Bismuth‐Based Coordination Polymers with Efficient Aggregation‐Induced Phosphorescence and Reversible Mechanochromic Luminescence

Abstract

Two bismuth coordination polymers (CPs), (TBA)[BiBr4 (bp4mo)] (TBA=tetrabutylammonium) and [BiBr3 (bp4mo)2 ], which are based on the rarely used simple ditopic ligand N-oxide-4,4'-bipyridine (bp4mo), show mechanochromic luminescence (MCL). High solid-state phosphorescence quantum yields of up to 85 % were determined for (TBA)[BiBr4 (bp4mo)] (λem =540 nm). Thorough investigations of the luminescence properties combined with DFT and TDDFT calculations revealed that the emission is due to aggregation-induced phosphorescence (AIP). Upon grinding, both samples became amorphous, and their luminescence changed from yellow to orange and red, respectively. Heating or exposure to water vapor led to the recovery of the initial luminescence. These materials are the first examples of mechanochromic phosphors based on bismuth(III).

α‐ and β‐[Bmim][BiCl4(2,2′‐bpy)]: Two Polymorphic Bismuth‐Containing Ionic Liquids with Crystallization‐Induced Phosphorescence

“…Comparison of the absorption spectra with that of 2,2′‐bpy indicates that intra‐ligand (IL) transitions may play major roles in the absorption process between 250 and 330 nm, which are in line with the shoulder peaks below 350 nm in the excitation spectra. Meanwhile, the lower absorption above 350 nm recorded at room temperature can be attributed to a charge‐transfer process from the inorganic moieties of the complexes (Bi and Cl) to the organic ligands, which has been evidenced in previously reported hybrid complexes . Thus, the phosphorescence emission may mainly originate from a metal‐to‐ligand charge‐transfer (MLCT) excited state, although the contribution of metal‐centered (MC) sp excited states of the n s 2 electrons of Bi 3+ could not be ignored.…”

“…Under excitation at different wavelengths, the shapes of the spectra remain unchanged, but there is a slight decrease in emission intensity (Figure S20). The quantum yields were evaluated as 26.07 % for 1 and 36.59 % for 2 , which are relatively high compared with those of reported hybrid halobismuthate compounds (Table S11), but lower than that of [TBA][BiBr 3 (bp4mo)] (TBA=tetrabutylammonium; bp4mo= N ‐oxide‐4,4′‐bipyridine) . Lifetime measurements (8.045 μs for 1 and 12.56 μs for 2 ) (Table S10, Figures S21 and S22) suggested that their emissions originate from triplet states exhibiting phosphorescence in the solid state.…”

“…Mercier et al. have recently studied the luminescence properties of hybrid Bi‐containing complexes based on alkylated or oxidized bipyridine derivatives, such as N ‐methyl‐4,4′‐bipyridine, N ‐methyl‐ N ′‐oxide‐4,4′‐bipyridine, N ‐oxide‐4,4′‐bipyridine, and N ‐oxide‐2,2′‐bipyridine, with BiX 3 (X=Cl, Br), whereby Bi−N and/or Bi−O bonds were established . According to their theoretical calculations, the HOMOs were distributed on the inorganic moieties of the complexes, whereas the LUMOs were mainly localized on the organic ligands.…”

Homodinuclear Lanthanide Complexes with the Divergent Heterotopic 4,4′‐Bipyridine N‐Oxide (bipyMO) Ligand

“…Among the neutral ditopic rigid ligands, the homotopic 4,4′‐bipyridine (bipy) has been employed in a huge amount of complexes with d metal centres while 4,4′‐bipyridine‐ N , N′ ‐dioxide (bipyDO) has been shown to be very effective in binding lanthanides . Conversely, the heterotopic divergent 4,4′‐bipyridine N ‐oxide (bipyMO, Scheme ) has been scarcely used …”

“…In the literature, a few complexes have been reported where the bipyMO ligand behaves as connector producing homometallic CPs with metal centres belonging to the p ‐block [Pb II ,[3a], [3d] Bi III[3c] ] as well as to the d‐block [M II = Mn, Co, Cu and Zn] . These polymers are characterized by the presence of two different regularly alternated coordination sites, M*[N] 2 and M*[O] 2 , (M* is the complementary metal coordination sphere and [N] and [O] specify the donor atom of the connector).…”