Transient absorption spectral dynamics of hybrid associates of CdS quantum dots and methylene blue dye

The transient absorption spectra dynamics for hybrid associates of colloidal CdS quantum dots, passivated by thioglycolic acid (CdS/TGA QDs), and methylene blue cationic dye molecules (MB+) were studied by femtosecond spectroscopy. It was established that one of the main channels of relaxation of the CdS/TGA QDs excitation energy in hybrid associates based on CdS/TGA QDs and MB+ is a fast energy transfer to the reduced forms of MB+ (MBOH•, MB•) that are formed still at the synthesis stage of samples. This channel strongly competes with the resonant energy transfer from the centers of radiative recombination in quantum dots to MB+. Therefore, for hybrid associates based on QDs/TGA and methylene blue, there is no any noticeable signal of the transient absorption corresponding to the triplet state of MB+ dye, which is then known to be actively involved in charge transfer.