Photochemical up-conversion is a spectrally versatile approach to harvesting high energy light from low energy light. Understanding and manipulating the energy transfer process is vital to increasing the energy conversion yield. Photon upconversion can potentially enhance the conversion of solar energy to electricity, while making multi-photon imaging cheaper and more accessible. It would make solar energy competitive with electricity from fossil fuels, and bioimaging in the near-infrared window routine. In our hybrid platform, semiconductor nanocrystals absorb light, and donate energy to molecular triplet states. These excited triplet states then undergo triplet-triplet annihilation (TTA) in a spin-allowed and energy-conserved process to generate high energy photons from low energy photons. We found that the up-conversion yield is enhanced in the presence of a molecular transmitter that mediates this triplet energy transfer. Preliminary investigations reveal that upconversion quantum yield strongly depends on the molecular orientation of this transmitter. Using carboxylic acid and dithio-carbamate functional groups to bind the anthracene transmitter to the CdSe nanocrystal, we discover that energy transfer is most efficient when the triplet dipole is parallel to the nanocrystal surface. We will present the experimental details and theoretical explanations regarding the observed overlap between the nanocrystal wavefunction and molecular orbitals necessary for efficient triplet transfer in this hybrid upconversion platform.

Effect of transmitter dipole moment on the upconversion efficiency in hybrid inorganic-organic nanocrystal-molecule systems

251st National Meeting (2016)

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