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Nonaromatic, cross-conjugated, and highly twisted luminogens consisting of acylated succinimides demonstrate aggregation-induced emission characteristics along with tunable multicolor photoluminescence and afterglows in their single crystals. Effective through-space conjugation among different moieties bearing n/π electrons promote the spin-orbit coupling and intersystem crossing and lead to diverse emissive clusters with concurrently rigidified conformations, thus allowing readily tunable emissions. Derived from it, the proof-of-concept application for advanced anti-counterfeiting is illustrated. These results should spur the rational design of novel nonaromatic AIEgens, and moreover advance understandings of the non-traditional intrinsic luminescence and the origin of tunable multicolor afterglows.

Compounds bearing aliphatic amines could be emissive under proper conditions. Their ionized counterparts, quaternary ammonium salts (QASs), which are widely used as phase-transfer catalysts, ionic liquids, disinfectants and surfactants, however, are known as luminescence quenchers and thought to be nonemissive. Here we report the unprecedented intrinsic fluorescence-phosphorescence dual emission from a diversity of QASs, which can also be finely regulated by excitation wavelength, alkyl chain length, counter ions, mechanical stimuli, etc. The bright photoluminescence along with distinct afterglow and tunable multicolor emissions enables advanced multimode anticounterfeiting for QAS solids. This finding refreshes the cognition of QASs and would inspire emerging applications by utilizing their intrinsic luminescence. Furthermore, it opens opportunities for the investigation of QAS related processes and functions in a photophysical approach and affords strong implications for the fabrication of novel nonconventional luminophores.

Nonconventional luminophores without significant conjugations generally possess excitation-dependent photoluminescence (PL) owing to the coexistence of diverse clustered chromophores, which strongly implies the possibility of achieving color-tunable PL and/or persistent room temperature phosphorescence (p-RTP) from their crystals assisted by effective intermolecular interactions. Compared with traditional luminogens, however, nonconventional luminophores generally suffer from poor PL efficiencies. Here, inspired by the highly stable double-helix structure and multiple hydrogen bonds in DNA, we report a series of planar or twisted nonconventional luminophores based on hydantoin (HA), demonstrating unprecedentedly high PL/p-RTP efficiencies and p-RTP lifetimes of up to 87.5%/21.8% and 1.74 s, respectively, accompanying color-tunable p-RTP from sky-blue to yellowish-green. These findings will advance the exploitation of efficient nonconventional luminophores and provide deeper mechanistic insights into the origin of color-tunable p-RTP.

Pure organic luminogens with long-persistent luminescence have been extensively studied, on account of their fundamental research significance and diverse utilizations in anticounterfeiting, bioimaging, encryption, organic light-emitting diodes, chemo-sensing, etc. However, time-dependent color-tunable afterglow is rarely reported, especially for single-component materials. In this work, we reported an organic luminogen with time-dependent afterglow, namely, benzoyleneurea (BEU), with multiple persistent room-temperature phosphorescence (p-RTP) and thermally activated delayed fluorescence (TADF) in single crystals. While the lifetime of TADF is relatively short (~1.2 ms), those for p-RTP are as long as around 369~754 ms. The comparable but different decay rates of diversified p-RTP emissions endow BEU crystals with obvious time-dependent afterglow. The existence of multiple emissions can be reasonably illustrated by the clustering-triggered emission (CTE) mechanism. Single-crystal structure illustrates that the combination of benzene ring and nonconventional chromophores of ureide helps facilitate divergent intermolecular interactions, which contribute to the formation of varying emissive species. Moreover, its methyl- and chloro-substituted derivatives show similar multiple p-RTP emissions. However, no time-dependent afterglows are observed in their crystals, due to the highly approaching lifetimes. The afterglow color variation of BEU crystals grants its applications in advanced anticounterfeiting field and information encryption.

In recent years, nonconventional luminogens free of aromatic groups have attracted extensive attention due to their academic importance and promising wide applications. Whilst previous studies generally focused on fluorescence from aliphatic amine or carbonyl-containing systems, less attention has been paid to room temperature phosphorescence (RTP) and the systems with predominant oxygen functionalities. In this work, photophysical properties of the polyhydroxy polymers, including microcrystalline cellulose (MCC), 2-hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), and cellulose acetate (CA), were studied and compared. While MCC, HEC, and HPC solids showed bright emission alongside distinct RTP, CA demonstrated relatively low intensity of solid emission without noticeable RTP. Their emissions were explained in terms of the clustering-triggered emission (CTE) mechanism and conformation rigidification. Additionally, on account of its intrinsic emission, concentrated HEC aqueous solution could be used as the probe for the detection of 2,4,6-trinitrophenol (TNP).

Deciphering the emission mechanism of nonconventional luminogens and achieving persistent room temperature phosphorescence (p-RTP) from pure organic compounds have drawn increasing attention due to their significant fundamental importance and promising applications. Previous reports on nonconventional luminogens, however, mainly focus on fluorescence, while advances in pure organic p-RTP are generally restricted to aromatic crystals or host–guest systems. Herein, we report the unique intrinsic emission and moreover p-RTP in amorphous nonaromatic polymers of poly(acrylic acid) (PAA), polyacrylamide (PAM) and poly(N-isopropylacrylamide) (PNIPAM). These polymers are nonluminescent in dilute solutions, while being highly emissive in concentrated solutions, nanosuspensions and solid powders/films. This can be rationalized by the clustering-triggered emission (CTE) mechanism, as supported by further thermoresponsive emission, cryogenic and aggregation-induced emission (AIE) experiments, alongside single crystal analysis. Furthermore, PAA and PAM solids under ambient conditions, and PNIPAM solids under vacuum or under nitrogen, demonstrate distinct p-RTP, which can be enhanced through further ionization or pressurization. These results not only refresh our understanding of the emission mechanism of nonaromatic polymers, but also enable the facile fabrication and application of pure organic p-RTP luminogens from readily available compounds, thus providing an important step forward in both nonconventional luminogens and p-RTP.

Fabrication of efficient solid luminogens with tunable emission is both fundamentally significant and technically important. Herein, based on our previous strategy for the construction of efficient and multifunctional solid luminogens through the combination of diverse aggregation-induced emission (AIE) units with other functional moieties, a group of luminophores with electron donor-acceptor (D-A) structure and typical intramolecular charge transfer (ICT) characteristics, namely CZ-DCDPP, DPA-DCDPP and DBPA-DCDPP were synthesized and investigated. The presence of twisting and AIE-active 2,3-dicyano-5,6-diphenylpyrazine (DCDPP) moiety endows them highly emissive in the solid states, whereas the introduction of arylamines with varied electron-donating capacity and different conjugation render them with tunable solid emissions from green to red. While CZ-DCDPP and DPA-DCDPP solids exhibit distinct mechanochromism, both DPA-DCDPP and DBPA-DCDPP solids can generate efficient red emission. Owing to their high efficiency, remarkable thermal and morphological stabilities and moreover red emission, they are promising for diverse optoelectronic and biological applications.

Nonaromatic, cross-conjugated, and highly twisted luminogens consisting of acylated succinimides demonstrate aggregation-induced emission (AIE) characteristics and tunable multicolor photoluminescence and afterglows in their single crystals. Effective through-space conjugation among different moieties bearing n/π electrons promote the SOC and ISC transitions and lead to diverse emissive clusters with concurrently rigidified conformations, thus allowing readily tunable emissions. Derived from it, the proof of concept application for advanced anti-counterfeiting is illustrated. These results should spur the rational design of novel nonaromatic AIEgens, and moreover advance the understanding of the origin of tunable multicolor afterglows.

Persistent room-temperature phosphorescence (p-RTP) from pure organics is attractive due to its fundamental importance and potential applications in molecular imaging, sensing, encryption, anticounterfeiting, etc.1-4 Recently, efforts have been also made in obtaining color-tunable p-RTP in aromatic phosphors5 and nonconjugated polymers6,7. The origin of color-tunable p-RTP and the rational design of such luminogens, particularly those with explicit structure and molecular packing, remain challenging. Noteworthily, nonconventional luminophores without significant conjugations generally possess excitation-dependent photoluminescence (PL) because of the coexistence of diverse clustered chromophores6,8, which strongly implicates the possibility to achieve color-tunable p-RTP from their molecular crystals assisted by effective intermolecular interactions. Here, inspirited by the highly stable double-helix structure and multiple hydrogen bonds in DNA, we reported a series of nonconventional luminophores based on hydantoin (HA), which demonstrate excitation-dependent PL and color-tunable p-RTP from sky-blue to yellowish-green, accompanying unprecedentedly high PL and p-RTP efficiencies of up to 87.5% and 21.8%, respectively. Meanwhile, the p-RTP emissions are resistant to vigorous mechanical grinding, with lifetimes of up to 1.74 s. Such robust, color-tunable and highly efficient p-RTP render the luminophores promising for varying applications. These findings provide mechanism insights into the origin of color-tunable p-RTP, and surely advance the exploitation of efficient nonconventional luminophores.

Pure organic room-temperature phosphorescence (RTP) and luminescence from nonconventional luminophores have gained increasing attention. However, it remains challenging to achieve efficient RTP from unorthodox luminophores, on account of the unsophisticated understanding of the emission mechanism. Herein, we propose a strategy to realize efficient RTP in nonconventional luminophores through incorporation of lone pairs together with clustering and effective electronic interactions. The former promotes spin-orbit coupling and boosts the consequent intersystem crossing, whereas the latter narrows energy gaps and stabilizes the triplets, thus synergistically affording remarkable RTP. Experimental and theoretical results of urea and its derivatives verify the design rationale. Remarkably, RTP from thiourea solids with unprecedentedly high efficiency of up to 24.5 % is obtained. Further control experiments testify the crucial role of through-space delocalization on the emission. These results will spur the future fabrication of nonconventional phosphors and advance the understanding of the underlying emission mechanism.

Pure organic persistent room-temperature phosphorescence (p-RTP) under ambient conditions is attractive but challenging due to the slow intersystem crossing process and susceptibility of triplet excitons. Fabrication of pure organic RTP luminogens with simultaneously high efficiency and ultralong lifetime still remains a daunting job, owing to their conflicting requirements for the T1 nature of (n,π*) and (π,π*) characteristics, respectively. Herein, a group of amide-based derivatives with efficient p-RTP is developed through the incorporation of spin-orbital-coupling-promoting groups of carbonyl and aromatic π units, giving impressive p-RTP with lifetime and efficiency of up to 710.6 ms and 10.2%, respectively. Furthermore, two of the luminogens demonstrate intense p-RTP after vigorous mechanical stimulation, indicating their robust nature, which is rarely encountered. Efficient and robust p-RTP even in the amorphous state endows them promising potential for encryption and bioimaging with facile fabrication processes. A bioimaging study with live mice indicates that such highly robust p-RTP is tremendously beneficial for in vivo afterglow imaging with an ultrahigh signal-to-background ratio of 428. These results strongly imply the possibility of realizing efficient and robust p-RTP from pure organics even without meticulous protection, thus paving the way to their promising and versatile applications.