Triplet Migration Across Quantum Dot-Molecular Interfaces
Felix Castellano a
a North Carolina State University, Partners Way, 911, Raleigh, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)
#Exciup19. Excitonic up-downconversion
Berlin, Germany, 2019 November 3rd - 8th
Invited Speaker, Felix Castellano, presentation 047
DOI: https://doi.org/10.29363/nanoge.nfm.2019.047
Publication date: 18th July 2019

The generation and transfer of triplet excitons across semiconductor nanomaterial-molecular interfaces will play an important role in emerging photonic and optoelectronic technologies and understanding the rules that govern such phenomena is essential.[1] The ability to cooperatively merge the photophysical properties of semiconductor quantum dots, with those of well-understood molecular chromophores is therefore paramount. CdSe semiconductor nanocrystals, selectively excited by green light, engage in interfacial Dexter-like triplet-triplet energy transfer with surface-anchored polyaromatic carboxylic acid acceptors, thereby extending its excited state lifetime by 5 orders-of-magnitude.[2] Net triplet energy transfer also occurs from surface anchored molecular acceptors to freely diffusing molecular solutes, further extending the triplet exciton lifetime while sensitizing singlet oxygen in aerated solution. The successful translation of triplet excitons from semiconductor nanoparticles to bulk solution implies a general paradigm that such materials are effective surrogates for molecular triplets. Several examples of newly conceived donor-acceptor quantum dot-molecule constructs will be presented.   

Inspired by the notion that semiconductor nanocrystals present molecular-like photophysical and photochemical properties, 1-pyrenecarboxylic acid (PCA)-functionalized CdSe quantum dots are shown to undergo thermally activated delayed photoluminescence.[3] This phenomenon results from a near quantitative triplet-triplet energy transfer from the nanocrystals to PCA, producing a molecular triplet-state ‘reservoir’ that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet-triplet energy transfer. The resultant photoluminescence properties are systematically and predictably tuned through variation of the quantum dot–molecule energy gap, temperature, and the triplet-excited-state lifetime of the molecular adsorbate. The concepts developed here appear to be generally applicable to semiconductor nanocrystals interfaced with molecular chromophores enabling potential applications of their combined excited states.

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