Highly Efficient and Robust Full-Color Organic Afterglow through 2D Superlattices Embedment

Multi-Stimuli-Responsive Carbon Dots with Intrinsic Photochromism and In Situ Radical Afterglow

The combination of advanced photoluminescence characteristics to photochromism is highly attractive in preparing high-performance multifunctional photo-responsive materials for optoelectronic applications. However, this is rather challenging in material design owing to the limited mechanism understanding and construction principles. Here, an effective strategy to integrate photochromism and afterglow emission in carbon dots (CDs) is proposed through embedding naphthaleneimide (NI) structure in CDs followed by polyvinylpyrrolidone (PVP) encapsulation. The NI-structured CDs-PVP shows intrinsic photochromism owing to the in situ formation of NI-radical anions and controllable multi-stimuli-responsive afterglow behaviors related to the oxygen-trigged triplet exciton quenching and Förster resonance energy transfer (FRET) from the pristine CDs to the photoactivated CDs radicals. Notably, a wide range of appearance colors from colorless to brown, luminescence color transition from blue to yellow, and much elongated afterglow lifetime up to 253 ms are observed. With the extraordinary stimuli-chromic and stimuli-luminescent CDs-PVP film dynamically responsive to multiple external stimuli, reversible secure snapchat, data encryption/decryption and synaptic imaging recognition are realized. These findings demonstrate a fundamental principle to design multi-stimuli-responsive photochromic CDs with afterglow, providing important understandings on the synergic mechanism of dynamic photochromism and emission behaviors and thereby expanding their applications in advanced information anti-counterfeiting and artificial intelligence.

Stimulating Chiral Selective Expression of Room Temperature Phosphorescence for Chirality Recognition

Chiral recognition is crucial for applications in chiral purity assessment and biomedical fields. However, achieving chiral recognition through visible room temperature phosphorescence remains challenging. Here, two chiral molecules, designated as host and guest are synthesized, which possess similar structural configurations. A viable strategy involving a chiral configuration-dependent energy transfer process to enable selective phosphorescence expression is proposed, thereby enabling chiral recognition in a host-guest doping system. The chiral and structural similarity between host and guest facilitates efficient Dexter energy transfer due to the reduced spatial distance between the molecules. This mechanism significantly enhances the intensity of red phosphorescence from the guest molecule, characterized by an emission peak at 612 nm and a prolonged lifetime of 32.7 ms. This work elucidates the mechanism of chiral-dependent energy transfer, demonstrating its potential for selectively expressing phosphorescence in chiral recognition.

Exciton Dissociation and Recombination Afford Narrowband Organic Afterglow Through Efficient FRET

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33 nm, long persistent time over 10 s, and facile color-tuning in a wide range from deep-blue to orange (414-600 nm). Moreover, with the extraordinary narrowband LPL and easy processability of the material, centimeter-scale flexible optical waveguide fibers and integrated FWHM/color/lifetime-resolved multilevel encryption/decryption devices have been designed and fabricated. This novel EDR and singlet/triplet-to-singlet FRET strategy to achieve excellent LPL performances illustrates a promising way for constructing flexible organic afterglow with easy preparation methods, shedding valuable scientific insights into the design of narrow-band emission in organic afterglow.

Ultrahigh-Temperature Long-Persistent Luminescence from B2O3-Confined Polycyclic Aromatic Compounds

Organic molecules and polymers have recently been intensively explored for afterglow materials owing to their low cost and flexible design. However, they normally fail to generate long-persistent luminescence at elevated temperatures, mostly due to the fast deactivation of triplet excited states. Here, we report that polycyclic aromatic compounds (PACs) individually confined in a B2O3 crystalloid emit long-persistent luminescence at high temperatures up to 400 °C. This is facilely accomplished by dispersing a series of aromatic derivatives in an aqueous solution of boric acid, followed by drying, melting, and dehydrating. The resulting highly rigid and thermostable B2O3 crystalloid network provides a matched ultrastrong confinement effect and completely restricts the vibration and rotation of the molecularly distributed PACs even at ultrahigh temperatures and thereby prevents the nonradiative dissipation of triplet excitons and promotes the generation of ultrahigh-temperature long-persistent luminescence. The afterglow colors are responsive to both temperature and time, spanning from ultraviolet to near-infrared regions over a wide temperature range, which is substantially modulated by the subtle balance of phosphorescence and thermally activated delayed fluorescence. These features favor the creation of advanced afterglow materials for visual 3D temperature probing, anticounterfeiting, and data encryption in extreme environments.

Supramolecular Assembly of Hydrogen-Bonded Organic Frameworks with Carbon Dots: Realizing Ultralong Aqueous Room-Temperature Phosphorescence for Anticounterfeiting

Room-temperature phosphorescent carbon dots (RTP-CDs) have received increasing attention due to their excellent optical properties and potential applications. Nevertheless, the realization of RTP-CDs in aqueous solutions remains a considerable challenge due to the water-molecule- and oxygen-induced deactivation of the triplet excitons, which leads to phosphorescence quenching. In this study, ultralong phosphorescence in water was achieved by in situ self-assembly of CDs encapsulated in a rigid hydrogen-bonded organic framework (HOF). The phosphorescence lifetime reaches an impressive 956.96 ms and exhibits long-lasting optical and structural stability in water for more than 90 days. The composite material not only has ultralong luminescence life and excellent luminescence stability but also has two-color phosphorescence emission, as well as excellent antiphotobleaching and phosphorescence stability in aqueous solution, which can solve the current problem that RTP is easily burst out by water and moisture. In addition, this study introduced a fluorescent dye based on the triplet-singlet Förster resonance energy transfer system (TS-FRET) to fine-tune the afterglow properties. This work will inspire the design of RTP systems with dual phosphor light sources and provide new strategies for the development of smart RTP materials in water.

Targeting Compact and Ordered Emitters by Supramolecular Dynamic Interactions for High-performance Organic Ambient Phosphorescence

Purely organic room-temperature phosphorescence (RTP) materials have received intense attention due to their fascinating optical properties and advanced optoelectronic applications. The promotion of intersystem crossing (ISC) and minimalization of nonradiative dissipation under ambient conditions are key prerequisites for realizing high-performance organic RTP; However, the ISC process is generally inefficient for organic fluorogens and the populated triplet excitons are always too susceptible to be well stabilized by conventional means. Particularly, organizing organic fluorophores into compact and ordered entities by supramolecular dynamic interactions has proven to be a newly-emerged strategy to boost the ISC process greatly and suppress the non-radiative relaxations immensely, facilitating the population and stabilization of triplet excitons to access high-performance organic RTP. Consequently, well-defined organic emitters enable robust RTP emission even in the solution state, thus greatly extending the applications. Here, this review is focused on a timely and brief introduction to recent progress in tailoring ordered high-performance RTP emitters by supramolecular dynamic interactions. Their typical preparation strategies, optoelectronic properties, and applications are thoroughly summarized. In the summary section, key challenges and perspectives of this field are highlighted to suggest potential directions for future study.

Stepwise Stiffening Chromophore Strategy Realizes a Series of Ultralong Blue Room-Temperature Phosphorescent Materials

Ultralong room-temperature phosphorescent (URTP) materials have attracted wide attention in anti-counterfeiting, optoelectronic display, and bio-imaging due to their special optical properties. However, room-temperature blue phosphorescent materials are very scarce during applications because of the need to simultaneously populate and stabilize high-energy excited states. In this work, a stepwise stiffening chromophore strategy is proposed to suppress non-radiative jump by continuously reducing the internal spin of the chromophore, and successfully developing a series of blue phosphorescent materials. Phosphorescence lifetimes of more than 3 s are achieved, with the longest lifetime reaching 5.44 s and lasting more than 70 s in the naked eye. As far as is know, this is the best result that has been reported. By adjusting the chromophore conjugation, multicolor phosphorescences from cyan to green have been realized. In addition, these chromophores exhibit the same excellent optical properties in urea and polyvinyl alcohmance (PVA). Finally, these materials are successfully applied to luminescent displays.

Achieving Bright and Long-Lived Aqueous Room-Temperature Phosphorescence of Carbon Nitrogen Dots Through In Situ Host-Guest Binding

The development of bright and long-lived aqueous room-temperature phosphorescent (RTP) materials holds paramount importance in broadening the application scope of RTP material system. However, the conventional RTP materials usually exhibit low efficiency and short lifetime in aqueous solution. Herein, an in situ host-guest strategy is proposed to achieve cyanuric acid (CA)-derived phosphorescent carbon nitrogen dots (CNDs) composite (CNDs@CA) that demonstrates a significant enhancement of both quantum yield (QY) and lifetime mediated by water. Detailed investigations reveal that the robust hydrogen bonding networks between CNDs@CA and water effectively stabilize triplet excitons and suppress nonradiative decays, as well as facilitate efficient energy transfer from CA to CNDs, thereby prolonging the lifetime and enhancing the efficiency of RTP. The phosphorescent QY and lifetime of CNDs@CA can be increased to 26.89% (3.9-fold increase) and 951.25 ms (5.5-fold increase), respectively, with the incorporation of 50 wt% water under ambient conditions. Even in fully aqueous environments (with up to 400 wt% water added), CNDs@CA exhibits persistent water-boosted RTP properties, demonstrating exceptional stability. The robust water-boosted RTP property of CNDs@CA in aqueous solutions presents significant potential for high signal-to-noise ratio afterglow bioimaging as well as advanced information encryption.

Visible-light-excited robust room-temperature phosphorescence of dimeric single-component luminophores in the amorphous state

Organic room temperature phosphorescence (RTP) has significant potential in various applications of information storage, anti-counterfeiting, and bio-imaging. However, achieving robust organic RTP emission of the single-component system is challenging to overcome the restriction of the crystalline state or other rigid environments with cautious treatment. Herein, we report a single-component system with robust persistent RTP emission in various aggregated forms, such as crystal, fine powder, and even amorphous states. Our experimental data reveal that the vigorous RTP emissions rely on their tight dimers based on strong and large-overlap π-π interactions between polycyclic aromatic hydrocarbon (PAH) groups. The dimer structure can offer not only excitons in low energy levels for visible-light excited red long-lived RTP but also suppression of the nonradiative decays even in an amorphous state for good resistance of RTP to heat (up to 70 °C) or water. Furthermore, we demonstrate the water-dispersible nanoparticle with persistent RTP over 600 nm and a lifetime of 0.22 s for visible-light excited cellular and in-vivo imaging, prepared through the common microemulsion approach without overcaution for nanocrystal formation.

Anionic Hydrogen-Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone

Tautomers coexisting in an equilibrium system have significant potential for regulating luminescent properties because of their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this study, it is found that hydrogen-bonded organic frameworks (HOFs) composed of Br- anions can effectively separate and stabilize two proton-transfer tautomers of triarylformamidinium bromide: namely, the nitrogen cation (BA-N) and carbon cation (BA-C). The BA-N crystal consisting of a dense anionic HOF and parallelly aligned organic cations exhibits green thermally activated delayed fluorescence and red room-temperature phosphorescence (RTP). The BA-C crystal contains acetone molecules that induce an antiparallel arrangement of the organic cations to form a loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, switching of the HOFs between BA-N and BA-C can be achieved through the uptake and release of acetone, thereby dynamically adjusting multiple luminescent properties. Consequently, the HOF crystals can be used for the highly sensitive and specific sensing of acetone with a detection limit of 66.74 ppm. This study not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with a sensitive response to a stimulus.

Twofold rigidity activates ultralong organic high-temperature phosphorescence

A strategy is pioneered for achieving high-temperature phosphorescence using planar rigid molecules as guests and rigid polymers as host matrix. The planar rigid configuration can resist the thermal vibration of the guest at high temperatures, and the rigidity of the matrix further enhances the high-temperature resistance of the guest. The doped materials exhibit an afterglow of 40 s at 293 K, 20 s at 373 K, 6 s at 413 K, and a 1 s afterglow at 433 K. The experimental results indicate that as the rotational ability of the groups connected to the guests gradually increases, the high-temperature phosphorescence performance of the doped materials gradually decreases. In addition, utilizing the property of doped materials that can emit phosphorescence at high temperatures and in high smoke, the attempt is made to use organic phosphorescence materials to identify rescue workers and trapped personnel in fires.

Cucurbit[8]uril Confinement-Based Secondary Coassembly for High-Efficiency Phosphorescence Energy Transfer Behavior

Aqueous supramolecular long-lived near-infrared (NIR) material is highly attractive but still remains great challenge. Herein, we report cucurbit[8]uril confinement-based secondary coassembly for achieving NIR phosphorescence energy transfer in water, which is fabricated from dicationic dodecyl-chain-bridged 4-(4-bromophenyl)-pyridine derivative (G), cucurbit[8]uril (CB[8]), and polyelectrolyte poly(4-styrene-sulfonic sodium) (PSS) via the hierarchical confinement strategy. As compared to the dumbbell-shaped G, the formation of unprecedented linear polypseudorotaxane G⊂CB[8] with nanofiber morphology engenders an emerging phosphorescent emission at 510 nm due to the macrocyclic confinement effect. Moreover, benefiting from the following secondary assembly confinement, such tight polypseudorotaxane G⊂CB[8] can further assemble with anionic polyelectrolyte PSS to yield uniform spherical nanoparticle, thereby significantly strengthening phosphorescence performance with an extended lifetime (i.e., 2.39 ms, c.f., 45.0 μs). Subsequently, the organic dye Rhodamine 800 serving as energy acceptor can be slightly doped into the polyelectrolyte assembly, which enables the occurrence of efficient phosphorescence energy transfer process with efficiency up to 80.1% at a high donor/acceptor ratio, and concurrently endows the final system with red-shifted and long-lived NIR emission (710 nm). Ultimately, the as-prepared assembly is successfully exploited as versatile imaging agent for NIR window labeling and detecting in living cells.

Stimulating Phonon Bottleneck Effect in Organic Semiconductors by Charge-Transfer-Mediated J-Aggregation

Hot carriers rapidly lose kinetic energies on a subpicosecond time scale, posing significant limitations on semiconductors' photon-conversion efficiencies. To slow the hot carrier cooling, the phonon bottleneck effect is constructed prevalently in quantum-confined structures with discrete energy levels. However, the maximum energy separation (ΔEES) between the energy levels is in a range of several hundred meV, leading to unsatisfactory cooling time. To address this, we design a novel organic semiconductor capable of forming intermolecular charge transfer (CT) in J-aggregates, where the lowest singlet excited state (S1) splits into two states due to the significant interplay between the Coulomb interaction and intermolecular CT coupling. The ΔEES between the two states can be adjusted up to 1.02 eV, and an extremely slow carrier cooling process of ∼72.3 ps was observed by femtosecond transient absorption spectroscopy. Moreover, the phonon bottleneck effect was identified in organic materials for the first time, and CT-mediated J-aggregation with short-range interactions was found to be the key to achieving large ΔEES. The significantly prolonged carrier cooling time, compared to <100 fs in the isolated molecule (10-6 M), highlights the potential of organic molecules with diversified aggregation structures in achieving long-lived hot carriers. These findings provide valuable insights into the intrinsic photophysics of electron-phonon scattering in organic semiconductors.

High-Quality Circularly Polarized Organic Afterglow from Nonconjugated Amorphous Chiral Copolymers

Organic materials featuring circularly polarized luminescence (CPL) and/or afterglow emission represent an active research frontier with promising applications in various fields, but the achievement of high-performance CPL organic afterglow (CPOA) remains a huge challenge due to the intrinsic contradictions between the luminescent lifetime/dissymmetry factor (glum) and phosphorescent quantum efficiency (PhQY). Herein, we report a simple and universal approach to design efficient CPOA from amorphous copolymers by incorporating chiral chromophores into a nonconjugated clusterization-triggered emissive polymer with plenty of hydron-bonding interactions, followed by aggregation engineering using water dissolution and evaporation. With this chiral copolymerization and aggregation engineering (CCAE) strategy, high-performance CPOA polymers with PhQYs of up to 6.32%, ultralong lifetimes of over 650 ms, glum values of 3.54 × 10-3, and the highest figure-of-merit were achieved at room temperature. Given the impressive CPOA performance of these polymers, the applications in multilevel data anticounterfeiting and reversible displays with high stability were demonstrated. These findings through the CCAE strategy to overcome the inherent restraints of CPOA materials lay the foundation for the development of amorphous polymers with superior CPOA, significantly expanding the understanding of CPL and the design of organic afterglow materials.

Afterglow/Photothermal Bifunctional Polymeric Nanoparticles for Precise Postbreast-Conserving Surgery Adjuvant Therapy and Early Recurrence Theranostic

Adjuvant whole-breast radiotherapy is essential for breast cancer patients who adopted breast-conserving surgery (BCS) to reduce the risk of local recurrences, which however suffer from large-area and highly destructive ionizing radiation-induced adverse events. To tackle this issue, an afterglow/photothermal bifunctional polymeric nanoparticle (APPN) is developed that utilizes nonionizing light for precise afterglow imaging-guided post-BCS adjuvant second near-infrared (NIR-II) photothermal therapy. APPN consists of a tumor cell targeting afterglow agent, which is doped with a NIR dye as an afterglow initiator and a NIR-II light-absorbing semiconducting polymer as a photothermal transducer. Such a design realizes precise afterglow imaging-guided NIR-II photothermal ablation of minimal residual breast tumor foci after BCS, thus achieving complete inhibition of local recurrences. Moreover, APPN enables early diagnosis and treatment of local recurrence after BCS. This study thus provides a nonionizing modality for precision post-BCS adjuvant therapy and early recurrence theranostic.