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TIPS-pentacene triplet exciton generation on PbS quantum dots results from indirect sensitization

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Abstract

Many fundamental questions remain in the elucidation of energy migration mechanisms across the interface between semiconductor nanomaterials and molecular chromophores. The present transient absorption study focuses on PbS quantum dots (QDs) of variable size and band-edge exciton energy (ranging from 1.15 to 1.54 eV) post-synthetically modified with a carboxylic acid-functionalized TIPS-pentacene derivative (TPn) serving as the molecular triplet acceptor. In all instances, selective excitation of the PbS NCs at 743 nm leads to QD size-dependent formation of an intermediate with time constants ranging from 2–13 ps, uncorrelated to the PbS QD valence band potential. However, the rate constant for the delayed formation of the TPn triplet excited state markedly increases with increasing PbS conduction band energy, featuring a parabolic Marcus free energy dependence in the normal region. These observations provide evidence of an indirect triplet sensitization process being inconsistent with a concerted Dexter-like energy transfer process. The collective data are consistent with the generation of an intermediate resulting from hole trapping of the initial PbS excited state by midgap states, followed by formation of the TPn triplet excited state whose rate constant and yield increases with decreasing quantum dot size.

Graphical abstract: TIPS-pentacene triplet exciton generation on PbS quantum dots results from indirect sensitization

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Article information


Submitted
17 Jan 2020
Accepted
18 May 2020
First published
18 May 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020, Advance Article
Article type
Edge Article

TIPS-pentacene triplet exciton generation on PbS quantum dots results from indirect sensitization

C. M. Papa, S. Garakyaraghi, D. B. Granger, J. E. Anthony and F. N. Castellano, Chem. Sci., 2020, Advance Article , DOI: 10.1039/D0SC00310G

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