Photoexcitation dynamics in hybrid associates of Ag2S quantum dots with methylene blue

Abstract

Abstract The dynamics of electronic excitations in hybrid associates of Ag2S quantum dots with methylene blue (MB) molecules are studied by femtosecond transient absorption spectroscopy and nanosecond time-resolved spectroscopy. The situation is considered where the relative positions of the energy levels of the associate components allow photoinduced charge transfer. The luminescence quenching for MB+ cations and Ag2S quantum dots in the hybrid associates provides evidence for charge transfer, which is accompanied by a quick return of MB+ to the ground state (absorption is recovered). We propose that there is electron transfer from the MB LUMO level to the energy level of the luminescence center in the quantum dot. In this case, the bleaching band with a peak at 590 nm corresponding to the MBOH form of the dye is formed at a subpicosecond time scale. The corresponding decay time is about 100 ps.