Photoinduced interactions between coumarin 151 and colloidal CdS nanoparticles in aqueous suspension

The photophysical features of 7-amino-4-trifluoromethylcoumarin (C151) in colloidal suspension that contains CdS semiconductor nanoparticles were investigated by using molecular UV–Vis absorption, steady-state and time-resolved fluorescence, and electron spin resonance (ESR) spectroscopy techniques. For this aim, the fluorescence intensity quenching of C151 molecules in colloidal aqueous solution containing colloidal CdS nanoparticles were examined. It was found that electrostatic interactions of C151 molecules at the ground state with CdS nanoparticles cause adsorption of certain amount of dye molecules onto colloidal CdS nanoparticles. After that, molecular excitation of C151 in the colloidal suspension leads to the formation of singlet excited state of C151 molecules and then adsorbed C151 molecules, at the singlet excited state, onto surfaces of CdS nanoparticles cause charge injection process. Therefore, the apparent association constants (Kapp), occurring between C151 molecules and colloidal CdS nanoparticles, and charge injection rate constants (ket) were calculated and compared with the values reported in the literature.