Zhu Mao

Intermolecular Electronic Coupling of Organic Units for Efficient Persistent Room‐Temperature Phosphorescence

Abstract Although persistent room‐temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited‐state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.

Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties

Since the realization in 2011 that most aggregation-induced emission (AIE) molecules exhibit mechano-responsive luminescence (MRL), research regarding the MRL of AIE molecules has drawn much attention, and this area has been expanding tremendously. As one of the most extensively studied AIE cores, tetraphenylethylene (TPE) has been widely used to construct MRL molecules. This review will focus on recent advances in MRL of TPE derivatives with AIE properties, including a brief history of mechano-responsive AIE-active materials, mechanistic studies on MRL, mechano-responsive luminogens based on TPE, mechano-responsive luminogens containing multiple AIE-active units, mechano-memory chromism and mechanoluminescence of TPE derivatives. Moreover, this review will give a perspective on the possible opportunities and future challenges that exist in this research area.

Transient and Persistent Room‐Temperature Mechanoluminescence from a White‐Light‐Emitting AIEgen with Tricolor Emission Switching Triggered by Light

Persistent luminescence from purely organic materials is basically triggered by light and electricity, which largely confines its practical applications. A purely organic AIEgen exhibits not only persistent photoluminescence, but also transient and persistent room-temperature mechanoluminescence. By simply turning on and off a UV lamp, tricolor emission switching between blue, white, and yellow was achieved. The data from single-crystal structure analysis and theoretical calculation suggest that mechanism of the observed persistent mechanoluminescence (pML) is correlated with the strong spin-orbit coupling of the bromine atom, as well as the formation of H-aggregates and restriction of intramolecular motions in noncentrosymmetric crystal structure. These results outline a fundamental principle for the development of new pML materials, providing an important step forward in expanding the application scope of persistent luminescence.

A TPE–benzothiazole piezochromic and acidichromic molecular switch with high solid state luminescent efficiency

A new organic compound, namely B-TPEAN, was constructed by using tetraphenylethylene, acrylonitrile and benzothiazole as building blocks. Herein, results of single crystal structure analysis and theoretical calculation for the as-synthesized compound were presented. Photophysical properties, including UV-visible absorption, photoluminescence and fluorescent quantum yield, were also well studied. B-TPEAN was found to show excellent aggregation-induced emission (AIE) properties and high quantum yield (up to 85%) in the solid-state. These results should be attributed to the positive effect of a combination of two typical AIE moieties in one molecule. Upon grinding, the emission color of the pristine sample for B-TPEAN changed from bluish green (λem,max = 497 nm) to yellow (λem,max = 567 nm), exhibiting a remarkable piezochromism. Moreover, by fuming with acid vapor, both of the pristine and the ground samples of B-TPEAN showed dramatic decreases in fluorescence quantum yields and large bathochromic shifts in PL maxima up to 53 nm and 80 nm, respectively, indicating a success in achieving multi-stimuli-responsive luminophore with high contrast in both emission intensity and color. Further investigation revealed that the acidifluorochormism of the samples was caused by the protonation of the benzothiazole moiety, leading to an enhancement of ICT effect in the protonated molecules.

Recent progress in the mechanofluorochromism of cyanoethylene derivatives with aggregation-induced emission

As a class of smart materials, mechanofluorochromic (MFC) luminogens have promising applications in mechanosensors, security papers, and optical storage primarily based on their alternation in emission behaviors in response to mechanical stimuli. It has been discovered that most molecules having aggregation-induced emission (AIE) exhibit mechanofluorochromism. As one of the essential AIE cores, cyanoethylene has been widely used to build MFC molecules. This review focuses on the latest advances in the mechanofluorochromism of cyanoethylene derivatives with AIE properties, which incorporates mechanistic studies on mechanofluorochromism and MFC luminogens based on cyanoethylene. We hope that this review will provide a clear outlook on these novel functional materials to a broad range of scientists within exclusive disciplinary areas and attract more researchers to devote themselves to this exciting research area.

Alkyl Chain Introduction: In Situ Solar‐Renewable Colorful Organic Mechanoluminescence Materials

Mechanoluminescence (ML) materials are environmentally friendly and emit light by utilizing mechanical energy. This has been utilized in light sources, displays, bioimaging, and advanced sensors. Organic ML materials are strongly limited to application by in situ unrepeatable ML. Now, in situ solar-renewable organic ML materials can be formed by introducing a soft alkyl chain into an ML unit. For the first time, the ML from these polycrystalline thin films can be iteratively produced by simply recrystallizing the fractured crystal in situ after a contactless exposure to sunlight within a short time (≤60 s). Additionally, their ML color and lifetime can be also easily tuned by doping with organic luminescent dyes. Therefore, large-area sandwich-type organic ML devices can be fabricated, which can be repeatedly used in a colorful piezo-display, visual handwriting monitor, and sensitive optical sensor, showing a lowest pressure threshold for ML of about 5 kPa.

Recent progress in the mechanofluorochromism of distyrylanthracene derivatives with aggregation-induced emission

Mechanofluorochromic (MFC) luminogens, as a group of evidence-based, practical smart materials, have established immense interest with respect to mechanical stimuli, due to their promising applications in various fields like mechanosensors, safety papers, and optical storage. However, MFC luminogens were rare earlier than 2010. After the discovery that MFC is an essential unique feature of aggregation-induced emission (AIE)-active molecules in 2011, researchers are encouraged to pay more attentions toward MCF luminogens, in which field the investigations are hastened steadily and focused distinctly. As one of the most vital AIE cores, distyrylanthracene (DSA) has been extensively used to assemble MFC motifs. As part of the interest in MFC luminogens, this contemporary overview is targeted on recent advances in the mechanofluorochromism of DSA derivatives with AIE properties and mechanistic study, which encourages more researchers to dedicate themselves to this interesting exploration discipline.