Described herein is an efficient strategy for assembling a new library of functionalized polycyclic purinium salts with a wide range of anions through RhIII-catalyzed C–H activation/annulation of 6-arylpurine nucleosides with alkynes under mild reaction conditions. The resulting products displayed tunable photoluminescence covering most of the visible spectrum. Mechanistic insights delineated the rhodium catalyst’s mode of action. A purinoisoquinolinium-coordinated rhodium­(I) sandwich complex was well characterized and identified as the key intermediate.