Chalcohalides compounds represent a promising class of optoelectronic materials. Among them, $Q\mathrm{SeI}$ $(Q=\mathrm{In}, \mathrm{Ga}, \mathrm{Al})$ stands out due to its one-dimensional van der Waals structure and helical chain configuration. In this study, we investigate the pressure-tunable optical and electronic properties of InSeI. Optical absorption measurements reveal a rapid narrowing of the band gap at a rate of −0.1 eV/GPa, followed by a sharp collapse of 0.4 eV above 4.1 GPa. Meanwhile, the sample exhibits a striking color change from yellow to black, indicative of pronounced piezochromic behavior. Electrical transport measurements uncover an insulator-to-metal transition at 37.8 GPa, followed by the emergence of superconductivity with a critical temperature $\left(T_{\mathrm{c}}\right)$ of $\sim 5.8\mathrm{K}$. Synchrotron x-ray diffraction and Raman spectroscopy reveal that pressure-induced amorphization occurs at relatively low pressures, involving primarily intrachain disorder, which accounts for the abrupt band-gap reduction and coloration change. Upon further compression, the tubular framework collapses, and long-range disorder gives rise to a possible polyamorphic transformation, leading to metallization and superconductivity. The tunable tubular-chain structure and associated polyamorphism make InSeI a promising platform for optoelectronic application, such as optical switches, broadband absorbers, and pressure-sensitive photonic devices, and provide a fertile ground for exploring polyamorphic superconductivity in low-dimensional chalcohalide systems.

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• Phase transitions
• Pressure effects
• Superconductivity
• Amorphous materials
• Semiconductors
• Raman spectroscopy
• X-ray diffraction