Unconventional Fluorescence Quenching in Naphthalimide-Capped
CdSe/ZnS Nanoparticles
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Abstract
Core–shell
(CS) CdSe/ZnS quantum dots (QD) capped with ligands
that possess a mercapto or an amino group and a naphthalimide (NI)
as chromophore unit, linked by a short ethylene chain (CS@S–NI
and CS@H<sub>2</sub>N–NI, respectively), have been synthesized
and fully characterized by infrared and nuclear magnetic resonance
spectroscopies, high-resolution transmission electron microscopy,
and voltammetry as well as by steady-state absorption and emission
spectroscopies. The organic ligands HS–NI and H<sub>2</sub>N–NI act as bidentate ligands, thereby causing a drastic decrease
in the QD emission. This was particularly evident in the case of CS@S–NI.
This behavior has been compared with that of commercially available
QDs with octadecylamine as the surface ligand and a QD capped with
decanethiol ligands (CS@S–D). The interaction between the anchor
groups and the QD surface brings about different consequences for
the radiative and nonradiative kinetics, depending on the nature of
the anchor group. Our results suggest that the naphthalimide group
“stabilizes” empty deep trap states due to the carbonyl
group capacity to act as both a σ-donor and a π-acceptor
toward cations. In addition, the thiolate group can induce the location
of electron density at shallow trap states close to the conduction
band edge due to the alteration of the QD surface provoked by the
thiolate binding