Photon Upconversion in a Glowing Metal-Organic Framework.

The interaction of low-energy light with matter that leads to the production of high-energy light is known as photon upconversion. This phenomenon is of importance because of its potential applications in optoelectronics, energy harvesting, and the biomedical arena. Herein, we report a pillared-paddlewheel metal-organic framework (MOF), constructed from a tetrakis(4-carboxyphenyl)porphyrin sensitizer and a dipyridyl thiazolothiazole annihilator, designed for efficient triplet-triplet annihilation upconversion (TTA-UC). Single-crystal X-ray diffraction studies reveal that the Zn-metalated sensitizers are coordinated to Zn2 nodes in a paddlewheel fashion, forming 2D sheets, to which are linked annihilators, such that each sensitizer is connected to five of them. The precise arrangements of sensitizers with respect to annihilators, and the high annihilator-to-sensitizer ratio, facilitate Dexter energy transfer. This level of organization in an extended structure leads to a high TTA-UC efficiency of 1.95% (theoretical maximum = 50%) at an excitation power density of 25 mW cm-2.