Dual Role of Electron-Accepting Metal-Carboxylate Ligands: Reversible Expansion of Exciton Delocalization and Passivation of Nonradiative Trap-States in Molecule-like CdSe Nanocrystals.
This paper reports large bathochromic shifts of up to 260 meV in both the excitonic absorption and emission peaks of oleylamine (OLA)-passivated molecule-like (CdSe)34nanocrystals caused by postsynthetic treatment with the electron accepting Cd(O2CPh)2complex at room temperature. These shifts are found to be reversible upon removal of Cd(O2CPh)2by N,N,N',N'-tetramethylethylene-1,2-diamine.1H NMR and FTIR characterizations of the nanocrystals demonstrate that the OLA remained attached to the surface of the nanocrystals during the reversible removal of Cd(O2CPh)2. On the basis of surface ligand characterization, X-ray powder diffraction measurements, and additional control experiments, we propose that these peak red shifts are a consequence of the delocalization of confined exciton wave functions into the interfacial electronic states that are formed from interaction of the LUMO of the nanocrystals and the LUMO of Cd(O2CPh)2, as opposed to originating from a change in size or reorganization of the inorganic core. Furthermore, attachment of Cd(O2CPh)2to the OLA-passivated (CdSe)34nanocrystal surface increases the photoluminescence quantum yield from 5% to an unprecedentedly high 70% and causes a 3-fold increase of the photoluminescence lifetime, which are attributed to a combination of passivation of nonradiative surface trap states and relaxation of exciton confinement. Taken together, our work demonstrates the unique aspects of surface ligand chemistry in controlling the excitonic absorption and emission properties of ultrasmall (CdSe)34nanocrystals, which could expedite their potential applications in solid-state device fabrication.
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.
Katie N
KN
Lawrence
Department of Chemistry, Michigan State University , 578 South Shaw Lane, East Lansing, Michigan 48824, United States.
Poulami
P
Dutta
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.
Mulpuri
M
Nagaraju
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.
Meghan B
MB
Teunis
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.
Barry B
BB
Muhoberac
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.|Integrated Nanosystems Development Institute, Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, Indianapolis, Indiana 46202, United States.
Rajesh
R
Sardar