The triplet lifetimes of ZnPc and ZnPc-AuNPs conjugate were determined using laser flash photolysis. Figure shows the triplet decay curves of ZnPc and ZnPc clicked to AuNPs and the triplet lifetimes are shown in Table . The observed triplet lifetime of ZnPc-AuNPs conjugates (69.9 µs) was higher than that of the ZnPc alone (49.3 s), Table . The increase in the lifetime suggests that the ZnPc is protected by AuNPs as the size of AuNPs is much larger than the Pc ∼ 1 nm. Singlet oxygen quantum yield. O2 generation depends on the energy transfer from the triplet state of the photosensitizer to ground state molecular oxygen. Thus, the 1 O2 quantum yield is a measure of the efficiency of the processes involving in the generation of 1 O2. Therefore, in order to determine the 1 O2 quantum yield of ZnPc and ZnPc-AuNPs, the chemical photodegradation of a 1 O2 probe, DPBF, in DMSO was monitored over a period of time (Figure ) under ambient conditions. The absorption band of DPBF at 417 nm gradually decreased with increasing irradiation time while the Q band of Pc did not change, indicating the Pcs photostability. A significant increase in 1 O2 generation was observed as proven by the 1 O2 quantum yield (Table ) after conjugation of ZnPc with AuNPs. The following equation was used to determine the 1 O2 quantum yield: