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).

The zwitterionic bipyridinium carboxylate ligand 1-(4-carboxyphenyl)-4,4'-bipyridinium (hpc1) in the presence of 1,4-benzenedicarboxylate anions (BDC(2-)) and Zn(2+) ions affords three porous coordination polymers (PCPs): [Zn5(hpc1)2(BDC)4(HCO2)2]·2DMF·EtOH·H2O (1), [Zn3(hpc1)(BDC)2(HCO2)(OH)(H2O)]·DMF·EtOH·H2O (2), and [Zn10(hpc1)4(BDC)7(HCO2)2(OH)4(EtOH)2]·3DMF·3H2O (3), with the formate anions resulting from the in situ decomposition of dimethylformamide (DMF) solvent molecules. 1 and 3 are photo- and thermochromic, turning dark green as a result of the formation of bipyridinium radicals, as shown by electron paramagnetic resonance measurements. Particularly, crystals of 3 are very photosensitive, giving an eye-detectable color change upon exposure to the light of the microscope in air within 1-2 min. A very nice and interesting feature is the regular discoloration of crystals from the "edge" to the "core" upon exposition to O2 (reoxidation of organic radicals) due to the diffusion of O2 inside the pores, with this discoloration being slower in an oxygen-poor atmosphere. The formation of organic radicals is explained by an electron transfer from the oxygen atoms of the carboxylate groups to pyridinium cycles. In the structure of 3', [Zn10(hpc1)4(BDC)7(OH)6(H2O)2], resulting from the heating of sample 3 (desolvation and loss of CO molecules due to the decomposition of formate anions), no suitable donor-acceptor interaction is present, and as a consequence, this compound does not exhibit any chromic properties. The presence of permanent porosity in desolvated 1, 2, and 3' is confirmed by methanol adsorption at 25 °C with the adsorbed amount reaching 5 wt % for 1, 10 wt % for 3', and 13 wt % for 2. The incomplete desorption of methanol at 25 °C under vacuum points to strong host-guest interactions.

Using a slow liquid-gas diffusion method, the mixed-valence viologen salt (MV)2(BF4)3 (1) and the radical cation salt (MV)(BF4) (2) are crystallized. Both structures contain regular stacks of MV˙(+) radical cations (2) or alternating MV˙(+) and MV(2+) entities (1). A short intrastack intermolecular separation (3.23 Å) unprecedently reveals strong interactions between MV(2+) and MV˙(+) in 1.

Unprecedented bismuth complexes, based on the rarely used ditopic ligand N-oxide-2,2'-bipyridine (bp2mo), crystallizing as three polymorphs, α- (), β- () and γ-[BiBr3(bp2mo)2] (), exhibit phosphorescence with a quantum yield up to 17% for the crystal phase (), while the complex displays a weak fluorescence in solution. A study of the luminescence properties combined with DFT/TDDFT calculations reveals that the lighting phenomenon originated by aggregation induced phosphorescence correlated with the weak intermolecular interactions present in the different crystal phases.

Three bismuth complexes based on N-methyl-4,4Ј-bipyridinium (hMV + ), (hMV)[Bi(hMV)Cl 5 ] (1), and N-methyl-NЈ-oxide-4,4Ј-bipyridinium (MVO + ), [Bi(MVO)X 4 (dmso)]·dmso [X = Cl (2), Br (3)], are reported. All three compounds show luminescence in the solid state with maxima at 545 nm (yellow for 1) and 560 nm (orange for 2 and 3) with quantum yields [a]

The association of Bi 3+ ions and N,N′-dioxide-4,4′bipyridine (bp4do) ligands has led to three related compounds [Bi 2 Br 6 (bp4do)(dmso) 4 ] (1), [BiBr 3 (bp4do)(dmso)] (2), and [Bi 2 Br 6 (bp4do) 3 ] (3). 2 can be described from 1, and 3 from 2, by the substitution of two dmso molecules by one bp4do molecule, the octahedral geometry of bismuth ions being kept as BiBr 3 O-(bp4do)O 2 (dmso) in 1, BiBr 3 O 2 (bp4do)O(dmso) in 2, and BiBr 3 O 3 (bp4do) in 3. In the absorption spectra of 1−3, as well as Bi/bp4do complexes in solution, a metal-to-ligand charge transfer band is observed as a result of the formation of Bi−O(Noxide) bonds. All 1−3 materials exhibit luminescence properties of phosphorescence type with quantum yields up to 54% for 1. In contrast with 1 (isolated complexes in the solid state), 1D coordination polymer type compounds 2 and 3 exhibit mechanochromic luminescence (MCL) properties: upon grindinga few seconds for 2the broad emission bands of the pristine compounds centered at 575 nm (2, yellow emission) and 600 nm (3, orange emission) are shifted by 75 nm (2) or 50 nm (3) (bands centered at 650 nm), leading to a strong red emission, whereas the process is reversible by heating, fuming, or recrystallization in a few drops of solvent. These MCL properties of 2 and 3 may be related to conformational changes of polymeric chains upon grinding.

In the strong orange luminescent material of [Pb(bp4mo)Cl 2 ], two different types of octahedra, namely PbCl 4 N 2 and PbCl 4 O 2 , are bridged by the N-oxide-4,49-bipyridine (bp4mo) ligand, while its protonated form, Hbp4mo + , coordinates to Pb 2+ center only with the N-oxide group in [Pb(Hbp4mo) 2 Cl 2 ](NO 3 ) 2 . Important relationships between structures and luminescence properties are revealed.

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