Yunxi Liu, Yi Peng, Lin‐Han Jiang, Dongxue Guo, Yu Li, Qin He, Ling Huang
We report the synthesis of a novel dimeric anthracene derivative by covalently tethering two blue-fluorescent anthracene-based annihilators via a flexible alkyl linker. This dimer, combined with a far-red-responsive sensitizer (PtTNP), enables photon upconversion based on an intramolecular triplet-triplet annihilation (TTA) mechanism. Upon far-red light excitation, the system emits blue light with a high upconversion quantum yield of up to 17.4% (out of a theoretical maximum of 50%). Combined theoretical calculations and photophysical characterization reveal that the flexible linker effectively couples the two annihilator units, forming dual-triplet sites that facilitate rapid intramolecular TTA. This molecular design allows the triplet excited state annihilator to maintain a high intramolecular TTA quantum yield at low concentrations (100 μM, 1.39%), resulting in approximately a 3-fold enhancement in upconversion emission intensity compared to its monomeric counterpart. This work presents the first demonstration of far-red excited intramolecular TTA to enhance photon upconversion performance at low concentrations, advancing the practical applications of photon upconversion materials.