Supercooled Liquid β-Diketones with Mechanoresponsive Emission

Abstract

Shear-induced crystallization of dyes in the amorphous state is an effective strategy for generating higher energy emission after mechanical perturbationa rare phenomenon in mechanoresponsive materials. Recently, we reported that a β-diketone with a 3,4,5-trimethoxy-substituted phenyl ring formed a stable supercooled liquid (SCL) phase after melting and cooling in air. To tune the lifetime of β-diketones in the SCL phase, a series of dyes with 3,4,5-trimethoxy-substituted phenyl rings were synthesized. Derivatives with naphthyl and phenyl rings were prepared in order to modulate crystallization through arene interactions. Additionally, dyes were substituted with alkoxy chains of varying length to promote crystallization through increased van der Waals interactions. Video screening in conjunction with differential scanning calorimetry and X-ray diffraction studies indicated that naphthyl-substituted derivatives exhibited increased melted state lifetimes and that increasing the alkoxy chain length can induce crystallization. Analysis of molecular packing of single crystals of PH, PC1, PC3, and PC5 revealed that the central para-substituted methoxy group of the trimethoxy-substituted ring was forced out of the molecular plane because of steric interactions with neighboring methoxy groups. The stabilities of the SCLs were generally correlated with the torsion angles of the para methoxy groups, where derivatives with smaller angles exhibited faster rates of crystallization. Mechanical perturbation of the SCL phases resulted in shear-induced crystallization of PH, PC1, PC3, and NC6 derivatives. In some cases, traditional mechanochromic luminescence with a crystalline-to-amorphous phase transition was also observed, which indicates that some trimethoxy-substituted β-diketones exhibit more than one type of mechanoresponsive luminescence.

Stacking-dependent tetracolour luminescence and mechanofluorochromic properties of an isoquinoline derivative with aggregation-induced emission

“…Organic molecules with solid-state fluorescence have drawn great attention in the past two decades because of their wide applications in the field of anti-counterfeiting materials, optical sensors, and organic light-emitting devices. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The solid-state emission of an organic molecule is directly associated with its morphology, which is strongly influenced by the molecular conformation, intermolecular interaction, and stacking mode. [15][16][17][18] According to the reports in the literature, 19,20 nearly one-third of organic compounds can adopt more than one crystalline structure and some of them might have polymorphs emitting fluorescence with different colours.…”

Molecular copper iodide clusters: a distinguishing family of mechanochromic luminescent compounds

“…Examples of Zn, [42][43][44][45][46][47][48][49] Al, 50,51 Ir [52][53][54][55][56][57][58][59][60][61][62] and Ag [63][64][65][66][67][68][69][70][71] -based compounds have been also described as well as organoboron complexes. [72][73][74][75][76][77][78][79][80][81][82] Several Cu complexes have been reported too and in addition to their original mechanochromic properties, their economical interest compared with other metals, open appealing perspectives of applications. 106 The first copper-based mechanochromic complex was indeed a molecular copper iodide cluster of cubane geometry, formulated [Cu 4 I 4 L 4 ] (L = phosphine ligand), reported by our group.…”

Pyranone–Arylbenzene Molecules Controlled by the Competition of Local Excited State and Twisted Intramolecular Charge-Transfer State: Dual-State Emission, Polymorphism, and Mechanofluorochromism

“…Organic luminogens have been widely investigated by researchers owing to their wide applications in chemosensors, biological fields, optoelectronic devices, and security systems. − The luminous essence of materials is that the absorbed photons are transferred from the excited state to the ground state through radiation, and there are many factors that affect the luminescent properties of the materials, such as conjugation degrees, free motions, strong intermolecular interactions, and the quenching groups. − It is possible to ensure that the materials have strong luminous efficiency in solution by designing their molecular structures to have relatively flat and rigid molecular configurations . By restricting the motions of molecules to suppress the nonradiative transitions of energy, the materials can also exhibit an ideal luminescence phenomenon in the aggregate state. ,− Even by increasing the distortion of the molecular spatial configuration under the premise that the molecules maintain a certain degree of conjugation, dual-state emission (DSE) materials with strong fluorescence in both the solution state and the aggregate state might be obtained. − …”