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.