The role of O2 on the synthesis of phthalocyanines has remained unclarified in the past one century.Here wedemonstrate that O2,in cooperation with the solvent n-pentanol molecule,participates in the cyclic tetramerizationof phthalonitriles over the half-sandwich complex template Lu(Pc)(acac) and makes the reaction terminate at thestage of uncyclized isoindole oligomeric derivatives rather than phthalocyanine chromophores,resulting in theisolation of heteroleptic(phthalocyaninato)(triisoindole-1-one) lutetium double-decker complexes(Pc)Lu(TIO-Ⅰ/Ⅱ)(1,2) with the help of bulky substituents at the phthalonitrile periphery and unsubstitutedphthalocyanine ligand in the double-decker skeleton.