Recent Advances of Cocrystals with Room Temperature Phosphorescence

Abstract

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...

Persistent Room‐Temperature Phosphorescence from Purely Organic Molecules and Multi‐Component Systems

“…Intense study has shown that heteroatoms (N, O, and S) or corresponding functional groups are especially useful in realizing efficient RTP. [ 106 ] Therefore, carbazole, [ 107 ] indoline, [ 108 ] quinoline, [ 109 ] phenothiazine, [ 110 ] and their derivatives [ 111 ] account for the majority of RTP luminophores. The reason is simple: these atoms and related moieties bear lone pairs which enhance the rate of the ISC process through El‐Sayed's rule.…”

Halide-containing organic persistent luminescent materials for environmental sensing applications

“…[11][12][13][14] Among them, halogen substitution has been proved to be one of the most effective design strategies. 15,16 The introduction of different halogen elements will realize OPL emission with signicantly tuneable intensity and lifetimes, making halide-containing OPL materials applicable to different environment sensing scenarios. 10,17 In addition, halogen elements contribute to the formation of halogen bond networks, remarkably restricting molecular motion or vibration and boosting the OPL emission.…”

Tuning Organic Room‐Temperature Phosphorescence through the Confinement Effect of Inorganic Micro/Nanostructures

“…Compared with fluorescence, phosphorescence involves longer excited lifetimes, larger Stokes shifts, and higher signal‐to‐noise ratios. [ 1–3 ] Because of these advantages, phosphorescent materials have great potential for use in sensors, [ 4,5 ] biological imaging, [ 6,7 ] light‐emitting diodes (LEDs), [ 8,9 ] information encryption, [ 10,11 ] and anticounterfeiting. [ 12,13 ]…”