Broadband visible-light-harvesting trans-bis(alkylphosphine) platinum(II)-alkynyl complexes with singlet energy transfer between BODIPY and naphthalene diimide ligands

Article abstract of DOI:10.1002/chem.201403780

A heteroleptic bis(tributylphosphine) platinum(II)-alkynyl complex (Pt-1) showing broadband visible-light absorption was prepared. Two different visible-light-absorbing ligands, that is, ethynylated boron-dipyrromethene (BODIPY) and a functionalized naphthalene diimide (NDI) were used in the molecule. Two reference complexes, Pt-2 and Pt-3, which contain only the NDI or BODIPY ligand, respectively, were also prepared. The coordinated BODIPY ligand shows absorption at 503 nm and fluorescence at 516 nm, whereas the coordinated NDI ligand absorbs at 594 nm; the spectral overlap between the two ligands ensures intramolecular resonance energy transfer in Pt-1, with BODIPY as the singlet energy donor and NDI as the energy acceptor. The complex shows strong absorption in the region 450 nm-640 nm, with molar absorption coefficient up to 88 000 m^-1 cm^-1. Longlived triplet excited states lifetimes were observed for Pt-1-Pt-3 (36.9 μs, 28.3 μs, and 818.6 μs, respectively). Singlet and triplet energy transfer processes were studied by the fluorescence/ phosphorescence excitation spectra, steady-state and time-resolved UV/Vis absorption and luminescence spectra, as well as nanosecond time-resolved transient difference absorption spectra. A triplet-state equilibrium was observed for Pt-1. The complexes were used as triplet photosensitizers for triplet-triplet annihilation upconversion, with upconversion quantum yields up to 18.4% being observed for Pt-1.

Full text of DOI:10.1002/chem.201403780

DOI: 10.1002/chem.201403780
Full Paper
&
Photochemistry |Hot Paper|
Broadband Visible-Light-Harvesting trans-Bis(alkylphosphine)
Platinum(II)-Alkynyl Complexes with Singlet Energy Transfer
between BODIPY and Naphthalene Diimide Ligands
Lianlian Liu,[a] Song Guo,[a] Jie Ma,[a] Kejing Xu,[a] Jianzhang Zhao,*[a] and Tierui Zhang*[b]
Abstract: A heteroleptic bis(tributylphosphine) platinum(II)-
alkynyl complex (Pt-1) showing broadband visible-light ab-
sorption was prepared. Two different visible-light-absorbing
ligands, that is, ethynylated boron-dipyrromethene (BODIPY)
and a functionalized naphthalene diimide (NDI) were used in
the molecule. Two reference complexes, Pt-2 and Pt-3,
which contain only the NDI or BODIPY ligand, respectively,
were also prepared. The coordinated BODIPY ligand shows
absorption at 503 nm and fluorescence at 516 nm, whereas
the coordinated NDI ligand absorbs at 594 nm; the spectral
overlap between the two ligands ensures intramolecular res-
onance energy transfer in Pt-1, with BODIPY as the singlet
energy donor and NDI as the energy acceptor. The complex
shows strong absorption in the region 450 nm–640 nm, with
molar absorption coefficient up to 88000mꢀ1 cmꢀ1. Long-
lived triplet excited states lifetimes were observed for Pt-1–
Pt-3 (36.9 ms, 28.3 ms, and 818.6 ms, respectively). Singlet and
triplet energy transfer processes were studied by the fluores-
cence/phosphorescence excitation spectra, steady-state and
time-resolved UV/Vis absorption and luminescence spectra,
as well as nanosecond time-resolved transient difference ab-
sorption spectra. A triplet-state equilibrium was observed for
Pt-1. The complexes were used as triplet photosensitizers
for triplet–triplet annihilation upconversion, with upconver-
sion quantum yields up to 18.4% being observed for Pt-1.
Introduction
with longer excited-state lifetimes. Therefore, it is tremendous-
ly important to develop transition-metal complexes that show
strong absorption of visible light, as well as long-lived triplet
excited states.[28]
Transition-metal complexes,[1–9] for example, PtII acetylides
complexes,[10–14] have been widely used in photocatalysis,[15–19]
luminescent bioimaging and electroluminescence,[3,4] molecular
devices,[20,21] and more recently, triplet–triplet annihilation (TTA)
upconversion.[22–26] These applications are mainly based on in-
termolecular energy transfer, or electron transfer at triplet ex-
cited state.[27] As a result, the visible-light-harvesting ability and
the triplet-state lifetimes of the complexes are crucial. Intense
absorption of photoexcitation light produces more complex
molecules in the triplet excited states, as a result, the intermo-
lecular electron transfer and the triplet-state energy-transfer
processes can be enhanced.[27] Longer triplet excited state life-
times are also beneficial for these intermolecular processes, for
instance, the Stern–Volmer constants will become much larger
Conventional PtII, RuII, and IrIII complexes usually show weak
absorption in the visible spectral region.[2,14,27–30] For example,
N^N-PtII bisacetylide complexes,[10,12,31] or trans-bis(alkylphos-
phine) platinum(II)-alkynyl complexes,[8,32,33] usually show molar
absorption coefficients smaller than 10000mꢀ1 cmꢀ1 in the visi-
ble spectral region. This is also true to a large extent for other
RuII, PtII, ReI, or IrIII complexes.[2,30,34] Furthermore, the triplet-
state lifetimes of these complexes are usually shorter than
5 ms. Therefore, there is room to enhance the photophysical
properties of the complexes, such as to improve the visible-
light-harvesting ability, and to prolong the triplet-state life-
times of these complexes.
We propose that the weak visible-light absorption of these
1
complexes is due to the low-lying S0! MLCT (metal-to-ligand
[a] L. Liu, S. Guo, J. Ma, K. Xu, Prof. J. Zhao
State Key Laboratory of Fine Chemicals
E-208, West Campus
charge transfer) transition, which is actually a weakly allowed
transition because the molecular orbitals involved in the transi-
tion share limited spatial overlap, owing to the charge-transfer
feature of the transition. This limited spatial molecular orbital
overlap renders a small overlap integral for the transition and
only weakly satisfies the transition selection rules.[35] To over-
come this challenge, we proposed to use organic visible-light-
harvesting chromophores as ligands to introduce a low-lying
Dalian University of Technology
Dalian 116024 (China)
E-mail: zhaojzh@dlut.edu.cn
Homepage: http://finechem.dlut.edu.cn/photochem
[b] Prof. T. Zhang
Key Laboratory of Photochemical Conversion and Optoelectronic Materials
Technical Institute of Physics and Chemistry
Chinese Academy of Sciences, Beijing 100190 (China)
E-mail: tierui@mail.ipc.ac.cn
1
S0! IL transition to the complexes;[27] this is a strongly allowed
transition owing to the p–p* feature of the transition. As
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201403780.
a result, strong absorption of visible light can be achieved.[27]
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We previously prepared a series of RuII, PtII, IrIII, and ReI com-
plexes to explore this method and the complexes showed
strong absorption of visible light and long-lived triplet excited
states.[23,27,28,36,37]
fer, widely used with the singlet state manifold to achieve
broadband light-harvesting,[45–50] we use two different acetylide
ligands to prepare a heteroleptic trans-bis(alkylphosphine) plat-
inum(II)-alkynyl complex, Pt-1 (Scheme 1). This kind of molecu-
lar structural profile was selected because it is feasible to intro-
duce two different acetylide ligands.[51] The two acetylide li-
gands (ethynylated boron-dipyrromethene (BODIPY) and
a functionalized naphthalene diimide (NDI), Scheme 1) show
strong visible-light absorption at different wavelengths, and
the emission of the BODIPY ligand overlaps with the absorp-
tion of the NDI acetylide ligand; thus, RET is highly likely to
occur, with the coordinated NDI section as the singlet energy
acceptor and spin converter.[27] As a result, broadband visible-
light absorption was achieved with Pt-1, with an absorption
band that covered 450–640 nm. The photophysical properties
of the complex were studied with steady-state and time-re-
solved absorption and emission spectroscopy, as well as DFT
calculations. Singlet energy transfer and triplet-state equilibria
were observed for the complexes. Intermolecular triplet energy
transfer was studied with nanosecond time-resolved transient
absorption spectroscopy. Our work to achieve broadband ab-
sorption in transition-metal complexes will be significant for
the development of transition-metal complexes that show
broadband visible-light absorption, the study of photophysical
There is still a major challenge in this area. Up to now, most
of the transition-metal complexes contain only a single kind of
visible-light-harvesting chromophore, as a result, there is only
one major absorption band in the visible spectral region for
these complexes.[27,36–39] Thus, the visible-light-absorption
bands of these complexes are narrow. Therefore, only a small
part of the photoexcitation energy can be harvested by the
complexes, especially if a broadband photoexcitation source is
used, such as solar light. Broadband visible-light-absorbing
complexes are very interesting because broadband photoexci-
tation energy can be more efficiently harvested with these
novel complexes. Recently, we prepared organic, broadband
visible-light-absorbing triplet photosensitizers.[40–42] However, to
the best of our knowledge, broadband visible-light-absorbing
transition-metal complexes have not been reported.[2,14,43,44]
It is unlikely that broadband absorption of visible light can
be achieved with a single light-absorbing ligand in the com-
plex because no one chromophore shows two strong absorp-
tion bands in visible spectral region. Thus, inspired by the reso-
nance energy transfer (RET), or the through band energy trans-
Scheme 1. Synthesis of the complexes Pt-1, Pt-2, Pt-3 and the ligands L-1 and L-2. i) NHEt2, 458C, 8 h; ii) dibromoisocyanuric acid (DBI), oleum, 408C, 5 h;
iii) 2,6-diisopropyl aniline, acetic acid, 1208C, 2 h; iv) 2-ethyl hexyl amine, 2-methoxyethanol, 1208C, 8 h; v) trimethylsilylacetylene, [Pd(PPh3)2Cl2], PPh3, CuI,
NEt3, reflux, 7 h; vi) K2CO3, CH2Cl2/MeOH, RT; vii) dry CH2Cl2, BF3·OEt2, NEt3; viii) THF/iPr2NH, CuI, RT, 30 min; ix) THF/HNEt2, CuI, RT, 30 min.
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properties of multi-chromophore complexes, and applications
of these complexes in photocatalysis and upconversion, etc.
ficients of Pt-2 (e=28300mꢀ1 cmꢀ1 at 594 nm) is higher than
its ligand, L-1 (e=15300mꢀ1 cmꢀ1 at 538 nm). Thus, the con-
nection profile of an organic ligand to the PtII center, through
either a p-conjugation or non-p-conjugation protocol, will
impose significant impact on the UV/Vis absorption properties
of the complex.
Results and Discussion
Molecular design and synthesis
With two different visible-light-harvesting ligands, Pt-
1 shows two major absorption bands in visible region; at
503 nm (e=87600mꢀ1 cmꢀ1) and 591 nm (29500mꢀ1 cmꢀ1).
Thus, broadband absorption in visible spectral region was ach-
ieved in Pt-1. The absorption wavelength and the molar ab-
sorption coefficients of Pt-1 at 503 nm and 591 nm are very
close to those of Pt-2 and Pt-3 (Figure 1a). These results indi-
cate that electronic interactions between the BODIPY and the
NDI ligands in Pt-1 are very weak in the ground state.
The photoluminescence of the complexes were studied
(Figure 2). Interestingly, Pt-1 shows three emission bands (Fig-
ure 2a). By comparison with the reference compounds, these
emission bands can be assigned to the fluorescence of the
BODIPY and the NDI ligand, as well as the phosphorescence of
the coordinated NDI moiety. It should be pointed out that the
luminescence quantum yields of Pt-1 are very low; thus, effi-
cient RET and ISC processes are expected for Pt-1.
The design goal is to achieve broadband absorption of visible
light. Two different light-harvesting ligands were used in Pt-
1 (Scheme 1), that is, functionalized NDI (L-1) and ethynylated
BODIPY (L-2) and, owing to their strong absorption of visible
light, good photostability, and versatile derivatization chemis-
try.[52–55] Singlet energy transfer from the BODIPY moiety to the
NDI ligand is expected, because the fluorescence emission of
BODIPY overlaps well with the absorption of NDI (see
below).[55,56] Furthermore, we previously observed RT near-IR
emission of the PtII-coordinated ethynyl NDI ligand at 784 nm
(1.58 eV).[57] It is known that BODIPY has a T1 state energy level
at 1.69 eV.[38] Thus, triplet-state energy transfer from the coordi-
nated BODIPY moiety to NDI ligand is envisaged. Experimental
results support these molecular designing rationales. Both the
singlet energy transfer and the triplet energy transfer can pro-
duce the triplet excited state of NDI, because the NDI unit is
a “spin converter”, that is, the p-conjugated core of NDI is di-
rectly attached to the PtII coordination center, thus, efficient in-
tersystem crossing (ISC) is expected for this coordination
moiety.[27,58–61]
UV/Vis absorption and emission spectra
The UV/Vis absorption spectra of the ligands and the com-
plexes were studied. For L-2, intense absorption at 505 nm
was observed. For L-1, the absorption band is at 538 nm. Previ-
ously, it was shown that upon p-conjugated coordination, the
absorption bands of the ligands show substantial red-
shifts.[36,37,39,57,62] L-2 is connected to PtII center through a non-
conjugated bond; thus, the absorption of BODIPY will not be
redshifted.[36–38] However, the NDI ligand is attached to the PtII
center through a p-conjugation profile, thus, a substantial red-
shift is expected.[57,62]
Figure 2. The photoluminescence spectra of PtII complexes and ligands
under different atmospheres. (a) Pt-1 (lex =488 nm), (b) Pt-2 (lex =580 nm),
(c) Pt-3 (lex =488 nm), (d) L-1 (lex =525 nm) (deaerated toluene, 1.0ꢁ10ꢀ5 m,
208C).
The absorption spectra of the complexes were studied
(Figure 1). Pt-3 shows an intense absorption band at 503 nm;
no significant redshift was observed compared with the ligand
L-2 (Figure 1b). For Pt-2, an absorption band at 594 nm was
observed, which is redshifted by 56 nm compared with that of
ligand L-1 (Figure 1b). Furthermore, the molar absorption coef-
For Pt-2, dual emission bands were observed (Figure 2b).
The emission intensity at 610 nm is not sensitive to oxygen
(O2), whereas the emission intensity at 789 nm can be dramati-
cally reduced in aerated solution. The luminescence lifetimes
of the emission bands at 610 nm and 789 nm were determined
as 0.3 ns and 37.7 ms, respectively. Thus, the emission band at
789 nm is attributed to phosphorescence. The emission band
at 610 nm is unlikely to be due to any uncoordinated ligand
impurities because the emission wavelength is drastically dif-
ferent from those of the free ligands (558 nm and 520 nm; Fig-
ure 2d and Figure S25 in the Supporting Information). Previ-
ously, it was shown that residual fluorescence can be observed
if a bulky ligand is attached to the coordination center.[63,64]
These complexes can be used as ratiometric O2 sensors and lu-
minescent bioimaging reagents.[5,65]
Figure 1. UV/Vis absorption of (a) the PtII complexes and (b) the acetylide li-
gands. c=1.0ꢁ10ꢀ5 m in toluene at 208C.
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Singlet/triplet energy transfer and electron transfer
Study of the luminescence excitation spectra
The postulated singlet- and triplet-state energy transfer in Pt-
1 was studied from luminescence spectra of the compounds,
as well as the luminescence excitation spectra (Figure 3 and
Figure 4, respectively). First, the luminescence of L-1 and the
corresponding complex, Pt-2, was compared. The emission of
L-1 (quantum yield FF =85.5%) is quenched in Pt-2 (FF =
0.5%: Note that the optical density is the same for both solu-
tions at the excitation wavelength. This condition was also ap-
plied to all other experiments comparing the emission intensi-
ty of two compounds). This quenching effect is mostly due to
the ISC because the p-conjugation core of NDI is directly
linked to the PtII coordination center.[27,36,66–69] This postulation
was confirmed by the high singlet oxygen quantum yield (FD)
Figure 4. The normalized excitation spectra and UV/Vis absorption for Pt-1.
(a) With emission wavelength set at lem =786 nm and (b) with emission
wavelength set at lem =615 nm. c=1.0ꢁ10ꢀ5 m in deaerated toluene at
208C. The peaks annotated with asterisks are due to the secondary transmis-
sion of the monochromator.
in Pt-1. Thus, singlet excited state energy transfer is proposed
for Pt-1, presumably with the BODIPY coordination part as the
energy donor and the NDI coordination part as the energy ac-
ceptor.
The emission of Pt-1 and Pt-2 was also compared. Pt-
1 shows stronger emission intensity than Pt-2 at 792 nm (Fig-
ure 3d). Therefore, the photo-induced electron transfer in Pt-
1 is not significant, at least in the triplet state, otherwise the
phosphorescence band at 792 nm would be quenched.[41,70–72]
Comparison of the luminescence excitation spectra with the
UV/Vis absorption spectra of dyads is a reliable method to
evaluate intramolecular energy transfer.[40,41,46] First, the phos-
phorescent excitation spectrum of Pt-1 was compared with
the UV/Vis absorption spectrum (Figure 4a). A band at 502 nm
was observed in the phosphorescence excitation spectrum, in-
dicating energy transfer to produce the phosphorescence of
the NDI moiety at 789 nm by excitation into the energy donor
(BODIPY). Excitation into the BODIPY moiety in Pt-1 may lead
to both the singlet excited state energy (demonstrated by the
fluorescence quenching studies, Figure 3c) and the triplet ex-
cited state energy transfer (please see the nanosecond time-re-
solved transient difference absorption spectroscopy section).
Figure 3. The emission spectra of the PtII complexes and ligands. (a) Pt-2
and L-1 (lex =525 nm), (b) Pt-3 and L-2 (lex =488 nm), (c) Pt-1 and Pt-3
(lex =488 nm), (d) Pt-1 and Pt-2 (lex =570 nm). The absorbance of the two
solutions at the excitation wavelength were identical within experimental
error. c=1.0ꢁ10ꢀ5 m in deaerated toluene at 208C.
of Pt-2 (65.4%, Table 1). For L-2
Table 1. Photophysical properties of Pt-1–Pt-3, L-1, and L-2.
and Pt-3, exactly the same emis-
sion intensity was observed. This
lack of quenching effect of L-2
in its complex Pt-3 does not
necessarily mean that no ISC
exists for Pt-3; note that the FF
of L-2 is only 25.4%. Thus, the
other nonradiative portion of
the singlet excited state of L-2
may undergo ISC in Pt-3. Actual-
ly, this is the case for Pt-3, which
shows a FD value of 71.3%
[a]
[c]
labs
e[b]
lem
FF [%][d] FP
tF [ns][f]
tP [ms][g]
298 K/77 K
tT [ms][h] FD [%][i]
[%][e] 298 K/77 K
Pt-1 503/591 8.76/2.95 516/610/789 0.92
0.05 1.2/0.3,3.6/1.2 37.7/45.9
36.9
28.3
818.6
82.3/82.9
65.4
Pt-2 594
Pt-3 503
2.83
7.27
1.53
10.61
614/794
516
558
0.5
0.04 2.2/2.9
27.2/46.0
[j]
[j]
28.2
85.5
25.4
–
–
–
2.7/7.6
10.8/–[k]
2.7/–[k]
–
–
–
71.3
[k]
[k]
[k]
[k]
[k]
L-1
L-2
538
505
–
–
–
[k]
[k]
[k]
520
–
[a] In toluene (1.0ꢁ10ꢀ5 m). [b] Molar absorption coefficient at the absorption maxima. e: 104 cmꢀ1 molꢀ1 dm3.
[c] In toluene. [d] In toluene, with 2,6-diiodo-BODIPY (FF =2.7% in CH3CN), B-6 (FF =10.5% in toluene) and 4-
(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (F=0.1 in CH2Cl2) as standards. [e] In tolu-
ene, with 2,6-diiodo-BODIPY and B-6 as standards. [f] Luminescence lifetime, lex =473 nm, at RT (in deaerated
toluene, Pt-1: lem =516 nm and 610 nm) and 77 K (in deaerated ethanol/methanol, 4:1, v/v, Pt-1: lem =510 nm
and 609 nm). [g] Phosphorescence lifetime, Pt-1 (lex =488 nm), Pt-2 (lex =580 nm), Pt-3 (lex =488 nm) at RT (in
deaerated toluene) and 77 K (in deaerated ethanol/methanol, 4:1, v/v). [h] Triplet-state lifetime, determined
when
excited
at
490 nm
(Table 1). The fluorescence quan-
tum yield of Pt-3 is 28.2%.
The emission of Pt-3 and Pt-
1 was compared (Figure 3c). The
strong fluorescence emission of
Pt-3 was completely quenched
with nanosecond time-resolved transient difference absorption spectroscopy, Pt-1 (lex =532 nm), Pt-2 (lex
=
532 nm), Pt-3 (lex =495 nm). 1.0ꢁ10ꢀ5 m in deaerated toluene. [i] Quantum yield of singlet oxygen (1O2), Pt-1 ex-
cited with 490 nm and 570 nm with 2,6-diiodo-BODIPY and MB as standards, respectively (FD =0.83 and 0.57
in CH2Cl2, respectively), 1.0ꢁ10ꢀ5 m in CH2Cl2. Pt-2 excited with 570 nm with MB as standard and Pt-3 excited
with 490 nm with 2,6-diiodo-BODIPY as standard, c=1.0ꢁ10ꢀ5 m in CH2Cl2. [j] Too weak to be determined. [k]
Not measured.
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To prove the singlet excited state energy transfer in Pt-1,
the luminescence excitation spectrum with 615 nm as the
emission wavelength was recorded (Figure 4b). In the excita-
tion spectra, a band at 503 nm was observed; thus, excitation
into the BODIPY moiety will produce the fluorescence emission
of the coordinated NDI moiety, that is, singlet energy transfer
exists in Pt-1.
Table 2. Electrochemical data of Pt-1–Pt-3, L-1, and L-2.[a]
Compound
Oxidation [V]
II
Reduction [V]
I
I
II
III
Pt-1
Pt-2
Pt-3
L-1
+0.94
+1.26
ꢀ1.21
ꢀ1.22
ꢀ1.51
ꢀ1.03
ꢀ0.75
ꢀ1.53
ꢀ1.72
ꢀ1.72
[b]
+0.91
+0.91
+1.13
–
–
–
–
[b]
[b]
[b]
–
–
–
[b]
[b]
[b]
–
ꢀ1.53
[b]
[b]
L-2
+0.94
+1.17
–
[a] Recorded with [Bu4N][PF6] as the electrolyte in CH2Cl2 (0.1m) at ambi-
ent temperature with a scan rate of 50 mVsꢀ1. Potentials are expressed as
the half-wave potentials (E1/2) in volts versus SCE using ferrocene as an in-
ternal reference. [b] Not applicable.
Cyclic voltammetry: electrochemical properties
The electrochemical properties of the complexes and the li-
gands were studied with cyclic voltammetry (Figure 5). First,
the electrochemical properties of Pt-2 and Pt-3 were com-
pared with those of the ligands (Figure 5b and c). Pt-3 shows
a reversible reduction potential at ꢀ1.51 V (Table 2). A pseudo
reversible oxidation potential at +0.91 V was observed. The re-
duction and oxidation potentials of Pt-3 are identical to L-2
(Figure 5c), indicating that there is no significant perturbation
of the p-conjugation framework of the BODIPY ligand upon
coordination. This conclusion is reasonable because the
BODIPY chromophore is not attached to the PtII center at its p-
conjugation core (Scheme 1).
Thus, the electrochemical data demonstrated that there is no
significant interaction between the coordinated NDI and the
coordinated BODIPY moieties in Pt-1 in the ground state.[2b]
The possibility of photo-induced intramolecular electron
transfer for Pt-1 was studied by calculation of the free energy
change (see the Supporting Information for the calculation de-
tails).[73–77] Based on the Weller equation and the T1 state
energy level, the free energy change of the electron transfer
with the T1 state of NDI as the electron acceptor, was calculat-
ed as +0.50 eV. Therefore, the T1 state of complex Pt-1 is un-
likely to be quenched by any intramolecular electron transfer
process. This postulation was supported by the unquenched
triplet-state lifetime and the phosphorescence of the coordi-
nated NDI part in Pt-1.
Nanosecond time-resolved transient absorption spectra: local-
ization of the T1 state and intramolecular/intermolecular trip-
let energy transfer
The triplet excited states of the complexes were studied with
nanosecond time-resolved transient absorption spectroscopy
(Figure 6). For Pt-3, a bleaching band at 505 nm was observed
upon nanosecond pulsed laser excitation (Figure 6e). More-
over, transient absorption bands at 400 nm and in the region
of 500–800 nm were observed. These features are typical for
the transient absorption of triplet excited state of
BODIPY.[37,38,78] The triplet-state lifetime was determined as
818.6 ms (c=1.0ꢁ10ꢀ5 m, Figure 6 f). To the best of our knowl-
edge, this is the longest triplet-state lifetime observed for
a BODIPY moiety in a transition-metal complex. The triplet-
state lifetimes of BODIPY moieties in transition-metal com-
plexes are usually shorter than 50 ms.[37,38,66]
Figure 5. Cyclic voltammograms of (a) Pt-1, Pt-2, and Pt-3; (b) Pt-2 and L-1;
(c) Pt-3 and L-2 in deaerated CH2Cl2 solutions. The concentration of Pt-1, Pt-
2, and Pt-3 was 0.5 mm each, for L-1 and L-2, c=1.0 mm. 0.10m Bu4NPF6
was used as the supporting electrode and Ag/AgNO3 was used as the refer-
ence electrode. Scan rates: 50 mVsꢀ1. Ferrocene (Fc) was used as an internal
reference.
For Pt-2 and its ligand L-1, however, the reduction poten-
tials show notable changes upon coordination. For example,
the reduction potentials of L-1 are at ꢀ1.03 V and ꢀ1.53 V. In
Pt-2, these peaks move cathodically to ꢀ1.22 V and ꢀ1.72 V.
This change means the coordinated NDI ligand is more difficult
to reduce. Two irreversible oxidation bands at +0.91 V and
+1.13 V were observed for Pt-2.
For Pt-1, three reversible reduction potentials at ꢀ1.21 V,
ꢀ1.53 V, and ꢀ1.72 V were observed. These reduction poten-
tials are superimposable to the sum of Pt-2 and Pt-3. A pseu-
doreversible oxidation potential at +0.94 V was observed for
Pt-1. Similar results were observed for the oxidation bands.
For Pt-2, a bleaching band at 591 nm was observed upon
pulsed laser excitation (Figure 6c). A transient absorption band
at 438 nm was observed. The triplet-state lifetime was deter-
mined as 28.3 ms. These features are typical for the triplet-state
absorption of the NDI moiety.[57,62]
The nanosecond time-resolved transient absorption spectra
of Pt-1 were also studied (Figure 6a). Although Pt-1 was selec-
tively photoexcited into the BODIPY ligand (nanosecond
pulsed laser excitation at lex =503 nm), in principle, the transi-
ent absorption features are the same as those of Pt-2; thus,
the triplet state is mainly localized on the coordinated NDI
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dence, the nanosecond transient absorption spectra of Pt-
1 and Pt-2 were measured under exactly the same condition
(Supporting Information, Figure S31; pulsed laser excitation at
lex =503 nm). The results show that the DO.D. value of Pt-1 is
approximately twice that of Pt-2, indicating that the photoex-
citation energy harvested by the BODIPY ligand was trans-
ferred to the NDI ligand.
It should be pointed out that the long-lived triplet excited
state lifetime is dependent on the concentration of the solu-
tion used for the lifetime measurement.[40] The TTA effect is sig-
nificant at high concentration, as a result, the lifetime observed
will be shorter than that at lower concentration. Therefore, we
measured the triplet excited state lifetime of the complexes at
different concentrations (Figure S29, see the Supporting Infor-
mation). The intrinsic triplet excited state lifetimes were ob-
tained by extrapolation to infinitely dilute solution, as 64.8 ms,
59.3 ms, and 2.78 ms for Pt-1, Pt-2, and Pt-3, respectively. It is
clear that the intrinsic triplet excited state lifetimes are much
longer than those observed at 1.0ꢁ10ꢀ5 m.
Intermolecular triplet energy transfer is important, for exam-
ple, in aspects of photovoltaics, the photochemistry of DNA,
and molecular devices.[81] Therefore, we studied the intermo-
lecular triplet energy transfer between Pt-3 and Pt-2 (Figure 7),
as a comparison with the fast intramolecular triplet energy
transfer in Pt-1 (Figure 6a). For complex Pt-3 alone, a strong
bleaching bond at 508 nm was observed (Figure 7). Upon in-
creasing the concentration of Pt-2, the triplet-state quencher,
the lifetime of the bleaching band at 500 nm decreased from
Figure 6. Nanosecond time-resolved transient absorption difference spectra
of (a) Pt-1 and (b) decay trace at 590 nm (lex =503 nm); (c) Pt-2 and
(d) decay trace at 592 nm (lex =590 nm); (e) Pt-3 (lex =495 nm) and (f) decay
trace at 500 nm (lex =495 nm). c=1.0ꢁ10ꢀ5 m in deaerated toluene upon
pulsed excitation at 208C.
moiety in Pt-1. Thus, singlet and triplet energy transfer from
the BODIPY ligand to the NDI ligand occurred. Similar transient
absorption spectra were obtained with excitation at 592 nm
(see the Supporting Information, Figure S30). There is a minor
bleaching band at 502 nm, along with the major bleaching
band at 588 nm. By comparison with the transient absorption
spectra of Pt-3, we propose that the triplet state of the
BODIPY moiety in Pt-1 was also populated. The bleaching
bands at 502 nm and 588 nm decay uniformly; thus, a triplet-
state equilibrium exists in Pt-1. The triplet-state lifetime of Pt-
1 is 36.9 ms, slightly longer than Pt-2, which is evidence for the
presence of triplet-state equilibrium.[40,79,80] The triplet excited
state is more localized on the NDI moiety than on the BODIPY
moiety, based on the relative intensity of the bleaching band
in the transient absorption spectra of Pt-1. This conclusion is
also supported by the observation of the coordinated NDI
phosphorescence in Pt-1, as in that of Pt-2 (Figure 2). The RT
phosphorescence of the NDI moiety will be quenched given
that the triplet state energy level of the NDI moiety is higher
than that of the BODIPY ligand. Based on the ratio of the
DO.D. values at 502 nm and 588 nm in Figure 6a, and the
steady-state UV/Vis absorption (Figure 1a), the equilibrium
constant Keq was calculated as 0.027. According to DG=
ꢀRTlnKeq and the T1 state energy level of Pt-2 (1.57 eV), where
R is the gas constant and T is temperature, the T1 state energy
level of Pt-3 was calculated as 1.67 eV, which is very close to
the experimental value (1.69 eV).[38]
Figure 7. Transient absorption spectra of the mixture of Pt-3 and Pt-2, with
increasing the concentration of Pt-2. c[Pt-3]=1.0ꢁ10ꢀ5 m. (a) c[Pt-2]=0.0m,
(b) c[Pt-2]=1.0ꢁ10ꢀ6 m, (c) c[Pt-2]=0.5ꢁ10ꢀ5 m, (d) c[Pt-2]=1.0ꢁ10ꢀ5 m and
decay traces of the mixture at (e) 500 nm and (f) 590 nm with c[Pt-
2]=0.5ꢁ10ꢀ5 m. lex =495 nm. In deaerated toluene after nanosecond pulsed
laser excitation, 208C.
The phosphorescence and fluorescence excitation spectra of
Pt-1 show that both singlet energy transfer and triplet energy
transfer are playing a role in the photophysics of Pt-1. As evi-
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818.6 ms to 149.5 ms, indicating triplet-state energy transfer
from Pt-3 to Pt-2. The quenching of the triplet excited state of
Pt-3 by Pt-2 was plotted following the Stern–Volmer equation
[Eq. (1)]:[56]
t0=t ¼ 1 þ KSV½Quencherꢁ
ð1Þ
Stern–Volmer quenching constants were calculated as KSV =
2.28ꢁ105 mꢀ1. The bimolecular quenching constant was calcu-
lated as kq =KSV/t0 =2.8ꢁ108 mꢀ1
s
ꢀ1, where t0 is the triplet-
Figure 8. Stern–Volmer plot for lifetime quenching of Pt-3 with increasing
concentration of Pt-2. lex =495 nm, c[photosensitizers]=1.0ꢁ10ꢀ5 m in de-
aerated toluene. 208C.
state lifetime of the triplet energy donor (Pt-3, 818.6 ms). The
quenching efficiency is given by fQ =kq/k0, where k0 is the diffu-
sion-controlled bimolecular quenching rate constant and can
be calculated with the Smoluchowski equation [Eq. (2)]:[56]
4pN
1000
ð2Þ
k0 ¼ 4pRND=1000 ¼
ðRf þ RqÞðDf þ DqÞ
where D is the sum of the diffusion coefficients of the energy
donor (Df) and quencher (Dq), N is Avogadro’s number. R is the
collision radius, the sum of the molecule radii of the energy
donor (Rf) and the quencher (Rq). Diffusion coefficients can be
obtained from the Stokes–Einstein equation:[56]
Figure 9. Spin density of the complexes Pt-1, Pt-2, Pt-3, and the ligands
L-1 and L-2. Calculated based on the optimized triplet state by DFT at the
B3LYP/6-31G(d) and B3LYP/GENECP/LanL2DZ level by using Gaussian 09W.
D ¼ kT=6phR
ð3Þ
where k is Boltzmann’s constant, h is the solvent viscosity, R is
the molecule radius. The molecule radii of the energy donor
(Pt-3) is 16 ꢂ and is 14 ꢂ for the quencher (Pt-2). According to
Eq. (3), the diffusion coefficients of the energy donor (Pt-3) is
2.29ꢁ10ꢀ6 cm2 sꢀ1 and quencher (Pt-2) is 2.62ꢁ10ꢀ6 cm2 sꢀ1 (in
for Pt-3, that is, the triplet excited state of Pt-3 is localized on
the BODIPY moiety.
For the heteroleptic complex Pt-1, the spin density surface
is exclusively confined on the NDI moiety; the BODIPY moiety
does not contribute to the spin density surface. Thus, the T1
state of Pt-1 is localized on the NDI moiety. This conclusion is
in agreement with the nanosecond time-resolved transient dif-
ference absorption spectra of Pt-1, in which the major bleach-
ing band is at 588 nm (Figure 6a).
toluene at 208C). Thus, k0 was calculated as 1.11ꢁ1010 mꢀ1 sꢀ1
.
The quenching efficiency fQ =kq/k0 =2.5%, which indicates
a non-efficient triplet-state energy transfer between Pt-2 and
Pt-3 in the mixture.
It should be pointed out that the intermolecular triplet-state
energy transfer kTT (given by Eq. (4)) is on the same scale as
that of the decay rate constants of the triplet energy acceptor
(Pt-2).[82] For example, with Pt-2 at 2.0ꢁ10ꢀ5 m, kTT was deter-
mined as 5.5ꢁ103 sꢀ1 (Figure 8, Eq. (4)). At this concentration,
the decay rate constant of the triplet state of Pt-2 was deter-
mined as 4.3ꢁ104 sꢀ1.
Next, the frontier molecular orbitals of Pt-1 were plotted
(Figure 10). The vertical singlet excitation energies (UV/Vis ab-
sorption) are presented in Table 3. A dark state of S1 was ob-
tained, in which the HOMO and LUMO are involved in
1
t
1
t0
ð4Þ
kTT
¼
ꢀ
DFT calculations
Localization of the triplet excited states
DFT calculations were used to study the triplet excited states
of the complexes. First, the spin density surfaces were comput-
ed (Figure 9). For Pt-2, the spin density surface is localized on
the NDI moiety; thus, the triplet state is localized on the NDI
moiety. This conclusion is in agreement with the nanosecond
transient absorption spectroscopy results. The PtII center
makes only a minor contribution to the spin density surface.
Thus, the triplet excited state of Pt-2 can be assigned as an
intraligand triplet excited state. Similar results were observed
Figure 10. Electron density maps of the frontier molecular orbitals of com-
plex Pt-1 based on the optimized ground-state geometry. Toluene was used
as the solvent in the calculations (PCM model). Calculated at the B3LYP/
GENECP/LanL2DZ level with Gaussian 09W.
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Table 3. Electronic excitation energies (eV) and corresponding oscillator
strengths (f), main configurations, and configuration interaction (CI) coef-
ficients of the low-lying excited states of complex Pt-1.[a]
Electronic TDDFT//GENECP/6-31G
transition
Energy
f
Composition CI[c]
Character[d]
[eV/nm][b]
Singlet S0!S1
S0!S2
2.01/617 0.0020 H!L
2.30/539 0.3714 Hꢀ2!L
2.84/437 0.0015 Hꢀ4!L
Hꢀ3!L
0.6840 MLCT
0.7027 ILCT
0.4454
S0!S5
0.5038
S0!S6
2.87/432 0.6125 Hꢀ1!L+1 0.6998 ILCT
1.53/808 0.0000[e] Hꢀ1!L+1 0.7078 ILCT
Triplet S0!T1
S0!T2
1.56/793 0.0000 Hꢀ2!L
1.97/629 0.0000 H!L
2.34/529 0.0000 Hꢀ1!L
0.6838 ILCT
0.6678 MLCT
0.7050 LLCT
S0!T3
Figure 11. TTA upconversion of the complexes. (a) Emission of the pure
complexes with 589 nm (5 mW) laser excitation. (b) The upconverted pery-
lene (Py) fluorescence and the residual fluorescence of the triplet photosen-
sitizers. c[Py]=6.0ꢁ10ꢀ5 m; c[photosensitizers]=1.0ꢁ10ꢀ5 m in deaerated
toluene. (c) Emission of the pure complexes (lex =473 nm). (d) The upcon-
verted perylene (Py) fluorescence and the residual fluorescence of the triplet
photosensitizers. c[Py]=1.0ꢁ10ꢀ4 m; c[photosensitizers]=1.0ꢁ10ꢀ5 m.
Owing to the strong fluorescence, Pt-3 was measured at 2.5ꢁ10ꢀ6 m with
c[Py]=2.5ꢁ10ꢀ5 m in deaerated toluene. The asterisks indicate the scattered
excitation laser. 208C.
S0!T4
[a] Calculated by TDDFT//B3LYP/GENECP/LanL2DZ, based on the DFT//
B3LYP/LanL2DZ optimized ground-state geometries. Toluene was used as
the solvent in the calculations (PCM model). [b] Only selected low-lying
excited states are presented. [c] H stands for HOMO and L stands for
LUMO. Only the main configurations are presented. [d] The CI coefficients
are in absolute values. [e] No spin-orbital coupling effect was considered,
thus the f values are zero.
a charge-transfer state from the PtII coordination center to the
NDI moiety. Two major absorption bands were identified at
539 nm and 437 nm. These two bands can be assigned as the
transitions localized on the BODIPY and the NDI moiety, re-
spectively (Figure 10 and Table 3).
have been used as triplet photosensitizer for TTA
upconversion.[23]
First, the complexes were excited with a 589 nm continuous
laser (Figure 11a). Under the experimental conditions, the
phosphorescence emission of the complexes is very weak.
With addition of the triplet acceptor (emitter) perylene, howev-
er, strong blue emission in the range 450–550 nm was ob-
served with Pt-1 and Pt-2 as the triplet photosensitizers. The
emission profile is identical to the prompt fluorescence of per-
ylene. Thus, the new emission band is due to the upconverted
fluorescence of perylene. No upconversion was observed with
Pt-3 as the photosensitizer owing to the unmatched excitation
wavelength for Pt-3. The upconversion quantum yields with
Pt-1 and Pt-2 were determined as 18.4% and 14.3%, respec-
tively. The higher upconversion quantum yield with Pt-1 is due
to the longer triplet excited state lifetime of Pt-1 compared
with that of Pt-2 (see the triplet state lifetime quenching sec-
tion). These results show that a broadband photoexcitation
can be used for TTA upconversion with Pt-1. We found that
non-coherent, dim light can be used as the excitation light
source for TTA upconversion. For example, the light from the
spectrofluorometer was used as the excitation light source for
the TTA upconversion (see the Supporting Information,
Figure S35).
Two degenerate triplet states with energy levels of 1.53 eV
and 1.56 eV were found. Based on the molecular orbitals in-
volved in these transitions (Table 3), the two triplet states are
localized on the BODIPY and the NDI moieties, respectively.
This conclusion is in agreement with the nanosecond transient
difference absorption spectra, which indicated a triplet-state
equilibrium for Pt-1 (Figure 9).
Application of the broadband absorbing complexes: multi-
wavelength excitable triplet–triplet annihilation upconversion
The complex Pt-1 shows strong absorption of visible light and
a long-lived triplet excited state, thus, this complex can be
used for triplet photosensitizers.[27,28] Herein, we studied the
application of the complexes for TTA upconversion (Figure 11).
TTA upconversion is an interesting upconversion method
owing to its strong absorption of visible light, high upconver-
sion quantum yield, and tunable excitation and emission wave-
lengths.
The complex Pt-1 is multi-wavelength excitable, so we used
a 473 nm laser for excitation to carry out the TTA upconversion
(Figure 11c,d). At 473 nm, Pt-1 and Pt-3 showed strong ab-
sorption, but Pt-2 showed only weak absorption. Interestingly,
Pt-1 shows much stronger TTA upconversion compared with
Pt-3. This result may be due to the RET, which occurs from the
BODIPY moiety to the coordinated NDI moiety and was con-
firmed by the fluorescence quenching experiments, as well as
the higher singlet oxygen quantum yield of Pt-1 than that of
Conventional triplet photosensitizers for TTA upconversion
are PtII/PdII porphyrin complexes, which show only moderate
absorption in the visible spectral region.[22–25] In recent years,
we have developed a series of transition-metal complexes as
triplet photosensitizers for TTA upconversion. These new com-
plexes usually show strong absorption of visible light and
long-lived triplet excited states.[23,27,28] However, until now, no
broadband visible-light-absorbing transition-metal complexes
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Pt-3. It should be pointed out that Pt-3 has stronger absorp-
tion at 473 nm than at 589 nm, thus, the fluorescence of Pt-3
is more significant at 473 nm excitation.
with nanosecond time-resolved transient absorption spectros-
copy. Stern–Volmer quenching curves were plotted. Pt-1 gives
a Stern–Volmer constant of KSV =1.02ꢁ105 mꢀ1, which is ap-
proximately twice that of Pt-2 (KSV =4.56ꢁ104 mꢀ1). The larger
Stern–Volmer constant of Pt-1 compared with Pt-2 is probably
due to the longer triplet excited state lifetime of Pt-1. By using
a similar analysis with the Stern–Volmer quenching curve, the
The results of the upconversion are clearly visible to the un-
aided eye (Figure 12). For the PtII complexes alone, no emission
can be observed upon 589 nm excitation (the color of the
beam path in the cuvette is due to the scattering excitation
laser). In the presence of perylene, strong blue emission was
observed with Pt-1 and Pt-2 as the photosensitizer. No upcon-
verted emission was observed for Pt-3 owing to the unmatch-
ed excited wavelength. The emission color was quantified with
CIE coordinates. The photo of the TTA upconversion with exci-
tation at 473 nm was also recorded, similar results were ob-
served. Pt-1 gives the strongest upconversion; for Pt-3, the up-
conversion is negligible (Figure S38 in the Supporting
Information).
bimolecular quenching constant of Pt-1 is kq =2.8ꢁ109 mꢀ1 sꢀ1
,
which is close to the diffusion-limited quenching constants, in-
dicating that the triplet-state energy transfer is efficient
(Table 4).
Table 4. Triplet excited state lifetimes (tt), Stern–Volmer quenching con-
stant (KSV) and bimolecular quenching constants (kq) of the PtII sensitizers.
In deaerated toluene solution. 208C.
[a]
[h]
tT [ms] KSV
[103 Mꢀ1
kq
FUC [%]
k0
[1010 Mꢀ1 sꢀ1
f[i]
[%]
]
[109 Mꢀ1 sꢀ1
]
]
Pt-1 36.9[b] 102.1[b]
Pt-2 28.3[c] 45.6[c]
2.8
1.6
18.4[e]/6.0[f] 3.7
14.3[e]/15.0[f] 3.5
7.6
4.6
19.0
Pt-3 818.6[d] 4806.9[d] 5.9
–
[g]/0.1[f]
3.1
[a] Upconversion quantum yields. [b] Excited with 532 nm. [c] Excited
with 532 nm. [d] Excited with 495 nm. [e] 589 nm (5 mW) laser excitation,
with B-6 as the standard (FUC =10.5% in toluene). [f] 473 nm (5 mW)
laser excitation, with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylami-
nostyryl)-4H-pyran as the standard (FF =10% in CH2Cl2). [g] Cannot be
excited with 589 nm. [h] Diffusion-controlled bimolecular quenching rate
constants. [i] Quenching efficiency.
The delayed luminescence lifetime and the time-resolved
emission spectra of the complexes and the TTA upconversion
were studied (Figures 14 and 15). First, the emission of Pt-
1 alone was studied. With picosecond laser excitation, fluores-
cence emission in the 500–650 nm region was observed. With
nanosecond pulsed laser excitation, a long-lived phosphores-
cence band in the range of 750–850 nm was observed, the
phosphorescence lifetime is 37.7 ms.
Figure 12. (a) Photographs of the emission of the pure triplet photosensitiz-
ers and (b) the upconversion in the presence of perylene. (c) CIE diagram of
the emission of the pure sensitizers and (d) in the presence of perylene (up-
conversion). lex =589 nm (laser power: 5 mW). Pt-3 cannot be excited by
589 nm laser. In deaerated toluene, c[photosensitizer]=1.0ꢁ10ꢀ5 m,
c[Py]=6.0ꢁ10ꢀ5 m, 208C.
The time-resolved emission in the presence of triplet accept-
or (perylene) was also studied. No substantial changes were
found for the fluorescence emission bands at 516 nm and
610 nm; the lifetimes were determined as 1.2 ns and 0.3 ns, re-
To study the origin of the higher upconversion quantum
yield with Pt-1 than with Pt-2, triplet-state lifetime quenching
experiments were carried out (Figure 13). The quenching of
the triplet excited state lifetime of the complexes with increas-
ing the triplet energy acceptor (quenching) was measured
Figure 14. (a) Delayed fluorescence observed in the TTA upconversion with
Pt-1 and Pt-2 as triplet photosensitizer and perylene (Py) as the triplet ac-
ceptor. Excited at 589 nm and monitored at 445 nm. (b) The prompt fluores-
cence decay of perylene determined in a different experiment (excited with
picosecond 405 nm laser, the decay of the emission was monitored at
420 nm). c[Py]=6.0ꢁ10ꢀ5 m; c[sensitizers]=1.0ꢁ10ꢀ5 m. In deaerated tolu-
ene. 208C.
Figure 13. (a) Stern–Volmer plots for lifetime quenching of Pt-
1 (lex =532 nm), Pt-2 (lex =532 nm), and Pt-3 (lex =495 nm) with increasing
concentration of perylene (Py). (b) Comparison of Pt-1 and Pt-2, the data
are from (a). c[photosensitizers]=1.0ꢁ10ꢀ5 m in deaerated toluene. 208C.
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Figure 16. Photosensitizing of 1O2 with the complexes as photosensitizers. Ir-
radiation time-dependent decrease of absorbance at 414 nm of 1,3-diphen-
1
ylisobenzofuran (DPBF) (1.0ꢁ10ꢀ4 m) with different O2 sensitizers: (a) Pt-1,
(b) Pt-2, (c) [Ir(ppy)2bpy]. (d) Plots of ln(Ct/C0) versus irradiation time. c[pho-
tosensitizers]=1.0ꢁ10ꢀ5 m. In CH2Cl2/MeOH (9:1, v/v), 1 mWcm2, 208C.
Figure 15. Time-resolved emission spectra (TRES) of pure Pt-1 and the TTA
upconversion in the presence of perylene (Py as triplet acceptor). Pure Pt-1:
(a) the fluorescence region was measured (460–770 nm, tF =1.2 ns at
516 nm, tF =0.3 ns at 610 nm) excited with pico-second pulsed laser
(473 nm). (b) Phosphorescence region of Pt-1 was measured (700–880 nm,
tP =37.7 ms) excited with nanosecond pulsed laser (589 nm). TRES of Pt-1 in
the presence of Py: (c) fluorescence was observed (tF =1.2 ns at 516 nm,
tF =0.3 ns at 610 nm) excited with pico-second pulsed laser (473 nm) and
(d) upconverted emission in the range of 410–730 nm was observed
(t=160.8 ms) with nanosecond pulsed laser (589 nm). c[Py]=6.0ꢁ10ꢀ5 m;
c[photosensitizers]=1.0ꢁ10ꢀ5 m. In deaerated toluene. 258C.
1
stability of the complexes in the presence of O2 is satisfactory
(Figure S44 in the Supporting Information).
1
To quantitatively compare the kinetics of the O2 production,
ln(Ct/C0)–irradiation time curves were plotted. Pt-1 is the most
efficient triplet photosensitizer and Pt-3 gives the lowest rate.
The efficient photosensitizing ability of Pt-1 is attributed to its
broadband visible-light absorption and efficient intersystem
crossing. For Pt-3, however, the absorption band is much “nar-
rower’, thus, the photosensitizing ability is much lower than
that of Pt-1 and Pt-2. Pt-1 is more efficient than mono-chro-
mophore triplet photosensitizers such as MB. Complex [Ir-
(ppy)2bpy] gives negligible 1O2 production under the experi-
mental conditions. Thus, the broadband visible-light-absorbing
complexes are promising for applications in photocatalysis.
spectively. These results are in agreement with the steady-state
upconversion spectra. Interestingly, the phosphorescence
bands in the 750–850 nm region were completely quenched.
An emission band at 450 nm was observed; the lifetime of the
luminescence was 160.8 ms. This long-lived delayed fluores-
cence confirmed the upconverted fluorescence emis-
sion.[59,66,83–86] Similar results were observed for Pt-2 (Fig-
ures S36 and S39 in the Supporting Information).
Conclusion
A heteroleptic trans-bis(tributylphosphine) platinum(II)-alkynyl
complex showing broadband absorption of visible light was
prepared. The broadband visible-light absorption is based on
the resonance energy transfer (RET) effect between the two
different visible-light-harvesting acetylide ligands in the com-
plex, that is, ethynylated BODIPY and a functionalized naphtha-
lene diimide (NDI) ligand. No transition-metal complexes that
are capable of absorbing broadband visible light have been
previously reported. The singlet energy acceptor NDI moiety
also acts as the intramolecular spin converter to ensure effi-
cient intersystem crossing (ISC) and to transform the harvested
photoexcitation energy to produce the triplet excited state.
The energy transfer, in both the singlet-state and the triplet-
state manifolds, was demonstrated by fluorescence/phosphor-
escence excitation spectra, steady-state and nanosecond time-
resolved transient absorption and luminescence spectra. Pho-
toinduced electron transfer was proved to not be significant
from the steady-state and time-resolved luminescence spectra,
as well as from the calculation of free energy changes of the
electron transfer with the Weller equation. Intermolecular trip-
Photosensitizing singlet oxygen (1O2)
As complex Pt-1 shows broadband visible-light absorption,
photooxidation was investigated as a way to transduce the en-
hanced visible-light absorption. The 1O2 photosensitizing ability
of the complexes was studied with 1,3-diphenylisobenzofuran
1
1
(DPBF) as the O2 scavenger (Figure 16). The kinetics of the O2
production with Pt-1, Pt-2, and Pt-3 were followed by moni-
toring the absorption change at 414 nm.
For Pt-1 and Pt-2, significant changes in the UV/Vis absorp-
tion spectra were observed. The absorption change at 414 nm
with Pt-3 as the triplet photosensitizer is less significant. A
known triplet photosensitizer, methylene blue (MB), was also
studied, which gave substantial absorption change at 414 nm.
An IrIII complex, [Ir(ppy)2bpy] (ppy=2-phenylpyridine; bpy=
2,2’-bipridyl), which has been used as photocatalyst previous-
ly,[15–17,86,87] was studied but no changes were observed under
the experimental conditions. We studied the photostability of
the complexes in the aerated solution; the absorption bands
of the complexes did not show any change, that is, the photo-
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under Ar. After cooling to RT, the mixture was poured into cold
water (100 mL). The solid was collected by filtration, and was
washed with water and methanol. After drying under vacuum, the
resulting red solid was purified by column chromatography (silica
gel, CH2Cl2/petroleum ether=1:1, v/v) to give 5 as light yellow
solid (0.51 g, 34.3%). 1H NMR (400 MHz, CDCl3): d=9.12 (s, 2H),
7.54–7.51 (m, 4H), 7.35 (d, 2H, J=8.0 Hz), 2.67–2.63 (m, 4H),
1.16 ppm (d, 24H, J=8.0 Hz); MALDI-TOF HRMS: m/z calcd for
[C38H36N2O4Br2]ꢀ: 742.1042; found: 742.1021.
let energy transfer was also studied with nanosecond time-re-
solved transient absorption spectroscopy. We confirmed that
both the S1 state and the T1 state of the complex is highly con-
fined on one of the two coordination sections. The complex
proved to be more efficient as a singlet oxygen (1O2) photosen-
sitizer than the reference complexes, which contain only one
visible-light-harvesting ligand. Our molecular design rationale
of using two (or more) different visible-light-harvesting ligands
and the RET between the different coordination ligands will be
useful for the development of additional broadband visible-
light-absorbing transition-metal complexes, and for the appli-
cation of these complexes in the areas of photocatalysis, trip-
let–triplet annihilation upconversion, photoresponsive molecu-
lar devices, as well as for the study of the fundamental photo-
chemistry of transition-metal complexes.
6: Under Ar, 2-ethyl hexylamine (46.5 mg, 0.360 mmol, 59 mL) was
added to a solution of 5 (223.4 mg, 0.300 mmol) in 2-methoxyetha-
nol (10 mL) through a syringe. The mixture was stirred for 8 h at
1208C. After completely consumption of the starting material, the
solvents were evaporated under reduced pressure. The crude prod-
uct was further purified by using column chromatography (silica
gel, CH2Cl2/petroleum ether=1:1, v/v) to give 6 as a red solid
1
(100.0 mg, 42.0%). M.p. 88.2–90.28C; H NMR (400 MHz, CDCl3): d=
10.16 (s, 1H), 8.99 (s, 1H), 8.40 (s, 1H), 7.54–7.48 (m, 2H), 7.33 (t,
4H, J=8.0 Hz), 3.49 (t, 2H, J=4.0 Hz), 2.72–2.63 (m, 4H), 1.73–1.68
(m, 1H), 1.52–1.37 (m, 6H), 1.18–1.14 (m, 26H), 0.94–0.83 ppm (m,
6H); MALDI-TOF HRMS: m/z calcd for [C46H54N3O4Br+H]+:
792.3376; found: 792.3442.
Experimental Section
Analytical measurements
All the chemicals were analytically pure and were used as received.
Solvents were dried and distilled before use. NMR spectra were re-
corded on a 400 MHz Varian Unity Inova spectrophotometer (with
tetramethylsilane (TMS) as an internal standard). UV/Vis absorption
spectra were measured with an Agilent 8453 UV/Vis spectropho-
tometer. Fluorescence spectra were recorded on a Shimadzu RF-
5301PC spectrofluorometer. The upconversion luminescence quan-
tum yields were measured with 2,6-diiodo-BODIPY (FF =0.027 in
CNCH3), B-6 (see Scheme 1, FF =0.105 in toluene) and 4-(dicyano-
methylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (FF =0.1
in CH2Cl2) as standards. Luminescence lifetimes were measured on
an OB920 luminescence lifetime spectrometer (Edinburgh Instru-
ments, UK) and a FLS920 spectrofluorometer (Edinburgh Instru-
ments, UK).
L-1: Under Ar atmosphere, [Pd(PPh3)2Cl2] (8.8 mg, 0.013 mmol),
PPh3 (6.6 mg, 0.025 mmol), and CuI (4.8 mg, 0.025 mmol) were
added to a solution of 5 (100.0 mg, 0.126 mmol) in a mixed solvent
of THF/Et3N (8 mL/4 mL). Then, trimethylsilylacetylene (136.1 mg,
1.39 mmol, 0.2 mL) was added through a syringe. The mixture was
stirred for 8 h at 758C. After completely consumption of the start-
ing material, deionized water was added, then CH2Cl2 was added
to extract the product (4ꢁ30 mL). The organic phase was dried
over anhydrous Na2SO4, filtered, and the solvent was removed
under reduced pressure. The residue was purified by column chro-
matography (silica gel, CH2Cl2/petroleum ether=1:1, v/v) to give
a red solid (80.2 mg, 42.0%). Then, K2CO3 (41.0 mg, 0.300 mmol)
was added to a solution of the above trimethylsilane-protected in-
termediate (80.0 mg, 0.099 mmol) in the mixed solvent of CH2Cl2/
MeOH (10 mL/5 mL). The mixture was stirred at room temperature
for 1 h. After completely consumption of the starting material, de-
ionized water was added, then the mixture was extracted with
CH2Cl2 (4ꢁ30 mL). The organic phase was dried over anhydrous
Na2SO4. The solvent was evaporated under reduced pressure. The
residue was purified by column chromatography (silica gel, CH2Cl2/
petroleum ether=1:1, v/v) to give L-1 as a red solid (53.0 mg,
Synthesis
2: Under Ar atmosphere, phenylacetylene (25.5 mg, 0.250 mmol,
30 mL) was added to a solution of cis-[Pt{P(nBu)3}2Cl2] (1) (200 mg,
0.298 mmol) in diethylamine (NHEt2) (10 mL). Then the mixture was
stirred for 6 h at 458C. After completely consumption of the start-
ing material, the solvents were evaporated under reduced pres-
sure. The crude product was then purified by using column chro-
matography (silica gel, CH2Cl2/petroleum ether=1:2, v/v) to give 2
1
72.6%). M.p. 200.4–201.48C; H NMR (400 MHz, CDCl3): d=10.23 (s,
1H), 8.90 (s, 1H), 8.39 (s, 1H), 7.54–7.46 (m, 2H), 7.38–7.33 (m, 4H),
3.64 (s, 1H), 3.51 (t, 2H, J=4.0 Hz), 2.72–2.66 (m, 4H), 1.75–1.71 (m,
1H), 1.49–1.39 (m, 6H), 1.19–1.15 (m, 26H), 0.91 (t, 3H, J=8.0 Hz),
0.84 ppm (t, 3H, J=8.0 Hz); 13C NMR (100 MHz, CDCl3): d=166.64,
162.63, 162.48, 162.11, 153.08, 145.71, 138.66, 130.56, 130.41,
130.03, 128.34, 127.10, 124.42, 123.32, 121.35, 120.96, 120.11,
100.12, 86.50, 82.00, 46.78, 39.55, 31.30, 29.88, 29.47, 28.88, 24.63,
24.15, 23.08, 14.12, 11.09 ppm; MALDI-TOF HRMS: m/z calcd for
[C48H55N3O4 +H]+: 738.4271; found: 738.4324.
1
as a light yellow oil (145.1 mg, 78.8%). H NMR (400 MHz, CDCl3):
d=7.24–7.11 (m, 5H), 2.03–2.00 (m, 12H), 1.58–1.56 (m, 12H),
1.49–1.40 (m, 12H), 0.91 ppm (t, 18H, J=8.0 Hz); MALDI-TOF
HRMS: m/z calcd for [C32H59P2PtClꢀCl]+
: 700.3740; found:
700.3683.
4: A solution of dibromoisocyanuric acid (DBI) (0.75 g, 2.6 mmol) in
oleum (20 mL, 20% SO3) was added dropwise to a solution of
1,4,5,8-naphthalenetetracarboxylic
dianhydride
(3)
(0.67 g,
8: Under Ar, 4-bromobenzaldehyde (7) (1.0 g, 5.40 mmol), [Pd-
(PPh3)2Cl2] (37.9 mg, 0.054 mmol), PPh3 (28.3 mg, 0.108 mmol), CuI
(20.6 mg, 0.108 mmol), and KOH (2.85 mol, 160 mg) were dissolved
in Et3N (30 mL). The mixture was stirred at RT for 10 min. Ethynyltri-
methylsilane (848.6 mg, 8.64 mmol, 1.2 mL) was added through
a syringe and the mixture was heated at reflux at 758C for 8 h.
After completely consumption of the starting material, the solvent
was removed under reduced pressure. The crude product was puri-
fied by column chromatography (silica gel, CH2Cl2/petroleum
ether=3:1, v/v) to give a yellow solid (675.5 mg, 71.8%). K2CO3
2.5 mmol) in oleum (20 mL, 20% SO3) over 1 h at RT. The mixture
was stirred for 5 h at 408C, then poured into crushed ice (100 g),
diluted with water (100 mL), and then stirred for 1 h at RT. The pre-
cipitate was collected with a Buchner funnel, washed with water
and methanol, and dried under vacuum to give 4 as a light yellow
solid (0.88 g, 82.2%). The crude product 4 was used for the next
step without further purification.
5: A mixture of 4 (0.85 g, 2.0 mmol), 2,6-diisopropylaniline (1.06 g,
6.0 mmol), and acetic acid (30 mL) was stirred for 2 h at 1208C
Chem. Eur. J. 2014, 20, 14282 – 14295
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
(1.61 g, 11.6 mmol) was added to a solution of the above trimethyl-
silane-protected intermediate (670.0 mg, 3.84 mmol) in methanol
(50 mL), the mixture was stirred at RT for 3 h. After completely con-
sumption of the starting material, deionized water was added. The
mixture was extracted with CH2Cl2 (4ꢁ30 mL). The organic phase
was dried over Na2SO4. The solvent was evaporated under reduced
pressure. The residue was purified by column chromatography
(silica gel, CH2Cl2/petroleum ether=2:1, v/v) to give 8 as a light-
yellow solid (324.8 mg, 65.0%). M.p. 87.1–88.98C; 1H NMR
(400 MHz, CDCl3): d=10.04 (s, 1H), 7.85 (d, 2H, J=8.0 Hz), 7.65 (d,
2H, J=8.0 Hz), 3.31 ppm (s, 1H); EI-HRMS: m/z calcd for [C9H6O]+:
130.0419; found: 130.0414.
ether=1:1, v/v) to give Pt-2 as a purple solid (17.5 mg, 89.5%).
M.p. 89.9–91.98C; H NMR (400 MHz, CD3COCD3): d=10.02 (s, 1H),
1
8.67 (s, 1H), 8.36 (s, 1H), 7.50–7.45 (m, 2H), 7.38–7.35 (m, 4H),
7.25–7.18 (m, 4H), 7.07 (t, 1H, J=8.0 Hz), 3.61 (t, 2H, J=4.0 Hz),
2.89–2.77 (m, 4H), 2.23–2.20 (m, 12H), 1.78–1.74 (m, 1H), 1.68–1.62
(m, 12H), 1.53–1.29 (m, 20H), 1.20–1.15 (m, 24H), 0.95 (t, 3H, J=
8.0 Hz), 0.88–0.79 ppm (m, 21H); 13C NMR (100 MHz, CD3COCD3):
d=166.61, 162.58, 162.05, 151.80, 145.84, 145.76, 138.48, 131.69,
131.48, 130.51, 129.33, 129.12, 129.04, 128.05, 127.87, 127,60,
124.76, 123.73, 123.56, 122.76, 121.24, 119.32, 110.64, 109.47,
107.69, 100.55, 45.72, 39.30, 31.08, 26.32, 24.45, 24.02, 23.95, 23.76,
23.61, 23.35, 23.29, 22.76, 13.39, 13.30, 10.48 ppm; MALDI-TOF
HRMS: m/z calcd for [C80H113N3O4P2Pt+H]+ 1437.7932; found:
1437.8007.
L-2: Under Ar atmosphere, to a solution of 4-ethynylbenzaldehyde
(200.0 mg, 1.54 mmol, 8) and 2,4-dimethylpyrrole (336.8 mg,
3.54 mmol) in CH2Cl2 (80 mL) was added trifluoroacetic acid
(11.7 mL, 0.154 mmol). The mixture was stirred at RT for 1 h; then,
p-chloranil (378.8 mg, 1.54 mmol) was added. The mixture was
stirred at RT for another 1 h. Then, NEt3 (2.63 g, 26.0 mmol, 3.6 mL)
was added, 10 min later BF3·OEt2 (4.01 g, 27.7 mmol) was added
and stirred for another 10 min. Then, the reaction mixture was
washed with water (4ꢁ60 mL) and dried with anhydrous Na2SO4.
The solvent was removed under vacuum and the residue was puri-
fied by chromatography (silica gel, hexane/CH2Cl2 =1:1, v/v) to
give compound L-2 as a red solid (155.0 mg, 28.9%). M.p. 233.2–
Pt-3: Under Ar atmosphere, 2 (10.6 mg, 0.0144 mmol) and L-2
(5.0 mg, 0.0144 mmol) were dissolved in mixed solvent THF/Et2NH
(3 mL/3 mL). The flask was evacuated and back-filled with argon
three times. Then, CuI (3.0 mg, 0.015 mmol) was added, the mix-
ture was stirred at RT for 30 min. Deionized water was used to
quench the reaction, CH2Cl2 was added to extract the product (4ꢁ
25 mL). The organic phase was dried with Na2SO4. The solvent was
removed under reduced pressure. The crude product was further
purified by using column chromatography (silica gel, CH2Cl2/petro-
leum ether=1:1, v/v) to give Pt-3 as an orange solid (12.4 mg,
82.0%). M.p. 96.6–98.08C; 1H NMR (400 MHz, CDCl3): d=7.36 (d,
2H, J=8.0 Hz), 7.26 (d, 2H, J=8.0 Hz), 7.19 (t, 2H, J=8.0 Hz), 7.13–
7.07 (m, 3H), 5.97 (s, 2H), 2.55 (s, 6H), 2.16–2.14 (m, 12H), 1.63–
1.62 (m, 12H), 1.47–1.44 (m, 18H), 0.90 ppm (t, 18H, J=8.0 Hz);
13C NMR (100 MHz, CDCl3): d=155.19, 143.26, 142.33, 131.49,
131.12, 130.74, 129.77, 128.99, 127.88, 127.49, 124.88, 121.04,
110.78, 108.92, 108.83, 107.62, 107.47, 31.94, 29.71, 29.38, 26.38,
26.28, 24.49, 24.42, 24.35, 24.16, 22.70, 14.59, 14.13, 13.80 ppm;
MALDI-TOF HRMS: m/z calcd for [C53H77N2PtF2BP2]+: 1047.5271;
found: 1047.5304.
1
234.38C; H NMR (400 MHz, CDCl3): d=7.62 (d, 2H, J=8.0 Hz), 7.26
(d, 2H, J=8.0 Hz), 5.99 (s, 2H), 3.18 (s, 1H), 2.56 (s, 6H), 1.40 ppm
(s, 6H); EI-HRMS: m/z calcd for [C21H19BF2N2]+: 348.1609; found:
348.1615.
9: The synthetic procedure is similar to that of 2, except that L-2
(51.5 mg, 0.150 mmol) was used. The crude product was purified
by using column chromatography (silica gel, CH2Cl2/petroleum
ether=1:1, v/v) to give 9 as an orange solid (114.5 mg, 75.8%).
1
M.p. 101.2–103.18C; H NMR (400 MHz, CDCl3): d=7.33 (d, 2H, J=
8.0 Hz), 7.08 (d, 2H, J=8.0 Hz), 5.97 (s, 2H), 2.55 (s, 6H), 2.05–2.01
(m, 12H), 1.60–1.57 (m, 12H), 1.47–1.42 (m, 18H), 0.90 ppm (t,
18H,
J=8.0 Hz);
MALDI-TOF
HRMS:
m/z
calcd
for
Nanosecond time-resolved transient difference absorption
spectroscopy
[C45H72BN2F2P2PtCl]+ 981.4568; found: 981.4560.
Pt-1: Under Ar, 7 (13.6 mg, 0.0136 mmol) and L-1 (10.0 mg,
0.0136 mmol) were dissolved in mixed solvent THF/iPr2NH (3 mL/
2 mL). The flask was evacuated and back-filled with argon three
times; then, CuI (3.0 mg, 0.015 mmol) was added and the mixture
was stirred at RT for 30 min. Deionized water was used to quench
the reaction, CH2Cl2 was added to extract the product (4ꢁ30 mL).
The organic phase was dried with Na2SO4 and filtered. The solvent
was removed under reduced pressure. The crude product was fur-
ther purified by using column chromatography (silica gel, CH2Cl2/
petroleum ether=1:1, v/v) to give Pt-1 as a dark-red solid (8.2 mg,
49.0%). M.p. 113.5–115.08C; 1H NMR (400 MHz, CD3COCD3): d=
10.03 (s, 1H), 8.67 (s, 1H), 8.36 (s, 1H), 7.36–7.48 (m, 8H), 7.21 (d,
2H, J=8.0 Hz), 6.11 (s, 2H), 3.62 (t, 2H, J=4.0 Hz), 2.90–2.79 (m,
4H), 2.50 (s, 6H), 2.25–2.21 (m, 12H), 1.78–1.76 (m, 1H), 1.67–1.64
(m, 12H), 1.53–1.29 (m, 20H), 1.20–1.15 (m, 24H), 0.95 (t, 3H, J=
8.0 Hz), 0.88–0.79 ppm (m, 27H); 13C NMR (100 MHz, CD3COCD3):
d=166.61, 162.60, 162.08, 155.01, 151.83, 145.84, 145.76, 142.99,
142.65, 138.42, 131.67, 131.48, 131.22, 130.93, 130.22, 129.12,
129.06, 128.06, 127.69, 127.37, 123.74, 123.58, 122.79, 121.23,
121.07, 119.38, 110.83, 110.63, 109.37, 100.53, 45.71, 39.30, 31.08,
26.36, 24.45, 24.10, 24.03, 23.96, 23.76, 23.60, 23.28, 22.75, 13.83,
13.68, 13.37, 13.28, 10.47 ppm; MALDI-TOF HRMS: m/z calcd for
[C93H126N5O4P2BPt+H]+: 1683.9072; found: 1683.8936.
The spectra were recorded with a LP920 laser flash photolysis spec-
trometer (Edinburgh Instruments, UK). Excitation was done with
a nanosecond pulsed laser (OpoletteTM 355II+UV nanosecond
pulsed laser, OPOTEK, USA), typical pulse length: 7 ns, pulse repeti-
tion: 20 Hz, peak OPO energy: 4 mJ. The wavelength is tunable in
the range of 210–355 nm and 410–2200 nm. The data were buf-
fered on a Tektronix TDS 3012B oscilloscope. LP900 software was
used to obtain the lifetime values. All samples measured in flash
photolysis experiments were deaerated with N2 for about 15 min
and the gas flow was maintained during the measurement.
Triplet–triplet annihilation upconversion
The excitation source for the upconversion was a diode-pumped
solid-state (DPSS) continuous laser (473 nm and 589 nm). The
power of the laser was measured with a VLP-2000 pyroelectric
laser power meter and the diameter of the 473 nm and 589 nm
laser spot was approximately 3 mm. The mixed solution of the PtII
compound (triplet photosensitizers) and perylene was degassed
with N2 for about 15 min. A small black box behind the fluorescent
cuvette was used to trap the laser beam so as to repress the scat-
tered laser.
Pt-2: The synthetic procedure is similar to that of Pt-1, except that
2 (10.0 mg, 0.0136 mmol) was used. The crude product was puri-
fied by column chromatography (silica gel, CH2Cl2/petroleum
The delayed fluorescence lifetime and time-resolved emission spec-
tra (TRES) were measured by a FLS920 spectrofluorometer (Edin-
burgh Instruments, UK) with an OPO nanosecond pulse laser. The
Chem. Eur. J. 2014, 20, 14282 – 14295
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14293
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[5] Y. Feng, J. Cheng, L. Zhou, X. Zhou, H. Xiang, Analyst 2012, 137, 4885–
4901.
[6] Y. You, W. Nam, Chem. Soc. Rev. 2012, 41, 7061–7084.
[7] M. S. Lowry, S. Bernhard, Chem. Eur. J. 2006, 12, 7970–7977.
[8] W. S. Tang, X. X. Lu, K. M. C. Wong, V. W. W. Yam, J. Mater. Chem. 2005,
15, 2714–2720.
prompt fluorescence lifetime was measured with EPL picosecond
pulsed laser (473 nm and 405 nm) synchronized to the FLS 920
spectrofluorometer. The mixed solution of the PtII compound (trip-
let photosensitizers) and perylene was degassed with N2 for ap-
proximately 15 min before measurement.
The upconversion quantum yields (FUC) were determined with the
prompt fluorescence of 4-(dicyanomethylene)-2-methyl-6-(4-di-
methylaminostyryl)-4H-pyran (FF =10% in dichloromethane).
Eq. (5) was used to calculate the upconversion quantum
yields,[9,23–26] FUC, Asam, Isam, and hsam represent the quantum yield,
absorbance, integrated photoluminescence intensity, and the re-
fractive index of the solvents, respectively, where the subscript
“std” is for the standard used in the measurement and the “sam” is
for the samples measured. The equation is multiplied by a factor
of 2 so as to set the maximum quantum yield to unity. All these
data were independently measured three times with different
sample solutions.
[9] P. Wu, E. L. M. Wong, D. L. Ma, G. S. M. Tong, K. M. Ng, C. M. Che, Chem.
Eur. J. 2009, 15, 3652–3656.
[10] C. E. Whittle, J. A. Weinstein, M. W. George, K. S. Schanze, Inorg. Chem.
2001, 40, 4053–4062.
[11] C. J. Adams, N. Fey, Z. A. Harrison, I. V. Sazanovich, M. Towrie, J. A. Wein-
stein, Inorg. Chem. 2008, 47, 8242–8257.
[12] a) S. Chakraborty, T. J. Wadas, H. Hester, R. Schmehl, R. Eisenberg, Inorg.
Chem. 2005, 44, 6865–6878; b) F. Guo, W. Sun, Inorg. Chem. 2005, 44,
4055–4065; c) R. Liu, D. Zhou, A. Azenkeng, Z. Li, Y. Li, K. D. Glusac, W.
Sun, Chem. Eur. J. 2012, 18, 11440–11448; d) R. Liu, A. Azenkeng, D.
Zhou, Y. Li, K. D. Glusac, W. Sun, J. Phys. Chem. A 2013, 117, 1907–1917.
[13] S. Develay, O. Blackburn, A. L. Thompson, J. A. G. Williams, Inorg. Chem.
2008, 47, 11129–11142.
[14] J. A. G. Williams, Top. Curr. Chem. 2007, 281, 205–268.
[15] D. Ravelli, M. Fagnoni, A. Albini, Chem. Soc. Rev. 2013, 42, 97–113.
[16] L. Shi, W. Xia, Chem. Soc. Rev. 2012, 41, 7687–7697.
[17] J. Xuan, W. J. Xiao, Angew. Chem. 2012, 124, 6934–6944; Angew. Chem.
Int. Ed. 2012, 51, 6828–6838.
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
2
Astd
Asam
Isam
Istd
hsam
hstd
ð5Þ
ꢀUC ¼ 2ꢀstd
Density functional theory (DFT) calculations
[18] M. Kobayashi, S. Masaoka, K. Sakai, Angew. Chem. 2012, 124, 7549–
7552; Angew. Chem. Int. Ed. 2012, 51, 7431–7434.
B3LYP/6–31G(d) were used to optimize both the singlet states and
triplet states. The energy level of the T1 state (energy gap between
S0 state and T1 state) was calculated with time-dependent DFT
(TDDFT), which is based on the optimized singlet ground state ge-
ometries (S0 state). All the calculations were performed with
Gaussian 09W.[88]
[19] F. Gꢅrtner, S. Denurra, S. Losse, A. Neubauer, A. Boddien, A. Gopinathan,
A. Spannenberg, H. Junge, S. Lochbrunner, M. Blug, S. Hoch, J. Busse, S.
Gladiali, M. Beller, Chem. Eur. J. 2012, 18, 3220–3225.
[20] S. W. Lai, Y. Chen, W. M. Kwok, X. J. Zhao, W. P. To, W. F. Fu, C. M. Che,
Chem. Asian J. 2010, 5, 60–65.
[21] S. Sun, W. Gao, F. Liu, F. Li, J. Fan, X. Peng, Phys. Chem. Chem. Phys.
2011, 13, 570–575.
[22] T.N. Singh-Rachford, F.N. Castellano, Coord. Chem. Rev. 2010, 254,
2560–2573.
[23] J. Zhao, S. Ji, H. Guo, RSC Adv. 2011, 1, 937–950.
[24] R. Tubino, S. Hoseinkhani, F. Meinardi, Phys. Chem. Chem. Phys. 2012,
14, 4322–4332.
[25] Y. C. Simon, C. Weder, J. Mater. Chem. 2012, 22, 20817–20830.
[26] P. Ceroni, Chem. Eur. J. 2011, 17, 9560–9564.
[27] J. Zhao, W. Wu, J. Sun, S. Guo, Chem. Soc. Rev. 2013, 42, 5323–5351.
[28] J. Zhao, S. Ji, W. Wu, W. Wu, H. Guo, J. Sun, H. Sun, Y. Liu, Q. Li, L.
Huang, RSC Adv. 2012, 2, 1712–1728.
Acknowledgements
We thank the NSFC (21273028, 21473020, 21421005, and
91127005), Ministry of Education (SRFDP-20120041130005),
Program for Changjiang Scholars and Innovative Research
Team in University (IRT 13R06), State Key Laboratory of Fine
Chemicals (KF1203), the Fundamental Research Funds for the
Central Universities (DUT14ZD226) and Dalian University of
Technology (DUT2013TB07) for financial support.
[29] N. D. McClenaghan, Y. Leydet, B. Maubert, M. T. Indelli, S. Campagna,
Coord. Chem. Rev. 2005, 249, 1336–1350.
[30] S. Campagna, F. Puntoriero, F. Nastasi, G. Bergamini, V. Balzani, Top. Curr.
Chem. 2007, 280, 117–214.
[31] W. Lu, BX. Mi, Z. Hui, CM. Che, N. Zhu, S. T. Lee, J. Am. Chem. Soc. 2004,
126, 4958–4971.
[32] C. K. M. Chan, C. H. Tao, K. F. Li, K. M. C. Wong, N. Zhu, K. W. Cheah,
V. W. W. Yam, Dalton Trans. 2011, 40, 10670–10685.
Keywords: bodipy · energy transfer · naphthalene diimide ·
photosensitizer · triplet state
[33] A. Y. Y. Tam, V. W. W. Yam, Chem. Soc. Rev. 2013, 42, 1540–1567.
[34] J. D. Routledge, A. J. Hallett, J. A. Platts, P. N. Horton, S. J. Coles, S. J. A.
Pope, Eur. J. Inorg. Chem. 2012, 4065–4075.
[35] N. J. Turro, V. Ramamurthy, J. C. Scaiano, Principles of Molecular Photo-
chemistry, An Introduction, University Science Books, Sausalito, 2009.
[36] W. Wu, J. Zhao, H. Guo, J. Sun, S. Ji, Z. Wang, Chem. Eur. J. 2012, 18,
1961–1968.
[37] J. Sun, F. Zhong, X. Yi, J. Zhao, Inorg. Chem. 2013, 52, 6299–6310.
[38] A. A. Rachford, R. Ziessel, T. Bura, P. Retailleau, F. N. Castellano, Inorg.
Chem. 2010, 49, 3730–3736.
[39] A. A. Rachford, S. Goeb, F. N. Castellano, J. Am. Chem. Soc. 2008, 130,
2766–2767.
[1] P. T. Chou, Y. Chi, M. W. Chung, C. C. Lin, Coord. Chem. Rev. 2011, 255,
2653–2665.
[2] a) L. Flamigni, A. Barbieri, C. Sabatini, B. Ventura, F. Barigelletti, Top. Curr.
Chem. 2007, 281, 143–203; b) M. T. Indelli, T. Bura, R. Ziessel, Inorg.
Chem. 2013, 52, 2918–2926; c) M. P. Coogan, V. Fernꢃndez-Moreira, J. B.
Hess, S. J. A. Pope, C. Williams, New J. Chem. 2009, 33, 1094–1099.
[3] a) V. Fernꢃndez-Moreira, F. L. Thorp-Greenwood, M. P. Coogan, Chem.
Commun. 2010, 46, 186–202; b) F. Schmitt, J. Freudenreich, N. P. E.
Barry, L. Juillerat-Jeanneret, G. Sꢄss-Fink, B. Therrien, J. Am. Chem. Soc.
2012, 134, 754–757; c) I. Stengel, C. A. Strassert, E. A. Plummer, C.-H.
Chien, L. De Cola, P. Bꢅuerle, Eur. J. Inorg. Chem. 2012, 1795–1809; d) E.
Rossi, A. Colombo, C. Dragonetti, D. Roberto, R. Ugo, A. Valore, L. Falcio-
la, P. Brulatti, M. Cocchi, J. A. G. Williams, J. Mater. Chem. 2012, 22,
10650–10655; e) P.-H. Lanoꢆ, H. Le Bozec, J. A. G. Williams, J.-L. Fillaut,
V. Guerchais, Dalton Trans. 2010, 39, 707–710.
[40] C. Zhang, J. Zhao, S. Wu, Z. Wang, W. Wu, J. Ma, S. Guo, L. Huang, J.
Am. Chem. Soc. 2013, 135, 10566–10578.
[41] a) S. Guo, L. Ma, J. Zhao, B. KꢄÅꢄkçz, A. Karatay, M. Hayvali, H. G. Yaglio-
glu, A. Elmali, Chem. Sci. 2014, 5, 489–500; b) J. Ma, X. Yuan, B. KꢄÅꢄ-
kçz, S. Li, C. Zhang, P. Majumdar, A. Karatay, X. Li, H. Gul Yaglioglu, A.
Elmali, J. Zhao, M. Hayvali, J. Mater. Chem. C 2014, 2, 3900–3913.
[42] L. Huang, X. Cui, B. Therrien, J. Zhao, Chem. Eur. J. 2013, 19, 17472–
17482.
[4] a) Q. Zhao, F. Li, C. Huang, Chem. Soc. Rev. 2010, 39, 3007–3030; b) Y.
Tang, H.-R. Yang, H.-B. Sun, S.-J. Liu, J.-X. Wang, Q. Zhao, X.-M. Liu, W.-J.
Xu, S.-B. Li, W. Huang, Chem. Eur. J. 2013, 19, 1311–1319; c) W.-J. Xu, S.-
J. Liu, X. Zhao, N. Zhao, Z.-Q. Liu, H. Xu, H. Liang, Q. Zhao, X.-Q. Yu, W.
Huang, Chem. Eur. J. 2013, 19, 621–629.
Chem. Eur. J. 2014, 20, 14282 – 14295
www.chemeurj.org
14294
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[43] A. Kumar, S. S. Sun, A. J. Lees, Top. Organomet. Chem. 2010, 29, 1–35.
[44] K. K. W. Lo, K. Y. Zhang, S. P. Y. Li, Eur. J. Inorg. Chem. 2011, 3551–3568.
[45] X. Zhang, Y. Xiao, X. Qian, Org. Lett. 2008, 10, 29–32.
[46] Z. Kostereli, T. Ozdemir, O. Buyukcakir, E. U. Akkaya, Org. Lett. 2012, 14,
3636–3639.
[47] A. Harriman, M. A. H. Alamiry, J. P. Hagon, D. Hablot, R. Ziessel, Angew.
Chem. 2013, 125, 6743–6747; Angew. Chem. Int. Ed. 2013, 52, 6611–
6615.
[71] M. Yuan, X. Yin, H. Zheng, C. Ouyang, Z, Zuo, H. Liu, Y. Li, Chem. Asian
J. 2009, 4, 707–713.
[72] T. Bura, F. Nastasi, F. Puntoriero, S. Campagna, R. Ziessel, Chem. Eur. J.
2013, 19, 8900–8912.
[73] R. Ziessel, B. D. Allen, D. B. Rewinska, A. Harriman, Chem. Eur. J. 2009,
15, 7382–7393.
[74] Y. Rio, W. Seitz, A. Gouloumis, P. Vꢃzquez, J. L. Sessler, D. M. Guldi, T.
Torres, Chem. Eur. J. 2010, 16, 1929–1940.
[48] O. A. Bozdemir, S. Erbas-Cakmak, O. O. Ekiz, A. Dana, E. U. Akkaya,
Angew. Chem. 2011, 123, 11099–11104; Angew. Chem. Int. Ed. 2011, 50,
10907–10912.
[49] C. W. Wan, A. Burghart, J. Chen, F. Bergstrçm, L. B. A. Johansson, M. F.
Wolford, T. G. Kim, M. R. Topp, R. M. Hochstrasser, K. Burgess, Chem. Eur.
J. 2003, 9, 4430–4441.
[75] J. Y. Liu, M. E. El-Khouly, S. Fukuzumi, D. K. P. Ng, Chem. Asian J. 2011, 6,
174–179.
[76] J. Hankache, O. S. Wenger, Chem. Eur. J. 2012, 18, 6443–6447.
[77] M. Urbani, K. Ohkubo, D. M. Shafiqul lslam, S. Fukuzumi, F. Langa, Chem.
Eur. J. 2012, 18, 7473–7485.
[78] W. Wu, H. Guo, W. Wu, S. Ji, J. Zhao, J. Org. Chem. 2011, 76, 7056–7064.
[79] J. E. Yarnell, J. C. Deaton, C. E. McCusker, F.N. Castellano, Inorg. Chem.
2011, 50, 7820–7830.
[50] R. Bandichhor, A. D. Petrescu, A. Vespa, A. B. Kier, F. Schroeder, K. Bur-
gess, J. Am. Chem. Soc. 2006, 128, 10688–10689.
[51] W. Y. Wong, C. L. Ho, Coord. Chem. Rev. 2006, 250, 2627–2690.
[52] G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. 2008, 120, 1202–1219;
Angew. Chem. Int. Ed. 2008, 47, 1184–1201.
[80] M. T. Whited, P. I. Djurovich, S. T. Roberts, A. C. Durrell, C. W. Schlenker,
S. E. Bradforth, M. E. Thompson, J. Am. Chem. Soc. 2011, 133, 88–96.
[81] a) A. Cnossen, L. Hou, M. M. Pollard, P. V. Wesenhagen, W. R. Browne,
B. L. Feringa, J. Am. Chem. Soc. 2012, 134, 17613–17619; b) P. D. Wood,
R. W. Redmond, J. Am. Chem. Soc. 1996, 118, 4256–4263; c) J. J. Apper-
loo, C. Martineau, P. A. van Hal, J. Roncali, R. A. J. Janssen, J. Phys. Chem.
A 2002, 106, 21–31.
[82] X.-H. Xu, X.-G. Fu, L.-Z. Wu, B. Chen, L.-P. Zhang, C.-H. Tung, H.-F. Ji, K. S.
Schanze, R.-Q. Zhang, Chem. Eur. J. 2006, 12, 5238–5245.
[83] T. N. Singh-Rachford, A. Nayak, M. L. Muro-Small, S. Goeb, M. J. Therien,
F. N. Castellano, J. Am. Chem. Soc. 2010, 132, 14203–14211.
[84] W. Wu, J. Sun, X. Cui, J. Zhao, J. Mater. Chem. C 2013, 1, 4577–4589.
[85] X. Cui, J. Zhao, P. Yang, J. Sun, Chem. Commun. 2013, 49, 10221–10223.
[86] S.-y. Takizawa, R. Aboshi, S. Murata, Photochem. Photobiol. Sci. 2011, 10,
895–903.
[53] R. Ziessel, A. Harriman, Chem. Commun. 2011, 47, 611–631.
[54] C. Thalacker, C. Rçger, F. Wꢄrthner, J. Org. Chem. 2006, 71, 8098–8105.
[55] a) S. V. Bhosale, S. V. Bhosale, M. B. Kalyankar, S. J. Langford, Org. Lett.
2009, 11, 5418–5421; b) L. Gai, J. Mack, H. Lu, H. Yamada, D. Kuzuhara,
G. Lai, Z. Li, Z. Shen, Chem. Eur. J. 2014, 20, 1091–1102; c) T. D. M. Bell,
S. Yap, C. H. Jani, S. V. Bhosale, J. Hofkens, F. C. De Schryver, S. J. Lang-
ford, K. P. Ghiggino, Chem. Asian J. 2009, 4, 1542–1550; d) Y. Ding, T. Li,
X. Li, W. Zhu, Y. Xie, Org. Biomol. Chem. 2013, 11, 2685–2692; e) Y. Ding,
X. Li, T. Li, W. Zhu, Y. Xie, J. Org. Chem. 2013, 78, 5328–5338.
[56] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2ednd edKluwer
Academic/Plenum Publishers, New York, 1999.
[57] Y. Liu, W. Wu, J. Zhao, X. Zhang, H. Guo, Dalton Trans. 2011, 40, 9085–
9089.
[58] W. Wu, J. Zhao, J. Sun, S. Guo, J. Org. Chem. 2012, 77, 5305–5312.
[59] D. Huang, J. Zhao, W. Wu, X. Yi, P. Yang, J. Ma, Asian J. Org. Chem. 2012,
1, 264–273.
[87] a) D. P. Hari, B. Kçnig, Angew. Chem. 2013, 125, 4832–4842; Angew.
Chem. Int. Ed. 2013, 52, 4734–4743; b) J. M. R. Narayanam, C. R. J. Ste-
phenson, Chem. Soc. Rev. 2011, 40, 102–113; c) Y. Xi, H. Yi, A. Lei, Org.
Biomol. Chem. 2013, 11, 2387–2403.
[60] P. Yang, W. Wu, J. Zhao, D. Huang, X. Yi, J. Mater. Chem. 2012, 22,
20273–20283.
[61] L. Huang, X. Yu, W. Wu, J. Zhao, Org. Lett. 2012, 14, 2594–2597.
[62] L. Ma, S. Guo, J. Sun, C. Zhang, J. Zhao, H. Guo, Dalton Trans. 2013, 42,
6478–6488.
[63] Y. Liu, H. Guo, J. Zhao, Chem. Commun. 2011, 47, 11471–11473.
[64] D. N. Kozhevnikov, V. N. Kozhevnikov, M. Z. Shafikov, A. M. Prokhorov,
D. W. Bruce, J. A. G. Williams, Inorg. Chem. 2011, 50, 3804–3815.
[65] H. Xiang, J. Cheng, X. Ma, X. Zhou, J. J. Chruma, Chem. Soc. Rev. 2013,
42, 6128–6185.
[88] Gaussian 09, Revision 01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[66] W. Wu, J. Zhao, J. Sun, L. Huang, X. Yu, J. Mater. Chem. C 2013, 1, 705–
716.
[67] L. Liu, D. Huang, S. M. Draper, X. Yi, W. Wu, J. Zhao, Dalton Trans. 2013,
42, 10694–10706.
[68] A. Kamkaew, S. H. Lim, H. B. Lee, L. V. Kiew, L. Y. Chung, K. Burgess,
Chem. Soc. Rev. 2013, 42, 77–88.
[69] S. G. Awuah, Y. You, RSC Adv. 2012, 2, 11169–11183.
[70] M. E. El-Khouly, A. N. Amin, M. E. Zandler, S. Fukuzumi, F. D’Souza, Chem.
Eur. J. 2012, 18, 5239–5247.
Received: June 2, 2014
Published online on September 15, 2014
Chem. Eur. J. 2014, 20, 14282 – 14295
www.chemeurj.org
14295
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim