Dimensionality Tuning in Low-Dimensional Lead-Bromide Hybrids through Systematic Variation of Quaternary-Substituted Organic Cation Cores

Low-dimensional lead-bromide hybrids exhibit remarkable structural diversity and optoelectronic tunability, yet the factors governing their inorganic framework dimensionality remain poorly understood. Herein, we systematically vary the core structure of benzyl-functionalized quaternary ammonium/pyridinium cations to elucidate their templating effect on the Pb–Br lattice assembly. A small trimethylammonium core ( 1 ) yields a rare two-dimensional (2D) layered structure ( 1 ) 4 Pb 3 Br 10 composed of face-sharing Pb 3 Br 10 trimers interconnected by corner-sharing μ 2 -Br bridges. Larger alicyclic cores, such as pyrrolidinium ( 2 ), piperidinium ( 3 ), and quinuclidinium ( 4 ), produce one-dimensional (1D) face-sharing chains with a progressively increasing PbBr 6 4– octahedral distortion. The bulkiest N -methylpyridinium core ( 5 ) templates discrete zero-dimensional (0D) Pb 3 Br 12 6– trimers ( 5 ) 6 Pb 3 Br 12 . Dimensionality reduction correlates strongly with cation volume and the resulting steric demand at the inorganic–organic interface. Solid-state 207 Pb NMR and Raman spectroscopy confirm increasing octahedral distortion across the series, which induces strong exciton self-trapping. Consequently, all five compounds display intense broadband white-light emission (fwhm up to 226 nm), with tunable CIE (Commission Internationale de l’Éclairage) coordinates from (0.41, 0.50) to (0.52, 0.38) and correlated color temperature (CCT) values of 2000–4000 K. This study establishes clear design rules linking organic cation core structure to inorganic framework dimensionality and emissive performance in low-dimensional lead-halide hybrids.