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We report on the results of a detailed quantitative experimental evaluation of exciton relaxation pathways as well as direct measurement of singlet oxygen (1O2) generation efficiencies for CdSe/ZnS quantum dot (QD)– porphyrin nanocomposites in toluene at 295 K. QD photoluminescence quenching in nanocomposites is caused by two main factors: electron tunneling in the quantum confined QD (efficiency 0.85–0.90) and Förster resonance energy transfer (FRET) QD→porphyrin (quenching efficiency 0.10–0.15). Efficiencies of 1O2 generation γΔ by nanocomposites are essentially higher with respect to those obtained for QDs alone. For nanocomposites, the nonlinear decrease of 1O2 generation efficiency γΔ on the laser pulse energy is caused by nonradiative intraband Auger processes, realized in the QD counterpart. Finally, FRET efficiencies found from the direct sensitization data for porphyrin fluorescence in nanocomposites (ΦFRET = 0.14 ± 0.02) are in good agreement with the corresponding values obtained via the direct 1O2 generation measurements at low laser excitation (ΦFRET Δ = 0.12 ± 0.03). The obtained quantitative results provide for the first time strong evidence that a FRET process QD→porphyrin is the reason for singlet oxygen generation by nanocomposites.

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