Metal halide hybrids (MHHs) have emerged as a versatile class of materials due to their distinctive electronic structures, which endow them with optoelectronic functionalities suitable for a broad spectrum of applications, including photovoltaics, solid-state lighting, scintillation, photodetection, lasing, and ferroelectric technologies. Zero-dimensional (0D) MHHs comprising discrete metal halide units spatially isolated within an organic cation matrix represent a promising subclass for solid-state lighting, owing to strong exciton confinement within individual halometallate units and the resultant high radiative recombination efficiencies. However, potential difficulties with solubility and chemical incompatibility hinder large-scale utility of 0D MHHs for device applications.

To overcome these challenges, low-temperature melt-processing has emerged as a viable alternative, wherein effective suppression of the melting temperature (Tm) relative to the decomposition temperature (Td) is required. Such Tm suppression can be achieved through judicious selection of organic cations that promote the formation of stable liquid melts.

Here, we report a targeted molecular design strategy that enables access to ambient-stable, melt-processable supercooled liquid (SCL) multimetallic bromide hybrids incorporating Mn²⁺/Cd²⁺ or Mn²⁺/Zn²⁺ metal centers with benzyltributylammonium cations. These systems exhibit markedly low glass transition temperatures (Tg = 15-16 °C), substantially reduced melting points (Tm = 90–100 °C), Mn²⁺-activated green photoluminescence, and high optical transparency. Comprehensive structural, optical, thermal, and electronic-structure analyses elucidate the chemical design principles governing phase behavior and confirm the dopant-mediated luminescence mechanism. Rheological characterization validates the presence of the SCL phase, revealing pronounced thermal hysteresis and enabling quantification of relaxation time scales characteristic of metastable liquid states.

Collectively, this work introduces a new class of phase-engineered MHH materials with enhanced melt-processability suitable for molding and device fabrication, while establishing fundamental correlations between chemical composition, phase stability, and functional properties. These findings expand the accessible phase space of MHHs and provide a framework for rational design of hybrid materials exhibiting SCL behavior.