Dictating Excited State Pathways at the Perovskite Nanocrystals-NIR Dye Interface by Thermodynamics-Governed Kinetics

Elucidating the intricate mechanisms of excited state interactions within inorganic semiconductor-organic molecule conjugates is of great scientific and practical significance, as it enables the control of energy transfer and electron transfer processes across the inorganic-organic interface. Herein, we report the distinct excited state interactions upon selective excitation of individual components in a conjugate comprising perovskite nanocrystals (NCs) and the near-infrared (NIR) dye IR808. Transient absorption investigation reveals that upon excitation of IR808 by NIR light, electron transfer from excited singlet IR808 to the NCs occurs with a time constant of 8.2 ps. This is followed by charge recombination with a time constant of 407 ps, ultimately forming triplet IR808. In contrast, selective excitation of the NCs with red photons, a one-step triplet energy transfer (k_TET = 1.22 ns^-1) from the excited NCs to IR808 rather than stepwise charge transfers, is observed during the triplet IR808 formation. Energy transfer outcompetes charge transfers in this case despite both processes being thermodynamically favorable because charge transfer falls deeper into the inverted region of Marcus theory than the triplet energy transfer. Thermodynamics can govern the kinetics in the excited state interactions within NCs and organic hybrids, thereby enabling excitation wavelength-controlled excited state interaction pathways. The effective generation of triplet IR808 and the broad spectral response of the NCs-IR808 conjugate enable applications in the sensitization of singlet oxygen and photochemical upconversion through visible to NIR excitation.