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...

X-ray-induced photodynamic therapy utilizes penetrating X-rays to activate reactive oxygen species in deep tissues for cancer treatment, which combines the advantages of photodynamic therapy and radiotherapy. Conventional therapy usually requires heavy-metal-containing inorganic scintillators and organic photosensitizers to generate singlet oxygen. Here, we report a more convenient strategy for X-ray-induced photodynamic therapy based on a class of organic phosphorescence nanoscintillators, that act in a dual capacity as scintillators and photosensitizers. The resulting low dose of 0.4 Gy and negligible adverse effects demonstrate the great potential for the treatment of deep tumours. These findings provide an optional route that leverages the optical properties of purely organic scintillators for deep-tissue photodynamic therapy. Furthermore, these organic nanoscintillators offer an opportunity to expand applications in the fields of biomaterials and nanobiotechnology.

There are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X-ray irradiation, both m-BA and p-BA show excellent radioluminescence, while o-BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non-radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.Scintillators are a type of luminescence materials that can convert high energy photons or particles to visible photons, [1] which receive extensive attention in various fields, such as medical imaging [2] and irradiation detecting. [3] To date, scintillators are mainly divided into two categories, inorganic and organic scintillators. Compared with inorganic scintilla-

There are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X-ray irradiation, both m-BA and p-BA show excellent radioluminescence, while o-BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non-radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.Scintillators are a type of luminescence materials that can convert high energy photons or particles to visible photons, [1] which receive extensive attention in various fields, such as medical imaging [2] and irradiation detecting. [3] To date, scintillators are mainly divided into two categories, inorganic and organic scintillators. Compared with inorganic scintilla-

Purely organic room‐temperature phosphorescence (RTP) materials have attracted increasing attention due to their unique photophysical properties and widespread optoelectrical applications, but the pursuit of high quantum yield is still a continual struggle for RTP emission under ambient conditions. Here, a series of novel RTP molecules (26CIM, 246CIM, 24CIM, and 25CIM) are developed on the basis of indole luminophore, in which a carbonyl group bridges indole and chloro‐substituted phenyl group. The structural isomerism is systematically regulated toward enhancing the intramolecular‐space heavy‐atom effect, thus promoting the spin–orbit coupling and intersystem crossing for high RTP efficiency. While rationally modulating the intramolecular‐space heavy‐atom effect, the phosphorescence efficiency is dramatically increased by 16‐fold from 2.9% (24CIM) to 48.9% (26CIM). Basically, the fully occupied chlorine atoms at the positions 2 and 6 can effectively favor the stronger intramolecular H…Cl effect, and the tight lock coupling with anti‐parallel stacking in 26CIM further boosts RTP emission synergistically. The experimental findings along with deeper theoretical insights elucidate the structure–performance relationship clearly, and further suggest a general strategy for rationally constructing high‐efficiency RTP materials.

Phosphorescent cocrystal is one of the emerging room-temperature phosphorescence (RTP) materials. However, it remains a great challenge to understand the relationship between the phosphorescent properties and molecular aggregation. Herein, we prepared a series of organic cocrystals with RTP features composed of different alkyl chain lengths. It is worth noting that the phosphorescent lifetime varied by the different lengths of alkyl chains. For melamine−succinic acid cocrystal, the phosphorescence lifetime can reach up to 512 ms. From the single-crystal analysis, the longer lifetime was mainly attributed to the shorter distance of molecular stacking between phosphorescent chromophores resulting in smaller free volume. This study not only provides a simple method to prepare RTP materials but also explores the relationship between phosphorescent properties and molecular stacking in organic phosphorescent cocrystals.