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10.1002/chem.201901052
Chemistry - A European Journal
FULL PAPER
Electronic Communication in Confined Space Coronas of Shell-by-
Shell Structured Al2O3-Nanoparticle Hybrids Containing Two
Layers of Functional Organic Ligands
Lisa M. S. Stiegler[a] and Andreas Hirsch*[a]
Abstract: A first series of examples for confined space interactions
of electron-rich and electron-poor molecules organized in an internal
into charged polymer solutions to built-up multilayer assemblies
onto substrates by employing electrostatic interactions between
corona of shell-by-shell (SbS)-structured Al2O3-NP-hybrids is reported. oppositely charged building blocks.
The assembly concept of the corresponding hierarchical architectures
relies on both, covalent grafting of phosphonic acids on the NPs
surface (SAMs formation), and exohedral interdigitation of orthogonal
In a recent project, we manufactured Al2O3 NPs with mixed shells
consisting of three phosphonic acid derivatives with different
polarities in combination with a pyrene-terminated phosphonic
amphiphiles as second ligand layer driven by solvophobic interactions. acid.[5] For these systems, the optoelectronic properties of the
The electronic communication between the chromophores of different
electron demand, such as pyrenes, PDIs (with and without pyridinium-
bromide headgroups) and fullerenes was promoted at the layer
interface. We have demonstrated that the efficient construction
principle of the bilayer hybrids assembled around the electronically
“innocent” Al2O3 core is robust enough to achieve control over
electronic communication between electron-donors and –acceptors in
the interlayer region. The electronic interactions between the electron-
accepting and electron-donating moieties approaching each other at
the layer interface were monitored by fluorescence measurements.
pyrene core in a series of environments were investigated by
fluorescence spectroscopy investigations. Furthermore, we have
attached different types of amphiphiles onto the corresponding
first-shell-systems, which caused the embedding of pyrene
chromophores in a defined environmental corona around the NPs.
This allowed for tuning of the optical properties (fluorescence
behavior). In general, our SbS-concept offers very exciting
opportunities for the investigation of chemical and physical
processes in a confined space, namely the interface between the
two organic layers.
Herein, we report on a first series of examples for the successful
realization of this idea. We developed SbS-structured Al2O3-NP-
hybrids, where electronic communication between various
chromophores of different electron demand can be promoted at
the layer interface. We have demonstrated that the efficient
construction principle of the bilayer hybrids assembled around the
electronically “innocent” Al2O3 core is robust enough to achieve
control over electronic communication between electron-donors
and –acceptors in the interlayer region. The composition of the
corresponding micellar arrangements is depicted in Scheme 1.
The electronic interactions between the electron-accepting and
electron-donating moieties approaching each other at the layer
interface were monitored by fluorescence measurements.
For the synthesis of the targeted micellar nano-hybrids, Al2O3-
NPs were functionalized both with long chain phosphonic acids
(PAR1) acting as isolating spacers and with functional, electron
donor bearing phosphonic acids PAR2-3 in different ratios.
Employing a combination of both pyrene and/or phenanthrene
containing ligands (PAR2 and PAR3) together with an electron
accepting phosphonic acid involving C60 (PAR4) leads to a
fluorescence quenching. This is an indication of pronounced
donor-acceptor (EDA) complex formation[6] events in the first
ligand shell. PAR1 was also combined with PAR2 and/or PAR3 in
the first shell, together with the electron-accepting
perylenediimides A1 and A2 (with either pyridinium-bromide or
carboxylic acid head groups) in the second shell. The apolar tails
of the amphiphiles were incorporated into the first-shell system,
whereas the polar head groups were pointing outwards.[7] At the
shell-shell interface, donor-acceptor complexation of the pyrene
and/or phenanthrene (PAR2/PAR3) together with the PDI-cores
occurs, which was figured out by quenching fluorescence
measurements. An additional push-pull system was built-up by
Introduction
We have recently introduced a new concept – the so-called shell-
by-shell (SbS) coating method – which allows for the assembly of
unprecedented nanoparticles (NPs) coated with two layers of
organic ligands.[1] The binding of the first ligand shell was carried
out by covalent attachment of an organic molecule bearing a
phosphonic acid terminus. This allows for efficient grafting to the
surface of metal oxide NPs resulting in the formation of densely
packed self-assembled monolayers (SAMs).[2] In a second step
this first-shell functionalized NPs were converted into a bilayer
architecture by non-covalent interdigitation of amphiphiles
forming the second layer. As a consequence, a micellar-like
arrangement around the first-shell functionalized NPs was formed.
The only example of a somewhat related concept involves an
amphiphilic polymeric shell to hydrophobic coated nanocrystals.[3]
Such a construction of a hierarchically ordered core-shell system
is driven by solvophobic interactions. Inspired is the shell-by-shell
coating concept by the layer-by-layer (LbL) approach, firstly
described by Decher et al.[4] The layer-by-layer technique
describes a concept, where substrates are alternatingly immersed
[a]
L. M. S. Stiegler, Prof. Dr. A. Hirsch
Chair of Organic Chemistry II, Department of Chemistry & Pharmacy
Friedrich-Alexander-Universität Erlangen-Nürnberg
Nikolaus-Fiebiger-Strasse 10, 91058 Erlangen (Germany)
E-mail: andreas.hirsch@fau.de
Supporting information for this article is given via a link at the end of
the document.
1
This article is protected by copyright. All rights reserved.
Stiegler, Lisa M. S.
