Hydrogen Bond Dominated Glass Formation and Excitation-Dependent Photoluminescence in Metal–Organic Complex Glasses

Metal–organic complex (MOC) glasses are emerging as a new family of hybrid glasses. Unlike zeolitic imidazolate framework (ZIF) glasses—which encounter a significant challenge of framework decomposition during vitrification—the broader diversity of available ligands and structures enables the production of super-sized MOC glass monoliths. The glass formation mechanism of hybrid materials (e.g., metal–organic frameworks) has been investigated, while a little attention has been paid to the vitrification mechanisms of MOCs, despite their processability and multifunctionality. In this work, we synthesized a series of MOC crystals (ZnCl2L2, where L comprises varying ratios of imidazole and benzimidazole) and subsequently melt-quenched them to bulk glass samples. In contrast to ZIFs, these MOCs exhibit ligand ratio–dependent glass forming ability and thermal behaviors. Based on spectroscopic and structural analyses, we found that the hydrogen bonded network played a pivotal role in glass formation. Specifically, the original hydrogen bonds are first broken and then reorganized into a disordered network, thereby leading to MOC vitrification. Remarkably, vitrification also modulates the photoluminescent behavior of the MOCs, imparting excitation-dependent fluorescence to the glassy state. This work provides insights into the glass formation of MOC materials and explores their intrinsic luminescent properties, opening new avenues for photonic applications of MOC glasses.