Polymerized Hybrid Metal Halides with Yellow Emissive Helical Polyacetylene Skeleton via Pressure-Induced Polymerization

Hybrid metal halides (HMHs) with typical host-guest structures exhibit intentional, unique, and synergistic features of organic and inorganic components. Here, a novel 2D HMH with a conjugated polyacetylene skeleton is synthesized by pressure-induced solid-state topochemical polymerization (SSTP) of (C3H6N)2CdCl4 (C3H6N⁺ = propargylamine cation, PA-CdCl). Compared with the faint emission of PA-CdCl, polymerized (C3H6N)2CdCl4 (P-PA-CdCl) exhibits a strong yellow emission from the helical polyacetylene skeletons. Furthermore, P-PA-CdCl exhibits a narrowed bandgap of 2.26 eV, almost half the initial PA-CdCl. Theoretical calculations reveal that the transformation of optical properties is due to the reconstruction of the band alignment from type-I to reverse type-I via SSTP. Such an SSTP can be replicated in other 2D HMHs to yield polymerized HMHs with identical emissive polyacetylene skeletons. This study showcases the potential of pressure-induced SSTP in developing novel materials with intriguing properties, establishing it as a valuable platform for the structural regulation of HMHs and polymer synthesis.