Mechanochromic aromatic hydrocarbons that bear one simple substituent

Structurally simple aromatic hydrocarbons that possess only one isocyano group show luminescent mechanochromism. The structural isomers of these aromatic hydrocarbons exhibit blue- and red-shifted emission bands upon mechanical stress. Their low molecular weight enables their sublimation under mild conditions.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Stimuli-Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration-Controlled Vapochromism

Stimulus-responsive organic materials with luminescence switching properties have attracted considerable attention for their practical applications in sensing, security, and display devices. In this paper, bent-type bisbenzofuropyrazine derivatives, Bent-H and Bent-sBu, with good solubilities were synthesized, and their physical and optical properties were investigated in detail. Bent-H gave three crystalline polymorphs, and they showed different luminescence properties depending on their crystal packing structures. In addition, Bent-H exhibited mechanochromic luminescence in spite of its rigid skeleton. Bent-sBu exhibited unique concentration-dependent vapochromic luminescence. Ground Bent-sBu was converted to blue-emissive, green-emissive, and green-emissive high-viscosity solution states at low, moderate, and high concentrations of CHCl3 vapor, respectively. This finding represents a concentration-dependent multi-phase transition with an organic solvent, which is of potent interest for application in sensing systems.

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Polymorphic organic crystals that can switch their photophysical properties in response to mechanical stimuli are highlighted.

Influence of additives on the polymorphic manipulation of organic fluorescent crystals and its mechanism

The influence and mechanism behind using additives to isolate metastable fluorescent polymorphs were carefully investigated.

Solid-State Fluorescence of A Quasi-Isostructural Polymorphic Biphenyl Based Michael Addition Product

Polymorphic materials have gained significant attention owing to their fascinating physicochemical properties. Herein, a biphenyl based Michael addition product (Compound A) with an active methylene group (dimedone) was synthesized. Compound...

Color polymorphism in organic crystals

Color polymorphism is an interesting property of chemical systems which present crystal polymorphs of different colors. It is a rare phenomenon, with only a few examples reported in the literature hitherto. Nevertheless, systems exhibiting color polymorphism have many potential applications in different domains, such as pigment, sensor, and technology industries. Here, known representative chemical systems showing color polymorphism are reviewed, and the reasons for them to present such property discussed. Also, since some of the concepts related to color polymorphism have been frequently used imprecisely in the scientific literature, this article provides concise, systematic definitions for these concepts.

Vapochromic crystals: understanding vapochromism from the perspective of crystal engineering

Vapochromic materials, which undergo colour and/or emission changes upon exposure to certain vapours or gases, have received increasing attention recently because of their wide range of applications in, e.g., chemical sensors, light-emitting diodes, and environmental monitors. Vapochromic crystals, as a specific kind of vapochromic materials, can be investigated from the perspective of crystal engineering to understand the mechanism of vapochromism. Moreover, understanding the vapochromism mechanism will be beneficial to design and prepare task-specific vapochromic crystals as one kind of low-cost 'electronic nose' to detect toxic gases or volatile organic compounds. This review provides important information in a broad scientific context to develop new vapochromic materials, which covers organometallic or coordination complexes and organic crystals, as well as the different mechanisms of the related vapochromic behaviour. In addition, recent examples of supramolecular vapochromic crystals and metal-organic-framework (MOFs) vapochromic crystals are introduced.

Three new metastable polymorphs of 1-(9-anthryl)-2-(1-naphthyl)ethylene and the polymorph-dependent phase transition and fluorescence change properties

Three new metastable polymorphs of 1-(9-anthryl)-2-(1-naphthyl)ethylene (ANE) were successfully obtained, displaying different phase transition processes and fluorescence change properties.

Reversible two-channel mechanochromic luminescence for a pyridinium-based white-light emitter with room-temperature fluorescence–phosphorescence dual emission

For a pyridinium-based emitter with fluorescence–phosphorescence dual emission, mechanical grinding induces phosphorescence disappearance and mechanical pressing induces extraordinary phosphorescence enhancement.

Multi-Stimuli-Responsive Fluorescence Switching from a Pyridine-Functionalized Tetraphenylethene AIEgen

The discovery of the striking aggregation-induced emission (AIE) phenomenon has opened a new avenue for smart light-emitting materials. Herein, a new AIE luminogen (AIEgen), 1,1,2,2-tetrakis(4-((E)-2-(pyridin-2-yl)vinyl)phenyl)ethene (TP2VPE), has been designed and synthesized by introducing the vinylpyridine motifs into the tetraphenylethene backbone. The emission spectrum of the new obtained AIEgen crystalline material can be switched in response to not only mechanical grinding and hydrostatic compression but also the protonation effect with excellent reversibility and reproducibility. Single-crystal X-ray structural analysis disclosed the supramolecular porous channel structure, which provides a shrinkable volume to maintain the fluorescence emission upon high pressure. Furthermore, protonation-deprotonation of the pyridine moieties in TP2VPE has a significant effect on the frontier molecular orbitals as well as very distinctive emission characteristics upon acid and base stimuli. The dual-response performance and the ease of its preparation and renewal endow the material with potential applications in pressure and acid/alkali fluorescence sensing.

Synthesis of tunable, red fluorescent aggregation-enhanced emissive organic fluorophores: stimuli-responsive high contrast off–on fluorescence switching

Molecular conformation controlled tunable and stimuli-responsive off–on fluorescence switching.

Diarylmaleimide-based branched oligomers: strong full-color emission in both solution and solid films

An effective design method is presented to construct highly efficient fluorescent materials in both solution and solid films, by non-conjugately linking fluorophores into branched oligomers. Surface aryl groups are changed to tune the luminescent color from blue (λ_em = 480 nm) to red (λ_em = 651 nm), and realize full-color emission.

Emission behaviours of novel V- and X-shaped fluorophores in response to pH and force stimuli

The solid-state emission behaviours of a series of V- and X-shaped fluorophores exposed to mechanical force and pH stimuli are dependent on the ICT effect as well as the size- and morphology-effect.

Tunable solid state emission of novel V-shaped fluorophores by subtle structure modification: polymorphism, mechanofluoro-chromism and micro-fabrication

A largely wide and nearly successive range of solid-state emission wavelengths can be achievedviapolymorphism, mechanofluorochromism and micro-fabrication on rationally designed V-shaped fluorophores with subtle structure modification.

Mechanoresponsive Luminescent Molecular Assemblies: An Emerging Class of Materials

The possibility to change the molecular assembled structures of organic and organometallic materials through mechanical stimulation is emerging as a general and powerful concept for the design of functional materials. In particular, the photophysical properties such as photoluminescence color, quantum yield, and emission lifetime of organic and organometallic fluorophores can significantly depend on the molecular packing, enabling the development of molecular materials with mechanoresponsive luminescence characteristics. Indeed, an increasing number of studies have shown in recent years that mechanical force can be utilized to change the molecular arrangement, and thereby the optical response, of luminescent molecular assemblies of π-conjugated organic or organometallic molecules. Here, the development of such mechanoresponsive luminescent (MRL) molecular assemblies consisting of organic or organometallic molecules is reviewed and emerging trends in this research field are summarized. After a brief introduction of mechanoresponsive luminescence observed in molecular assemblies, the concept of "luminescent molecular domino" is introduced, before molecular materials that show turn-on/off of photoluminescence in response to mechanical stimulation are reviewed. Mechanically stimulated multicolor changes and water-soluble MRL materials are also highlighted and approaches that combine the concept of MRL molecular assemblies with other materials types are presented in the last part of this progress report.

Continuously-tunable fluorescent polypeptides through a polymer-assisted assembly strategy

We developed a versatile method to continuously tune the packing and fluorescence of organic chromophores through a polymer-assisted assembly (PAA) strategy, affording a catalog of fluorescent polymers with continuously-tunable fluorescence emission.