Organic luminogens with persistent room temperature phosphorescence (RTP) have attracted great attention for their wide applications in optoelectronic devices and bioimaging. However, these materials are still very scarce, partially due to the unclear mechanism and lack of designing guidelines. Herein we develop seven 10-phenyl-10H-phenothiazine-5,5-dioxide-based derivatives, reveal their different RTP properties and underlying mechanism, and exploit their potential imaging applications. Coupled with the preliminary theoretical calculations, it is found that strong π–π interactions in solid state can promote the persistent RTP. Particularly, CS-CF3 shows the unique photo-induced phosphorescence in response to the changes in molecular packing, further confirming the key influence of the molecular packing on the RTP property. Furthermore, CS-F with its long RTP lifetime could be utilized for real-time excitation-free phosphorescent imaging in living mice. Thus, our study paves the way for the development of persistent RTP materials, in both the practical applications and the inherent mechanism.

Persistent room temperature phosphorescence (RTP) from pure organic luminogens can be rationally realized based on the crystallization-induced phosphorescence phenomenon and severe crystallization. A perfect crystal with dense molecular packing and effective inter-molecular interactions isolates the triplet excitons from quenching sites and significantly blocks the high-energy vibrational dissipation, thus yielding long-lasting RTP.

Afterglow imaging that detects photons after cessation of optical excitation avoids tissue autofluorescence and thus possesses higher sensitivity than traditional fluorescence imaging. Purely organic molecules with room‐temperature phosphorescence (RTP) have emerged as a new library of benign afterglow agents. However, most RTP luminogens only emit visible light with shallow tissue penetration, constraining their in vivo applications. This study presents an organic RTP nanoprobe (mTPA‐N) with emission in the NIR range for in vivo afterglow imaging. Such a probe is composed of RTP molecule (mTPA) as the phosphorescent generator and an NIR‐fluorescent dye as the energy acceptor to enable room‐temperature phosphorescence resonance energy transfer (RT‐PRET), ultimately resulting in redshifted phosphorescent emission at 780 nm. Because of the elimination of background noise and redshifted afterglow luminescence in a biologically transparent window, mTPA‐N permits imaging of lymph nodes in living mice with a high signal‐to‐noise ratio. This study thus opens up a universal approach to develop organic RTP luminogens into NIR afterglow imaging agents via construction of RT‐PRET.

Long-lived phosphorescence at room temperature (RTP) from pure organic molecules is rare. Recent research reveals various crystalline organic molecules can realize RTP with lifetimes extending to the magnitude of second. There is little research on how molecular packing affecting RTP. Three compounds are designed with similar optical properties in solution, but tremendously different solid emission characteristics. By investigating the molecular packing arrangement in single crystals, it is found that the packing style of the compact face to face favors of long phosphorescence lifetime and high photoluminescence efficiency, with the lifetime up to 748 ms observed in the crystal of CPM ((9H-carbazol-9-yl)(phenyl)methanone). Theoretical calculation analysis also reveals this kind of packing style can remarkably reduce the singlet excited energy level and prompt electron communication between dimers. Surprisingly, CPM has two very similar single crystals, labeled as CPM and CPM-A, with almost identical crystal data, and the only difference is that molecules in CPM-A crystal take a little looser packing arrangement. X-ray diffraction and cross-polarization under magic spinning C NMR spectra double confirm that they are different crystals. Interestingly, CPM-A crystal shows negligible RTP compared to the CPM crystal, once again proving that the packing style is critical to the RTP property.

In this review, we survey the progress of triboluminescent compounds, which exhibit attractive emissions upon mechanical stimuli without the need for other stimulation or irritation. In particular, we present the research history, observed phenomena, proposed possible mechanisms, different types of triboluminescent compounds, and potential applications in an attempt to find the inherent clues hidden in the scattered literature. Accordingly, we provide some outlooks at the end of the paper for further exploration in this field.

We report the first example of an AIEgen (DPP-BO) with fluorescence-phosphorescence dual emission under mechanical stimulation. By carefully analyzing the crystal structure of DPP-BO, the efficient intermolecular and intramolecular interactions should account for its unique mechanoluminescence (ML) properties, especially the abnormal phosphorescence, as further confirmed by controlled experiments and theoretical calculations for the presence of ISC transitions. These results provide important information for understanding the complex ML process, possibly opening up a new way to study the inherent mechanism of ML by broadening the application of AIEgens.

Long-lived RT phosphorescence was achieved with a series of organic boron-containing compounds due to the rigid conformation and effective π–π stacking in the solid states.

Two crystalline polymorphs of TMPE (Cp-form and Cc-form) exhibit totally different mechanoluminescence properties.