Planar donor and acceptor (D–A) conjugated structures are generally believed to be the standard for architecting highly efficient photothermal theranostic agents, in order to restrict intramolecular ...motions in aggregates (nanoparticles). However, other channels of extra nonradiative decay may be blocked. Now this challenge is addressed by proposing an “abnormal” strategy based on molecular motion in aggregates. Molecular rotors and bulky alkyl chains are grafted to the central D–A core to lower intermolecular interaction. The enhanced molecular motion favors the formation of a dark twisted intramolecular charge transfer state, whose nonradiative decay enhances the photothermal properties. Result shows that small-molecule NIRb14 with long alkyl chains branched at the second carbon exhibits enhanced photothermal properties compared with NIRb6, with short branched chains, and much higher than NIR6, with short linear chains, and the commercial gold nanorods. Both in vitro and in vivo experiments demonstrate that NIRb14 nanoparticles can be used as nanoagents for photoacoustic imaging-guided photothermal therapy. Moreover, charge reversal poly(β-amino ester) makes NIRb14 specifically accumulate at tumor sites. This study thus provides an excited molecular motion approach toward efficient phototheranostic agents.
Aggregation‐induced emission (AIE) describes a photophysical phenomenon in which molecular aggregates exhibit stronger emission than the single molecules. Over the course of the last 20 years, AIE ...research has made great strides in material development, mechanistic study and high‐tech applications. The achievements of AIE research demonstrate that molecular aggregates show many properties and functions that are absent in molecular species. In this review, we summarize the advances in the field of AIE and its related areas. We specifically focus on the new properties of materials attained by molecular aggregates beyond the microscopic molecular level. We hope this review will inspire more research into molecular ensembles at and beyond the meso level and lead to the significant progress in material and biological science.
The importance of the whole picture: Aggregation‐induced emission (AIE) research demonstrates that many properties and functions that are absent in molecular species can be found in molecular aggregates. AIE research thus emphasizes the significance of aggregate science in addition to molecular science for materials development.
“United we stand, divided we fall.”–Aesop.Aggregation‐induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non‐emissive when they are ...dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM‐based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high‐tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.
“United we stand, divided we fall!” Aggregate formation changes non‐emissive luminogens to efficient emitters – this process is referred to as aggregation‐induced emission (AIE). The AIE effect is caused by the restriction of intramolecular motions of luminogens in aggregate state. The AIE materials have found a wide variety of high‐tech applications in the areas of optoelectronics, chemosensors, and biomedical probes.
Aggregation‐induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE ...molecules such as tetraphenylethene (TPE). However, as the family of AIE‐active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzoa,d7annulenylidene (THBDBA), and 5,5′‐bidibenzoa,d7annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).
Luminescence turn‐on: Through theoretical calculations to explain empirical observation, it is now possible to more fully explain the phenomenon of aggregation‐induced emission. By comparing tetraphenylethene and its structurally similar analogues, deeper insight has been gained into this photophysical phenomenon in which luminescence can be turned on in the aggregated or solid state.
Persistent luminescence is a fascinating phenomenon with exceptional applications. However, the development of organic materials capable of persistent luminescence, such as organic persistent ...room-temperature phosphorescence, lags behind for their normally low efficiency. Moreover, enhancing the phosphorescence efficiency of organic luminophores often results in short lifetime, which sets an irreconcilable obstacle. Here we report a strategy to boost the efficiency of phosphorescence by intramolecular triplet-triplet energy transfer. Incorpotation of (bromo)dibenzofuran or (bromo)dibenzothiophene to carbazole has boosted the intersystem crossing and provided an intramolecular triplet-state bridge to offer a near quantitative exothermic triplet-triplet energy transfer to repopulate the lowest triplet-state of carbazole. All these factors work together to contribute the efficient phosphorescence. The generation and transfer of triplet excitons within a single molecule is revealed by low-temperature spectra, energy level and lifetime investigations. The strategy developed here will enable the development of efficient phosphorescent materials for potential high-tech applications.
Aggregation-induced emission (AIE) is a cutting-edge fluorescence technology, giving highly-efficient solid-state photoluminescence. Particularly, AIE luminogens (AIEgens) with emission in the range ...of second near-infrared window (NIR-II, 1000-1700 nm) have displayed salient advantages for biomedical imaging and therapy. However, the molecular design strategy and underlying mechanism for regulating the balance between fluorescence (radiative pathway) and photothermal effect (non-radiative pathway) in these narrow bandgap materials remain obscure. In this review, we outline the latest achievements in the molecular guidelines and photophysical process control for developing highly efficient NIR-II emitters or photothermal agents with aggregation-induced emission (AIE) attributes. We provide insights to optimize fluorescence efficiency by regulating multi-hierarchical structures from single molecules (flexibilization) to molecular aggregates (rigidification). We also discuss the crucial role of intramolecular motions in molecular aggregates for balancing the functions of fluorescence imaging and photothermal therapy. The superiority of the NIR-II region is demonstrated by fluorescence/photoacoustic imaging of blood vessels and the brain as well as photothermal ablation of the tumor. Finally, a summary of the challenges and perspectives of NIR-II AIEgens for
in vivo
theranostics is given.
Structural and process controls of NIR-II AIEgens realize manipulating of radiative (R) and nonradiative (NR) decay for precise theranostics.
The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli‐responsive AIEgens have received ...particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli‐responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli‐responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next‐generation stimuli‐responsive luminescent materials for more broad applications.
Aggregation‐induced emission (AIE) luminogens (AIEgens) are one of the optimal choices for smart luminescent materials to be applied in real life and they have sparked much of the current interest in the smart materials area. Therefore, a myriad of AIE materials with diverse stimuli‐responsive properties have been developed in recent years, and they exhibit broad application prospects.
Efficient organic photosensitizers (PSs) have attracted much attention because of their promising applications in photodynamic therapy (PDT). However, guidelines on their molecular design are rarely ...reported. In this work, a series of PSs are designed and synthesized based on a triphenylamine-azafluorenone core. Their structure–property-application relationships are systematically studied. Cationization is an effective strategy to enhance the PDT efficiency of PSs by targeting mitochondria. From the molecularly dispersed state to the aggregate state, the fluorescence and the reactive oxygen species generation efficiency of PSs with aggregation-induced emission (AIE) increase due to the restriction of the intramolecular motions and enhancement of intersystem crossing. Cationized mitochondrion-targeting PSs show higher PDT efficiency than that of nonionized ones targeting lipid droplets. The ability of AIE PSs to kill cancer cells can be further enhanced by combination of PDT with radiotherapy. Such results should trigger research enthusiasm for designing and synthesizing AIE PSs with better PDT efficiency and properties.
The exciting applications of molecular motion are still limited and are in urgent pursuit, although some fascinating concepts such as molecular motors and molecular machines have been proposed for ...years. Utilizing molecular motion in a nanoplatform for practical application has been scarcely explored due to some unconquered challenges such as how to achieve effective molecular motion in the aggregate state within nanoparticles. Here, we introduce a class of near infrared-absorbing organic molecules with intramolecular motion-induced photothermy inside nanoparticles, which enables most absorbed light energy to dissipate as heat. Such a property makes the nanoparticles a superior photoacoustic imaging agent compared to widely used methylene blue and semiconducting polymer nanoparticles and allow them for high-contrast photoacoustic imaging of tumours in live mice. This study not only provides a strategy for developing advanced photothermal/photoacoustic imaging nanoagents, but also enables molecular motion in a nanoplatform to find a way for practical application.
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