Communications
DOI: 10.1002/anie.201104690
Nanoparticles
A Dual Emissive BODIPY Dye and Its Use in Functionalizing Highly
Monodispersed PbS Nanoparticles**
Jia-sheng Lu, Huiying Fu, Yanguang Zhang, Zygmunt J. Jakubek, Ye Tao, and Suning Wang*
BODIPY (boron-dipyrromethene) dyes and derivatives are
well-known to be very effective in light-harvesting and
energy-transfer processes, owing to their high fluorescence
quantum yields, large molar absorption coefficients, relatively
long excited-state lifetimes, and excellent photochemical
stability.[1] Thus, they have frequently been used in light-
harvesting molecules, as dye sensitizers, and as probes and
labels for biomolecules.[1–2] One important class of materials
for various optoelectronic applications, including solar cells, is
the class of semiconductor nanoparticles (NPs). The optical
and energetic properties of these nanoparticles can be tuned
by varying their shape, size, or surface ligands.[3–4] Lead sulfide
NPs are particularly attractive among NPs owing to their
narrow band gap, large exciton Bohr radii, and their
absorption and emission in the near-IR region.[3e,5] Several
recent reports have shown that PbS NPs are very promising
materials for achieving high-performance photovoltaic devi-
ces.[4e,5,6] The most commonly used surface ligand for PbS NPs
is oleic acid, which can effectively protect the NPs from
oxidation and can facilitate their dispersion in organic
solvents.[3,5–7] However, because they lack any interesting
photophysical properties, oleic acid capping ligands do not
engage in any electronic communication or interactions with
the NPs and thus have little influence on the properties of the
NPs and insulate NPs from each other and the surrounding
medium. New surface ligands that can communicate elec-
tronically with PbS NPs and enhance their performance in
optoelectronic devices are therefore in demand. Based on this
consideration and the very attractive photophysical proper-
ties of BODIPY dyes, we initiated the investigation of new
BODIPY dyes as potential new surface ligands for PbS NPs.
Herein, we report the synthesis and photophysical properties
of a new BODIPY dye (BDY) and its use in PbS NPs
functionalization.
The procedure used to synthesize BDY is illustrated in
Scheme 1. The bromophenyl-BODIPY starting material 1
was synthesized by using a modified literature procedure.[8]
Scheme 1. Synthetic procedure for BDY.
[*] J.-s. Lu, Prof. Dr. S. Wang
The 3- and 5-methyl groups in 1 are acidic enough to undergo
Knoevenagel condensation,[9] which allowed the introduction
of two p-octyl styryl groups to the core to produce 2.
Department of Chemistry, Queen’s University
Kingston, Ontario, K7L 3N6 (Canada)
E-mail: wangs@chem.queensu.ca
The octyl groups are necessary to provide the desired
solubility of the functionalized NPs in organic solvents. The
conjugated terminal carboxylate group was connected to the
BODIPY core by using a standard Suzuki coupling method
between 2 and the corresponding boronic acid to produce 3.
Replacement of the ester group by a carboxylic acid converts
3 to the final product BDY, which was fully characterized by
1H NMR spectroscopy, HRMS, and elemental analysis. BDY
has a moderate solubility in most organic solvents, including
toluene and hexanes. Although we have not been able to
obtain single crystals of BDY, the structure of its ester (3) was
determined successfully by X-ray diffraction analysis.[10]
Compound 3 forms needlelike crystals that aggregate into
black balls of spikes. The crystal structure of 3 is shown in
Figure 1. In the crystal lattice, molecules of 3 arrange in a
head-to-head and tail-to-tail fashion, with extensive intermo-
lecular interactions involving the styryl groups, the biphenyl
H. Fu, Y. Zhang, Y. Tao
Institute for Microstructural Science
National Research Council
Ottawa, 1200 Montreal Road, K1A 0R6 (Canada)
Dr. Z. J. Jakubek
Steacie Institute for Molecular Science
National Research Council
100 Sussex Drive, Ottawa, K1A 0R6 (Canada)
[**] This work is supported financially by the Natural Sciences and
Engineering Research Council of Canada, Business Development
Bank of Canada, the National Research Council of Canada. We thank
Dr. Jian-ping Lu for his assistance in PbS NPs synthesis.
Supporting information (including synthetic procedure and char-
acterization data of BDY, PbS nanoparticle synthesis, crystal-
structure data, TD-DFT computational details, photophysical prop-
erty characterization, and electrochemical data) for this article is
11658
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 11658 –11662