Mechanochromic Luminescence of Aggregation-Induced Emission Luminogens

Abstract

Mechanochromic (MC) luminogens have found promising applications in mechanosensors, security papers, and optical storage for their change in emission behaviors in response to mechanical stimuli. Examples on MC luminescent materials are rare before the discovery of MC luminescence in aggregation-induced emission (AIE) luminogens. The twisted conformations of AIE luminogens (AIEgens) with appropriate crystallization capability afford loosely packing patterns, which facilitates their phase transformation in the solid state. The amorphous films of AIEgens exhibit enhanced emission intensity upon pressurization due to the increased molecular interactions, whereas crystals of AIEgens exhibit MC luminescence due to their amorphization by mechanical stimuli. AIEgens enrich the type of MC luminogens but those showing high emission contrast and multicolor emission switching and those working in a turn-on emission mode are seldom reported. Disclosure of the design strategy of high performance MC luminogens and exploration of their high-tech applications may be the future research directions for MC luminogens.

Multifunctional AIEgens: Ready Synthesis, Tunable Emission, Mechanochromism, Mitochondrial, and Bacterial Imaging

“…While in DMSO-water mixtures of 98 vol% water fraction, the formation of aggregates increases the hydrophobicity of the local environment and excludes the polar solvent molecules, so the emission was blueshifted. As these AIE compounds show morphologydependent emission which will be discussed in the mechanochromism part, [17] the redshifted emission of the forming aggregates suggests their poor crystallinity (or amorphous state) where the molecules were loosely packed and may adopt a more planar conformation, thus showing a redder emission.…”

“…Fluorescent materials with mechanochromic property are highly desirable in the applications of sensors, memory chips, optical storage, security inks, optoelectronic devices, and so forth. [17,19] Therefore, we attempt to investigate the mechanochromism of the new AIEgens IQ-Naph, IQ-DPA, and IQ-TPA. When the as-prepared powders were ground with a pestle on a glass slide, their apparent colors and fluorescent emissions were gradually redshifted and weakened with a large color contrast ( Figure S19, Supporting Information and Figure 4A).…”

“…While in the amorphous state, they adopted a more planar conformation and thus showing a redder emission. [17] Besides studying the color change after grinding, the reversible color switching of these mechanochromic compounds was also investigated. Using IQ-Naph as an example, after exposure to dichloromethane or tetrahydrofuran vapor, the yellow emission of grinded IQ-Naph was reverted to blue emission due to the solvent vapor-induced recrystallization process ( Figure 4C,D).…”

Unraveling the aggregation effect on amorphous phase AIE luminogens: a computational study

“…Depending on the type and phases of AIE luminogens, their optical properties are usually dramatically different. For example, the AIE-active propeller-shaped siloles in amorphous phase show redder and weaker fluorescence than their crystalline counterparts 18 , while the aggregation enhanced emission active amorphous-phased 2-Amino-3-((E)-(4-(diethylamino)benzylidene)amino)maleonitrile (A3MN) exhibits considerably bluer and stronger fluorescence than that of crystal 19 .…”

Mechanochromic Luminescent Properties of Difluoroboron β-Diketonate Dyes

“…[26][27][28][29][30] However, developing reliable design strategies for fabricating mechanofunctional materials is challenging and a cutting edge area of materials science research. 26,27 Mechanochromic luminescent (ML) materials are so named because a change in their luminescence colors can be caused by mechanical stimuli.…”