Boron‐Cluster‐Enhanced Ultralong Organic Phosphorescence

Abstract

Although carborane‐based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron‐cluster‐based persistent phosphors obtained by linking a σ‐aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B−H⋅⋅⋅π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non‐metal/heavy‐atom boron clusters can be used to develop multifunctional high‐performance phosphors for potential applications.

Synthesis and Characterization of New o‐Carboranes‐Based Aggregation‐Induced Emission Molecules with Ultra‐Large Stokes Shift

“…This is because with the increase of water content, the intermolecular steric resistance becomes larger and the C cage −C cage vibration of o ‐carborane is hindered, thus the fluorescence is enhanced [25] . The luminescent bands around 360–410 nm in pure THF and 620 nm in f w = 99 % should be assigned to the locally excited (LE) state of the carbazole derivative moiety and the ICT state, respectively [18,22,39] . Meanwhile, a broad emission appears at 639 nm in an amorphous state compared to that in a pure THF solution.…”

“…When substituents on the carbon vertices of the carborane exhibit strong electron‐withdrawing ability [13–16] . Based on these properties , o ‐carborane is used to develop new types of thermally activated delayed fluorescence (TADF) molecules, aggregation‐induced delayed fluorescence (AIDF) molecules and phosphorescent molecules [17–24] . Furthermore, its unique three‐dimensional cage conformation can inhibit π‐π stacking, which could be an advantage for the development of AIE molecules [25–30] …”

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.…”