Communication
Inorganic Chemistry, Vol. 48, No. 24, 2009 11485
coordinated to the P atom, they are not in direct π conjuga-
tion with the fluorophore π system. It is also important to
note that phosphorus lone pairs do not participate in the π
system to the same extent18-20 as do nitrogen lone pairs.21,22
It follows that coordination to a metal center does not lead to
dramatic spectral wavelength shifts, and this observation is
also in line with the trend observed in other chromophoric
phosphine complexes.9 The polymers P1 and P2 do have
lower Φ values than LHP1, even though coordination to a
metal center eliminates the lone-pair-derived PET as a
possible quenching mechanism. In this case, the diminished
Φ is due to the heavy-atom effect, whereby highly polarizable
heavy elements such as platinum and palladium are classic
fluorescence quenchers.23-25 The lifetime of P1 (Table 1) is
also worth noting; platinum-containing materials are often of
interest as triplet-emissive (phosphorescent) materials be-
cause of the ability of platinum to facilitate intersystem
crossing via enhanced spin-orbit coupling.26 In the current
case, however, the Pt atom is not an integral part of the
luminophore, and thus the lifetime observed correlates
with simple fluorescence derived from the LHP1-centered
π system. The lifetime of P2 (Table 1) was difficult to acquire
reliably because of its very low intensity, so it is not reported
here.
Despite the low Φ values for P1 and P2, these materials
may prove to be useful components in applications where
luminescence is not needed (i.e., electrochromics) or even
undesirable (i.e., photovoltaics). We also anticipate that the
further elaboration of the metal centers with additional
π systems in place of the chloro substituents may provide
materials capable of interesting energy-transfer processes.
In conclusion, a modular synthesis easily extendable to
various chromophoric phosphines has been described, and
the utility of these phosphines in the preparation of lumines-
cent metallopolymers has been demonstrated. The prepara-
tion of a series of chromophoric phosphines and their metal
complexes is currently underway.
Figure 2. 31P NMR spectrum of P1 with resonances attributed to
platinum-coordinated P atoms (*) and uncoordinated terminal phos-
phines (#).
equation17 allows us to calculate a respectable extent of
reaction of ∼0.97 for both P1 and P2. The 31P NMR
spectrum of P1 (Figure 2) shows especially well-defined
resonances attributable to main-chain platinum-coordinated
P atoms (15.0 ppm) and uncoordinated end-group P atoms
with a chemical shift (-4.5 ppm) nearly identical with that of
LHP1 (-4.6 ppm). The 31P NMR resonances for end groups
in P2 are very close to those of the coordinated, main-chain P
atoms near 24 ppm (31P NMR spectrum provided in the
Supporting Information), indicating that the end groups
have oxidized in air during workup and manipulation of
the solutions.
The photophysical properties of P1 and P2 are summar-
ized in Table 1, and their absorption and photoluminescence
spectra are overlaid with those of LHP1 and LHPO in
Figure 1. λmax and λem of the polymers are not significantly
different from those of LHP1, with only a small shoulder to
the red distinguishing P1 from the other nearly coincident
photoluminescence spectra in Figure 2B, and all materials
exhibit an optical band gap (estimated from the peak onset in
the absorption spectrum) of about 2.7 eV. These similarities
are expected because, regardless of what atoms are bound or
Acknowledgment. The authors thank Clemson Univer-
sity and the Center for Optical Material Science and
Engineering Technologies for support.
Supporting Information Available: X-ray crystallographic
data in CIF format, experimental details, 1H, 31P, and 13C
NMR spectra, absorption and photoluminescence spectra,
and an ORTEP drawing of 1. This material is available free of
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