M-PHI ( M = Na +, K +, Rb +, Cs + ) crystals after ion insertion and to establish the intrinsic relationship between charge-carrier transfer and packing modes. Na + maintains the hexagonal symmetry of PHI through uniform coordination, thereby preserving long-range π-conjugation and enabling the highest charge-carrier mobility, whereas larger cations induce structural distortions in other M-PHI crystals by disrupting the heptazine packing symmetry. The higher symmetry and shorter intermolecular distances in Na-PHI endow it with rapid charge-transfer rates and excellent photocatalytic performance compared to other M-PHI samples. This study provides fundamental insights into the connection between atomic structure and charge-transport properties in PHI materials and establishes a theoretical foundation for the rational design of conjugated polymer semiconductors with optimized charge mobility for photocatalytic applications.