Double-Layer Hydrogels with Tunable Mechanofluorochromic Response for Smart Display

Mechanofluorochromic materials that render sensitive fluorescence color/pattern change upon mechanical stimuli have drawn extensive attention.However,traditional mechanofluorochromism relies on the chemical transformations of mechanophores,but their types are quite few.It remains challenging to develop mechanofluorochromic materials with customized fluorescence color changing response.Herein,a generally applicable strategy is proposed to present a class of double-layer mechanofluorochromic hydrogels based on the facile integration of two different-colored fluorescent hydrogels.Due to the UV transmittance change of top layer under Poisson’s effect,the emission intensity ratio of the upper and lower hydrogels exhibits a strain-dependent change,resulting in a force-triggered overlapping color variation.Both the UV transmittance of top layer and the fluorescence emission of bottom layer can be readily modulated to enrich the variety of mechanofluorochromism.Besides,the bottom layer is available to be printed by ion inks to fabricate patterned double-layer fluorescent hydrogel,holding great potential to design flexible mechanofluorochromic platforms for smart display and information encryption.

Recent progress in organic mechanoluminescent materials

Mechanoluminescence（ML） refers to the light emission from various organic and inorganic materials upon mechanical stimulus. As a new class of smart materials, mechanoluminescent materials are widely applicable for fluorescence switches, mechanosensors, security papers, optoelectronic devices and data storage etc. In the past few years, systematic investigations have been carried out, resulting in the production of a variety of mechanoluminescent materials. In this review, recent progress in pure organic mechanoluminescent materials is summarized, including mechanofluorescent and triboluminescent effects from conjugated small molecules.

Multi-responsive red solid emitter: Detection of trace water and sense of relative humidity

A multi-responsive D-A type compound(CYQ)based on pyrone and triphenylamine was designed and successfully synthesized. The target compound exhibited distinct aggregation-enhanced emission(AEE) effect.Solvatochromic experiment and density functional theory(DFT) indicated CYQ possessed excellent intramolecular charge transfer(ICT) ability. Besides, its mechanofluorochromic property(MFC) was found with a 37 nm redshift. Powder wide-angle X-ray diffraction(PXRD) and differential scanning calorimetry(DSC) measurements were performed to demonstrate the transformation from the crystalline to amorphous states upon grinding. Surprisingly,CYQ displayed a hypersensitive response to trace water in organic solvents with an excellent detection limit as low as 0.0096% in tetrahydrofuran(THF). Furthermore, it was found that the fluorescent intensity of CYQ declined progressively upon humidity rise, and its color change can be witnessed by naked eyes. Therefore, the relative humidity(RH) sensing strategy guarantees the AIEgen to become a colorimetric sensor under various conditions.

Aggregation-induced emission or aggregation-caused quenching?Impact of covale nt bridge between tetraphenylethene and naphthalimide

Understanding the physical mechanisms governing aggregation-induced-emission(AIE)and aggrega-tion-caused-quenching plays a vital role in developing functional AIE materials.In this work,tetraphenylethene(TPE,a classical AiEgen)and naphthalimide(NI,a popular fluorophore with ACQ characteristics)were connected through non-conjugated linkages and conjugated linkages.We showed that the nonconjugated-linkage of TPE to NI fragments leads to substantial PET in molecular aggregates and ACQ.In con trast,the conjugated conn ection between TPE and NI moieties results in the AIE phenomenon by suppressing twisted intramolecular charge transfer.This work provides an important guideline for the rational design of AIE materials.