Materials that exhibit X-ray excited luminescence have great potential in radiation detection, security inspection, biomedical applications, and X-ray astronomy [1][2][3][4] . However, such materials are almost exclusively limited to inorganic crystals, which are typically prepared under high temperatures 5 . Herein, we report a design principle of purely organic phosphors to boost X-ray excited luminescence with sufficient utilization of triplet excitons. Our experimental data reveal that proportion of emission from bright triplet excitons is significantly improved upon X-ray irradiation, compared with UV excitation. These organic phosphors have a detection limit of 33 nGy/s, which is 167 times lower than the standard dosage for X-ray medical examinations. We further demonstrated their potential application in X-ray radiography, which can be conveniently recorded using a digital camera. These findings illustrate a fundamental principle to design efficient X-ray excited purely organic phosphors, propelling the development of radioluminescence related applications.X-ray-responsive materials generally display large X-ray attenuation coefficients because of high atomic number elements, which have aroused intense research interest owing to their wide applications in bioimaging, radiotherapy, and non-destructive defect detection of industrial products [6][7][8][9][10] . Such X-ray-responsive materials include non-emissive radiocontrast agents (e.g., iohexol and iopromide) and scintillators that can convert high energy X-ray beam into low-energy visible photons 2,11,12 . To date, almost all reported X-ray-sensitive materials are limited to inorganic phosphors or organometallic materials containing heavy metals 13 . Purely organic materials, also termed as metal-free organic phosphors, have congenital advantages as scintillator candidates, including abundant resources, flexibility, mild preparation conditions, and environmental friendliness. However, weak X-ray absorption and low exciton utilization hinder the development of purely organic scintillators 12 , leaving it a formidable challenge. Purely organic phosphors are mainly made up of light atoms, such as C, H, N, etc., resulting in weak absorbance of X-ray (attenuation coefficient μ ∝Z , Equation S1). Besides, there only exists fluorescence from singlet excitons upon irradiation owing to weak spin-orbit coupling (SOC). In principle, almost all triplet excitons,

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bioavailability, etc.) can be modified by cocrystallization with coformers. Beyond active pharmaceutical ingredients, cocrystallization is being extensively or has also been established as a effective technique to change or improve the photoluminescence (PL) properties of the organic materials, [2][3][4][5][6] along with to discover the structure-property associations at a molecular level. [7,8] Room temperature phosphorescence (RTP), continuously one of the dynamic research fields in science and technology currently, due to extensive applications in various fields such as optoelectronics, [9] photomedicine, [10,11] sensing, [12,13] bioimaging, [14][15][16] encryption, [17,18] lighting, [19] logic gates, [20] and so on. The luminescence characteristics (such as lifetime, intensity and color) of RTP, can be effectively modified through molecular crystal engineering. [21][22][23] Phosphorescence is a radiative relaxation of excitons from the excited state having different spin multiplicity (triplet excited states) to ground state (Figure 1). Based on the quantum mechanics theory, [24] the transition between singlet to triplet is forbidden, that is, electrons cannot jump from singlet to triplet states. Generally, in all organic molecules ground states (S 0 ) are singlets; therefore, the emissive transition of singlet excitons from S 1 (lowest singlet excited state) to the S 0 is theoretically allowed, which is a fast process (fluorescence) with a very short lifetime (generally in nanoseconds). Contrary, the emissive transition of triplet excitons from T 1 (lowest triplet excited state) to the S 0, that is, phosphorescence exhibits comparatively much longer lifetime (microseconds to hours, may be in days), is theoretically forbidden and it is highly concerned with external conditions too, such as heat and oxygen (nonradiative transition). Therefore, for pure organic molecules with energy gaps (between S 1 and T 1 ) >0.5 eV, it is hard to achieve RTP, and the persistent RTP is even rare (typically lifetime > 0.1 s). Besides these, purely organic RTP materials have special features and advantages such as excellent molecular designable capability with modified properties, flexibility, being light weight, good stability, and processability, low toxicity, reduced manufacturing costs and compatibility with a vast range of substrates.Although, to date, many effective approaches, including design principles (based on halogen bonding, [25][26] H-aggregation, [16,27] and n-π transition [28,29] ) and RTP enhancement strategies Organic phosphorescent materials have attracted wide attention in recent years owing to their opportunities in various functional applications. Through appropriate molecular design strategies and synthetic perspectives to modulate their weak spin-orbit coupling, highly active triplet excitons, and ultrafast deactivation, the organic phosphors can be endowed with long-lived room temperature phosphorescence (RTP) characteristics. Organic cocrystals constructed by noncovalent intermolecular interactions (hyd...

Organic optoelectronic functional materials featuring circularly polarized emission and persistent luminescence represent a novel research frontier and show promising applications in data encryption, displays, biological imaging, and so on. Herein, we present a simple and universal approach to achieve circularly polarized organic phosphorescence (CPP) from amorphous copolymers by the incorporation of axial chiral chromophores into polymer chains via radical cross-linked polymerization. Our experimental data reveal that copolymers (R/S)-PBNA exhibit a maximum CPP efficiency of 30.6% and the largest dissymmetric factor of 9.4 × 10–3 and copolymers (R/S)-PNA show the longest lifetime of 0.68 s under ambient conditions. Given the CPP property of these copolymers, their potential applications in multiple information encryption and displays are demonstrated, respectively. These findings not only lay the foundation for the development of amorphous polymers with superior CPP but also expand the outlook of room-temperature phosphorescent materials.

Dynamic room-temperature phosphorescence (RTP) in organic materials is highly sensitive toward changes of external stimulus, representing the expansion of static RTP materials with fixed properties, and has gradually captured considerable attention. Different from the big breakthroughs in static organic RTP materials, dynamic organic RTP materials remain a clear improvement over luminescent mechanisms and molecular design rule. Therefore, we have reviewed the progress of organic RTP materials from static to dynamic phosphorescence and provide insight into the dynamic behaviors of RTP lifetime, color, intensity, and efficiency under different external stimuli, especially changes to the excitation source, such as irradiation time, intensity, and excitation wavelengths. Subsequently, we present some viewpoints on this promising field to strengthen the understanding of dynamic RTP characteristics. This Perspective may be beneficial for the future development of smart materials with dynamic RTP.

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Developing ultralong organic phosphorescence (UOP) materials with smart response to external stimuli is of great interest in photonics applications, whereas the manipulation of molecular stacking on tuning such dynamic UOP is still a formidable challenge. Herein, we have reported two polymorphs with distinct photoactivated dynamic UOP behavior based on a pyridine derivative for the first time. Our experiment revealed that the dynamic UOP behavior including photoactivation and deactivation feature is highly dependent on irradiation intensity and environmental atmosphere. Additionally, given the unique dynamic UOP feature, these phosphors have been successfully applied to phosphorescence-dependent molecular logic gate and timing data storage. This result not only paves a way to design smart functional materials but also expands the scope of the applications on organic phosphorescence materials.