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Room‐temperature phosphorescence (RTP) materials have attracted significant attention due to their applications in various fields such as information storage and encryption, organic light‐emitting diode (OLED), sensing, lighting and display, biological imaging, and photodynamic therapy. Traditionally, RTP materials can be efficiently developed using inorganic systems with noble metals or rare earth elements. Recently, many efforts have been devoted to the development of RTP materials based on small organic molecules. The strategies to construct RTP materials include hydrogen bonding, heavy atom effect, n–π* transitions, π–π stacking, donor–acceptor effect, and host–guest doping. Herein, we summarize the recent examples of RTP materials based on small organic molecules primarily focusing on their design strategies and properties. Moreover, their promising applications in information encryption, OLED, as well as bio‐imaging and phototherapy are discussed. The challenges and perspectives are given to provide inspiration toward the future development of organic RTP materials. This review summarizes the design strategies to construct room‐temperature phosphorescence (RTP) materials based on small organic molecules and their promising applications in information encryption, organic light‐emitting diode, as well as bio‐imaging and phototherapy. The challenges and perspectives are given to provide inspiration toward the future development of organic RTP materials.

The development of organic room-temperature phosphorescent (ORTP) materials represents an active field of research due to their significant advantages with respect to their organometallic counterparts. Two cyclic triimidazole (TT) derivatives bearing one and three hexyl-thiophene moieties, TT-HThio and TT-(HThio)3, have been prepared and characterized. Both compounds display enhanced quantum yields in their crystalline form with respect to those in a solution state, revealing crystallization-enhanced emissive (CEE) behavior. Importantly, while single fluorescence is observed in solution, crystalline powders also feature dual ORTP, whose respective molecular and aggregate origins have been disclosed through X-ray diffraction analysis and DFT/TDDFT calculations. The relation between the photophysical properties of TT-HThio and its crystallinity degree has been confirmed by a decrease in photoluminescent quantum yield (Φ) and loss of vibronic resolution when its crystals are ground in a mortar, revealing mechanochromic behavior and confirming CEE features.

The strong light emission of organic luminogens in the aggregated state is essential to their applications as optoelectronic materials with good performance. In this review, with respect to the aggregation‐induced emission and room‐temperature phosphorescence luminogens, the important role of molecular packing modes is highlighted. As demonstrated in the selected examples, the molecular packing status in the aggregate state is affected by many factors, including the molecular configurations, the inherent electronic properties, the special functional groups, and so on. With the consideration of all these parameters, the strong fluorescence and phosphorescence in the aggregated state could be achieved in the rationally designed organic luminogens, providing some guidance for the further development. The packing modes in aggregated state play an crucial role in the light‐emission behaviors, especially for aggregation‐induced emission and room‐temperature phosphorescence luminogens. In this review, the possible correlation of molecular structures, packing modes, and the fluorescence and phosphorescence in solid state, has been summarized by the investigation of corresponding crystal structures in typical examples.

Currently, there is a strong drive to discover alternative materials that exhibit room‐temperature phosphorescence (RTP) for displays, bioimaging, and data security. Ideally, these materials should be nontoxic, cheap, and possess controllable photoluminescent properties. Carbon dots (CDs) possess each of these characteristics, but to date, less attention has been paid to their RTP mechanism. Herein, we synthesized a series of CDs by self‐crosslinking and carbonization of precursor. The resultant CDs were luminescent and exhibited a bright, micro‐second afterglow lifetime. To increase the RTP, a second microwave processing step was used to coat the CDs with polyvinyl alcohol (PVA), polyacrylamide (PAM), or tetraethyl orthosilicate (TEOS), producing CDs@PVA, CDs@PAM, and CDs@TEOS composites. The core–shell structure acted to enhance crosslinking at the surface of the CDs to boost the RTP, creating abundant energy levels for intersystem crossover. In situ X‐ray photoelectron spectroscopy verified electron transfer during luminescence. Finally, we present a design rule that can be used to tune the quantum yields and RTP lifetime of CDs, based on the effective stabilization of triplet excited states through the extent and strength of cross‐linking. This simple strategy provides a flexible route for guiding the further development of CDs with tailored RTP properties for various applications. We propose a method to enhance phosphorescence emission by crosslinking. By controlling the degree and strength of crosslinking, the phosphorescence emission of carbon dots (CDs) can be tunable, and the CDs with the highest degree of crosslinking achieve a quantum yield of 55.49 and a lifetime of 750 ms.

Metal‐free room‐temperature phosphorescence (RTP) materials are of great significance for many applications; however, they usually exhibit low efficiency and weak intensity. This article reports a new strategy for the preparation of a high‐efficiency and strong RTP materials from crystalline thermal‐annealed carbon dots (CDs) and boric acid (BA) composite (g‐t‐CD@BA) through grinding‐induced amorphous to crystallization transition. Amorphous thermal‐annealed CDs and BA composite (t‐CD@BA) is prepared following a thermal melting and super‐cooling route, where the CDs are fully dispersed in molten BA liquid and uniformly frozen in an amorphous thermal annealed BA matrix after super‐cooling to room temperature. Upon grinding treatment, the fracture and fragmentation caused by grinding promote the transformation of the high‐energy amorphous state to the lower energy crystalline counterparts. As a result, the CDs are uniformly in situ embedded in the BA crystal matrix. This method affords maximum uniform embedding of the CDs in the BA crystals, decreases nonradiative decay, and promotes intersystem crossing by restraining the free vibration of the CDs, thus producing strong RTP materials with the highest reported phosphorescence quantum yield (48%). Remarkably, RTP from g‐t‐CD@BA powder is strong enough to illuminate items with a delay time exceeding 9 s. We present a new grinding‐induced amorphous‐to‐crystalline transition method for the preparation of crystalline carbon dots (CDs) and boric acid (BA) composite (g‐t‐CD@BA), that exhibits a world‐record phosphorescence efficiency of 48% and ultra‐strong RTP. Remarkably, the intense green phosphorescence of the g‐t‐CD@BA can illuminate items for more than 9 s to the unaided eye.

Purely organic room‐temperature phosphorescence (RTP) materials generally exhibit low phosphorescence quantum yield (ϕP) and long phosphorescence lifetime (τP) due to the theoretically spin‐forbidden triplet state. Herein, by introducing a donor–acceptor (D–A) skeleton with a phenoxaselenine donor, three nonaromatic amine donor containing compounds with high ϕP and short τP in amorphous films are developed. Besides the enhanced spin–orbit coupling (SOC) by the heavy‐atom effect of selenium, the D–A skeleton which facilitates orbital angular momentum change can further boost SOC, and severe nonradiative energy dissipation is also suppressed by the rigid molecular structure. Consequently, a record‐high external quantum efficiency of 19.5% are achieved for the RTP organic light‐emitting diode (OLED) based on 2‐(phenoxaselenin‐3‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (PXSeDRZ). Moreover, voltage‐dependent color‐tunable emission and single‐molecule white emission are also realized. These results shed light on the broad prospects of purely organic phosphorescence materials as highly efficient OLED emitters especially for potential charming lighting applications. A record‐high external quantum efficiency approaching 20%, voltage‐dependent color‐tunable emissions and single‐molecule white emissions are realized for purely organic electro‐phosphorescence device employing a room‐temperature phosphorescence emitter with a planar donor–acceptor skeleton and a phenoxaselenine donor.

Persistent luminescence has attracted great attention due to the unique applications in molecular imaging, photodynamic therapy, and information storage, among many others. However, tuning the dynamic persistent luminescence through molecular design and materials engineering remains a challenge. In this work, the first example of excitation‐dependent persistent luminescence in a reverse mode for smart optical materials through tailoring the excited‐state proton transfer process of metal cytosine halide hybrids is reported. This approach enables ultralong phosphorescence and thermally activated delayed fluorescence emission colors highly tuned by modulation of excitation wavelength, time evolution, and temperature, which realize multi‐mode dynamic color adjustment from green to blue or cyan to yellow‐green. At the single crystal level, the 2D excitation/space/time‐resolved optical waveguides with triple color conversion have been constructed on the organic‐metal halide microsheets, which represent a new strategy for multi‐dimensional information encryption and optical logic gate applications. Reversed excitation‐dependent persistent luminescence can be obtained in metal cytosine halides by controlling the process of excited‐state proton transfer (ESIPT). The metal cytosine halides further exhibit multi‐mode (excitation/space/time) triple‐color luminescent conversion, which have promising applications in multi‐dimensional information encryption and photonic logic gates.

In order to improve the performance of organic luminescent materials, lots of studies have been carried out at the molecular level. However, these materials are mostly applied as solids or aggregates in practical applications, in which the relationship between aggregation structure and luminescent property should be paid more attention. Here, we obtained five phenothiazine 5,5‐dioxide (O‐PTZ) derivatives with distinct molecular conformations by rational design of chemical structures, and systematically studied their room‐temperature phosphorescence (RTP) effect in solid state. It was found that O‐PTZ dimers with quasi‐equatorial (eq) conformation tended to show stronger π‐π interaction than quasi‐axial (ax) conformers in crystal state, which was more conducive to the generation of RTP. Based on this result, a multi‐level structural model of organic solids was proposed to draw the relationship between aggregation structure and RTP effect, just like the research for the structure‐property relationship of proteins. Using this structural model as the guide, boosted RTP efficiency from 1% to 20% was successfully achieved in the corresponding host‐guest doping system, showing its wide applicability. Five phenothiazine 5,5‐dioxide (O‐PTZ) derivatives with distinct molecular conformations were obtained, and their room‐temperature phosphorescence (RTP) effects were studied. It was found that O‐PTZ dimers with quasi‐equatorial (eq) conformation were more conducive to generate RTP than quasi‐axial (ax)‐ones in crystal state. Accordingly, a multi‐level structural model of organic solids was proposed to draw the relationship between aggregation structure and RTP effect.

Despite ongoing research into photocontrolled supramolecular switches, reversible photoswitching between room‐temperature phosphorescence (RTP) and delayed fluorescence is rare in the aqueous phase. Herein, an efficient RTP‐fluorescence switch based on a cascaded supramolecular assembly is reported, which is constructed using a 6‐bromoisoquinoline derivative (G3), cucurbit[7]uril (CB[7]), sulfonatocalix[4]arene (SC4A4), and a photochromic spiropyran (SP) derivative. Benefiting from the confinement effect of CB[7], initial complexation with CB[7] arouses an emerging RTP signal at 540 nm for G3. This structure subsequently coassembles with amphiphilic SC4A4 to form tight spherical nanoparticles, thereby further facilitating RTP emission (≈12 times) in addition to a prolonged lifetime (i.e., 1.80 ms c.f., 50.1 µs). Interestingly, following cascaded assembly with a photocontrolled energy acceptor (i.e., SP), the efficient light‐driven RTP energy transfer occurs when SP is transformed to its fluorescent merocyanine (MC) state. Ultimately, this endows the final system with an excellent RTP–fluorescence photoswitching property accompanied by multicolor tunable long‐lived emission. Moreover, this switching process can be reversibly modulated over multiple cycles under alternating UV and visible photoirradiation. Finally, the prepared switch is successfully applied to photocontrolled multicolor cell labeling to offer a new approach for the design and fabrication of novel advanced light‐responsive RTP materials in aqueous environments. A highly reversible supramolecular photoswitch between room‐temperature phosphorescence (RTP) and delayed fluorescence is constructed. This photoswitch is based on a bromoisoquinoline cascaded assembly and is successfully prepared in the aqueous phase. It benefits from light‐driven supramolecular RTP energy transfer to exhibit multicolor tunable long‐lived emission, and is successfully applied to photocontrolled multicolor cell labeling.

Inorganic boric acid (BA) is generally not considered an efficient afterglow material, and several groups have reported its extremely weak room‐temperature phosphorescence (RTP) in the blue spectral region. It is discovered that heat treatment of BA results in increased afterglow intensity (27‐fold increase) and prolonged emission lifetime (from 0.83 to 1.59 s), attributed to enhanced through‐space conjugation (TSC) of BA. The afterglow intensity of BA can be increased further (≈415 folds) by introducing p‐hydroxybenzoic acid (PHA), which contains a conjugated molecular motif, to further promote the TSC of the BA system. This combination results in the production of afterglow materials with a photoluminescence quantum yield of 83.8% and an emission lifetime of 2.01 s. In addition, a tunable multicolor afterglow in the 420–490 nm range is achieved owing to the enhancement of the RTP and thermally activated delayed fluorescence of PHA, where BA exerts a confinement effect on the guest molecules. Thus, this study demonstrates promising afterglow materials produced from extremely abundant and simple precursor materials for various applications. By excluding the contribution of impurities to the afterglow of boric acid, the introduction of p‐hydroxybenzoic acid into the boric acid system leads to a 415‐fold increase in the afterglow intensity along with enhanced emission quantum yield of 83.8% and emission lifetime of 2.01 s.