Manipulation of Triplet Excited States in Two‐Component Systems for High‐Performance Organic Afterglow Materials

Abstract

The past several years have witnessed the tremendous development of novel chemical structures, new design strategies and intriguing applications in the field of room‐temperature phosphorescence (RTP) and organic afterglow materials. This Review article focuses on recent advancements of high‐performance organic afterglow materials obtained by two‐component design strategies such as a dopant‐matrix, donor–acceptor, sensitization, and energy‐transfer strategies. Based on some cutting‐edge studies, organic afterglow efficiency has been largely improved, exceeding 90 % in several cases. Organic afterglow durations reach tens of seconds in phosphorescence systems and hours in donor–acceptor systems. Organic afterglow brightness outcompetes some inorganic afterglow materials in the first several seconds after ceasing excitation source. Organic afterglow colors cover the whole visible regions and extend to near‐infrared regions with respectful afterglow efficiency. On the basis of these achievements, researchers demonstrate promising applications of organic afterglow materials in diverse fields, which has also been reviewed.

A direct observation of up-converted room-temperature phosphorescence in an anti-Kasha dopant-matrix system

“…We use dopant-matrix design strategy to construct organic afterglow materials, where the selection of organic matrix is very important. The selection guideline of organic matrix is based on its role in BF 2 bdk-matrix afterglow system 37 , where BF 2 bdk represents difluoroboron β - diketonate compound. (a) Organic matrix should suppress nonradiative decay and oxygen quenching of BF 2 bdk’s T 1 states, so that crystalline matrix is preferred.…”

Cascade Synthesis of Luminescent Difluoroboron Diketonate Compounds forRoom‐TemperatureOrganic Afterglow Materials

“…Because of their long‐lived triplet excited states, organic room‐temperature phosphorescence (RTP) materials exhibit intriguing applications in oxygen sensing and mapping, anti‐counterfeiting and data encryption, time‐gated bioimaging and other areas. [ 1‐9 ] To address the issue of spin‐forbidden phosphorescence emission, pioneering studies demonstrate that organic RTP efficiency and lifetimes can be largely improved through rational design strategies based on judicious molecular design, control of molecular aggregation, and supramolecular assembly. [ 10‐21 ]…”

“…Besides the essential role of organic matrices, the design and selection of luminescent dopants are very important for the fabrication of organic RTP materials with long afterglow duration and high afterglow efficiency. [ 3‐8 ] Difluoroboron β‐diketonate (BF 2 bdk) compounds possess intriguing optical properties, have been reported to show large molar absorption coefficients, high photoluminescence quantum yields in both solution and solid states, and exhibit wide‐range tunable emission spectra of intramolecular charge transfer characters. [ 39‐45 ] BF 2 bdk compounds have also emerged as a very useful building block (used as luminescent dopants) for devising high‐performance organic RTP materials via dopant‐matrix design strategy.…”

Host Surface-Induced Excitation Wavelength-Dependent Organic Afterglow

“…Pure organic afterglow materials with long lifetime features lasting from several seconds to hours at room temperature have received considerable attention over the past few years due to their tunable and long-lived emission for great potential applications, including bioimaging, information security, and optical sensing. − There are two main subclasses of materials: (1) room-temperature phosphorescence (RTP) materials and (2) organic long-persistent luminescence (OLPL) materials. ,, Compared with OLPL, which is mainly based on the formation of an exciplex emitter, RTP has been vigorously studied and has become the primary method for facilitating afterglow emission. − Therefore, the efficient generation and utilization of triplet excitons constitute the coveted theme of RTP emission. However, the exciton spin-flip is not allowed between the well-separated singlet and triplet excited states due to the violation of Winger’s law. , Increasingly sophisticated molecular design principles have been introduced to regulate the molecular structure, packing, and/or communication between the host and guest. − In addition, the designed RTP materials often have (1) a large energy band gap between the singlet and triplet (Δ E ST ) to inhibit the reverse intersystem crossing (RISC) process; (2) introduced n –π* states or (σ, B p ) → (π, B p ) transition to facilitate the intersystem crossing (ISC) process and increase the population of triplet excitons; − and (3) a rigid environment to suppress the nonradiative processes. , Following these principles, many RTP systems have been developed and applied in various fields.…”