Room-temperature phosphorescence from organic aggregates

Advances in molecular-structure design and modulation of the aggregation behaviour have enabled much progress in the observation of room-temperature phosphorescence from organic aggregates. This Review analyses key photophysical processes related to triplet excitons, illustrating the intrinsic structure-property relationships and identifying strategies to design efficient and persistent room-temperature-phosphorescent systems. Triplet excitons in organic molecules underscore a variety of processes and technologies as a result of their long lifetime and spin multiplicity. Organic phosphorescence, which originates from triplet excitons, has potential for the development of a new generation of organic optoelectronic materials and biomedical agents. However, organic phosphorescence is typically only observed at cryogenic temperatures and under inert conditions in solution, which severely restricts its practical applications. In the past few years, room-temperature-phosphorescent systems have been obtained based on organic aggregates. Rapid advances in molecular-structure design and aggregation-behaviour modulation have enabled substantial progress, but the mechanistic picture is still not fully understood because of the high sensitivity and complexity of triplet-exciton behaviour. This Review analyses key photophysical processes related to triplet excitons, including intersystem crossing, radiative and non-radiative decay, and quenching processes, to illustrate the intrinsic structure-property relationships and draw clear and integrated design principles. The resulting strategies for the development of efficient and persistent room-temperature-phosphorescent systems are discussed, and newly emerged applications based on these materials are highlighted.