Fluorene as π-conjugation linker in N^N Pt(ii) bisacetylide complexes and their applications for triplet-triplet annihilation based upconversion

Article abstract of DOI:10.1039/c2jm32074f

Fluorene-containing N^N Pt(ii) bisacetylide complexes were prepared, in which the fluorene moieties were connected to the Pt(ii) center via acetylide bonds (-CC-). Different aryl groups were attached to the fluorene moiety, such as phenylacetylide (Pt-4), naphthalimide-4-acetylide (Pt-1) and in Pt-2, the fluorene moiety was changed to carbozale moiety. We found that with the fluorene linker between the arylacetylide and the Pt(ii) center, the absorption of complexes in the visible range were intensified. All the complexes show room temperature (RT) phosphorescence. Furthermore, Pt-1 shows much longer triplet excited state lifetime (τ = 138.1 μs) than the analogue Pt-3 (τ = 47.4 μs). For Pt-2, with changing the fluorene moiety to carbazole moiety, the T₁ state lifetime becomes much shorter (τ = 23.0 μs). Thus the one-atom (N vs. C) difference is crucial for the photophysical properties. The triplet excited state of Pt-1 was proved to be the intraligand excited state (³IL) by nanosecond time-resolved transient absorption spectroscopy, spin density analysis and emission at 77 K. The complexes were used as triplet sensitizers for triplet-triplet annihilation (TTA) upconversion. Upconversion quantum yield (Φ_UC) up to 24.3% was observed for Pt-1. Under the same conditions the model complex Pt-4 shows no upconversion. The overall upconversion efficiency (η) of the new complexes are improved compared to the model complexes, such as Pt-2, Pt-3 and Pt-4. The improved upconversion efficiency was attributed to either the prolonged T₁ excited state lifetime or the intensified absorption in the visible range. Our study on the fluorene-containing N^N Pt(ii) bisacetylide complexes will be useful for designing new phosphorescent Pt(ii) complexes and for their applications.

Full text of DOI:10.1039/c2jm32074f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2012, 22, 15757
www.rsc.org/materials
PAPER
Fluorene as p-conjugation linker in N^N Pt(II) bisacetylide complexes and
their applications for triplet–triplet annihilation based upconversion†
*
Huimin Guo, Qiuting Li, Lihua Ma and Jianzhang Zhao
Received 3rd April 2012, Accepted 6th June 2012
DOI: 10.1039/c2jm32074f
Fluorene-containing N^N Pt(II) bisacetylide complexes were prepared, in which the fluorene moieties
were connected to the Pt(II) center via acetylide bonds (–C^C–). Different aryl groups were attached to
the fluorene moiety, such as phenylacetylide (Pt-4), naphthalimide-4-acetylide (Pt-1) and in Pt-2, the
fluorene moiety was changed to carbozale moiety. We found that with the fluorene linker between the
arylacetylide and the Pt(II) center, the absorption of complexes in the visible range were intensified. All
the complexes show room temperature (RT) phosphorescence. Furthermore, Pt-1 shows much longer
triplet excited state lifetime (s ¼ 138.1 ms) than the analogue Pt-3 (s ¼ 47.4 ms). For Pt-2, with changing
the fluorene moiety to carbazole moiety, the T1 state lifetime becomes much shorter (s ¼ 23.0 ms). Thus
the one-atom (N vs. C) difference is crucial for the photophysical properties. The triplet excited state of
Pt-1 was proved to be the intraligand excited state (3IL) by nanosecond time-resolved transient
absorption spectroscopy, spin density analysis and emission at 77 K. The complexes were used as triplet
sensitizers for triplet–triplet annihilation (TTA) upconversion. Upconversion quantum yield (FUC) up
to 24.3% was observed for Pt-1. Under the same conditions the model complex Pt-4 shows no
upconversion. The overall upconversion efficiency (h) of the new complexes are improved compared to
the model complexes, such as Pt-2, Pt-3 and Pt-4. The improved upconversion efficiency was attributed
to either the prolonged T1 excited state lifetime or the intensified absorption in the visible range. Our
study on the fluorene-containing N^N Pt(II) bisacetylide complexes will be useful for designing new
phosphorescent Pt(II) complexes and for their applications.
upconversion cycle.6-8 The excitation energy is harvested by the
Introduction
triplet sensitizer, thus transition S0 / S1 was imparted and was
followed by the intersystem crossing (ISC), by which the triplet
excited state of the sensitizer was populated. Then the energy was
transferred to the triplet acceptors via the Dexter mechanism,8,20
i.e. the triplet–triplet-energy-transfer (TTET) process. Thus the
triplet acceptor was promoted to the T1 excited state. Then with
collision and annihilation, the acceptor at the singlet excited state
will be produced, with the probability of 11.1%, determined by
the spin statistic law.21,22 Radiative decay of the singlet excited
state of the acceptor will produce the upconverted fluorescence,
at shorter wavelength than the excitation of the triplet sensitizer.
The major challenge facing the TTA upconversion is the
development of triplet sensitizers.6–19 It is desirable to develop
new triplet sensitizers that show readily tunable excitation and
emission wavelength. Furthermore, the lifetime of the T1 excited
state of the sensitizer should be much longer than a few micro-
seconds (ms), in order to enhance the TTET process.12,14,16,17,19
Concerning this aspect, the Pt(II) acetylide complexes in
particular are interesting because the photophysical properties of
Pt(II) acetylide can be tuned by using different acetylide ligands,
and these complexes have been used for nonlinear optics and
photo-induced charge separation, etc.15,16,23–39 The tunable
Upconversion, that is, emission at shorter wavelength, or more
generally, population of the excited state at higher energy level
than the excitation, has attracted much attention due to the
application in optics, photovoltaics, artificial photosynthesis,
etc.1–4 Among the upconversion techniques, such as with two-
photon absorption dyes,5 or with rare earth nanoparticles,3 the
upconversion based on triplet–triplet annihilation (TTA) has
attracted much attention, due to the advantages of strong
absorption of the excitation light, high upconversion quantum
yield, readily tunable excitation/emission wavelength and non-
coherent low excitation power requirement (solar light is suffi-
cient as excitation source).6–19
In TTA upconversion, triplet sensitizers and triplet acceptors
(annihilator/emitter) were combined to accomplish the
State Key Laboratory of Fine Chemicals, School of Chemical Engineering,
Dalian University of Technology, Dalian 116024, China. E-mail: zhaojzh@
dlut.edu.cn; Web: http://finechem.dlut.edu.cn/photochem; Fax: +86 (0)
411 8498 6236; Tel: +86 (0)411 8498 6236
† Electronic supplementary information (ESI) available: Molecular
structural characterization data, UV-vis absorption and emission of the
complexes in different solvents, delayed fluorescence and the z-matrixes
of the optimized geometries. See DOI: 10.1039/c2jm32074f
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15757

View Article Online
photophysical property of the Pt(II) acetylide complexes is ideal
for application as triplet sensitizers for TTA upconversion.6,7
However, the disadvantage of the normal Pt(II) acetylide
complexes is the weak absorption in the visible region and the
short lifetime of the T1 excited state.20,29,30,32,40 Usually the life-
time of the T1 excited state of the Pt(II) acetylide complexes is less
than 5 ms.40 These properties have to be improved to optimize the
TTA upconversion. For example, recently a Pt(II) acetylide
complex was used as triplet sensitizer.41 However, the complex
shows only moderate absorption in the visible range (3 ¼ 8750/
7600 Mꢀ1 cmꢀ1 at 429/476 nm), and the lifetime of the T1 excited
state is short (4.6 ms). As a result, upconversion quantum yield of
less than 1.5% was observed for this sensitizer, far lower than that
with Pt(II) porphyrin complexes.6
of the new complex is 5.7-fold of the previous result with the
Pt(II) NI acetylide complex as the triplet sensitizer.16a
Results and discussions
Design and synthesis of the complexes
The synthesis of Pt-1 was illustrated in Scheme 1. Pt-3 was
reported to show long-lived triplet excited state, but the
absorption in the visible range is weak. Fluorene has been
extensively used in luminescence study but not in Pt(II) acety-
lide complexes.23 Thus we used fluorene to extend the p-
conjugation of the acetylide ligand of Pt-1. The preparation of
the ligand is based on Sonogashira coupling reaction. Alkyl
chains were induced at the 9-position of the moiety to improve
the solubility and the chemical stability of the complexes.
Complex Pt-5, in which the NI moiety is replaced by phenyl
moiety, was prepared as the model complex for comparison of
the photophysical properties. All the complexes were obtained
in satisfying yields. Recently we prepared Pt(II) bisacetylide
complexes with fluorene ligands,16b but here different aryl
groups were attached to the fluorene moiety and the photo-
physical properties of the complexes differ substantially from
the previous complexes.
In order to address these aforementioned challenges, recently
we used cyclometalated Pt(II) complexes,19 Ru(II) polyimine
complexes,12,13 Pt(II) acetylide complexes,15,16,39 cyclometalated
Ir(III) complexes,17 and organic triplet sensitizers,14 as novel
triplet photosensitizers to improve the TTA upconversion. These
complexes share the feature of intense absorption in the visible
range and exceptionally prolonged T1 excited state lifetime.7a We
also proposed that non-emissive phosphorescent complexes can
be used as triplet sensitizers for TTA upconversion.13
We proposed that in order to access the Pt(II) acetylide
complexes that show intense absorption of the visible light and
the long-lived T1 excited state, one effective approach is to
attach an organic chromophore to the Pt(II) center. We and
others have demonstrated this is an effective approach.15,16,39,42
The 3IL state can be predicted by the DFT calculations.43
However, we noticed the limitations of this method, that is, with
the red-shifted absorption wavelength, the energy level of the T1
excited state decreases sharply. This effect is detrimental for
application in TTA upconversion because with decreased T1
excited state energy level, the available triplet acceptor will be
limited and the anti-Stokes shift of the upconversion will
become smaller (please refer to the Jablonski energy diagram of
the TTA upconversion).6,7 Thus, the next challenge for the
development of the triplet sensitizers for TTA upconversion is to
move the absorption of the sensitizer to the red-end of the
spectrum but without decreasing the energy level of the T1
excited state. Furthermore, Pt-3 shows long-lived triplet excited
state (Scheme 1), but its absorption of visible light is weak,37
thus the overall upconversion capability (hUC ¼ FUC ꢁ 3, where
FUC is the upconversion quantum yield and 3 is the molar
extinction coefficient of the sensitizer at the excitation wave-
length) will be weak.7a
Steady-state electronic spectroscopy
The UV-vis absorption of the ligands and the complexes were
studied (Fig. 1). The ligands L-3 and L-5 give absorption in the
UV range (Fig. 1a). For the fluorene-containing ligands L-1 and
carbazole-containing ligand L-2, however, the absorption is
much red-shifted, with absorption maximum at 417 nm and
430 nm for L-1 and L-2, respectively. This is due to the extended
p-conjugation framework of the ligands with the fluorene
moiety.
The absorption of the complexes were also compared (Fig. 1b).
The model complex, Pt-4, gives very weak absorption in the
visible range. Pt-5 gives slightly enhanced absorption in the
visible region (400–520 nm), with 3 ¼ 1.31 ꢁ 104 Mꢀ1 cmꢀ1 at
431 nm (Fig. 1b) and more intense absorption in the 350–400 nm
region.
With the fluorene substituents, Pt-1 and Pt-2 show enhanced
and red-shifted absorption compared to the model complex Pt-3,
Pt-4 and Pt-5. For example, the absorption maximum of Pt-1
and Pt-2 are 433 nm (3 ¼ 65 400 Mꢀ1 cmꢀ1) and 458 nm (3 ¼
28 700 Mꢀ1 cmꢀ1), respectively. It should be pointed out that the
absorption are stronger than most of the unsubstituted Pt(II)
biascetylide complexes.28–30,40
In order to improve the absorption of Pt-3 (Scheme 1) in the
visible range, and to maintain the long-lived T1 excited state,
herein we demonstrate the proof-of-concept of such a molecular
design strategy with the fluorene as the p-linker between the
organic chromophore and the Pt(II) center. The chromophore we
selected is the naphthalimide (NI) moiety. Compared to the Pt(II)
NI-acetylide complexes, the new complexes shows red-shift
absorption by 1690 cmꢀ1, but the T1 state energy level decreased
by only 525 cmꢀ1, with that of Pt-3 as the model complex. The
new complex with the fluorene linker shows a very long lifetime
of T1 excited state (138.1 ms). Upconversion quantum yield 24.3%
was observed. We propose the upconversion performance can be
evaluated by the 3 ꢁ FUC. With this parameter, the upconversion
The room temperature (RT) emission of the ligands and the
complexes were also investigated (Fig. 2). The emission of L-5 is
with significant vibration progression (Fig. 2a). The emission of
the ligands are roughly related to the p-conjugation framework.
For example, the ligands L-1 and L-2 show the most red-shifted
emission. Notably with one atom difference, L-2 is more red-
shifted than L-1.
The complexes show much more red-shifted emission than the
ligands. The emission band of Pt-1 is structured, which is similar
to the emission spectrum of Pt-3. Pt-3 is known for its intra-
ligand triplet excited state (3IL).37,38a Usually the 3IL excited
state gives structured emission band, whereas the normal
15758 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Scheme 1 Synthesis of the complexes Pt-1 and Pt-2. The known complexes Pt-3, Pt-4 and Pt-5 are presented for comparison. The triplet sensitizer used
in the triplet–triplet annihilation upconversion is also presented. (i) Pd(PPh3)Cl2, CuI, PPh3, NEt3, reflux, 8 h; (ii) trimethylsilyl acetylene, Pd(PPh3)4,
CuI, NEt3, reflux, 8 h; (iii) K2CO3, CH3OH, CH2Cl2, 2 h and (iv) CH2Cl2, CuI, (i-Pr)2NH, r.t., 12 h.
metal-to-ligand charge transfer state (3MLCT) give structureless
emission band, which is demonstrated by the emission of Pt-4
(Fig. 2b). Thus based on the emission profile, we propose that the
T1 excited state of Pt-1 is with significant 3IL character,
conversely, the emissive T1 state of Pt-2 is with more significant
3MLCT character.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15759

View Article Online
Fig. 1 UV-vis absorption spectra of (a) ligands (L-1, L-2, L-3 and L-5)
and (b) complexes (Pt-1, Pt-2, Pt-3, Pt-4 and Pt-5). c ¼ 1.0 ꢁ 10ꢀ5 M in
toluene. 25 ꢂC.
Fig. 3 (a) Emission spectra of Pt-1 (lex ¼ 440 nm) under N2, air and O2;
(b) emission spectra of Pt-4 (lex ¼ 380 nm) under N2, air and O2; (c)
emission spectra of Pt-1 (lex ¼ 440 nm), under different volume fractions
of O2 and (d) the fitting curves of the oxygen sensing properties of Pt-1
with Stern–Volmer equation. c ¼ 1.0 ꢁ 10ꢀ5 M, in toluene. 25 ꢂC.
Fig. 2 Normalized emission spectra of (a) ligands (L-1, lex ¼ 400 nm; L-
2, lex ¼ 410 nm; L-3, lex ¼ 330 nm; L-5, lex ¼ 340 nm) and (b) complexes
among the complexes studied (KSV ¼ 33.75 torrꢀ1) The quench-
ing constant of Pt-3 is slightly larger than that of Pt-2. Pt-4 and
Pt-5 give much smaller quenching constants. This trend is in
agreement with the lifetime of the T1 excited state (Table 1 and
Fig. 4), which is known that the complex with longer T1 excited
state lifetime gives higher O2 sensitivity.48–50
(Pt-1, lex ¼ 440 nm; Pt-2, lex ¼ 460 nm; Pt-3, lex ¼ 420 nm; Pt-4, lex
380 nm; Pt-5, lex ¼ 410 nm). c ¼ 1.0 ꢁ 10ꢀ5 M in toluene. 25 ꢂC.
¼
The fluorescence quantum yields of the ligands varied signifi-
cantly, with the lowest fluorescence quantum yield was observed
for L-3 (F ¼ 4.4%). For the fluorene-containing ligands L-1, L-2
and L-5, much higher quantum yields were observed (up to
84.3%). The fluorescence lifetime of the ligands are in the range
of 1.57–3.86 ns. Compared to the fluorescence quantum yields of
the ligands, the complexes give lower quantum yields. However,
the luminescence lifetimes of the complexes are significantly
longer than the lifetimes of the ligands. Notably, the lifetime up
to 286.0 ms was observed for Pt-1. Furthermore, the lifetime of
Pt-2 (s ¼ 19.7 ms) is much longer than the model complex (s ¼
0.9 ms). Pt-3 was reported to show long-lived T1 excited state.37,38a
The long-lived T1 excited state is usually an indication of the 3IL
feature of the triplet excited state.16,17,32,37,39,44–47
77 K emission spectra
In order to assign the emissive triplet excited states of the
complexes, emission at 77 K were studied (Fig. 5). The thermally
induced Stokes shift (DES), i.e. the energy difference between the
RT emission and the emission at 77 K, is an indication of the IL
feature of the triplet excited state. For the complex with small
value, the T1 state can be recognized as 3IL excited state.17,18,44,51
For Pt-1 and Pt-2, the emission maxima are slightly red-shif-
ted compared to that at RT. Thus the T1 state is with significant
3IL feature. For Pt-5, however, the emission band gives a blue
shift of 43 nm at 77 K compared to the emission at RT, the large
thermally induced Stokes shift (DEs) of 1423 cmꢀ1 indicates the
3MLCT feature of the triplet excited state.16b
Sensitivity of the emission intensity to O2
The emission intensity of the complexes is sensitive to O2, i.e. the
emission can be remarkably quenched by O2 (Fig. 3). Thus these
complexes can be used for luminescent O2 sensing.38,46,47 For
example, the emission of Pt-4 is significantly quenched in air
condition than that in nitrogen atmosphere (Fig. 3b). For Pt-1,
which is with much longer lifetime than Pt-4, the sensitivity is
higher than that of Pt-4. For example, the emission is completely
quenched in air atmosphere (Fig. 3b). Similarly the emission
intensity of Pt-2 is also sensitive to O2 (see ESI†). The quenching
of the emission of the complexes was studied with small steps of
variation of the O2 concentrations (Fig. 3c). The quenching data
were plotted by the Stern–Volmer equation (Fig. 3d). It was
found that the quenching constant of Pt-1 is the largest one
Nanosecond time-resolved transient difference absorption spectra
In order to study the long-lived triplet excited state of the
complexes, the nanosecond time-resolved transient difference
absorption spectra of the complexes were measured (Fig. 6). For
Pt-1 and Pt-2, ground state depletion is clearly demonstrated by
the bleaching at 440 nm and 460 nm, respectively. At the same
time, intense transient absorption in the 500–850 nm region were
observed.
These transient features are drastically different from that of
the model complex Pt-4.45 Instead, the transient absorptions in
the region of 500–850 nm are similar to that of Pt-3, for which a
15760 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Table 1 Photophysical parameters of the ligands and the platinum complexesa
labs (nm)
3 ꢁ 10ꢀ4 (Mꢀ1 cmꢀ1
)
lex (nm)
lem (nm)
F
sd
L-1
L-2
L-3
L-5
Pt-1
Pt-2
Pt-3
Pt-4
Pt-5
306/330/396/417
414/430
350/368
313/334/352
433/450
458
414
424
357/373/431
2.19/2.72/3.14/2.79
2.26/2.28
1.98/1.89
3.17/5.54/4.71
6.54/6.21
2.87
3.91
0.72
11.50/11.50/1.31
414
437
365
350
440
466
410
415
380
446
484
399
357, 375
642, 704
613
623, 678
565
586
0.469b
0.818b
0.044b
0.843b
0.022c
0.016c
0.111c
0.293c
0.179c
1.7 ns
2.9 ns
1.6 ns
3.9 ns
286.0 ms
19.7 ms
63.9 ms
0.9 ms
0.7 ms
a
Recorded in deaerated toluene at 25 ꢂC. b With quinine sulfate (F ¼ 0.547 in 0.05 M sulfuric acid) as the standard. c With complex [Ru(dmb)3][PF6]2
d
(F ¼ 0.073 in MeCN) as the standard. Luminescence lifetimes.
Fig. 4 Phosphorescence lifetime decay curves of Pt-1 (lex ¼ 442 nm), Pt-
2 (lex ¼ 442 nm), Pt-3 (lex ¼ 442 nm) and Pt-5 (lex ¼ 405 nm), c ¼ 1.0 ꢁ
10ꢀ5 M, in toluene. 25 ꢂC.
Fig.
6 Nanosecond time-resolved transient difference absorption
spectra of (a) Pt-1 and (b) Pt-2. The corresponding decay curves of (c) Pt-
1 at 440 nm and (d) Pt-2 at 530 nm. Excited with 532 nm pulsed-laser. c ¼
1.0 ꢁ 10ꢀ5 M, in toluene. 25 ꢂC.
analysis (Fig. 7).13,14,16,17,39,52 Pt-4 is known to show the MLCT/
LLCT mixed T1 excited state.15 From Fig. 7, it is clear that the
spin density is distributed on the phenylacetylide ligand, Pt(II)
center and dbbpy ligand. For Pt-3, it has been shown the T1 state
Fig. 5 Emission spectra of the complexes (a) Pt-1, (b) Pt-2 at 77 K and
RT. For Pt-1, lex ¼ 440 nm; Pt-2, lex ¼ 460 nm. c ¼ 1.0 ꢁ 10ꢀ5 M in
EtOH : MeOH ¼ 4 : 1 (v/v).
3IL state localized on the NI moiety was assigned.37,38 Thus we
propose that the T1 state of Pt-1 and Pt-2 can be assigned with
significant IL components.
Table 2 Photophysical properties of Pt (II) complexes with 3MLCT
excited states and 3IL excited states
The lifetime of the T1 excited state of the complexes were
determined by the transient absorption. Lifetimes of 138.1 ms
23.0 ms and 47.4 ms were determined for Pt-1, Pt-2, Pt-3,
respectively (Table 2). We noticed the difference between the
lifetimes determined with the luminescence method (Table 1) and
the transient absorption methods (Table 2). The exact reason for
these discrepancies is unknown.
a
b
c
d
FUC
sT (ms)
Ksv (103 Mꢀ1
)
Ksv (torrꢀ1
)
Pt-1
Pt-2
Pt-3
Pt-4
Pt-5
0.243
0.147
0.192
0.0
138.1e
23.0
47.4
0.9
1647
36.6
273.6
2.9
33.8
0.7
1.9
0.036
0.024
0.0
0.7
2.2
a
Result in deaerated toluene upconversion quantum yield with coumarin
b
6 as the standard (F ¼ 0.78 in CH3CH2OH). Triplet state lifetimes.
c
Spin density analysis of the complexes
Stern–Volmer plots for phosphorescence quenching. With DPA as the
quencher. Stern–Volmer plots for O2 quenching. Average lifetime.
Results of bis-exponential fitting, 156.4 ms (82.8%) and 38.5 ms (17.2%).
d
e
The features of the triplet state of the complexes were also
studied from a theoretical perspective, i.e. the spin density
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15761

View Article Online
is a 3IL state. The spin density analysis shows that the spin
density surface is distributed on the NI ligand, the Pt(II) center
and the dbbpy ligand contribute a very small portion to the spin
density surface. Thus the spin density analysis is in agreement
with the experimental results for Pt-3 and Pt-4.
sensitizers.6–19 It is desired to develop new triplet sensitizers for
TTA upconversion.
The TTA upconversion with the Pt(II) complexes as the triplet
sensitizers can be summarized in Scheme 2. The photoexcitation
of the complexes will produce the singlet excited states, such as
the 1MLCT or the 1IL state. Then the triplet excited states of the
complexes were populated via the internal conversion (IC). It
For Pt-5, the spin density is distributed on the fluorene moiety,
the Pt(II) center and the dbbpy ligand, which is similar to the
result of the Pt-4. Thus we propose that the T1 state of Pt-5 is
featured with MLCT/LLCT components. This is in agreement
with the short lifetime of the T1 state of Pt-5 (s ¼ 0.74 ms).
For Pt-1, the spin density is distributed on the NI-fluorene
moiety, the Pt(II) center and the dbbpy ligand make very small
contribution to the spin density of the complex. Thus we propose
that the T1 state of Pt-1 is featured with significant IL character.
This is in full agreement with the long lifetime of the T1 state of
Pt-1, measured by the luminescence method and the transient
absorption method. For Pt-2, however, the spin density surface is
similar to that of Pt-4 and Pt-5, thus we propose that the T1 state
is with significant MLCT feature. This is in agreement with the
relatively short lifetime of the triplet excited state of Pt-2. Thus
the spin density analysis is helpful for assignment of the character
of the triplet excited state of the transition metal complexes.
We have shown that the absorption of the complexes were
enhanced with the fluorene moiety and the lifetimes of T1 excited
states were extended.
3
should be noted that for complex Pt-1, the IL state is much
3
lower in energy level than that of the MLCT state of the N^N
Pt(II) bisacetylide complexes. Then the TTET occurs between the
triplet excited state of the sensitizer and the triplet acceptor, 9,10-
diphenylanthracene (DPA). It should be pointed out that the
quenching of the triplet excited state of the sensitizers, for which
both emissive or non-emissive, the principal rules of the Stern–
Volmer quenching was followed, i.e. the TTET efficiency is
proportional to the lifetime of the triplet excited state of the
sensitizers. Furthermore, since the TTA process is dependent on
the concentration of the acceptors at the triplet excited state, thus
the TTA, as well as the upconverted fluorescence emission, is
proportional to the concentration of the sensitizers at the triplet
excited state. Thus the light-harvesting ability and the inter-
system crossing (ISC) of the sensitizers are also important for the
TTA upconversion.
Based on the Jablonski diagram of the TTA upconversion
(Scheme 2), two parameters of the sensitizer are crucial for the
TTA upconversion, that is, the light-harvesting ability of the
sensitizer and the lifetime of the T1 excited state of sensitizer.
Strong absorption of the excitation light will produce more
concentrated sensitizer molecules at the triplet excited state, with
which the concentration of the acceptor molecules at the triplet
excited state will be highly populated. The long-lived T1 excited
state of the sensitizer will also enhance the TTET efficiency. Thus
the TTA upconversion can be improved with the sensitizer that
shows intense absorption of the visible light and the long-lived T1
excited state. Thus the complexes Pt-1–Pt-5 were used as triplet
sensitizers for TTA upconversion. Based on the T1 state energy
levels of these complexes, DPA was used as triplet acceptor. It
should be pointed out that the selection of the acceptor is also
dependent on the excitation wavelength. Only those triplet
acceptors that show no absorption at the excitation wavelength
of the sensitizer can be used as triplet sensitizer, otherwise the
triplet acceptor will be excited and significant interference with
the upconversion will be resulted.
Application of the complexes as triplet sensitizers for triplet–
triplet annihilation upconversion
As an application of the enhanced absorption of the complexes in
the visible region and the prolonged lifetime of the T1 excited
states, the complexes were used as triplet sensitizers for the TTA
based upconversions.6-19,53
Upconversions have attracted much attention due to their
applications in photovoltaics, fluorescence imaging, and
photonics. The recently developed TTA upconversion is partic-
ularly promising among the other upconversion methods, such as
the two-photon-absorption (TPA) dyes,5 the upconversion with
rare earth metal materials,3 etc., due to the advantages of TTA
upconversion of readily tunable excitation/emission wavelength,
intense absorption of the visible light, and high upconversion
quantum yields, etc.6,7
The current development of the TTA upconversion is facing
some disadvantages, such as the limited availability of the triplet
The emission of the complexes alone upon 473 nm laser exci-
tation were studied (Fig. 8a). Dependent on the phosphorescence
quantum yield and the absorbance at 474 nm, the complexes give
different emission intensity. Pt-1 and Pt-2 give relatively weaker
emission than other complexes, due to their smaller phospho-
rescence quantum yields than that of Pt-3, Pt-4 and Pt-5. It
should be noted that the absorbance of Pt-1 and Pt-2 are
stronger than other complexes.
In the presence of DPA, however, upconverted fluorescence
emission in the region of 400–550 nm were observed for Pt-1, Pt-
2 and Pt-3. These new emission bands are due to the upconverted
fluorescence of DPA. Excitation of the sensitizers or the DPA
alone did not produce this emission band, thus proved the
upconversion for the mixture of the complexes and DPA.
Interestingly, the upconversion with Pt-1 and Pt-2 are more
significant than that with Pt-3, despite the weak emission of Pt-1
Fig. 7 The spin density of Pt-1, Pt-2 and Pt-3 calculated by DFT at the
B3LYP/6-31G((d)/LanL2DZ level using Gaussian 09W.
15762 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Scheme 2 Jablonski diagram illustrating the sensitized TTA upconversion process between Pt(II) complexes (exemplified by Pt-1) and DPA. The effect
of the light-harvesting ability and the luminescence lifetime of the Pt(II) sensitizer is also shown. E is energy. GS is ground state (S0). 1IL* is intraligand
singlet excited state (NI-fluorene localized). IC is internal conversion. ISC is intersystem crossing. 3MLCT* is the Pt(II) based metal-to-ligand-charge-
transfer triplet excited state. 3IL* is intraligand triplet excited state (NI-fluorene localized). TTET is triplet–triplet energy transfer. 3DPA* is the triplet
excited state of DPA. TTA is triplet–triplet annihilation. 1DPA* is the singlet excited state of DPA. The emission bands observed for the sensitizers alone
3
3
is the IL emissive excited state. The emission bands observed in the TTA experiment is the simultaneous IL* emission (phosphorescence) and the
1DPA* emission (fluorescence).
and Pt-2 (Fig. 8a). The significant upconversion with Pt-1 and
Pt-2 as the triplet sensitizer is due to the enhanced absorption of
visible light and the long-lived T1 excited states of Pt-1, Pt-2 and
Pt-3. The upconversion with these complexes are red-shifted
compared to the fluorene-containing Pt(II) acetylide complexes
we reported recently.16b
The upconversion quantum yields were determined, the
complex Pt-1 shows the most significant upconversion with
quantum yield up to 24.3%. Similar upconversion quantum
yields were observed for Pt-2 and Pt-3 (14.7% and 19.2%,
respectively Table 2). We noticed the quantum yield is higher
than the previously expected 11.1% (based on the spin density
statistic).6,7 However, since the quartet excited state can also be
responsible for the upconversion, thus upconversion quantum
yields higher than 11.1% is possible. Previously upconversion
quantum yield higher than this value have been reported.6,9
Recently we propose that the overall upconversion capability
of transition metal complexes can be described as:
hUC ¼ 3 ꢁ FUC
(1)
where 3 is the molar extinction coefficients of the sensitizers as the
excitation wavelength and FUC is the upconversion quantum
yield.7 The upconversion capability (hUC) of a complex is
proportional to the molar extinction coefficient, that is, the
complexes that give larger molar extinction coefficients will give
stronger upconversion emission intensity (Pt-2 vs. Pt-3, Fig. 8b).
The upconversion quantum yield (FUC) itself is insufficient to
describe the upconversion property of the sensitizers, especially
for applications, such as photovoltaics. Based on this new
equation, the value of Pt-1 is 5.7-fold of Pt-3. Notably, Pt-2 and
Pt-3 give similar upconversion quantum yields (FUC is 14.7% and
19.2%, respectively), but the FUC value is different, the h value of
Pt-2 is 3.0-fold of Pt-3. The different value is due to the larger 3
value of Pt-2. This more reasonable description of the
Fig. 8 Emission and upconversion with the complexes as the triplet
sensitizer upon 473 nm laser excitation. (a) Emission of the Pt(II)
complexes without DPA. (b) Upconverted emission in the presence of
DPA. lex ¼ 473 nm, 5 mw, c[sensitizers] ¼ 1.0 ꢁ 10ꢀ5 M, c[DPA] ¼ 4.3 ꢁ
10ꢀ5 M, in toluene. 25 ꢂC.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15763

View Article Online
upconversion by the h value is proved by experiments (Fig. 8b),
in which the upconversion fluorescence intensity of Pt-2 is much
higher than that of Pt-3. We also noted that the upconversion
capability (hUC) of the new complexes are 2-fold of the fluorene-
containing Pt(II) bisacetylide complexes we reported recently.16b
In order to confirm that the blue emission in Fig. 8 is due to
upconversion, the lifetime of the blue emission band with Pt-1 as
the triplet photosensitizer in Fig. 8 were measured (Fig. 9a). The
lifetime was measured as 488.1 ms. This long-lived fluorescence
emission is characteristic of the TTA upconversion. The lifetime
of the prompt fluorescence of DPA was determined as 5.6 ns
(Fig. 9b). Similar long-lived delayed fluorescence were observed
with Pt-2 and Pt-3 as the triplet photosensitizers (sDF ¼ 175.1 ms
and 14.4 ms, respectively. See ESI†.). It should be pointed out
that the delayed fluorescence lifetime is resulted from the colli-
sion of the triplet photosensitizer and the triplet acceptor, as well
as energy pooling effect of the triplet photosensitizer, thus the
lifetime value is highly dependent on the experimental condi-
tions, such as the concentrations of the photosensitizers and the
acceptors (see ESI†).
The efficiency of the TTET process can be quantitatively
studied by the quenching experiments (Fig. 10). The emission of
the sensitizers can be quenched by DPA (Fig. 10a–c). The
quenching is due to TTET from the sensitizer’s triplet excited
state to the triplet acceptor. Herein the singlet state energy
transfer is impossible because of the unmatched energy levels.6-8
We found that the quenching of the phosphorescence of Pt-1 is
the most significant among the complexes. The quenching data
were plotted as the Stern–Volmer curves (Fig. 10). Fitting of the
data gives a second order quenching constant of 1647 Mꢀ1 for Pt-
1, which was followed by Pt-3 (KSV ¼ 273.6 Mꢀ1) and then Pt-2
(KSV ¼ 36.6 Mꢀ1). Pt-4 and Pt-5 give very small quenching
constants (Table 2). The quenching effect is due to the different
lifetime of the complexes.7,14,16ꢀ19,39
Fig. 10 Phosphorescence quenching of the complexes by triplet acceptor
DPA. (a) Pt-1 (lex ¼ 440 nm), (b) Pt-2 (lex ¼ 460 nm) and (c) Pt-3 (lex
¼
420 nm) with increasing DPA concentration in toluene, c[sensitizer] ¼
1.0 ꢁ 10ꢀ5 M, 25 ꢂC. (d) Stern–Volmer plots for phosphorescence
quenching of complexes Pt-1–Pt-5.
emissive triplet excited state of Pt-3 (FUC ¼ 19.2%) and the
triplet acceptor DPA. For Pt-1, however, the upconverted fluo-
rescence increased dramatically, but without any much phos-
phorescence to be quenched (Fig. 11a). The similar result was
observed for Pt-2 (Fig. 11b). The results of Pt-1 and Pt-2 clearly
demonstrated that the non-emissive triplet excited state of the
triplet sensitizers were involved in the TTET process. Thus we
propose that non-phosphorescent transition metal complexes
can be used as the triplet sensitizers for TTA
upconversion.13,14,16,17
The role of the dark excited state in the TTA upconversion was
unambiguously demonstrated in Fig. 11. For Pt-3 (see ESI†), the
phosphorescence was quenched with increased DPA concentra-
tion, concurrently the upconverted fluorescence was enhanced.
This result is reasonable since the TTET occurs between the
The upconversion is visible with un-aided eye (Fig. 12). For Pt-
4 and Pt-5, the emission color is yellow to orange and the
emission does not change in the presence of DPA, due to the lack
of upconversion with these two sensitizers (Fig. 8b). For Pt-1 and
Pt-2, however, the emission color of the sensitizers alone are red
to deep red, but the emission turns to bright blue in the presence
of DPA, due to the remarkable upconversion with the sensitizers.
Similar result was observed with Pt-3. It is observed that the
Fig. 9 (a) Delayed fluorescence observed in the TTA upconversion with
compound Pt-1 as triplet photosensitizer and DPA as the triplet acceptor.
Excited at 473 nm (nanosecond pulsed OPO laser synchronized with
spectrofluorometer) and monitored at 410 nm. Under this circumstance
the compound Pt-1 is selectively excited and the emission is due to the
upconversion of DPA. In deaerated toluene c[sensitizers] ¼ 1.0 ꢁ 10ꢀ5 M;
c[DPA] ¼ 4.3 ꢁ 10ꢀ4 M. (b) The prompt fluorescence decay of DPA
determined in a different experiment (excited with picosecond 405 nm
laser, the decay of the emission was monitored at 420 nm) 20 ꢂC.
Fig. 11 The upconversion of (a) Pt-1 and (b) Pt-2 with increased DPA
concentration. Excited with 473 nm laser. c[sensitizer] ¼ 1.0 ꢁ 10ꢀ5 M in
toluene. 25 ꢂC.
15764 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012

View Article Online
upconversion intensity of Pt-1 and Pt-2 are more intense than
that with Pt-3. This is exactly the demonstration of the h values
of the sensitizers.
upconversion efficiency (hUC
)
of the new complexes are
improved compared to the model complexes, such as Pt-3, Pt-4
and Pt-5. The improved upconversion efficiency (hUC) was
attributed to either the prolonged T1 excited state lifetime or the
intensified absorption in the visible range (3). Our study on the
fluorene-containing N^N Pt(II) bisacetylide complexes will be
useful for design new phosphorescent Pt(II) complexes and for
their applications.
Conclusions
In summary, fluorene-containing N^N Pt(II) bisacetylide
complex Pt-1 was prepared, in which the fluorene moiety was
directly connected to the Pt(II) center via C^C bond. Different
aryl groups were attached to the fluorene moiety, phenylacetylide
(Pt-4), naphthalimide-4-acetylide (Pt-1). In Pt-2, an analogue of
Pt-1, the fluorene moiety was changed to carbozale group. The
model complexes Pt-3, Pt-4 and Pt-5 were used for comparison
in the photophysical studies. We found that with the fluorene
linker between the arylacetilide and the Pt(II) center, the
absorption of complexes in the visible range were intensified. All
the complexes show room temperature phosphorescence.
Furthermore, we found that the Pt-1 shows much longer triplet
excited state lifetime (s ¼ 138.1 ms) than the analogue Pt-3 (s ¼
47.4 ms) without the fluorene linker, as well as Pt-2 (s ¼ 23.0 ms),
with one atom of substitution (difference between the fluorene
and carbazole moiety). Carbazole was used as the linker between
the naphthalimide and the Pt(II) center (Pt-2), however, much
shorter triplet excited state lifetime was observed (s ¼ 23.0 ms).
Thus the one-atom (N vs. C) difference is crucial for the photo-
physical properties. The triplet excited state of Pt-1 was proved
to be the intraligand excited state (3IL) by nano-second time-
resolved spectroscopy, spin density analysis and emission spectra
at 77 K. The complexes were used as triplet sensitizers for triplet–
triplet annihilation upconversion. Upconversion quantum yield
(FUC) up to 24.3% was observed for Pt-1. The overall
Experimental section
Physical measurements
The nanosecond time-resolved transient absorption spectra were
detected by laser flash photolysis instruments (LP920, Edinburgh
Instruments, UK) and recorded on a Tektronix TDS 3012B
oscilloscope. The lifetime values (by monitoring the decay trace
of the transients) were obtained with the LP900 software. All
samples were deaerated with argon for ca. 30 min before
measurement and the gas flow is kept during the measurement.
Triplet–triplet-annihilation upconversions
Diode pumped solid state (DPSS) laser (473 nm) was used for the
upconversions. The power of the laser beam is measured with
VLP-2000 (a pyroelectric power meter). The laser power used in
the upconversion was 5 mW, the laser spot diameter is 3 mm. The
samples were purged with N2 or Ar for 30 min before measure-
ment (note the upconversion can be significantly quenched by
O2). For the upconversion experiments, the mixed solution of the
complex (triplet sensitizer) and DPA (triplet acceptor) was
Fig. 12 Photographs of the phosphorescence and the TTA upconversion with complexes Pt-1–Pt-5 as the triplet sensitizers. (a) Images before and after
adding DPA in toluene. (b) The CIE of the emission of complexes. (c) The CIE of the upconversion of complexes. Excited with 473 nm laser c[complexes]
¼ 1.0 ꢁ 10ꢀ5 M, c[DPA] ¼ 4.33 ꢁ 10ꢀ5 M, 25 ꢂC.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15765

View Article Online
degassed for 30 min with N2 or Ar. Then the solution was excited
with laser. The upconverted fluorescence of DPA was observed
with spectrofluorometer. In order to suppress the laser scattering,
a black box with a small hole on it was put behind the fluorescent
cell to trap the laser beam behind the vial (the small hole as the
entrance of the laser into the black box).
1.98 (m, 5H), 1.42–1.31 (m, 8H), 1.22–1.08 (m, 20H), 0.96–0.87
(m, 6H), 0.83–0.79 (m, 6H), 0.64–0.60 (m, 4H). ESI-MS
C51H62NO2Br calculated m/z ¼ 799.3964, found m/z ¼ 799.3983.
1-(7-Ethynyl-9,9-dioctyl-9H-fluoren-2-ylethynyl) naphthalimide
(compound L-1)
The upconversion quantum yields were determined with a
laser dye Coumarin 6 as the quantum yield standard (Fstd ¼ 0.78
in CH3CH2OH) and the quantum yields were calculated with eqn
(2),6 where FUC, Aunk, Iunk and hunk represents the quantum
yield, absorbance, integrated photoluminescence intensity and
the refractive index of the samples and the solvents, respectively.
The equation is multiplied by a factor 2 in order to make the
maximum quantum yield to be unity.
Under Ar atmosphere, compound a (140.0 mg, 0.175 mmol),
Pd(PPh3)2Cl2 (13.5 mg, 0.0175 mmol), triphenylphosphine
(11.2 mg, 0.035 mmol), CuI (7.3 mg, 0.035 mmol) and dry tri-
ethylamine (1.0 mL) were mixed together. The mixture was
purged with Ar and then the trimethylsilyl acetylene (0.5 mL,
3.50 mmol) was added. The mixture was stirred and refluxed for
8 h. Then the reaction mixture was cooled to the room temper-
ature and the solvent was removed under reduced pressure. The
product was purified by column chromatography (silica gel,
hexane). P-1 was obtained as oil, 115.0 mg, yield 80.4%. Then P-
1, K2CO3 (220.0 mg, 1.52 mmol), methanol (10 mL), CH2Cl2 (3
mL) was mixed together. The mixture was stirred at room
temperature for 2 h. The product L-1 was obtained, 80.0 mg,
yield: 76.2%. 1H NMR (400 MHz, CDCl3): d 8.82 (d, 1H, J ¼ 8.0
Hz), 8.68 (d, 1H, J ¼ 8.0 Hz), 8.59 (d, 1H, J ¼ 8.0 Hz), 8.01 (d,
1H, J ¼ 8.0 Hz), 7.90 (t, 1H, J ¼ 8.0 Hz), 7.76 (d, 1H, J ¼ 8.0 Hz),
7.69–7.67 (m, 2H), 7.62 (s, 1H), 7.53–7.50 (m, 2H), 4.16–4.12 (m,
2H), 3.18 (s, 1H), 2.03–1.99 (m, 5H), 1.41–1.26 (m, 8H), 1.20–
1.07 (m, 20H), 0.96–0.88 (m, 6H), 0.83–0.79 (m, 6H), 0.65–0.59
(m, 4H). 13C NMR (100 MHz, CDCl3), d 164.6, 164.3, 151.6,
151.3, 141.8, 141.0, 140.9, 132.5, 131.9, 131.8, 131.6, 131.4, 131.0,
130.7, 128.4, 127.6, 127.6, 126.7, 126.4, 123.3, 123.3, 122.3, 121.4,
121.2, 120.5, 120.3, 100.3, 87.0, 84.7, 55.6, 44.5, 40.5, 38.2, 32.0,
31.07, 30.1, 29.4, 28.9, 24.3, 23.9, 23.3, 22.8, 14.3, 14.2, 10.6. HR-
MALDI-MS: [C53H53NO2 + H+] calculated m/z ¼ 746.4937,
found m/z ¼ 746.4908.
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
Astd
Iunk
Istd
hunk
hstd
FUC ¼ 2Fstd
(2)
Aunk
For the measurement of the TTET efficiency, i.e. the Stern–
Volmer quenching constants, the concentration of the sensitizer
was fixed at 1.0 ꢁ 10ꢀ5 M, the quenching of the phosphorescence
of the sensitizer was measured with increasing the DPA
concentration in the solution.
The CIE coordinates (x, y) of the emission of the sensitizers
alone and the emission of the upconversion were derived from
the emission spectra with the software of CIE color Matching
Linear Algebra.
DFT calculations
The density functional theory (DFT) calculations were used for
optimization of the ground state geometries of both singlet states
and triplet states. The energy level of the T1 state (energy gap
between S0 state and T1 state) were calculated with the time-
dependent DFT (TDDFT), based on the optimized singlet
ground state geometries (S0 state). TDDFT calculations were
also used for the prediction of the UV–vis absorption of the
triplet sensitizers at the triplet state, in our case it is the transient
absorption of the triplet sensitizers after laser flash. Please note
that the bleaching bands in the time-resolved transient absorp-
tion spectra cannot be predicted by the TDDFT calculations. All
the calculations were performed with Gaussian 09W.43
Complex Pt-1
Pt(dbbpy)Cl2 (17.0 mg, 0.03 mmol), CuI (2.0 mg, 0.03 mmol) and
diisopropylamine (1.0 mL) were dissolved in 5 mL CH2Cl2, the
mixture was stirred for 10 min. The mixture was purged with Ar,
L-1 (60.0 mg, 0.08 mmol) was added and the mixture was stirred
at room temperature for 12 h. The mixture was evaporated to
dryness, the residue was purified by column chromatography
(silica gel, CH2Cl2 : hexane ¼ 2 : 1, v/v). The product was
collected as the third fraction. 40.0 mg of yellow powder was
obtained, yield: 70.0%. M.p. ¼ 117.0–118.2 ꢂC. 1H NMR
(400 MHz, CDCl3): d 9.83 (d, 2H, J ¼ 8.0 Hz), 8.84 (d, 2H, J ¼
8.0 Hz), 8.67 (d, 2H, J ¼ 8.0 Hz), 8.58 (d, 2H, J ¼ 8.0 Hz), 8.00 (d,
4H, J ¼ 8.0 Hz), 7.86 (t, 2H, J ¼ 8.0 Hz), 7.71 (d, 2H, J ¼ 8.0 Hz),
7.64–7.57 (m, 12H), 4.16–4.12 (m, 4H), 2.03–1.99 (m, 10H), 1.48
(s, 18H), 1.41–1.38 (m, 8H), 1.32–1.25 (m, 8H), 1.19–1.07 (m,
40H), 0.96–0.87 (m, 12H), 0.81–0.78 (m, 12H), 0.69–0.65 (m,
8H). 13C NMR (100 MHz, CDCl3), d 164.6, 164.4, 163.6, 156.4,
151.5, 150.9, 143.1, 137.7, 132.7, 131.8, 131.7, 131.5, 131.3, 130.7,
128.4, 128.2, 127.5, 127.1, 126.2, 123.2, 122.0, 119.8, 118.9, 103.5,
101.1, 87.7, 86.6, 55.4, 44.4, 40.8, 38.1, 36.0, 32.0, 30.9, 30.4, 30.4,
29.9, 29.5, 28.9, 24.2, 24.0, 23.3, 22.8, 14.3, 10.8. HR-MALDI-
MS: C124H148N4O4Pt calculated m/z ¼ 1952.1123, found m/z ¼
1952.1148.
1-(2-(2-Ethynyl-9,9-dioctyl-9H-fluoren-7-yl)ethynyl)
naphthalimide (compound a)
4-Ethynylnaphthalimide (305.0 mg, 1.0 mmol), 9,9-dioctyl-2,7-
dibromofluorene (3.250 g, 5.0 mmol), CuI (10.0 mg, 0.05 mmol),
Pd(PPh3)2Cl2 (3.5 mg, 0.005 mmol), triphenylphosphine (5.0 mg,
0.02 mmol) and dry triethylamine (60 mL) were mixed. After the
solution was purged with N2 for 30 min, the mixture was stirred
and refluxed under N2 for 8 h. Then the reaction mixture was
filtered and the organic phase was evaporated under reduced
pressure. The residue was purified by column chromatography
(silica gel, hexane : CH2Cl2 ¼ 1 : 2, v/v). A yellow solid was
obtained, 200.0 mg, yield: 25.0%. M.p. ¼ 97.0–97.8 ꢂC. 1H NMR
(400 MHz, CDCl3): d 8.81 (d, 1H, J ¼ 8.0 Hz), 8.67 (d, 1H, J ¼
8.0 Hz), 8.59 (d, 1H, J ¼ 8.0 Hz), 8.01 (d, 1H, J ¼ 8.0 Hz), 7.89–
7.86 (m, 1H), 7.73 (d, 1H, J ¼ 4.0 Hz), 7.68 (d, 1H, J ¼ 8.0 Hz),
7.60 (d, 2H, J ¼ 4.0 Hz), 7.50 (s, 2H), 4.16–4.12 (m, 2H), 2.01–
15766 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012

View Article Online
9-Butyl-3-iodo-9H-carbazole-naphthalimide (compound b)
obtained, yield: 64.2%. M.p. ¼ 208.0–209.2 ꢂC. 1H NMR
(400 MHz, CDCl3): d 9.90 (d, 2H, J ¼ 8.0 Hz), 8.79 (d, 2H, J ¼
8.0 Hz), 8.58 (d, 2H, J ¼ 4.0 Hz), 8.50 (d, 2H, J ¼ 8.0 Hz), 8.41 (d,
4H, J ¼ 4.0 Hz), 7.99 (s, 2H), 7.92 (d, 2H, J ¼ 8.0 Hz), 7.80 (t, 4H,
J ¼ 8.0 Hz), 7.72 (d, 2H, J ¼ 8.0 Hz), 7.64 (d, 2H, J ¼ 4.0 Hz),
7.41 (d, 2H, J ¼ 8.0 Hz), 7.35 (d, 2H, J ¼ 8.0 Hz), 4.32–4.29 (m,
4H), 4.16–4.07 (m, 4H), 1.97–1.86 (m, 6H), 1.47 (s, 18H), 1.43–
1.30 (m, 20H), 0.98–0.87 (m, 18H). 13C NMR (100 MHz, CDCl3):
d 164.7, 164.4, 163.4, 156.5, 151.4, 141.2, 139.3, 132.8, 131.7,
130.7, 130.3, 131.5, 128.7, 128.3, 127.4, 124.9, 124.4, 123.6, 123.0,
122.3, 121.4, 118.9, 112.0, 109.2, 108.7, 102.0, 85.3, 84.2, 44.4,
43.4, 38.1, 36.0, 31.4, 31.0, 30.5, 29.0, 24.0, 23.3, 14.4, 14.1, 10.9.
HR-MALDI-MS: C98H98N6O4Pt calculated m/z ¼ 1617.7297,
found m/z ¼ 1617.7343.
4-Ethynylnaphthalimide (167.0 mg, 0.50 mmol), 9-butyl-3,6-
diiodo-9H-carbazole (716.0 mg, 1.5 mmol), CuI (10.0 mg, 0.05
mmol), Pd(PPh3)2Cl2 (3.5 mg, 0.005 mmol), triphenylphosphine
(5.0 mg, 0.02 mmol), and dry triethylamine (60 mL) were mixed.
After the solution was purged with nitrogen for 30 min, the
mixture was refluxed under N2 for 8 h. Then the reaction mixture
was filtered and the organic phase was evaporated under reduced
pressure. The residue was purified through column chromato-
graphy (silica gel, hexane : CH2Cl2 ¼ 1 : 2, v/v). A yellow solid
was obtained, 215.0 mg, yield: 63.2%. M.p. ¼ 141.0–142.6 ꢂC. 1H
NMR (400 MHz, CDCl3): d 8.83 (d, 1H, J ¼ 8.0 Hz), 8.66 (d, 1H,
J ¼ 4.0 Hz), 8.57 (d, 1H, J ¼ 8.0 Hz), 8.44 (s, 1H), 8.37 (s, 1H),
7.98–7.95 (m, 1H), 7.79–7.76 (m, 1H), 7.45 (d, 1H, J ¼ 8.0 Hz),
7.24 (d, 2H, J ¼ 8.0 Hz), 4.32–4.29 (m, 2H), 4.16–4.12 (m, 2H),
1.97–1.95 (m, 1H), 1.89–1.85 (m, 2H), 1.42–1.26 (m, 10H), 0.98–
0.87 (m, 9H). ESI-MS C38H37N2O2I calculated m/z ¼ 680.1900,
found m/z ¼ 680.1901.
Acknowledgements
We thank the NSFC (20972024, 21073028 and 21103015),
Fundamental Research Funds for the Central Universities
(DUT10ZD212 and DUT11LK19), Royal Society (UK) and
NSFC (China-UK Cost-Share program/21011130154), Ministry
of Education (SRF for ROCS, SRFDP-200801410004 and
NCET-08-0077) and the Education Department of Liaoning
Province (2009T015) for financial support.
9-Butyl-3-iodo-9H-carbazole-naphthalimide ethynyl-
naphthalimide (compound L-2)
Under argon atmosphere, compound a (163.0 mg, 0.24 mmol),
Pd(PPh3)2Cl2 (13.5 mg, 0.0175 mmol), triphenylphosphine (11.2
mg, 0.035 mmol), CuI (7.3 mg, 0.035 mmol) and dry triethyl-
amine (1.0 mL) were mixed together, The mixture was purged
with Ar and then the trimethylsilyl acetylene was added. The
mixture was stirred and refluxed for about 8 h. The reaction
mixture was cooled to room temperature and the solvent was
removed under reduced pressure. The product was purified by
column chromatography (silica gel, hexane : CH2Cl2 ¼ 2 : 1,
v/v). Yellow solid was obtained, 120.0 mg, yield 73.6%. Then P-2,
K2CO3 (220.0 mg, 1.52 mmol), methanol (10 mL), CH2Cl2
(3 mL) was mixed together. The mixture was stirred at room
temperature for 2 h. The product L-2 of was obtained yellow
References
€
1 C. Reinhard, R. Valiente and H. U. Gudel, J. Phys. Chem. B, 2002,
106, 10051.
2 I. Etchart, M. Berard, M. Laroche, A. Huignard, I. Hernandez,
W. P. Gillin, R. J. Curryd and A. K. Cheetham, Chem. Commun.,
2011, 47, 6263.
3 (a) M. Haase and H. Schafer, Angew. Chem., Int. Ed., 2011, 50, 5808;
€
(b) O. S. Wenger and H. U. Gudel, Inorg. Chem., 2001, 40, 5747–5753;
(c) F. Auzel, Chem. Rev., 2004, 104, 139–173; (d) S. R. Luthi,
€
€
M. Pollnau, H. U. Gudel and M. P. Hehlen, Phys. Rev. B: Condens.
Matter Mater. Phys., 1999, 60, 162–178; (e) O. S. Wenger,
€
D. R. Gamelin, H. U. Gudel, A. V. Butashin and A. A. Kaminskii,
Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 16530–
1
solid 105.0 mg, yield: 76.1%. M.p. ¼ 91.5–92.1 ꢂC. H NMR
(400 MHz, CDCl3): d 8.85 (d, 1H, J ¼ 8.0 Hz), 8.68 (d, 1H, J ¼
8.0 Hz), 8.59 (d, 1H, J ¼ 8.0 Hz), 8.41 (s, 1H), 8.31 (s, 1H), 8.00
(d, 1H, J ¼ 8.0 Hz), 7.90 (t, 1H, J ¼ 8.0 Hz), 7.80 (d, 1H, J ¼ 8.0
Hz), 7.66 (d, 1H, J ¼ 8.0 Hz), 7.47 (d, 1H, J ¼ 8.0 Hz), 7.40 (d,
1H, J ¼ 8.0 Hz), 4.36–4.32 (m, 2H), 4.16–4.12 (m, 2H), 3.1 (s,
1H), 1.98–1.95 (m, 1H), 1.90–1.86 (m, 2H), 1.43–1.30 (m, 10H),
0.99–0.87 (m, 9H). 13C NMR (100 MHz, CDCl3), d 164.6, 164.3,
141.2, 140.9, 132.6, 131.7, 131.6, 131.5, 131.4, 130.1, 128.4, 127.4,
125.0, 124.9, 123.2, 122.8, 122.4, 113.3, 113.0, 109.4, 109.3, 101.1,
85.5, 84.8, 75.8, 44.4, 43.4, 38.2, 31.2, 31.0, 28.9, 24.3, 23.2, 20.7,
14.2, 14.0, 10.9. HR-MALDI-MS: [C40H38N2O2+] calculated
m/z ¼ 578.2933, found m/z ¼ 578.2883.
ꢀ
ꢀ
16537; (f) A. A. D. Adikaari, I. Etchart, P.-H. Guering, M. Berard,
S. R. P. Silva, A. K. Cheetham and R. J. Curry, J. Appl. Phys.,
2012, 111, 094502; (g) J. Liu, Y. Liu, Q. Liu, C. Li, L. Sun and
F. Li, J. Am. Chem. Soc., 2011, 133, 15276; (h) Q. Liu, Y. Sun,
T. Yang, W. Feng, C. Li and F. Li, J. Am. Chem. Soc., 2011, 133,
17122; (i) L. Xiong, Z. Chen, Q. Tian, T. Cao, C. Xu and F. Li,
Anal. Chem., 2009, 81, 8687; (j) Q. Liu, Y. Sun, C. Li, J. Zhou,
C. Li, T. Yang, X. Zhang, T. Yi, D. Wu and F. Li, ACS Nano,
2011, 5, 3146.
4 (a) S. Baluschev, T. Miteva, V. Yakutkin, G. Nelles, A. Yasuda and
G. Wegner, Phys. Rev. Lett., 2006, 97, 143903; (b) Y. Y. Cheng,
B. Fueckel, R. W. MacQueen, T. Khoury, R. Georges, R. C. Clady,
T. F. Schulze, N. Ekins-Daukes, M. J. Crossley, B. Stannowski,
K. Lips and T. schmidt, Energy Environ. Sci., 2012, 5, 6953.
5 H. M. Kim and B. R. Cho, Acc. Chem. Res., 2009, 42, 863.
6 T. N. Singh-Rachford and F. N. Castellano, Coord. Chem. Rev., 2010,
254, 2560.
Complex Pt-2
7 (a) J. Zhao, S. Ji and H. Guo, RSC Adv., 2011, 1, 937; (b) P. Ceroni,
Chem.–Eur. J., 2011, 17, 9560.
8 A. Monguzzi, R. Tubino and F. Meinardi, Phys. Rev. B: Condens.
Matter Mater. Phys., 2008, 77, 155122(1).
9 Y. Y. Cheng, B. Fckel, T. Khoury, R. G. C. R. Clady,
M. J. Y. Tayebjee, N. J. Ekins-Daukes, M. J. Crossley and
T. W. Schmidt, J. Phys. Chem. Lett., 2010, 1, 1795.
10 (a) S. Baluschev, V. Yakutkin, T. Miteva, Y. Avlasevich, S. Chernov,
S. Aleshchenkov, G. Nelles, A. Cheprakov, A. Yasuda, K. Muellen
and G. Wegner, Angew. Chem., Int. Ed., 2007, 46, 7693; (b) Q. Liu,
T. Yang, W. Feng and F. Li, J. Am. Chem. Soc., 2012, 134, 5390.
Pt(dbbpy)Cl2 (26.0 mg, 0.05 mmol), CuI (2.0 mg, 0.03 mmol) and
diisopropylamine (1.0 mL) were dissolved in 5 mL CH2Cl2, the
mixture was stirred for 10 min. The mixture was purged with Ar,
L-5 (86.7 mg, 0.15 mmol) was added and the mixture was stirred
at room temperature for 12 h. The mixture was evaporated to
dryness, the residue was purified by column chromatography
(silica gel, CH2Cl2 : hexane ¼ 1 : 1, v/v). The product was
collected as the third fraction. 50.3 mg of yellow powder was
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 15757–15768 | 15767

View Article Online
11 H.-C. Chen, C.-Y. Hung, K.-H. Wang, H.-L. Chen, W. S. Fann,
F.-C. Chien, P. Chen, T. J. Chow, C.-P. Hsu and S.-S. Sun, Chem.
Commun., 2009, 4064.
12 (a) S. Ji, W. Wu, W. Wu, H. Guo and J. Zhao, Angew. Chem., Int. Ed.,
2011, 50, 1626; (b) W. Wu, S. Ji, W. Wu, J. Shao, H. Guo, T. D. James
and J. Zhao, Chem.–Eur. J., 2012, 18, 4953.
13 S. Ji, H. Guo, W. Wu, W. Wu and J. Zhao, Angew. Chem., Int. Ed.,
2011, 50, 8283.
14 (a) W. Wu, H. Guo, W. Wu, S. Ji and J. Zhao, J. Org. Chem., 2011,
76, 7056; (b) S. Guo, W. Wu, H. Guo and J. Zhao, J. Org. Chem.,
2012, 77, 3933; (c) Y. Chen, J. Zhao, L. Xie, H. Guo and Q. Li,
RSC Adv., 2012, 2, 3942.
15 H. Sun, H. Guo, W. Wu, X. Liu and J. Zhao, Dalton Trans., 2011, 40,
7834.
16 (a) Y. Liu, W. Wu, J. Zhao, X. Zhang and H. Guo, Dalton Trans.,
2011, 40, 9085; (b) Q. Li, H. Guo, L. Ma, W. Wu, Y. Liu and
J. Zhao, J. Mater. Chem., 2012, 22, 5319.
17 J. Sun, W. Wu, H. Guo and J. Zhao, Eur. J. Inorg. Chem., 2011, 3165.
18 W. Wu, J. Sun, S. Ji, W. Wu, J. Zhao and H. Guo, Dalton Trans.,
2011, 40, 11550.
29 C. E. Whittle, J. A. Weinstein, M. W. George and K. S. Schanze,
Inorg. Chem., 2001, 40, 4053.
30 M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah, D. Lipa,
R. J. Lachicotte and R. Eisenberg, Inorg. Chem., 2000, 39, 447.
31 F. G. W. Sun, Y. Liu and K. Schanze, Inorg. Chem., 2005, 44, 4055.
32 Q.-Z. Yang, L.-Z. Wu, Z.-X. Wu, L.-P. Zhang and C.-H. Tung, Inorg.
Chem., 2002, 41, 5653.
33 W.-Y. Wong, J. Organomet. Chem., 2009, 694, 2644.
34 G.-J. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2011, 40, 2541.
€
35 C. Latouche, P.-H. Lanoe, J. A. G. Williams, V. Guerchais,
A. Boucekkine and J.-L. Fillaut, New J. Chem., 2011, 35, 2196.
36 P.-H. Lanoe, H. L. Bozec, J. A. Gareth Williams, J.-L. Fillaut and
V. Guerchais, Dalton Trans., 2010, 39, 707.
37 H. Guo, M. L. Muro-Small, S. Ji, J. Zhao and F. N. Castellano, Inorg.
Chem., 2010, 49, 6802.
38 (a) H. Guo, S. Ji, W. Wu, W. Wu, J. Shao and J. Zhao, Analyst, 2010,
135, 2832; (b) D. Badocco, A. Mondin, A. Fusar, G. Favaro and
P. Pastore, J. Phys. Chem. C, 2009, 113, 15742–15750.
39 L. Huang, L. Zeng, H. Guo, W. Wu, W. Wu, S. Ji and J. Zhao, Eur. J.
Inorg. Chem., 2011, 4527–4533.
19 (a) W. Wu, W. Wu, S. Ji, H. Guo and J. Zhao, Dalton Trans., 2011, 40,
5953; (b) W. Wu, H. Guo, W. Wu, S. Ji and J. Zhao, Inorg. Chem.,
2011, 50, 11446; (c) W. Wu, J. Zhao, H. Guo, J. Sun, S. Ji and
Z. Wang, Chem.–Eur. J., 2012, 18, 1961.
40 J. A. G. Williams, Top. Curr. Chem., 2007, 281, 205.
41 P. Du and R. Eisenberg, Chem. Sci., 2010, 1, 502.
42 T. N. Singh-Rachford, A. Haefele, R. Ziessel and F. N. Castellano,
J. Am. Chem. Soc., 2008, 130, 16164.
20 W.-Y. Wong and C.-L. Ho, Coord. Chem. Rev., 2006, 250, 2627.
21 J. Saltiel, G. R. Marchand, W. K. Smothers, S. A. Stout and
J. L. Charlton, J. Am. Chem. Soc., 1981, 103, 7159.
43 M. G. Frisch, G. W. Truchs and H. B. Schlegel, et al., Gaussian 09W
Revision A.1, Gaussian Inc., Wallingford CT, 2009.
44 I. E. Pomestchenko, C. R. Luman, M. Hissler, R. Ziessel and
F. N. Castellano, Inorg. Chem., 2003, 42, 1394.
22 P. P. Levin, Dokl. Phys. Chem., 2003, 388, 10.
23 (a) S.-C. Chan, M. C. W. Chan, Y. Wang, C.-M. Che, K.-K. Cheung
and N. Zhu, Chem.–Eur. J., 2001, 7, 4180; (b) C.-W. Chan,
L.-K. Cheng and C.-M. Che, Coord. Chem. Rev., 1994, 132, 87; (c)
V. W.-W. Yam, R. P.-L. Tang, K. M.-C. Wong and K.-K. Cheung,
Organometallics, 2001, 20, 4476; (d) W.-Y. Wong, Dalton Trans.,
2007, 4495; (e) G. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2011,
40, 2541.
45 E. O. Danilov, I. E. Pomestchenko, S. Kinayyigit, P. L. Gentili,
M. Hissler, R. Ziessel and F. N. Castellano, J. Phys. Chem. A,
2005, 109, 2465.
46 S. Ji, W. Wu, W. Wu, P. Song, K. Han, Z. Wang, S. Liu, H. Guo and
J. Zhao, J. Mater. Chem., 2010, 20, 1953.
47 W. Wu, W. Wu, S. Ji, H. Guo, P. Song, K. Han, L. Chi, J. Shao and
J. Zhao, J. Mater. Chem., 2010, 20, 9775.
24 (a) W. Sun, B. Zhang, Y. Li, T. M. Pritchett, Z. Li and J. E. Haley,
Chem. Mater., 2010, 22, 6384; (b) P. Shao, Y. Li, J. Yi,
T. M. Pritchett and W. Sun, Inorg. Chem., 2010, 49, 4507; (c) J. Yi,
B. Zhang, P. Shao, Y. Li and W. Sun, J. Phys. Chem. A, 2010, 114,
7055; (d) R. Liu, Y. Li, Y. Li, H. Zhu and W. Sun, J. Phys. Chem.
A, 2010, 114, 12639.
25 G. Zhou, W.-Y. Wong, S.-Y. Poon, C. Ye and Z. Lin, Adv. Funct.
Mater., 2009, 19, 531.
26 G. Zhou, W.-Y. Wong, Z. Lin and C. Ye, Angew. Chem., Int. Ed.,
2006, 45, 6189.
48 E. R. Carraway, J. N. Demas, B. A. DeGraff and J. R. Bacon, Anal.
Chem., 1991, 63, 337.
49 J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Kluwer
Academic/Plenum Publishers, New York, 2nd edn, 1999.
50 O. Wolfbeis and R. Narayanaswamy, Optical Sensors: Industrial,
Environmental and Diagnostic Applications, Springer-Verlag, Berlin-
Heidelberg, 2004.
51 C.-M. Che, C.-C. Kwok, S.-W. Lai, A. F. Rausch, W. J. Finkenzeller,
N. Zhu and H. Yersin, Chem.–Eur. J., 2010, 16, 233.
52 K. Hanson, A. Tamayo, V. V. Diev, M. T. Whited, P. I. Djurovich
and M. E. Thompson, Inorg. Chem., 2010, 49, 6077.
53 Y. Y. Cheng, T. Khoury, R. G. C. R. Clady, M. J. Y. Tayebjee,
N. J. Ekins-Daukes, M. J. Crossley and T. W. Schmidt, Phys.
Chem. Chem. Phys., 2010, 12, 66.
27 A. A. Rachford, S. Goeb, R. Ziessel and F. N. Castellano, Inorg.
Chem., 2008, 47, 4348.
28 F. N. Castellano, I. E. Pomestchenko, E. Shikhova, F. Hua,
M. L. Muro and N. Rajapakse, Coord. Chem. Rev., 2006, 250, 1819.
15768 | J. Mater. Chem., 2012, 22, 15757–15768
This journal is ª The Royal Society of Chemistry 2012