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)4Pb3Br10 composed of face-sharing [Pb3Br10] trimers interconnected by corner-sharing μ2-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 [PbBr6]4- octahedral distortion. The bulkiest N-methylpyridinium core (5) templates discrete zero-dimensional (0D) [Pb3Br12]6- trimers (5)6Pb3Br12. Dimensionality reduction correlates strongly with cation volume and the resulting steric demand at the inorganic-organic interface. Solid-state 207Pb 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.