Based on the control experiments and previous literature , a plausible mechanism was proposed (Fig. ). The photocatalyst (PC) is irradiated by blue light to its excited state, which undergoes a single electron transfer event with 1aa to afford alkyl radical I. Electrophilic radical addition to the triple bond of alkyne forms vinyl radical II. Subsequently, radical II undergoes ipso-radical addition to the phenyl ring to form a spiro radical species III. Fragmentation, accompanied by the extrusion of SO2, produces alkyl radical IV. This transient species is then reduced via another SET event from PC -1 followed by protonation to give the desired alkene 3, concomitantly regenerating PC to complete the photo-redox cycle. Once product 3 is formed in the reaction system, photoinduced isomerization of the generated alkene occurs, which accounts for diminished Z/E ratio of the obtained products.