The fluorescence quenching mechanism of coumarin 120 with CdS nanoparticles in aqueous suspension

The interaction of coumarin 120 (C120) with CdS nanoparticles (CdS NPs) in aqueous suspension was examined by using UV-vis absorption, steady-state, time-resolved fluorescence, and electron paramagnetic resonance (EPR) spectroscopy techniques. The fluorescence intensity of C120 was quenched with increasing the amount of CdS NPs in the aqueous suspension. The spectroscopic data revealed that the C120 molecules adsorbed on CdS NPs via electrostatic interactions. The apparent association constant (Kapp) and the degree of association (α) for C120/CdS NPs were determined as 130.3 M−1 and 0.51 for 4 nm CdS NPs and 624.3 M−1 and 0.71 for 8 nm CdS NPs, respectively. The photoinduced EPR studies exhibited that no electron transfers between CdS and C120 taking place. The results revealed that the fluorescence quenching of C120 with different CdS NPs is due to the formation of a non-fluorescent complex.