Blue and white-light emitting 2D-coordination polymers and their solid-state photodimerization reaction

Two Pb(II) coordination polymers (CPs), namely [Pb(μ-bpe)(μ-O2CCH3)2]n (1) and [Pb(μ-bpe)(μ-O2CH)2]n (2), have been isolated from the reaction of Pb(OAc)2·3H2O with 1,2-bis(4-pyridyl)ethene (bpe) in the presence of acetate and formate anionic ligands, respectively. Compounds 1 and 2 formed 2D sheet-like structures, constructed by bridging acetate and formate carboxylate ligands. The bpe ligand containing the olefinic CC bonds was perfectly brought to the proximity of Schmidt topolochemical criteria for 2. The 2D sheet in 2 underwent 67% of the photodimerization reaction in the solid state, while the 2D sheet in 1 was photochemically stable. Therefore, the photochemical reactivity of 1 and 2 was rationalized based on the orientation of the olefinic CC bonds, which was brought close to each other due to the distinct bridging of the carboxylates and the Pb(II) metal ions. The room temperature solid-state photoluminescence (PL) revealed that compound 1 exhibited a near white-light emission and the blue-light emission for 2 upon excitation at 365 nm. The differences in the emission of the two 2D-sheets were correlated with the bridging carboxylate ligands.