Enhancing Ultralong Organic Phosphorescence by Effective π‐Type Halogen Bonding

Abstract

Efficient ultralong organic phosphorescent materials have potential applications in some fields, such as bioimaging, anti‐counterfeiting, and sensors. Nevertheless, phosphorescence efficiencies of metal‐free organic materials are low due to weak spin–orbit coupling and vigorous nonradiative transitions under ambient conditions. Here a chemical strategy to improve phosphorescence efficiency with intermolecular π‐type halogen bonding construction via isomerism is presented. X‐ray single crystal analysis reveals that different halogen bonding is formed among p‐BrTCz, m‐BrTCz, and o‐BrTCz crystals. Phosphorescence efficiency of m‐BrTCz in solid can reach 13.0%, seven times of o‐BrTCz in solid owing to effective π‐type halogen bonding, which is further confirmed by theoretical calculations. However, ultralong phosphorescence lifetimes are little affected, 155, 120, and 156 ms for p‐BrTCz, m‐BrTCz, and o‐BrTCz in the solid state, respectively. Furthermore, a simple pattern for data encryption and decryption is first demonstrated under sunlight. This result will provide an approach for improving the phosphorescent efficiency of metal‐free organic phosphors with ultralong luminescence.

Organic Room Temperature Phosphorescence Materials for Biomedical Applications

“…Furthermore, the phosphorescence quantum efficiency has been improved up to 38.1% through a valid strategy of intramolecular space heavy atom effect (molecule 2 ) . Besides, we have synthesized a serious of molecules 3 – 5 and compared the effect of different Br‐substituted positions which resulted in various π‐type halogen bonding . Introduction of hetero atoms is a significant way to boosting SOC due to their lone‐pair electrons which provide n‐orbitals.…”

“…[21] Besides, we have synthesized a serious of molecules 3-5 and compared the effect of different Brsubstituted positions which resulted in various π-type halogen bonding. [22] Introduction of hetero atoms is a significant way to boosting SOC due to their lone-pair electrons which provide norbitals. Hence, our group [23] designed and synthesized a serious of molecules 6-9 and 11 containing the O, N, P atoms with the assistance of H-aggregation stabilizing the triplet excitons to increase the emission lifetime to second scale.…”

“…One is to facilitatie the intersystem crossing (ISC) from the lowest excited singlet state (S 1 ) to a triplet state (T n ) to populate the triplet excitons, and the other is to inhibit nonradiative transitions from the lowest excited triplet state (T 1 ) to the ground state (S 0 ). On the basic of these factors, researchers have proposed various strategies and methods to moldulate phosphorescent performance, such as intruduction of heavy atoms, [20][21][22] heteroatoms [23][24][25] and aromatic carbony [26][27] to boost SOC; while suppressing non-radiation of the triplet excitons by host-guest doping method [28][29][30][31] crystalization [32][33][34] and organic flameworks. [35][36][37] Therefore, developing metal-free organic luminescent materials with highly efficient room temperature phosphorescence has been becoming a hot topic in recent years.…”

Controlling Organic Room Temperature Phosphorescence through External Heavy‐Atom Effect for White Light Emission and Luminescence Printing

“…In addition, there are six kinds of CH···Br interactions, with distances ranging from 2.79 to 3.22 Å, and three kinds of CH···π interactions, with distances ranging from 2.73 to 2.86 Å, as shown in Figure b,c. These intramolecular and intermolecular interactions could efficiently restrict molecular vibration to suppress the non‐radiative relaxation and enhance RTP . As in CBTP‐Br, the smallest distance between the heavy atom and the carbazole in CBTP‐Cl and CBTP‐I are 3.93 and 3.74 Å, respectively.…”

Amorphous Pure Organic Polymers for Heavy‐Atom‐Free Efficient Room‐Temperature Phosphorescence Emission

“…In these cases,the halogen atoms are essential units in order to facilitate the intersystem crossing. [30][31][32] While,i ti s well-known that the use of heavy atoms will cause the RTP emission hard to observe. [33] Although great efforts have been devoted, RTPf rom pure organic amorphous materials without halogen atoms remains aformidable challenge.…”