Mechanically Triggered Fluorescence/Phosphorescence Switching in the Excimers of Planar Trinuclear Copper(I) Pyrazolate Complexes

Abstract

Luminescence mechanochromism of the well-known Cu3Pz3-type (Pz = pyrazolate) complexes is reported here, which is unusual for this family. Two types of new Cu3Pz3 complexes, namely Cu3(EBPz)3 (1; EBPz = ethyl-4'-benzoate-3,5-dimethylpyrazolate) and Cu3(MBPz)3 (polymorphs 2a-c; MBPz = methyl-4'-benzoate-3,5-dimethylpyrazolate), have been synthesized and characterized. Their crystal structures exhibit a similar chairlike dimer stacking supported by short Cu···Cu contacts, which would facilitate the formation of photoinduced excimers. The dual emission from the organic fluorophore and excimeric copper cluster phosphor is found to undergo mechanically induced intensity switching between their high-energy (HE) and low-energy (LE) bands. Specifically, the relative intensities of crystalline samples are HE > LE, while the ground solid samples show LE > HE, resulting in the overall emission color interchanging between bluish violet and red. This switching can be reversed by application of solvent to the ground samples, presumably due to recrystallization, and also by heating. TD-DFT calculations reveal that the emissive singlet ligand localized state (S1) and triplet cluster centered state (T8) lie close in energy (separated by a gap of 0.1788 eV), suggesting the feasibility of dual emission and the possibility of reverse intersystem crossing, consistent with the long fluorescent lifetimes (10(2) ns scale) of the HE bands.

Cu(I) hybrid inorganic–organic materials with intriguing stimuli responsive and optoelectronic properties

“…Cu(I)-pyrazolate type complexes have in fact solid-state phosphorescent emission lying in the LE region (orange or red) thus pressure induced shortening of Cu···Cu distances has almost no visual result. Pyrazolate-compounds with mechanically induced shift of the emission have been reported only very recently [79]. Li et al prepared, by solvothermal reaction, [Cu 3 (EBPz) 3 ] (EBPz = ethyl-4-benzoate-3,5-dimethylpyrazolate), 88, and three polymorphs of [Cu 3 (MBPz) 3 ] (MBPz = methyl-4-benzoate-3,5-dimethylpyrazolate), 89a−c.…”

Trigonal Prismatic Cu6L3 Coordination Cage: Encapsulation of Aromatic Molecules and Tuned Photoluminescence

“…Our group also have explored and studied a family of fascinating luminescent CTCs. We utilized the cyclic trinuclear unit to construct a series of interesting materials, including dual‐emitting materials acting as sensor or thermometer, white‐light emitting material, and mechanical triggered luminescent material …”

“…We utilized the cyclic trinuclear unit to construct a series of interesting materials, including dualemitting materials acting as sensor or thermometer, [15] whitelight emitting material, [16] and mechanical triggered luminescent material. [17] Moreover, the cyclic trinuclear unit also could serve as a building unit to construct coordination cages. Thiel reported a series of isostructural hexanuclear pyrazolate complexes and their luminescence properties.…”

Emission properties and Cu(i)–Cu(i) interaction in 2-coordinate dicopper(i)-bis(N-heterocyclic)carbene complexes

“…Catalysis mediated by 1 was studied in the work, 32 but no photophysical properties of the complexes have been reported. Metal-metal interaction using multinuclear metal complexes, such as platinum(II)-platinum(II) 34 and gold(I)gold(I) 35 interactions, plays a key role in enhancing the photophysical properties; for copper(I) complexes, [12][13][14][15][16][17] notable effects of weak metal-metal interactions on the properties of complexes such as cubane-like tetranuclear copper(I) iodide complexes [14][15][16] have also been known. However, there are only limited number of reports studying the effect of the metalmetal interactions on the photophysical properties of Cu(I) complexes in contrast to the gold(I) complexes.…”