Observation of room-temperature deep-red/near-IR phosphorescence of pyrene with cycloplatinated complexes: An experimental and theoretical study

Article abstract of DOI:10.1002/ejic.201000488

Pyrene-containing cyclometallated PtII complexes, with the pyrene moiety directly cyclometallated (Pt-1) or connected to a 2-phenylpyridine (ppy) ligand through a C-C (Pt-2) orC′C bond (Pt-3), and a control complex with a phenyl group attached to the ppy

Full text of DOI:10.1002/ejic.201000488

FULL PAPER
DOI: 10.1002/ejic.201000488
Observation of Room-Temperature Deep-Red/Near-IR Phosphorescence of
Pyrene with Cycloplatinated Complexes: An Experimental and Theoretical
Study
Wenting Wu,[a] Wanhua Wu,[a] Shaomin Ji,[a] Huimin Guo,*[a] and Jianzhang Zhao*[a]
Keywords: Sensors / Phosphorescence / Platinum / Fluorescence / Density functional calculations
Pyrene-containing cyclometallated PtII complexes, with the
pyrene moiety directly cyclometallated (Pt-1) or connected to
a 2-phenylpyridine (ppy) ligand through a C–C (Pt-2) or CϵC
bond (Pt-3), and a control complex with a phenyl group at-
tached to the ppy ligand (Pt-4) have been prepared. Room-
temperature deep-red/near-IR (NIR) phosphorescence emis-
sion (650–800 nm) was observed for Pt-1, Pt-2 and Pt-3,
whereas Pt-4 showed emission at 528 nm. We found that Pt-
2, in which the pyrene moiety is not directly cyclometallated,
emission band at higher energy was observed. Thus, these
complexes can be described as unichromophore multi-emis-
sive materials. Normal 3MLCT/3IL emission at 528 nm was
observed for Pt-4. The UV/Vis absorption and phosphores-
cence emissions of the complexes were rationalized by DFT/
TDDFT calculations. Theoretical calculations propose py-
rene-localized T1 states (3IL) for Pt-1, Pt-2 and Pt-3, which is
supported by the experimental results. The complexes were
used in luminescent O2-sensing experiments. These studies
shows intense pyrene-based phosphorescence, which con- will be helpful in the development of room-temperature
trasts with a previous report that direct cyclometallation is
necessary for the observation of the phosphorescence of py-
rene in cyclometallated complexes. Besides the phosphores-
cence emission in the deep-red/near-IR range, a fluorescence
phosphorescent materials and their application as lumines-
cent molecular sensing or electroluminescent materials are
promising.
the ISC process and thus no fluorescence can be detected
for these cyclometallated complexes. Cyclometallated com-
plexes usually give emission in the blue-green range de-
pending on the structures of the ligands.[1,6] For example,
the emission of [(ppy)Pt(acac)] was observed at 486 nm.[5]
However, emission at longer wavelengths is also desired, for
example, emission at longer wavelengths (deep-red/near-IR
range) is important for optical communication and biomed-
ical imaging. Unfortunately it is difficult to access deep-red/
near-IR emission through cyclometallated complexes, espe-
cially with PtII.[1]
On the other hand, luminescent molecular sensors or
chemosensors usually employ fluorescent chromophores
such as pyrene.[10–12] Pyrene is a versatile fluorophore and
has been extensively used in fluorescent chemosensors.
However, the phosphorescence emission of pyrene has not
been employed in luminescent molecular sensors. Phos-
phorescence usually exhibits larger Stokes shifts, red-shifted
emission and much longer luminescent lifetimes compared
with fluorescence emission.[10] These photophysical proper-
ties are ideal for luminescent molecular sensor applica-
tions.[10,11] However, room-temperature phosphorescence of
aromatic fluorophores is difficult to obtain because the
weak spin–orbit coupling effect of the aromatic fluoro-
phores (π–π* transitions) and the large singlet–triplet en-
ergy gap makes S1ǞT1 ISC difficult. As a result, very few
aromatic polycyclic hydrocarbons show room-temperature
Introduction
Cyclometallated PtII/IrIII complexes such as [(ppy)Pt-
(acac)] (ppy = 2-phenylpyridine, acac = acetylacetonato)
have attracted considerable attention due to their applica-
tions in electroluminescence.[1–9] Some of the cyclometall-
ated PtII complexes are luminescent in fluid solution at
room temperature (r.t.).[1] The emissive excited states of
these complexes are usually IL/3MLCT (phenylǞpyridine,
3
PtǞpyridine) triplet states.[1] These complexes are ideal
phosphores for organic light-emitting diodes (OLEDs) be-
cause 75% of the excitons in the electroluminescence, which
show triplet-spin manifold, cannot be utilized by fluores-
cent materials. Concerning the photoluminescence with cy-
clometallated complexes, the population of the triplet state
is a result of the heavy-atom effect of Pt or Ir, through
which the singletǞtriplet intersystem crossing (ISC) is facil-
itated (S1ǞT1), and thus phosphorescence can be observed.
Usually the singlet excited state is completely quenched by
[a] State Key Laboratory of Fine Chemicals, School of Chemical
Engineering, Dalian University of Technology,
158 Zhongshan Road, Dalian 116012, P. R. China
Fax: +86-411-3960-8007
E-mail: zhaojzh@dlut.edu.cn
guohm@dlut.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic. 201000488 or from
the author.
View this journal online at
wileyonlinelibrary.com
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Phosphorescence of Pyrene with Cycloplatinated Complexes
phosphorescence and usually the phosphorescence can only calculations will be useful in the future design of functional
be observed at low temperatures in a rigid matrix.[10]
cyclometallated Pt complexes with predetermined photo-
Recently, we studied the room-temperature phosphores- physical properties, such as the 3IL emissive state (r.t. phos-
cence of heavy-transition-metal complexes such as phorescence of the ligands), to achieve room-temperature
RuII.[13–15] There are only very limited reports on the obser- phosphorescence of organic chromophores.
vation of room-temperature phosphorescence emission of
pyrene[16] and its application as sensing materials, such as
in luminescent oxygen sensing.[14,17–20]
Results and Discussions
Inspired by the recent elegant work on cyclometallated
Pt complexes and to tackle the aforementioned chal-
lenges,[1,5,11,17,18,21] we set out to tune the emission colour
of cyclometallated PtII complexes from the typical green to
deep-red/near-IR in order to achieve the room-temperature
Design and Synthesis of the Complexes
The design rationale of the complexes lies in the notion
phosphorescence of pyrene. The design rationale of these that the r.t. phosphorescence of pyrene may be switched on
complexes lies in the notion that room-temperature phos- by the heavy-atom effect of Pt.[16] Thus, complex Pt-1 was
phorescence of polycyclic aromatic hydrocarbons can be fa- designed with a view to the direct metallation of the pyrene
3
∧
cilitated by the heavy-atom effect of Pt. Thus, IL emission moiety. The C N ligand of Pt-1 was synthesized by Suzuki
will be accessible with a strong spin–orbit coupling effect. coupling reaction between 1-pyreneboronic acid and 2-bro-
Following this line, we designed and prepared complex Pt- mopyridine. Then the ligand 2-pyrenylpyridine was metall-
1 in which the pyrene moiety is directly metallated by PtII ated with [K2PtCl4]. The auxiliary ligand acetylacetonate
(Scheme 1). As a similar model complex, Pt-2 was synthe- (acac) was introduced in the presence of Na2CO3
sized with the pyrene moiety appended to the 4-position of (Scheme 1). To investigate the effect of the direct cycloplati-
the ppy ligand and not directly cyclometallated. A complex nation of the pyrene moiety on the photophysical proper-
with a pyrene-ethynyl moiety attached to ppy was also pre- ties, Pt-2 was designed with the pyrene moiety appended at
pared (Pt-3). A complex with a phenyl group attached to the 4-position of the ppy group through a C–C single bond
the ppy ligand (Pt-4) was prepared to study the effect of (pyrene is not directly cycloplatinated). First, 4-bromo-ppy
structure on the photophysics of the complexes. Room-tem- was synthesized and then the palladium-catalysed Sonoga-
perature phosphorescence in the deep-red and near-IR shira coupling reaction was carried out with 1-pyrene-
range (650–800 nm) was observed for Pt-1, Pt-2 and Pt-3. boronic acid to prepare ligand L-2.
The emission bands were assigned to the ligand-centred
Previously we found that an ethynylated ligand may im-
(3IL) phosphorescence of pyrene appends. Pt-1 shows emis- part a significant effect on the photophysics of polypyridyl
sion bands that are red-shifted by 50 nm relative to those ruthenium complexes.[14] To investigate the effect of π con-
of a previously reported cycloplatinated pyrene.[16] In par- jugation on the photophysics of the cyclometallated Pt
3
ticular, IL emission (phosphorescence of pyrene) was ob- complex, Pt-3 was designed in which ethynylene acts as the
served for Pt-2 in which the pyrene is not directly cyclo- linker between the pyrene and the ppy units. Note that we
metallated. These results contrast those of a previous report did not use a C=C double bond as the linker to extend
that the phosphorescence of pyrene requires direct cyclome- the π conjugation of the ppy ligand because the cis/trans
tallation.[16,22] In the case of new complex Pt-2, intense py- photoisomerization of the C=C double bond can substan-
rene-derived r.t. phosphorescence was observed without di- tially quench the luminescence of the excited lumo-
rect cyclometallation of the pyrene moiety. In addition to phores.[23] Instead, the CϵC triple bond is a rigid linker
the phosphorescence bands in the near-IR range, emissions and is effective for π conjugation and through-bond elec-
at higher energy were observed for Pt-1, Pt-2 and Pt-3. tron/energy transfer.[24] Note also that the CϵC linker may
These emission bands were assigned to the fluorescence induce complicated yet interesting photophysical properties
emission of the ligand, similarly to a previous report.[16] in the luminescent metal complexes.[14] To investigate the
Based on the experimental results, a frustrated ISC process, effect of the pyrene moiety on the photophysics of the PtII
1
1
that is, from the pyrene-localized IL to the MLCT and complexes, a model complex Pt-4 was synthesized with a
3MLCT states, was proposed to be responsible for the un- phenyl group attached to the 4-position of the ppy ligand.
ichromophore fluorescence/phosphorescence multi-emis- All the complexes were prepared in satisfactory yields.
sions. The photophysics of the complexes were studied by
As the energy of the triplet excited state (T1) of pyrene
performing theoretical calculations based on density func- (ca. 600 nm) is substantially lower than the T1 state of the
tional theory (DFT) and time-dependent DFT (TDDFT), [(ppy)Pt(acac)] complex (ca. 485 nm) we expected to ob-
which clearly indicate pyrene-localized triplet excited states serve phosphorescence emission from the pyrene in Pt-1,
for Pt-1, Pt-2 and Pt-3. The complexes were used in lumi- Pt-2 and Pt-3,[14] although this is not a guaranteed prop-
nescent O2-sensing experiments. Our strategy for achieving erty.[16] For Pt-4, however, as the energy of the triplet state
the deep-red/near-IR emission of pyrene through the use of of the phenyl group is substantially higher than that of
cyclometallated PtII complexes, the application of the com- [(ppy)Pt(acac)] (485 nm),[5] we do not expect any emission
plexes in luminescent O2-sensing, as well as the assignment other than the typical 3IL/3MLCT emission of [(ppy)Pt-
of the emissive triplet excited states by using DFT/TDDFT (acac)].
Eur. J. Inorg. Chem. 2010, 4470–4482
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W. Wu, W. Wu, S. Ji, H. Guo, J. Zhao
FULL PAPER
Scheme 1. Synthesis of the cyclometallated Pt complexes. (a) 2-Bromopyridine was used for the synthesis of L-1. 2-(4-Bromophenyl)-
pyridine was used for L-2. Base/Pd(PPh3)4 (3.6 mol-%), toluene/EtOH (3:1, v/v), Ar, 90 °C, 20 h. (b) i) K2PtCl4, 2-ethoxyethanol/water
(3:1, v/v), Ar, 80 °C, 20 h; ii) Hacac/Na2CO3, 2-ethoxyethanol, 100 °C, 20 h. (c) i) Ethynyltrimethylsilane, Pd(PPh3)Cl2 (2 mol-%), CuI
(4 mol-%), PPh3 (4.0 mol-%), NEt3/THF (3:1, v/v), Ar, 90 °C, 6 h; ii) K2CO3, MeOH/diethyl ether (2:1, v/v), r.t., 3 h. (d) Diisopropylamine,
Pd(PPh3)2Cl2 (6 mol-%), CuI (6 mol-%), PPh3 (12 mol-%), Ar, 90 °C, 4 h.
UV/Vis Absorption Spectra of the Ligands and the
Cyclometallated PtII Complexes
The UV/Vis absorption spectra of the ligands and the
complexes were studied (Figure 1). The UV/Vis absorption
spectra of the pyrene-containing ligands are different to
that of pyrene.[12,14] This indicates electronic coupling be-
tween the pyrene and the ppy moiety. For example, the ab-
sorption bands of L-1 and L-2 at 350 nm are red-shifted
relative to that of pyrene. Moreover, the absorption bands
of L-1 and L-2 are structureless, in contrast to the highly
structured absorption of pyrene at around 320 nm.[25,26]
These absorption bands mainly arise from pyrene-localized
transitions, which is supported by DFT calculations. For L-
4, however, the maximal absorption band is at a much
shorter wavelength (270 nm).
New absorption bands were observed for the PtII com-
plexes at wavelengths red-shifted in comparison with the
∧
C N ligands. For example, a structured intense absorption
band at 425 nm was observed for Pt-1. The spectra of li-
gand L-1 is devoid of this absorption band. The absorption
of Pt-1 in the visible range is red-shifted by around 50 nm
relative to that of previously reported cycloplatinated py-
Figure 1. UV/Vis absorption spectra of the ligands and complexes
rene complexes with 1-(diphenylphosphanyl)pyrene or 1,6- in CH2Cl2 (c = 1.0ϫ10–5 mol/L, 25 °C).
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Phosphorescence of Pyrene with Cycloplatinated Complexes
bis(diphenylphosphanyl)pyrene as ligands.[16] We propose
the red-shifted absorption of Pt-1 is a result of perturbation
of the molecular orbitals of pyrene by direct platination
(with the formation of a Pt–C covalent bond) and transi-
tions such as 1IL (pyreneǞpyridine) and 1MLCT (PtǞpyr-
ene/pyridine) are responsible for the red-shifted absorp-
tions. This assumption is supported by DFT calculations,
which indicate that the absorption at around 400–470 nm
is due to 1MLCT (PtǞpyridine), 1IL (pyrene-localized) and
1LLCT (pyreneǞpyridine) transitions.
For L-2, however, the UV/Vis absorption changes ob-
served upon metallation are different to those of L-1. First,
the main absorptions of L-2 persist in the UV/Vis absorp-
tion of Pt-2, namely the bands at 280 and 346 nm. Sec-
ondly, a new shoulder absorption at around 420 nm ap-
peared for Pt-2 not observed for L-2. We attribute the new
absorption at 420 nm to the absorption of the complex (e.g.,
3MLCT), whereas the absorption band at 350 nm is due to
the pyrene-localized transition. This assignment is sup-
ported by DFT/TDDFT calculations. These results demon-
strate that the metallation of L-2 imparts only a minor ef-
fect on the UV/Vis absorption of the pyrene moiety in con-
trast to the case of Pt-1. New absorption bands at 366 and
391 nm appeared for Pt-4 when compared with the absorp-
tion spectrum of L-4. We attribute the new absorption at
Figure 2. Emission spectra of (a) the ligands and (b) the complexes.
λex(L-1) = 360 nm, λex(L-2) = 367 nm, λex(L-3) = 367 nm, λex(L-4)
= 310 nm, λex(Pt-1) = 415 nm, λex(Pt-2) = 433 nm, λex(Pt-3) =
380 nm, λex(Pt-4) = 397 nm (c = 1.0ϫ10–5 mol/L in CH2Cl2,
25 °C).
3
391 nm to the Pt complexation effect, that is, to the IL/
3MLCT states. The intense absorption of L-4 at 275 nm
persists upon cyclometallation.
the previously reported cycloplatinated complexes with 1-
diphenylphosphanylpyrene or 1,6-bis(diphenylphosphanyl)-
pyrene as ligands.[16] We propose that the emission at
680 nm is due to a triplet emissive state with a substantial
3IL component, that is, the pyrene-localized excited state.[16]
Photoluminescence of the Ligands and Complexes
The emission spectra of the ligands and the cyclometall- This assignment was supported by DFT/TDDFT calcula-
ated complexes were also studied (Figure 2). For the py- tions. Besides the deep-red/near-IR emission at 680 nm,
rene-containing ligands of L-1 and L-2, structureless emis- minor emission bands at higher energies of 577 and 471 nm
sion bands at 393 and 417 nm were observed, respectively. were also observed for Pt-1. We propose that the emission
This emission profile is in contrast to the structured emis- at 577 nm is due to emission typical of [(ppy)Pt(acac)] com-
sion band of pyrene at 390 nm,[10,12] which points to signifi- plexes. This is supported by the sensitivity of the emission
cant electronic coupling between the pyrene and the pyr- intensity at 577 nm to O2 (the emission can be completely
idine or ppy appends. The red-shifted emission of L-2 at quenched under aerated conditions). Further, we propose
417 nm may be due to the extended π-conjugated frame- that the emission band at 471 nm is due to the fluorescence
work in comparison with L-1. For L-4, however, the emis- of the ligand. Similar fluorescence emission was previously
sion was observed at the much shorter wavelength of observed for pyrene-derived PtII or AuI complexes.[16,22]
348 nm. The slightly more structured emission at 428 nm The emission intensity of the peak at 471 nm is nearly unaf-
for L-3 may be due to the attachment of the electron-with- fected by O2, which is characteristic of fluorescent emis-
drawing ethynyl moiety on the pyrene.[12]
The emissions of the cyclometallated complexes are fold and the short luminescent lifetime of the emission.[10]
shown in Figure 2b. First we checked the emission of the In contrast to Pt-1, the pyrene unit of Pt-2 is not directly
sions; the insensitivity to oxygen is due to the singlet mani-
model complex Pt-4; an emission band at 528 nm was ob- cycloplatinated. The photoluminescence of Pt-2 shows a
served. The structured emission profile is a characteristic of structured emission band at 640 nm (Figure 2b), which is
[(ppy)Pt(acac)] complexes.[5] However, the emission of Pt-4 blueshifted by around 40 nm relative to that of Pt-1. Inter-
is red-shifted by around 40 nm relative to that of the parent estingly, the emission of Pt-2 is red-shifted by 112 nm rela-
complex [(ppy)Pt(acac)].[5]
tive to that of Pt-4. Thus, the deep-red emission is not due
Next we investigated the complex Pt-1 in which the py- to the normal 3MLCT emission of the [(ppy)Pt(acac)] com-
rene moiety is directly cycloplatinated. Interestingly, deep- plexation core. Based on DFT/TDDFT calculations we at-
red/near-IR emission at 680 nm (the emission spectrum co- tribute this emission band to the phosphorescence emission
3
vers the range of 650 to beyond 800 nm) was observed. The originating from the pyrene-localized triplet state IL and
emission band is red-shifted by around 50 nm relative to the pyreneǞpyridine LLCT mixed with PtǞppy MLCT
3
3
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W. Wu, W. Wu, S. Ji, H. Guo, J. Zhao
FULL PAPER
features. Similar emission was reported for cyclometallated rescence of the ethynyl ligand (Figure 2, a).[16] The principle
or dangling PtII complexes with 1-diphenylphosphanyl- photophysical data of the ligands and the complexes are
pyrene or 1,6-bis(diphenylphosphanyl)pyrene as ligands.[16] compiled in Table 1.
Note that an intense phosphorescence emission of pyrene is
observed for Pt-2 in which the pyrene moiety is not directly
The Excited States of the ComplexesϪDFT/TDDFT
cycloplatinated. Previously it was reported that a pyrene-
Calculations
derived complex with a dangling Pt ion shows very weak
phosphorescence, but strong fluorescence of the pyrene
moiety.[16] Emission at a higher energy is also observed for
Pt-2 (485 nm). We attribute the emission to typical [(ppy)-
Pt(acac)] emission.[26]
Recently, theoretical calculations, such as the DFT and
TDDFT methods, have been used to study the photophysi-
cal properties of fluorophores.[12,27–33] Investigation of the
photophysical properties from a theoretical point of view
will be beneficial for the design of new luminophores with
predetermined photophysical properties.[12,14,27]
The different photophysical properties of the structurally
related analogues Pt-1, Pt-2 and Pt-3 are fascinating and
we set out to evaluate the different photophysical properties
by theoretical calculations. The ground-state geometry of
Pt-1 was optimized; a square-planar coordination PtII cen-
tre was found with the pyrene moiety coplanar with the
pyridine group. We found that the frontier orbitals
(HOMO/LUMO) of Pt-1 are basically ligand-localized, that
is, pyrene-localized (Figure 3).
The excitation energies calculated for Pt-1 are in good
agreement with experimental observations. For example, the
predicted absorptions are located at 439, 421, 351/349 and
285 nm (Table 2). These predicted values are in good agree-
ment with the experimental values of 415, 394, 357 and
283 nm (Figure 1, b). Based on the electronic structures of
the transitions, we assigned the absorption bands at 400–
450 nm (Figure 1, b) to S0ǞS1 and S0ǞS2 transitions; the
orbitals involved are H–2ǞL, H–1ǞL, HǞL, HǞL+1. By
examining the distributions of the molecular orbitals, we
found that these transitions are pyrene-localized (1IL),
PtǞpyrene/pyridine (1MLCT), pyreneǞpyridine and
acacǞpyrene/pyridine (1LLCT) transitions.
Pt-1 shows deep-red/near-IR emission in the range of
650–800 nm. To investigate the emissive states, the triplet
excited states of Pt-1 were studied by the TDDFT method.
The calculated excitation energy of T1 is 672 nm. Note that
the calculation is based on the ground-state geometry, thus,
the anticipated emission will be more red-shifted than the
Interestingly, emission at 669 nm was observed for Pt-3,
which is red-shifted by around 30 nm relative to that of Pt-
2. Emission at a much higher energy (430 nm) is also ob-
served for Pt-3. We attribute this emission band to the fluo-
Table 1. Photophysical parameters of the ligands and the cyclo-
platinated complexes Pt-1–Pt-4.
[c]
λabs [nm] (ε
λex
λem
Φf[b] Φp
τ[d]
[104 –1cm–1])[a]
[nm] [nm]
280 (1.56), 345
360
393
3.0 ns
L-1 (1.34)
280 (4.36), 346
L-2 (3.83)
L-3 285 (2.16), 310
(2.46), 375 (3.16),
398 (3.22)
0.41
–
367
367
417
428
12.5 ns
1.49 ns
0.68
0.83
–
–
L-4 275 (10.81)
Pt-1 283 (5.64), 357
(2.25), 394 (2.61),
415 (3.43)
310
415
348
471,
577,
680
0.12
–
–
1.29 ns
[e]
0.49 471 nm (3.0 ns),
578 nm
(856.2 ns),
682 nm (6.22 µs)
Pt-2 280 (4.95), 346
(3.78)
Pt-3 286 (6.79), 350
(9.45)
Pt-4 296 (2.79), 332
(0.16), 366 (0.70),
391 (0.05)
433
380
397
485, 0.001 0.65 485 nm (2.4 ns),
640
669
640 nm (15.8 µs)
[e]
[e]
–
0.26
15.0
–
[e]
528
–
5.6 µs
[a] Extinction coefficients are shown in parentheses. [b] Quantum
yield of fluorescence in aerated CH2Cl2. [c] Quantum yield of phos-
phorescence in deoxygenated CH2Cl2. The values are multiplied by
102. [d] The lifetimes of the ligands were measured in aerated
CH2Cl2. The lifetimes of the complexes were measured in deoxy-
genated CH2Cl2. [e] Not determined.
Figure 3. Frontier molecular orbitals of Pt-1 calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level of theory using Gaussian
09.
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Phosphorescence of Pyrene with Cycloplatinated Complexes
Table 2. Electronic excitation energies and the corresponding oscillator strengths (f), the main configurations and CI coefficients of the
low-lying electronically excited states of complex Pt-1 calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ based on the DFT//B3LYP/6-
31G(d)/LanL2DZ-optimized ground-state geometries.
Electronic
transitions
TDDFT//B3LYP/6-31G(d)
Composition[c]
[b]
Energy[a]
f
CI[d]
Character
Singlet
S0ǞS1
2.83 eV, 439 nm
0.2998
H–1ǞL
HǞL
H–2ǞL
H–1ǞL
HǞL
0.5863
0.3032
0.1614
0.2663
0.5448
0.1131
0.6422
0.1485
0.1840
0.1070
0.2891
0.5989
0.1113
0.5843
0.2426
0.4741
0.2002
0.1143
0.1652
0.7392
0.1943
0.1376
IL & MLCT
IL
S0ǞS2
2.95 eV, 421 nm
0.3981
LLCT & MLCT
IL & MLCT
IL
LLCT
LLCT & MLCT
IL & MLCT
HǞL+1
H–2ǞL
H–1ǞL
HǞL+1
H–2ǞL
H–1ǞL+1
HǞL+1
H–2ǞL
H–1ǞL+1
HǞL+1
H–4ǞL+2
H–1ǞL+4
H–5ǞL+5
H–1ǞL
HǞL
S0ǞS4
S0ǞS5
S0ǞS6
3.29 eV, 377 nm
3.53 eV, 351 nm
3.56 eV, 349 nm
0.0261
0.0239
0.0573
IL
LLCT & MLCT
IL
IL
LLCT & MLCT
IL
IL
S0ǞS18
S0ǞT1
4.35 eV, 285 nm
1.85 eV, 672 nm
0.1474
LLCT & MLCT
LLCT & MLCT
LLCT & MLCT
IL & MLCT
IL
Triplet
0.0000[e]
HǞL+1
HǞL+3
IL
LLCT
[a] Only selected low-lying excited states are presented. [b] Oscillator strength. [c] H represents the HOMO and L the LUMO. Only the
main configurations are presented. [d] The CI coefficients are absolute values. [e] No spin–orbital coupling effect was considered and
thus the f values are zero.
calculated energy gap between S0 and T1 triplet excited state nated in Pt-2 (Scheme 1). The ground-state geometry of Pt-
(672 nm). Experiments indicated phosphorescence emission 2 was optimized (Figure 4) and it was found that the pyrene
at 680 nm.[34]
moiety is tilted by 55° with respect to the Pt coordination
By examining the electronic structures of the excited state plane. The calculated singlet excitation energies are 420,
and the corresponding molecular orbitals (Table 2 and Fig- 360, 355, 279 and 276 nm. These values are very similar to
ure 3) we found that the T1 state of Pt-1 is characterized the UV/Vis experimental absorption data of 400, 345, 279
by pyrene-localized (3IL), pyreneǞpyridine (3LLCT) and and 267 nm. By examining the electronic structures of the
PtǞpyrene/pyridine transitions (3MLCT), but that PtII S1 state we found that the absorption bands at 420 nm can
does not contribute significantly to the T1 state.
be assigned to pyreneǞppy (IL), PtǞpyrene/ppy (MLCT)
Based on these calculations, we anticipate that in con- and acacǞpyrene/ppy (LLCT) transitions. For the absorp-
trast to the parent complex [(ppy)Pt(acac)], for which an tion band at 345 nm, acacǞpyrene/ppy and PtǞpyrene/
3IL state was proposed (phenylǞpyridine of the ppy li- ppy features can be indentified, with the pyrene-localized
gand),[1,5] Pt-1 will show pyrene-localized emission. This transition (HǞL+1) being dominant (Table 3 and Fig-
prediction is supported by the experimental results, which ure 4).
show emission bands in the 600–800 nm range.[16] The ener-
To study the emission of the complex, the triplet states
gies of the HOMO and LUMO of Pt-1 were calculated to of Pt-2 were also studied using TDDFT calculations
be –5.14 and –1.96 eV, respectively, which compares with (Table 3). The calculated S0–T1 energy gap is 612 nm. This
the energies of the HOMO and LUMO of –5.41 and value is similar to the experimental results of the phos-
–1.66 eV for Pt-4. We found that the energy of the HOMO phorescence emission at 640 nm. By examining the T1 state,
of Pt-1 is higher, but the LUMO energy is lower than those we can attribute the emission band at 640 nm to the
of the model complex Pt-4, that is, the HOMO–LUMO en- pyreneǞppy (HOMOǞLUMO) and pyrene-localized
ergy gap of Pt-1 is smaller than that of Pt-4. Thus, red- (HOMOǞLUMO+1) transitions, the Pt atom contributing
shifted emission can be expected for Pt-1 when compared slightly to these transitions. With a small involvement of
with Pt-4. This expectation is supported by the experimen- the Pt atom in the T1 state (which is responsible for the
tal results (Figure 1 and Table 1).
emission at 640 nm) we anticipate a longer luminescent life-
Pt-2 shows blueshifted emission (by ca. 50 nm) compared time of this emission band compared with the normal emis-
with Pt-1, but is substantially red-shifted compared with sion of the [(ppy)Pt(acac)] complex. The luminescence life-
that of Pt-4. The structural difference between the two com- time of Pt-2 was determined to be τ = 15.8 µs, which com-
plexes is that the pyrene moiety is not directly cycloplati- pares with τ = 2.6 µs for [(ppy)Pt(acac)].[5] The energies of
Eur. J. Inorg. Chem. 2010, 4470–4482
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W. Wu, W. Wu, S. Ji, H. Guo, J. Zhao
FULL PAPER
Figure 4. Frontier molecular orbitals of Pt-2 calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level of theory using Gaussian
09.
Table 3. Electronic excitation energies and the corresponding oscillator strengths (f), the main configurations and CI coefficients of the
low-lying electronically excited states of complex Pt-2 calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ based on the DFT//B3LYP/6-
31G(d)/LanL2DZ-optimized ground-state geometries.
Electronic
transitions
TDDFT//B3LYP/6-31G(d)
Composition[c]
Energy[a]
f[b]
CI[d]
Character
Singlet
S0ǞS1
2.95 eV, 420 nm
0.3101
H–2ǞL
H–1ǞL
HǞL
0.1141
0.1868
0.6307
0.1084
0.2278
0.5186
0.3036
0.2923
0.1633
0.1968
0.4911
0.2467
0.3926
0.3533
0.3173
0.2711
0.3609
0.5112
0.5625
0.1697
0.1969
0.3386
0.4325
0.2934
0.2493
0.1419
LLCT & MLCT
LLCT & LMCT
IL & LLCT
IL & LLCT
MLCT
LLCT & MLCT
IL & LLCT
LLCT & MLCT
LLCT & LMCT
LLCT
IL & LLCT
LLCT & MLCT
IL & LLCT
IL & MLCT
LLCT & MLCT
IL & LLCT
IL
IL & LLCT
IL & LLCT
LLCT
HǞL+1
H–3ǞL
H–2ǞL
HǞL+1
H–2ǞL
H–1ǞL
H–1ǞL+1
HǞL+1
H–6ǞL
H–5ǞL+1
H–4ǞL+1
H–6ǞL
H–5ǞL+1
H–2ǞL+3
HǞL
HǞL+1
HǞL+2
H–5ǞL
H–2ǞL
H–1ǞL
HǞL
S0ǞS4
S0ǞS5
3.45 eV, 360 nm
3.50 eV, 355 nm
0.1037
0.1899
S0ǞS24
S0ǞS25
S0ǞT1
S0ǞT2
4.45 eV, 279 nm
4.50 eV, 276 nm
2.03 eV, 612 nm
2.56 eV, 484 nm
0.1412
0.1355
Triplet
0.0000[e]
0.0000[e]
IL & LLCT
LLCT & MLCT
LLCT & LMCT
IL & LLCT
IL & LLCT
LLCT
HǞL+1
HǞL+2
[a] Only selected low-lying excited states are presented. [b] Oscillator strength. [c] H represents HOMO and L the LUMO. Only the main
configurations are presented. [d] The CI coefficients are absolute values. [e] No spin–orbital coupling effect was considered, thus the f
values are zero.
the HOMO and LUMO of Pt-2 were calculated to be –5.06 the emission of Pt-3 centred at 669 nm and the emission
and –1.74 eV, respectively. The energy of the HOMO orbital band of Pt-2 at 635 nm (Figure 2 and Table 1).
is greater than that of the model complex Pt-4.
The vertical excitation energies of Pt-3 were calculated
Complex Pt-3 was studied by a similar method. The by the TDDFT method. The excitation energies calculated
ground-state geometry of the complex adopts a coplanar for the singlet excited states are 452, 421, 382 and 324 nm
conformation, that is, the pyrene is coplanar with the Pt (Table 4). These calculated values are in good agreement
coordination plane (Figure 5). This geometry ensures ef- with the UV/Vis absorption data (Figure 1).
ficient π conjugation between the pyrene and the ppy–Pt
To study the emissive state of Pt-3, the triplet excited
coordination moiety and thus we expect a longer wave- states were also studied (Table 4). Based on the electronic
length of emission for Pt-3 compared with Pt-2. This expec- configuration of the T1 excited state, which is responsible
tation was proven by the experimental results, which show for the phosphorescence emission, the T1 state is charac-
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Phosphorescence of Pyrene with Cycloplatinated Complexes
Figure 5. Frontier molecular orbitals of Pt-3 calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level of theory using Gaussian
09.
Table 4. Electronic excitation energies and the corresponding oscillator strengths (f), the main configurations and CI coefficients of the
low-lying electronically excited states of the complex Pt-3 calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ based on the DFT//B3LYP/
6-31G(d)/LanL2DZ-optimized ground-state geometries.
Electronic
transitions
TDDFT//B3LYP/6-31G(d)
Composition[c]
Energy[a]
f[b]
CI[d]
Character
Singlet
S0ǞS1
2.74 eV, 452 nm
1.0803
HǞL
HǞL+1
H–4ǞL
H–1ǞL
H–1ǞL+1
H–2ǞL
HǞL+1
H–5ǞL
H–4ǞL
H–2ǞL+1
HǞL+3
H–2ǞL+1
HǞL
0.6402
0.1023
0.1024
0.6312
0.1606
0.3544
0.5702
0.2412
0.3905
0.2493
0.2464
0.1326
0.6913
0.3409
LC
LLCT
MLCT
LC
S0ǞS2
2.95 eV, 421 nm
0.0854
LLCT
LLCT & MLCT
LLCT
MLCT
LC
LLCT
IL & LLCT
LLCT
S0ǞS3
3.25 eV, 382 nm
3.83 eV, 324 nm
0.1744
0.1779
S0ǞS10
Triplet
S0ǞT1
1.78 eV, 697 nm
0.0000[e]
LLCT
LLCT
HǞL+1
[a] Only selected low-lying excited states are presented. [b] Oscillator strength. [c] H represents the HOMO and L the LUMO. Only the
main configurations are presented. [d] The CI coefficients are absolute values. [e] No spin–orbital coupling effect was considered, thus
the f values are zero.
terized by pyrene-localized (3IL), pyreneǞppy (3IL) and (T1) was found. This value is in good agreement with the
PtǞppy (3MLCT) transitions. The energies of the HOMO experimental result of phosphorescence emission at
and LUMO of Pt-3 were calculated to be –5.01 and 527 nm.[34] By examining the electronic configuration of the
–2.01 eV, respectively. Compared to Pt-4, the HOMO of Pt- T1 state and the molecular orbitals, we found that the T1
3 is significantly higher and the LUMO is lower and thus state is characterized by ppy-localized phenylǞpyridine
we expect red-shifted emission for this complex.
and PtǞppy transitions, that is, the T1 state is a mixed
Pt-4 was designed as a model complex and does not con- 3MLCT/3IL state. Therefore the emissive state (T1) of Pt-4
3
tain the pyrene group. Therefore the normal MLCT/3IL is characterized by the normal profile of the [(ppy)Pt(acac)]
emissive state was expected for this complex.[1,5] The complexes. The HOMO and LUMO energies of Pt-4 were
ground-state geometry of the complex shows the phenyl calculated to be –5.41 and –1.66 eV, respectively.
group tilted by 37° with respect to the ppy coordination
The energy levels of electroluminescence materials are
plane, which rules out efficient π conjugation (Figure 6). important for device fabrication. The energies of the
The excited states of Pt-4 were also studied. The singlet HOMOs and LUMOs of the complexes were calculated
excited states of the complex were found to have the main (Figure 7.) and it is clear that Pt-4 and the model complex
excitation energies of 403, 361, 326, 305 and 282 nm [(ppy)Pt(acac)] share similar HOMO and LUMO energies.
(Table 5). These values are in good agreement with the ex- For Pt-1 and Pt-3, the energy gaps between the HOMO
perimental results, which show UV/Vis absorption bands at and the LUMO are smaller than that of complex [(ppy)-
391, 366, 332 and 296 nm.
Pt(acac)]. This is not surprising as the pyrene moiety is di-
By examining the electronic structure of the S1 state, the rectly cycloplatinated (Pt-1) or the pyrenyl-ethynyl conju-
transition can be attributed to PtǞppy and phenylǞpyrid- gated ppy ligand was used (Pt-3). The HOMO and LUMO
ine transitions. In contrast to Pt-1 and Pt-2, no aryl append energies of Pt-2 are very interesting. The pyrene moiety is
localized transitions (1IL) were found. The triplet states of neither directly cycloplatinated nor π-conjugated to the ppy
Pt-4 were also studied and an excitation energy of 490 nm ligand through a CϵC bond, however, the HOMO energy
Eur. J. Inorg. Chem. 2010, 4470–4482
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W. Wu, W. Wu, S. Ji, H. Guo, J. Zhao
FULL PAPER
Figure 6. Frontier molecular orbitals of Pt-4 calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level of theory using Gaussian
09.
Table 5. Electronic excitation energies [eV] and the corresponding oscillator strengths (f), the main configurations and CI coefficients of
the low-lying electronically excited states of complex Pt-4 calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ based on the DFT//B3LYP/
6-31G(d)/LanL2DZ-optimized ground-state geometries.
Electronic
transitions
TDDFT//B3LYP/6-31G(d)
Composition[c]
Energy[a]
f[b]
CI[d]
Character
Singlet
S0ǞS1
3.08 eV, 403 nm
0.0612
H–3ǞL
H–2ǞL
HǞL
H–3ǞL
H–2ǞL
H–1ǞL
HǞL
H–3ǞL
H–2ǞL
H–1ǞL+1
H–1ǞL
HǞL+1
H–1ǞL+1
H–3ǞL
H–2ǞL
H–2ǞL+1
H–1ǞL+1
H–1ǞL
HǞL
0.1372
0.1309
0.6448
0.3300
0.1669
0.5642
0.1008
0.3809
0.3147
0.2768
0.1633
0.3287
0.1968
0.1500
0.1221
0.2006
0.5745
0.3708
0.6021
0.1107
LLCT & MLCT
LLCT & MLCT
LLCT
LLCT & MLCT
LLCT & MLCT
LLCT
S0ǞS2
3.44 eV, 361 nm
3.80 eV, 326 nm
0.0888
0.1936
LLCT
S0ǞS5
LLCT & MLCT
LLCT & MLCT
LLCT
LLCT
LLCT
LLCT
S0ǞS8
S0ǞT1
4.07 eV, 305 nm
2.53 eV, 490 nm
0.1950
LLCT & MLCT
LLCT & MLCT
LLCT & MLCT
LLCT
Triplet
0.0000[e]
LLCT
LLCT
LLCT
HǞL+1
[a] Only selected low-lying excited states are presented. [b] Oscillator strength. [c] H represents the HOMO and L the LUMO. Only the
main configurations are presented. [d] The CI coefficients are absolute values. [e] No spin–orbital coupling effect was considered, thus
the f values are zero.
of Pt-2 is significantly higher than that of the model com-
plex [(ppy)Pt(acac)] (Figure 7). This increased HOMO en-
ergy cannot be rationalized by the electron-donating ability
of the pyrenyl group because no such effect was observed
for Pt-4 in which a phenyl ring is attached to the ppy li-
gand. DFT calculations revealed that the pyrene moiety
contributes significantly to the HOMOs (Figure 4) and thus
the high HOMO energy of Pt-2 can be rationalized.
Our theoretical calculations show that the DFT/TDDFT
method can be used to study the excited state of the cyclo-
metallated Pt complexes and for assignment of the UV/Vis
absorption (singlet excited states) and phosphorescence
emissions (triplet excited states). The calculations indicated
that the pyrene moiety is involved in the lowest-lying excited
states of Pt-1, Pt-2 and Pt-3. For Pt-4, however, normal
Figure 7. Calculated frontier energy levels of the complexes calcu-
lated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level of
3MLCT/3IL transitions were found. These theoretical pre-
dictions are fully supported by the experimental results, theory using Gaussian 09.
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Phosphorescence of Pyrene with Cycloplatinated Complexes
such as the deep-red/near-IR emission and the extended lu- a N2 atmosphere to 0.20% O2 will significantly quench the
minescent lifetimes of Pt-1, Pt-2 and Pt-3. For Pt-4, normal emission by 22.6% (see the Supporting Information).
3MLCT/3IL emission was predicted by the theoretical cal-
We noticed the phosphorescence emission of Pt-2 is
culations. Our assignment of the emissive state of the cyclo- highly sensitive to the presence of O2. For example, the
metallated Pt complexes by DFT/TDDFT calculations will emission intensity is nearly completely quenched in the
be useful in the design of luminescent complexes with pre- presence of 1.0% O2 (v/v; Figure 8, b). The O2-sensing data
determined photophysical properties, such as the ligand- were fitted to the Stern–Volmer equation (Figure 8, b).
localized triplet excited state (3IL).
Quenching constants of 0.17 and 1.45 Torr–1 were deter-
mined for Pt-1 and Pt-2, respectively. Thus, the emission of
Pt-2 is much more sensitive towards O2 than Pt-1. Similar
O2-sensing studies were performed for Pt-3 and Pt-4 (see
the Supporting Information). The quenching constants for
Pt-3 and Pt-4 were determined to be 1.16 and 0.18 Torr–1,
respectively.
Our results show that the O2 sensitivity of the emission
of the cycloplatinated complexes is in line with the lumines-
cent lifetimes of the complexes (Table 1). Pt-2 shows the
longest luminescence lifetimes and also shows the most sen-
sitive O2-sensing behaviour among the complexes studied
herein. Pt-1 and Pt-4 have relatively short luminescence life-
times compared with Pt-2 and lower sensitivity towards
oxygen. Thus, Pt-1 and Pt-4 can potentially be used as an
electroluminescence material and Pt-2 can be used as a
phosphorescent molecular probes (Table 6).
Luminescent O2-Sensing with the Emissive Pt Complexes
Recently, luminescent O2-sensing has attracted consider-
able attention.[11,13,21,35,36] Phosphorescent dyes, usually
transition-metal complexes, are employed for luminescent
O2 sensing as a result of their triplet nature and the long
lifetime of their luminescence (in the microsecond range,
µs). Typical compounds for this purpose are Pt–porphyrin
complexes, for example, PtOEP and RuII–polypyridine
complexes.[13,14,37–39] To the best of our knowledge, no cy-
clometallated Pt(acac) complexes have been systematically
studied for O2-sensing applications. Thus, we carried out
a preliminary investigation on the luminescent O2-sensing
properties of the complexes.
The changes in the emission of the complexes in solution
versus variation of O2 partial pressures were studied (Fig-
ure 8). We found the phosphorescence emission band of Pt-
1 at 680 nm is sensitive to O2. For example, changing from
Table 6. Parameters of O2 sensing of the complexes Pt-1, Pt-2, Pt-
3 and Pt-4 in CH2Cl2 (linear fitting result).
app[a]
[b]
KSV
pO2
r2[c]
Pt-1
Pt-2
Pt-3
Pt-4
0.17
5.88
0.69
0.86
5.56
0.99
0.98
0.99
0.99
1.45
1.16
0.18
[a] Quenching constant [Torr–1]. [b] Oxygen partial pressure at
which the initial emission intensity of the film is quenched by 50%,
and can be calculated as 1/KSV. [c] Determination coefficients.
Conclusions
We have prepared pyrene-containing cycloplatinated
complexes in which the pyrene moiety is directly cycloplati-
nated (Pt-1) or attached to the ppy ligand through a C–C
single bond (Pt-2) or through a CϵC triple bond (Pt-3). A
control complex with a phenyl group attached to the ppy
ligand (Pt-4), was also prepared. We observed room-tem-
perature deep-red/near-IR phosphorescence emission (650–
800 nm) for Pt-1, Pt-2 and Pt-3. Notably, room-tempera-
ture phosphorescence emission in the range of 600–700 nm
was observed for Pt-2 in which the pyrene moiety is not
directly cycloplatinated. This discovery contrasts the results
in a previous report on cycloplatinated complexes with 1-
diphenylphosphanylpyrene or 1,6-bis(diphenylphosphanyl)-
pyrene as ligands. To the best of our knowledge this is the
first report of room-temperature phosphorescence of py-
rene without direct cyclometallation. The photophysical
properties of the complexes were rationalized by DFT/
TDDFT calculations, which indicate pyrene-localized T1
states for Pt-1 and Pt-2. Our systematic study of the synthe-
Figure 8. Luminescent oxygen-sensing properties. Emission spectra
of (a) Pt-2 in CH2Cl2 solution saturated with 0.00, 0.02, 0.08, 0.12,
0.20, 1.00, 1.50, 3.50, 4.30, 21.0 and 100.0% oxygen (mixed gas
with N2, v/v). (b) Intensity ratios F0/F vs. O2 partial pressure [Torr].
Linear fitting of the O2-sensing data of Pt-1, Pt-2, Pt-3 and Pt-4
in CH2Cl2. The asterisk (*) in (a) indicates the second-order transi-
tion of the monochromator of the fluorescence spectrometer. c =
1.0ϫ10–5 mol/L, 12 °C.
Eur. J. Inorg. Chem. 2010, 4470–4482
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W. Wu, W. Wu, S. Ji, H. Guo, J. Zhao
FULL PAPER
Na2CO3 (279.0 mg, 2.63 mmol) in 2-ethoxyethanol (6 mL) at
100 °C for 20 h. Water (10 mL) was added and the precipitate was
collected and washed with water (2ϫ10 mL). After drying in vacuo
in an oven, the crude product was purified by column chromatog-
raphy (silica gel, CH2Cl2/petroleum ether = 1:1, v/v). A yellow solid
was obtained; yield 43.0 mg, 27.9%. 1H NMR (400 MHz, CDCl3):
δ = 9.22 (d, J = 8.0 Hz, 1 H), 8.69 (d, J = 9.6 Hz, 2 H), 8.39 (d, J
= 9.2 Hz, 2 H), 8.14–8.00 (m, 5 H), 7.95–7.90 (m, 2 H), 7.15 (t, J
= 8.0 Hz, 1 H), 5.54 (s, 1 H), 2.13 (s, 3 H), 2.06 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 184.7, 148.4, 138.2, 131.0, 129.8,
128.7, 128.6, 128.4, 127.2, 126.2, 125.6, 125.1, 123.2, 121.9, 120.8,
102.8, 28.5, 27.6 ppm. MS (MALDI-TOF): calcd. for
C26H19NO2Pt [M]+ 572.1064; found 572.1052. C26H19NO2Pt
(572.51): calcd. C 54.55, H 3.35, N 2.45; found C 54.84, H 3.55, N
2.31.
sis of the pyrene-substituted [(ppy)Pt(acac)] complexes, the
observation of the deep-red/near-IR phosphorescence emis-
sion of pyrene with Pt-1, the observation of the phos-
phorescence of pyrene without direct cyclometallation on
the pyrene moiety and the assignment of the emissive state
through DFT/TDDFT calculations will be useful in the de-
velopment of novel deep-red/near-IR-emitting complexes
and for their application as molecular sensors or electro-
luminescence materials.
Experimental Section
General: All the chemicals used were analytically pure and used as
received without further purification. NMR spectra were recorded
with a 400 MHz Varian Unity Inova spectrometer. Mass spectra
were recorded with a Q-TOF Micro MS spectrometer. UV/Vis
spectra were recorded with a HP8453 UV/Vis spectrophotometer.
Fluorescence spectra were recorded with a JASCO FP-6500 or
Sanco 970 CRT spectrofluorimeter. Fluorescence and phosphor-
escence quantum yields were measured with quinine sulfate (Φ =
54% in 0.5  H2SO4) or [Ru(bpy)2(phen)]·(PF6)2 as references (Φ
= 6.0% in CH3CN), respectively. Fluorescence lifetimes were mea-
sured with a Horiba Jobin Yvon Fluoro Max-4 (TCSPC) instru-
ment.
2-[4-(1-Pyrenyl)phenyl]pyridine (L-2): 2-(4-Bromophenyl)pyridine
(286.0 mg, 1.22 mmol), 1-pyrenylboronic acid (300.0 mg,
1.22 mmol), [Pd(PPh3)4] (52.1 mg, 0.045 mmol), aqueous Ba(OH)2
(2.286 g, 2.0 , 60 mL), EtOH (15 mL) and toluene (45 mL) were
mixed in a flask. The mixture was degassed with argon and heated
at reflux for 20 h. After being cooled, the solvent was evaporated
under vacuum and the residue was taken up in CH2Cl2, dried with
Na2SO4 and then evaporated to dryness. The crude product was
purified by column chromatography (silica gel, CH2Cl2/petroleum
ether = 2:1, v/v). A light-yellow solid was obtained; yield 0.19 g,
43.0%. 1H NMR (400 MHz, CDCl3): δ = 8.77 (d, J = 4.4 Hz, 1
H), 8.26–8.17 (m, 6 H), 8.11 (s, 2 H), 8.06–8.00 (m, 3 H), 7.88–7.82
(m, 2 H), 7.76 (t, J = 8.0 Hz, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 157.2, 149.7, 142.3, 138.1, 137.4, 137.3, 131.7, 131.3,
131.2, 131.0, 128.7, 127.8, 127.7, 127.6, 127.2, 126.2, 125.4, 125.2,
125.1, 124.9, 122.5, 121.0 ppm. MS (EI): calcd. for C27H17N [M]+
355.1361; found 355.1367.
1-Bromopyrene: A solution of NBS (4.09 g, 23 mmol) in DMF
(23 mL) was slowly added to a solution of pyrene (5.11 g, 25 mmol)
in DMF (35 mL) at 0 °C. After stirring at room temp. for 24 h, the
reaction mixture was poured into ice–water (150 mL) and the was
mixture was extracted with diethyl ether. The organic layer was
dried with anhydrous Na2SO4. After removal of the solvent by
evaporation the crude white solid was purified by column
chromatography (silica gel, petroleum ether). A white solid was ob-
Pt-2:
A mixture of 2-[4-(1-pyrenyl)phenyl]pyridine (155.0 mg,
1
tained; yield 3.5 g, 54.2%. H NMR (400 MHz, CDCl3): δ = 8.40
0.44 mmol) and [K2PtCl4] (91.0 mg, 0.22 mmol) in 2-ethoxyethanol
(6 mL) and water (2 mL) was heated at 80 °C for 20 h. After cool-
ing to room temperature, the mixture was added to water (20 mL)
and the precipitate was washed with water (2ϫ10 mL) and dried
under vacuum in a drying oven at 50 °C for 5 h. The precipitate
was treated with Hacac (65.5 mg, 0.65 mmol) in the presence of
Na2CO3 (231.0 mg, 2.18 mmol) in 2-ethoxyethanol (6 mL) at
100 °C for 20 h. Water (10 mL) was added and the yellow precipi-
tate was collected and washed with water (2ϫ10 mL). After drying
in vacuo in an oven the crude product was purified by column
chromatography (silica gel, CH2Cl2/petroleum ether = 1:1, v/v). A
yellow solid was obtained; yield 85.0 mg, 60.0%. 1H NMR
(400 MHz, CDCl3): δ = 9.07 (d, J = 5.2 Hz, 1 H), 8.32 (d, J =
8.8 Hz, 1 H), 8.23 (d, J = 8.0 Hz, 2 H), 8.20–7.99 (m, 8 H), 7.89–
7.85 (m, 2 H), 7.72 (d, J = 8.0 Hz, 1 H), 7.62 (d, J = 8.0 Hz, 1 H),
7.35 (d, J = 8.0 Hz, 1 H), 7.72 (t, J = 7.6 Hz, 1 H), 5.45 (s, 1 H),
2.02 (s, 3 H), 1.86 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 184.7, 148.4, 138.2, 131.0, 129.8, 128.7, 128.6, 128.4, 127.2, 126.2,
125.6, 125.1, 123.2, 121.9, 120.8, 102.8, 28.5, 27.6 ppm. MS
(MALDI-TOF): calcd. for C32H23NO2Pt [M]+ 648.1377; found
648.1340. C32H23NO2Pt (648.14): calcd. C 59.26, H 3.57, N 2.16;
found C 59.09, H 3.84, N 1.85.
(d, J = 9.2 Hz, 1 H), 8.20–8.17 (m, 3 H), 8.13 (d, J = 9.2 Hz, 1 H),
8.05–7.95 (m, 4 H) ppm. HRMS (ESI): calcd. for C16H9Br [M]+
279.9888; found 279.9889.
2-(1-Pyrenyl)pyridine
(L-1):
2-Bromopyridine
(192.8 mg,
1.22 mmol), 1-pyrenylboronic acid (300.0 mg, 1.22 mmol),
[Pd(PPh3)4] (52.1 mg, 0.045 mmol), aqueous Ba(OH)2 (2.286 g,
2.0 , 60 mL), EtOH (15 mL) and toluene (45 mL) were mixed.
The mixture was degassed with argon and heated at reflux for 20 h.
After being cooled, the solvent was evaporated under reduced pres-
sure and the residue was extracted with CH2Cl2. The organic layer
was dried with Na2SO4 and then evaporated to dryness. The crude
product was purified by column chromatography (silica gel,
CH2Cl2/petroleum ether = 2:1, v/v). A light-yellow solid was ob-
1
tained; yield 0.16 g, 47.0%. H NMR (400 MHz, CDCl3): δ = 8.87
(d, J = 4.4 Hz, 1 H), 8.37 (d, J = 9.2 Hz, 1 H), 8.24 (d, J = 8.0 Hz,
1 H), 8.20–8.14 (m, 3 H), 8.09–8.05 (m, 3 H), 8.00 (t, J = 7.2 Hz,
1 H), 7.86 (t, J = 8.0 Hz, 1 H), 7.70 (d, J = 8.0 Hz, 1 H), 7.36 (t,
J = 2.4 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 159.5,
149.7, 136.4, 135.6, 131.5, 131.4, 128.6, 128.0, 127.9, 127.6, 127.4,
126.0, 125.8, 125.4, 125.1, 124.9, 124.8, 122.0 ppm. MS (EI): calcd.
for C21H13N [M]+ 279.1042; found 279.1048.
Pt-1: A mixture of 2-(1-pyrenyl)pyridine (147.0 mg, 0.53 mmol)
1-Ethynylpyrene: Under argon, 1-bromopyrene (2.0 g, 3.57 mmol),
and [K2PtCl4] (109.2 mg, 0.26 mmol) in 2-ethoxyethanol (6 mL) [Pd(PPh3)2Cl2] (100 mg, 0.14 mmol), PPh3 (74.6 mg, 0.28 mmol)
and water (2 mL) was heated at 80 °C for 20 h. After cooling to
room temperature, the mixture was poured into water (20 mL) and
and CuI (54.3 mg, 0.28 mmol) were mixed in THF (20 mL) and
triethylamine (60 mL). Then trimethylsilylacetylene (414 mg,
the precipitate was collected and washed with water (2ϫ10 mL) 4.2 mmol) was added. The system was heated for 6 h at 90 °C. The
and dried under vacuum at 50 °C for 5 h. The precipitate with
treated with Hacac (78.9 mg, 0.79 mmol) in the presence of
reaction mixture was cooled to room temperature and filtered. The
filtrate was collected and the solvent removed under reduced pres-
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Phosphorescence of Pyrene with Cycloplatinated Complexes
sure. The residue was dissolved in n-hexane. The remaining solid
was filtered off and the filtrate was collected. Then the solvent was
removed and a yellow oily was obtained. The yellow oil was dis-
solved in diethyl ether (20 mL). Then methanol (40 mL) and potas-
sium carbonate (3.2 g) were added. The system was stirred at room
temp. for 3 h. The mixture was filtered and the filtrate was revolved
to dryness. The residue was purified by column chromatography
(silica gel, n-hexane/DCM = 50:1, v/v). The third fraction was col-
lected and the solvent was removed. The product was obtained as
a cinereous powder; yield 600 mg, 40.0%. 1H NMR (400 MHz,
CDCl3): δ = 8.54 (d, J = 8.6 Hz, 1 H), 8.11 (m, 4 H), 8.03 (m, 2
H), 7.97 (m, 2 H), 3.61 (s, 1 H) ppm. MS (EI): calcd. for C18H10
[M]+ 226.0783; found 226.0790.
CH2Cl2/petroleum ether = 2:1, v/v). A white solid was obtained;
yield 0.25 g, 54.8%. H NMR (400 MHz, CDCl3): δ = 8.71 (d, J =
4.4 Hz, 1 H), 8.07 (d, J = 8.0 Hz, 2 H), 7.78–7.76 (m, 2 H), 7.71
(d, J = 8.0 Hz, 2 H), 7.65 (d, J = 8.0 Hz, 2 H), 7.46 (t, J = 7.6 Hz,
2 H), 7.37 (t, J = 7.6 Hz, 1 H), 7.25–7.23 (m, 1 H) ppm. MS (EI):
calcd. for C17H13N [M]+ 231.1048; found 231.1051.
1
Pt-4: A mixture of 2-(4-biphenylyl)pyridine (115.6 mg, 0.50 mmol),
[K2PtCl4] (103.8 mg, 0.25 mmol) in ethoxyethanol (6 mL) and
water (2 mL) was heated at 80 °C for 20 h. After cooling to room
temperature, the mixture was poured into water (20 mL) and the
precipitate was collected and washed with water (2ϫ10 mL). The
crude product was dried under vacuum at 50 °C for 5 h. Reaction
of the precipitate with Hacac (75.0 mg, 0.75 mmol) in the presence
of Na2CO3 (265.0 mg, 2.50 mmol) in 2-ethoxyethanol (6 mL) at
100 °C for 20 h. After cooling to room temperature, water (10 mL)
was added and the precipitate was collected and washed with water
(2ϫ10 mL). The crude product was dried in vacuo in an oven and
then purified by column chromatography (silica gel, CH2Cl2/petro-
leum ether = 1:1, v/v). A yellow solid was obtained; yield 94.0 mg,
97.8%. 1H NMR (400 MHz, CDCl3): δ = 9.00 (d, J = 5.2 Hz, 1
H), 7.84 (s, 1 H), 7.79 (t, J = 7.2 Hz, 1 H), 7.70 (d, J = 7.6 Hz, 2
H), 7.61 (d, J = 8.0 Hz, 1 H), 7.50–7.43 (m, 3 H), 7.10 (t, J =
6.0 Hz, 1 H), 5.48 (s, 1 H), 2.01 (s, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 185.7, 184.2, 168.0, 147.3, 143.9, 141.9, 141.8, 139.1,
138.1, 129.0, 128.6, 127.4, 127.2, 123.3, 122.8, 121.1, 118.4, 102.5,
28.3, 27.2 ppm. MS (MALDI-TOF): calcd. for C22H19NO2Pt
[M]+ 524.1064; found 524.1099. C22H19NO2Pt (524.47): calcd. C
50.38, H 3.65, N 2.67; found C 50.53, H 3.57, N 2.38.
L-3: To
a degassed solution of 2-(4-bromophenyl)pyridine
(414.0 mg, 1.77 mmol), [PdCl2(PPh3)2] (74.0 mg, 0.106 mmol) and
PPh3 (56.0 mg, 0.21 mmol) in diisopropylanmine (50 mL) was
added the solution of ethynylpyrene (400.0 mg, 1.77 mmol) in THF
(10 mL). Then CuI (20.0 mg, 0.106 mmol) was added and the reac-
tion mixture was heated at 90 °C for 4 h. The mixture was poured
into water (20 mL) and extracted with CH2Cl2 (3ϫ30 mL). Then
the combined organic fractions were dried with Na2SO4 and the
solvents evaporated to dryness. The crude product was purified by
column chromatography (silica gel, ethyl acetate/hexane = 1:6,
v/v). A yellow solid was obtained; yield 263.2 mg, 39.2%. 1HNMR
(400 MHz, CDCl3): δ = 8.72 (d, J = 4.4 Hz, 1 H), 8.67 (d, J =
8.8 Hz, 1 H), 8.23–8.18 (m, 4 H), 8.13–8.00 (m, 6 H), 7.81 (d, J =
7.6 Hz, 2 H), 7.76 (d, J = 3.6 Hz, 2 H), 7.26–7.25 (m, 1 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 132.3, 132.1, 131.5, 131.3, 129.9,
128.6, 128.4, 127.4, 127.1, 126.4, 125.9, 125.8, 125.7, 124.7, 124.5,
124.4, 95.3, 90.2 ppm. HRMS (EI): calcd. for C29H17N [M]+
379.1361; found 379.1367.
DFT/TDDFT Calculations: The structures of the complexes were
optimized by using density functional theory (DFT) with the
B3LYP functional and 6-31G(d)/LanL2DZ basis set. The related
calculations in the excited state were carried out with time-depend-
ent DFT (TDDFT) with the ground-state geometries. The 6-
31G(d) basis set was employed for the C, H, N and O atoms, and
the LanL2DZ basis set was used for PtII. There are no imaginary
frequencies for any of the optimized structures. All the calculations
were performed with Gaussian 09.[40]
Pt-3: A mixture of L-3 (200.0 mg, 0.53 mmol) and [K2PtCl4]
(109.0 mg, 0.26 mmol) in ethoxyethanol (6 mL) and water (2 mL)
was heated at 80 °C for 20 h. After cooling to room temperature,
the mixture was poured into water (10 mL) and the precipitate was
collected and washed with water (2ϫ10 mL). The crude product
was dried under vacuum in a drying oven at 50 °C for 5 h. The
precipitate was treated with Hacac (79.1 mg, 0.79 mmol) in the
presence of Na2CO3 (279.0 mg, 2.63 mmol) in 2-ethoxyethanol
(6 mL) at 100 °C for 20 h. Water (10 mL) was added and the pre-
cipitate was collected and washed with water (2ϫ10 mL). After
drying in vacuo in an oven, the crude product was purified by col-
umn chromatography (silica gel, CH2Cl2/hexane = 1:1, v/v). A yel-
Supporting Information (see also the footnote on the first page of
this article): Characterization and calculation of the compounds.
Acknowledgments
We thank the National Natural Science Foundation of China
(NSFC, 20642003, 20634040 and 20972024), the Ministry of Edu-
cation, Scientific Research Foundation for the Returned Overseas
Chinese Scholars, Specialized Research Fund for the Doctoral Pro-
gram of Higher Education (200801410004) and the New Century
Excellent Talents in University (08–0077), the Changjiang Scholars
and Innovative Research Team in University (PCSIRT, IRT0711),
the State Key Laboratory of Fine Chemicals (KF0710 and
KF0802), the State Key Laboratory of Chemo/Biosensing and
Chemometrics (2008009), the Education Department of Liaoning
Province (2009T015) and the Dalian University of Technology
(SFDUT07005 and 1000–893394) for financial support. We are
grateful to the Royal Society of Chemistry (RSC) (UK) for the
China–UK Cost-Share Science Networks.
1
low solid was obtained; yield 20.0 mg, 5.6%. H NMR (400 MHz,
CDCl3): δ = 9.03 (d, J = 5.2 Hz, 1 H), 8.74 (d, J = 9.2 Hz, 1 H),
8.23–7.99 (m, 8 H), 7.93 (s, 1 H), 7.83 (t, J = 8.0 Hz, 1 H), 7.65 (d,
J = 7.6 Hz, 1 H), 7.49–7.46 (m, 2 H), 7.15 (t, J = 6.0 Hz, 1 H),
5.50 (s, 1 H), 2.22 (s, 3 H), 2.08 (s, 3 H) ppm. FTIR (KBr): ν =
˜
3435, 2923, 2852, 1631, 1608, 1578, 1561, 1517, 1479, 1427, 1390,
1312, 1262, 1095, 1025, 852, 825, 780, 755, 716 cm–1. MS (MALDI-
TOF): calcd. for C34H23NO2Pt [M]+ 672.1377; found 672.1414.
C34H23NO2Pt·H2O (690.65): calcd. C 59.13, H 3.65, N 2.03; found
C 59.40, H 3.39, N 1.90.
2-(4-Biphenylyl)pyridine
(L-4):
2-(4-Bromophenyl)pyridine
(405.4 mg, 2.00 mmol), phenylboronic acid (244.0 mg, 2.00 mmol),
[Pd(PPh3)4] (85.0 mg, 0.073 mmol), aqueous Na2CO3 (4.24 g, 2.0 ,
20 mL) and toluene (40 mL) were mixed in a flask. The mixture
was degassed with argon and heated at reflux for 20 h. After being
cooled, the solvent was evaporated under vacuum. The residue was
taken up in CH2Cl2 and washed with water. The organic phase was
dried with anhydrous Na2SO4 and then evaporated to dryness. The
crude product was purified by column chromatography (silica gel,
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Eur. J. Inorg. Chem. 2010, 4470–4482