Photoinduced interaction of CdSe quantum dot with coumarins

Cadmium selenide (CdSe) quantum dots (QDs) were synthesized with a cubic shape having a diameter of ~5.24 nm. The prepared CdSe QDs were characterized by using UV-visible, Fourier transform infrared (FTIR), powder X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The UV-visible absorption spectra indicate that the optical band gap of CdSe QDs is ~622 nm and the peak shift can mainly be due to the quantum size effects. The fluorescence decay kinetics for the synthesized QDs was followed by time-resolved fluorescence spectroscopy, and the spectra were analyzed in regard to a bi-exponential model to identify two lifetime values, that is, shorter-lifetime 1.37 ns (55%) and longer-lifetime 6.58 ns (45%). The interaction of coumarin 152 (C152) and coumarin 153 (C153) with QDs surface brings about further considerable changes in the absorption and fluorescence patterns. The calculated binding constant from fluorescence quenching method matches well with that determined from the absorption spectral changes. The static quenching mechanism was confirmed by large magnitude of KSV and unaltered fluorescence lifetime.