Effect of ring substituent position on the structural and optoelectronic properties of novel quasi low-dimensional hybrid 2-, 3-, and 4-(bromomethyl)pyridinium lead bromides†

In this work, the synthesis, crystal structure, morphology, and optoelectronic properties of novel quasi low-dimensional hybrid (bromomethyl)pyridinium crystalline phases (2-BrCH₂PyH)Pb₂Br₅, (3-BrCH₂PyH)PbBr₃, and (4-BrCH₂PyH)PbBr₃ are reported. The first compound formed quasi 2D crystals, while the other two species crystallized as quasi 1D structures. DFT calculations predicted that the bromides are semiconductors featuring electronic VB-to-CB transitions of ∼3.2 eV. (2-BrCH₂PyH)Pb₂Br₅ and (3-BrCH₂PyH)PbBr₃ exhibited low-temperature (77 K) photoluminescence (PL). However, PL was not observed in (4-BrCH₂PyH)PbBr₃, which was presumably due to the small distance between the lead cations and bromine atoms of the 4-BrCH₂PyH cations, resulting in a radiationless electronic transition. Furthermore, the studied species demonstrated quantum size effects.