Triplet–Triplet Annihilation Upconversion in a MOF with Acceptor‐Filled Channels.

Photon upconversion has enjoyed increased interest in the last years due to its high potential for solar‐energy harvesting and bioimaging. A challenge for triplet–triplet annihilation upconversion (TTA‐UC) processes is to realize these features in solid materials without undesired phase segregation and detrimental dye aggregation. To achieve this, we combine a palladium porphyrin sensitizer and a 9,10‐diphenylanthracene annihilator within a crystalline mesoporous metal–organic framework using an inverted design. In this modular TTA system, the framework walls constitute the fixed sensitizer, while caprylic acid coats the channels providing a solventlike environment for the mobile annihilator in the channels. The resulting solid material shows green‐to‐blue delayed upconverted emission with a luminescence lifetime of 373±5 μs, a threshold value of 329 mW cm−2 and a triplet–triplet energy transfer efficiency of 82 %. The versatile design allows straightforward changing of the acceptor amount and type. [ABSTRACT FROM AUTHOR]