A Ru(bipyridine)3[PF6]2Complex with a Rhodamine Unit - Synthesis, Photophysical Properties, and Application in Acid-Controllable Triplet-Triplet Annihilation Upconversion: A Ru(bipyridine)3[PF6]2 Complex with a Rhodamine Unit - Synthesis, Photophysical Properties, and Application in Acid-Controllabl