Fig. 1 TEM image of GNPs after functionalisation. Scale bar 20 nm.
Inset: histogram of particle diameters (n 4 200).
Fig. 2 Main: excitation and emission profiles of Re-2-GNP in water.
and rhenium (Ma1/2 at 1.8 eV)z as well as other lines
consistent with both elements.
Inset: lifetime decay.
The luminescence properties of the precursor reference
compounds Re-1 and Re-2 were typical of species that possess
known to effect excited state quenching, the spectral overlap of
the donor–acceptor components should be a primary con-
sideration, one which we have attempted to address in this
work. It is possible therefore that the minor quenched com-
ponents of Re-2-GNP may be attributed to the small fraction
3
MLCT emission (Table 1). In water–acetonitrile mixtures
(
95 : 5) the compounds were emissive at ca. 550 nm following
excitation at 380 nm (correlating with direct population of the
1
MLCT). The single component luminescence lifetimes were
(
ca. 5%) of GNPs that possess diameters of 45 nm and
are therefore more likely to participate in energy transfer
1
42 and 133 ns for Re-1 and Re-2, respectively, and charac-
3
teristic of rhenium-based MLCT emission for species of this
3
processes, resulting in partial quenching of the MLCT emission
1
3
type.
and shorter emission lifetimes.
The UV-Vis properties (ESIw) of Re-2-GNP in water con-
firmed the presence of the rhenium unit through assignment
In conclusion, this communication reports the synthetic
I
strategy to accessing examples of functionalised Re complexes
1
1
of MLCT (shoulder at 350–400 nm) and LC (bipy, pp*
80–320 nm) bands. The luminescence properties of the
allowing attachment to small diameter GNPs. The resultant
hybrid conjugates are water-soluble, retain exploitable
2
Re-2-GNP conjugate (Fig. 2) were then assessed in aqueous
3
solution with the GNP-bound species retaining useful MLCT
3
MLCT emission characteristics and represent a useful
consideration for the future development of luminescent
GNP-derived materials, which have the potential to be
exploited in a number of applications including fluorescence
microscopy and nanoelectronic devices.
emission at 549 nm. For Re-2-GNP the luminescence lifetime
profile was satisfactorily fitted to a biexponential decay. The
dominant lifetime component (110 ns) was consistent with
3
MLCT character in water, resulting from a solvated bipyridine
We thank EPSRC and RCUK (PC) for funding together
with the Universities of Cardiff and Manchester. The EPSRC
Mass Spectrometry National Service at the University of
Swansea is also acknowledged.
1
4
3
unit. The retention of MLCT emission can be attributed to
a number of factors. The small average diameter of the GNPs
results in a distortion and blue-shift of the absorption band
(
surface plasmon resonance) to ca. 475 nm (see ESIw), and
therefore does not significantly overlap with the emission
Notes and references
3
profile of the rhenium MLCT component. Secondly, the
z Syntheses and spectroscopic characterisation of the ligands (1 and 2),
the rhenium complexes (Re-1 and Re-2), GNP synthesis and GNP
conjugate (Re-2-GNP) are included in the ESI.w
rhenium chromophore is tethered via the axial pyridyl
ligand of the complex which allows conformations where the
bipyridine-localised excited state can be positioned away from
the GNP surface. Although a number of factors such as
dipolar orientation with respect to the GNP surface are also
1
(a) K. G. Thomas and P. V. Kamat, Acc. Chem. Res., 2003, 36,
88; (b) M. Montalti, N. Zaccheroni, L. Prodi, N. O’Reilly and
8
S. L. James, J. Am. Chem. Soc., 2007, 129, 2418; (c) M. C. Daniel
and D. Astruc, Chem. Rev., 2004, 104, 293.
2
(a) C. J. Ackerson, P. D. Jadzinski, G. J. Jensen and
R. D. Kornberg, J. Am. Chem. Soc., 2006, 128, 2635;
(b) D. Maysinger, Org. Biomol. Chem., 2007, 5, 2335;
Table 1 Luminescence properties of the complexes and
nanoparticle conjugate
(
c) C. Alric, J. Taleb, G. Le Duc, C. Mandon, C. Bilotey, A. Le
3
c
MLCT emission /nm
d
Compound
t /ns
Meur-Herland, T. Brochard, F. Vocanson, M. Janier, P. Perriat,
S. Roux and O. Tilement, J. Am. Chem. Soc., 2008, 130, 5908.
(a) J. Zhang, Y. Fu and J. R. Lakowicz, J. Phys. Chem. C, 2007,
1
5
a
Re-1
Re-2
548
549
549
142
133
3
a
11, 50; (b) A. Aguila and R. W. Murray, Langmuir, 2000, 16,
949; (c) A. C. Templeton, D. E. Cliffel and R. W. Murray, J. Am.
b
Re-2-GNP
6.8 (4%), 110 (96%)
a
b
O–MeCN. In H
c
d
O. Excitation at 380 nm. Excitation
Chem. Soc., 1999, 121, 7081; (d) B. I. Ipe and K. G. Thomas,
J. Phys. Chem. B, 2004, 108, 13265; (e) G. Battistini, P. G. Cozzi,
J. P. Jalkanen, M. Montalti, L. Prodi, N. Zaccheroni and
In 95 : 5 H
2
2
at 372 nm, emission at 550 nm.
This journal is ꢁc The Royal Society of Chemistry 2009
Chem. Commun., 2009, 4278–4280 | 4279