Nonconventional Luminescence of Halogenated Silanes: Mechanistic Insight

In this study, the luminescence properties and emission mechanisms of five halogenated silanes, hexamethyldisiloxane (HT), chloromethylsilane (CT), iodomethylsilane (IT), chlorosilane (CS), and 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (FS) are systematically investigated. The effects of halogen type, substitution position, and temperature on luminescence efficiency, Stokes shift, and phosphorescence lifetime are elucidated through fluorescence, phosphorescence analysis, and theoretical calculations (at room temperature and 77 K). The results revealed that CS exhibits excellent fluorescence emission at 365 nm and significantly prolonged low-temperature phosphorescence lifetime due to its reduced nonradiative transitions and minimized excited-state energy dissipation. IT exhibited enhanced phosphorescence under liquid nitrogen, which can be attributed to the heavy-atom effect of the iodine atom and strong spin-orbit coupling. The Stokes shift analysis of excitation-emission spectra demonstrated that the energy gap between the excited and ground states can be reduced by the substituted halogen atoms. Moreover, CS displays the smallest shift among the five halogenated silanes, and its maximum emission wavelength is red-shifted with induced temperature, reflecting increased energy dissipation. The electron-hole distribution analysis confirms that halogens regulate luminescence efficiency by modulating electron transfer pathways (from high-electronegativity atoms to low-electronegativity regions) and spin-coupling strength. This work not only enriches the understanding of nonconventional luminescence in pure liquids but also provides theoretical foundations for the design of high-performance silicon-based optoelectronic materials.