[Ru(bpy) ₃ ] ²⁺ : The Ongoing Story of a Photochemical Icon

[Ru(bpy) 3 ] 2+ has long served as the archetypal coordination complex for probing inorganic photophysics and photochemistry. Its intense visible MLCT absorption, quantitative intersystem crossing, and microsecond 3 MLCT lifetime established it as a benchmark photosensitizer across energy conversion, sensing, and catalysis. This review complements a recent historical perspective on [Ru(bpy) 3 ] 2+ by providing a contemporary view of its use as a versatile platform for advanced photochemical design. We first discuss updated views of its excited-state landscape, including refined descriptions of metal-centered states, minimum-energy crossing points, and photodissociation pathways, as well as the profound influence of counterions and microenvironments on excited-state energetics, stability, and reactivity. We then survey emerging applications, multiphoton solvated electron generation, mechanochemical ball-mill photoredox catalysis, and spin-forbidden red-light excitation. Next, we examine polynuclear complexes and dyads derived from the [Ru(bpy) 3 ] 2+ scaffold, emphasizing delocalized and antidissipative 3 MLCT states, long-lived charge separation, and integration into biohybrid or supramolecular architectures. Finally, we outline “real-life” applications in industrial photoredox chemistry, electrochemiluminescence immunoassays, oxygen sensing, and photodynamic therapy, and we position [Ru(bpy) 3 ] 2+ alongside emerging photosensitizers based on earth-abundant metals. Rather than being superseded, [Ru(bpy) 3 ] 2+ now functions as both a robust technological workhorse and an indispensable reference for next-generation photocatalyst design.