Abstract
AbstractTwo Ru(II) phenanthroline complexes (Ru‐ph and Ru‐py) were synthesized and their photophysical properties were systematically investigated. For Ru‐py, the conjugation of pyrene at 3‐ and 8‐positions of auxiliary ligand 1,10‐phenanthroline can increase the phosphorescence quantum yield, prolong the triplet lifetime and reduce the triplet energy level. The extended triplet lifetime of Ru‐py was revealed by using the density function theory calculations, which is originated from the triplet state equilibrium between the metal‐to‐ligand charge‐transfer (3MLCT) state and the intraligand (3IL) state. The upconversion fluorescence of 2‐substituted anthracene derivatives (DTACl, DTACN and DNACN) sensitized by Ru‐ph and Ru‐py in DMF was investigated under monochromatic 488 nm excitation with an ultralow power density of 40 mW/cm2. Among them, Ru‐py/DTACl presents the highest upconversion quantum yield (7.4 %). It is found that a small energy gap between the triplet states of sensitizer and emitter helps to increase upconversion quantum yield besides the high triplet‐triplet annihilation efficiency and fluorescence radiation of emitter and the long triplet lifetime of sensitizer.
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