Simultaneously Achieving Efficient Narrow-Band Emission and Large Emission Dissymmetry Factor in an Achiral Hybrid...

To achieve high contrast in three-dimensional display, circularly polarized luminescence (CPL) materials should simultaneously have narrow full width at half-maximum (FWHM), high photoluminescence quantum yield (PLQY), and large dissymmetry factor (g_lum). However, very few materials can fulfill it. Herein, we report a zero-dimensional hybrid indium chloride [BPy][InCl₄(dtbp)] (BPy = N-butylpyridinium, dtbp = 4,4'-di-tert-butyl-2,2'-dipyridyl). Although crystallizing in the achiral point group mm2, the compound demonstrates remarkable chiroptical activity. It shows efficient blue-green emission peaking at 481 nm with a FWHM of 49 nm. The coordination with In³⁺ in the inorganic unit, combined with abundant intermolecular interactions, effectively suppresses vibrational relaxation of the organic ligand dtbp, resulting in narrow-band emission. Moreover, owing to the synergy between this structural rigidity and the distortion of the InCl₄(dtbp) unit, this compound overcomes the trade-off between PLQY and g_lum, exhibiting a PLQY approaching 100% and a |g_lum| value of 0.283. Photophysical characterizations and density-functional theory calculations indicate that the high-efficiency emission originates from the ligand. As a rare example of optically active achiral crystals, this compound not only offers a promising candidate for CPL materials integrating narrow FWHM, high PLQY, and large g_lum, but also provides valuable insight into the chiroptical properties of achiral crystalline systems.