Molecular tailoring suppresses cationic flexibility for high PLQY in 0D MnBr4 organic-inorganic hybrids

This study investigates the impact of structural flexibility on the photoluminescence quantum yield (PLQY) in hybrid Mn 2+ -based materials by tailoring (Et 3 NCHF 2 ) 2 MnBr 4 (PLQY = 42.60 %) to (Me 3 NCHF 2 ) 2 MnBr 4 (PLQY = 81.79 %). Variable-temperature single-crystal and Raman spectroscopic analyses reveal that the methyl-derivative maintains long-range structural order, while the ethyl-derivative exhibits significant cationic positional disorder, which intensifies upon heating and directly correlates with its lower PLQY. Variable-temperature PLQY and fluorescence lifetime analyses reveal a more rapid thermal quenching in the flexible (Et 3 NCHF 2 ) 2 MnBr 4 . Quantitative recombination kinetics demonstrate that this efficiency loss stems from a dramatic increase in the non-radiative decay rate (k nr ), which rises sharply with temperature compared to the rigid (Me 3 NCHF 2 ) 2 MnBr 4 . Hirshfeld surface and 2D fingerprint analyses demonstrate that disorder-induced dynamic H⋯Mn contacts (increasing from 1.5 % to 5.9 %) shorten Mn-ligand distances and amplify tetrahedral distortion in the [MnBr 4 ] 2- luminescent center, quantified by an 80-fold increase in the Bond Length Distortion Index (BDI). This distortion enhances vibrational coupling, promoting phonon-assisted non-radiative decay and reducing luminescence efficiency. Additionally, to address moisture sensitivity in [MnBr 4 ] 2- hybrids, polyurethane elastomer composites that integrate high deformability with retained photoluminescence were developed, reducing water uptake and enabling applications in flexible coatings.© 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved.