Triboluminescence of Centrosymmetric Lanthanide β-Diketonate Complexes with Aggregation-Induced Emission

Abstract

Triboluminescence (TL) is a form of light emission induced upon mechanical forces on the material. However, our understanding of this phenomenon is still unclear and more examples are therefore needed in order to elucidate its mechanism. In this work, two types of TL complexes, [Eu(pp-dbm-Cl2)3phen] and [Eu(mm-dbm-Cl2)3phen], which also displays aggregation-induced emission (AIE) were synthesized and investigated for its photo-physical and crystal structural properties. These complexes were crystallized in a centro-symmetric space group P21/n, and remarkably, displayed TL upon grinding that may be due to the presence of extensive π···π, C-H···π and C-H···Cl-C interactions in the close molecular packing of its structure. This rare example deviates from the widely accepted mechanism of TL, hence widening the scope of our understanding in the area.

The Impact of the Alkali Metal Ion on the Crystal Structure and (Mechano)luminescence of Terbium(III) Tetrakis(β‐diketonates)

“…The complex [NaTb] 4 has the longest Tb–Tb distance between the layers 11.049(5) Å, while in [KTb] 5 and [CsTb] 6 these distances are 10.455(7) and 10.995(8) Å, respectively (Table S4). The previously proposed hypothesis of the cleavage planes[18e], [18j], within the crystal lattice in the complexes is valid for [NaTb] 4 . There is conditionally allotted spatial interlayer areas along the both b and c axes, which can be considered as destruction zones (Figures S26, S27).…”

“…For a number of organic and organometallic compounds it is noted the important role of randomly distributed sites and disordered arrangement of substituents with weak (van der Waals forces only) interactions in the design of mechanoluminescent systems. [6i], [8a], [8r], , Sweeing and Rheingold reported the disorder of phenyl rings and cations in [Et 3 NH] + [Eu(dbm) 4 ] – provided a sufficient source of localized polarity to induce mechanoluminescence activity. [17c] In another case, the weak intermolecular interaction of fluoroalkyl groups promoted the formation of mechanoluminescent polymeric structure with fluorinated diketonates oriented along one plane.…”

“…[17c] In another case, the weak intermolecular interaction of fluoroalkyl groups promoted the formation of mechanoluminescent polymeric structure with fluorinated diketonates oriented along one plane. [18f] Significantly, the known triboluminescent diketonates include the Ln III tris(β‐diketonates) with N , N ‐coligands or tetrakis(β‐diketonates) with positively charged N ‐ or P ‐organic molecules acting as cationic counterparts. [6i], [8a], [8q], , However, no similar properties were reported for Ln III tetrakis(β‐diketonates) producing coordination polymeric networks through the alkali metal ions.…”

“…[18f] Significantly, the known triboluminescent diketonates include the Ln III tris(β‐diketonates) with N , N ‐coligands or tetrakis(β‐diketonates) with positively charged N ‐ or P ‐organic molecules acting as cationic counterparts. [6i], [8a], [8q], , However, no similar properties were reported for Ln III tetrakis(β‐diketonates) producing coordination polymeric networks through the alkali metal ions. Moreover, the diketonates [(LnL 3 )(LiL)(MeOH)] with a discrete molecular structure were the first examples of heterometallic complexes exhibiting mechanoluminescence.…”

“…The polarization of the crystal occurs along these planes (the area of relatively weakened linkage between crystallographic regular layers) upon the mechanical impact. [18e], [18j], Therefore, weak intermolecular interactions, crystal packing and conformational freedom of a molecule affect the mechanoluminescence activity of complex [NaTb] 4 .…”