Direct observation of triplet energy transfer from semiconductor nanocrystals by Cédric Mongin, Sofia Garakyaraghi, Natalia Razgoniaeva, Mikhail Zamkov, and Felix N. Castellano Science Volume 351(6271):369-372 January 22, 2016 Published by AAAS

Fig. 1 Illustration of nanocrystal-to-solution triplet energy transfer, the associated energy levels, and the various TTET and decay pathways investigated in this study. Illustration of nanocrystal-to-solution triplet energy transfer, the associated energy levels, and the various TTET and decay pathways investigated in this study. PDT, photodynamic therapy. Cédric Mongin et al. Science 2016;351:369-372 Published by AAAS

Fig. 2 Ultrafast spectroscopic evidence for triplet energy transfer from optically excited CdSe nanocrystals to surface-bound ACA. Ultrafast spectroscopic evidence for triplet energy transfer from optically excited CdSe nanocrystals to surface-bound ACA. (A) Normalized electronic absorption (solid lines) and emission spectra (dashed lines) of ACA (blue) and CdSe nanocrystals (green) in toluene (OD, optical density). (B and C) Ultrafast TA difference spectra of CdSe-OA nanocrystals in toluene solution upon selective excitation of CdSe, using 500-nm pulsed laser excitation [0.05 μJ per pulse, 100 fs full width at half maximum (FWHM)], in (B) the absence and (C) the presence of surface-anchored ACA in toluene (ΔA, change in absorbance; 〈k〉, average rate constant). The inset in (C) shows TA kinetics monitored for the growth of 3ACA at 441 nm. (D) Ground-state recovery of CdSe monitored by kinetics at 490 nm, illustrating quantitative quenching of CdSe in the presence of surface-anchored ACA. Complementary data for PCA are shown in figs. S2 to S4. Cédric Mongin et al. Science 2016;351:369-372 Published by AAAS

Fig. 3 Kinetic profiles and quenching studies of ACA and PCA triplet states populated from excited CdSe nanocrystals. Kinetic profiles and quenching studies of ACA and PCA triplet states populated from excited CdSe nanocrystals. TA difference spectra of a toluene solution of (A) CdSe/ACA (8 μM) measured from 2 μs to 5 ms and (B) CdSe/PCA (8 μM) measured from 2 μs to 10 ms after a 505-nm laser pulse (1 mJ, 5 to 7 ns FWHM; 〈τ〉, average lifetime). The insets show TA decay kinetics at 430 nm (gray squares) and their respective fits to eq. S1, illustrating the triplet decay. (C and D) TA difference spectra (excitation wavelength, 505 nm; 5 to 7 ns FWHM; 1 mJ) measured at selected delay times after the laser pulse in (C) CdSe/ACA (5 μM) and CBPEA (6 μM) and (D) CdSe/PCA (5 μM) and CBPEA (6 μM) in deaearated toluene at room temperature. The insets show TA decay kinetics at 430 nm (red circles) and the rise and decay at 490 nm (blue squares), with their respective biexponential fit lines (solid and dashed), illustrating the triplet energy transfer reaction between 3ACA* and CBPEA. Cédric Mongin et al. Science 2016;351:369-372 Published by AAAS