Long Persistent Luminescence from Metal-Organic Compounds: State of the Art

The excited-state tuning of luminescent metal-organic compounds has made great progress in the fields of optical imaging, photocatalysis, photodynamic therapy, light-emitting devices, sensors, and so on. Although metal-organic compounds with high luminescence efficiency can be realized via enhanced molecular rigidity and heavy-atom effect, their corresponding luminescence lifetimes are still limited on the order of a nanosecond to a millisecond, owing to the inherent competition between luminous efficiency and lifetime. Therefore, the advanced applications (i.e., persistent afterglow imaging, information security, anti-counterfeiting, and smart materials, among others) related with long persistent luminescence (LPL, typically with the excited-state lifetime larger than millisecond) are seriously hindered. This review gives a timely and systematic summary of metal-organic compounds for realizing room-temperature phosphorescence (RTP)-type and thermally activated delayed fluorescence (TADF)-type LPL during last few years. Particularly, based on the perspectives of time, space, and energy dimensions, fundamental materials design and coordination assembly are systematically described for the first time. Moreover, the internal and external factors of influencing the LPL properties in terms of luminescence efficiency, lifetime, and color are illustrated. Last but not least, perspectives and challenges are also discussed for developing LPL from metal-organic compounds.

Automated summary

Excited-state tuning of luminescent metal-organic compounds has advanced applications in various fields. However, the luminescence lifetimes of these compounds are still limited due to the competition between luminous efficiency and lifetime. This review summarizes recent developments in realizing room-temperature phosphorescence and thermally activated delayed fluorescence, and discusses fundamental materials design, coordination assembly, and factors influencing luminescence properties.