To address this issue, later on, we designed the 2nd generation sulfonium ligand, L2, where the phenyl rings of the backbone are bridged by a carbonyl group (Scheme 2b). The rigidity of the resulting thioxanthone-based backbone proved imperative for stabilizing the highly electrophilic tris-cationic sulfonium-Pt(II) complex, which showed an excellent performance as a π-acid catalyst in carbophilic cycloisomerization reactions. Unfortunately, L2 was found to be extremely light-sensitive, both as a free ligand and when coordinated to Pt(II). This outcome was hardly surprising, given that aromatic sulfonium cations are known to decompose upon irradiation into diaryl sulfides and highly reactive aryl cations, a property that makes them widely employed as photoacids in nanolithography. 17 It then occurred to us that placing the sulfonium center at the bridgehead position of a triptycene-type framework might significantly enhance the photostability of our ligand, while also imparting the necessary rigidity to its backbone to prevent the S-Pt bond dissociation. We now describe the synthesis of such a bicyclic compound, the 3rd generation sulfonium ligand, L3 (Scheme 2c) and report its improved performance in π-acid catalysis.