Perylene-derived triplet acceptors with optimized excited state energy levels for triplet-triplet annihilation assisted upconversion

Article abstract of DOI:10.1021/jo402718e

A series of perylene derivatives are prepared as triplet energy acceptors for triplet-triplet annihilation (TTA) assisted upconversion. The aim is to optimize the energy levels of the T₁ and S₁ states of the triplet acceptors, so that the prerequisite for TTA (2E_T1 > E _S1) can be better satisfied, and eventually to increase the upconversion efficiency. Tuning of the energy levels of the excited states of the triplet acceptors is realized either by attaching aryl groups to perylene (via single or triple carbon-carbon bonds), or by assembling a perylene-BODIPY dyad, in which the components present complementary S₁ and T ₁ state energy levels. The S₁ state energy levels of the perylene derivatives are generally decreased compared to perylene. The anti-Stokes shift, TTA, and upconversion efficiencies of the new triplet acceptors are improved with respect to the perylene hallmark. For the perylene-BODIPY dyads, the fluorescence emission was substantially quenched in polar solvents. Moreover, we found that extension of the π-conjugation of BODIPY energy donor significantly reduces the energy level of the S₁ state. Low S₁ state energy level and high T₁ state energy level are beneficial for triplet photosensitizers.

Full text of DOI:10.1021/jo402718e

Article
pubs.acs.org/joc
Perylene-Derived Triplet Acceptors with Optimized Excited State
Energy Levels for Triplet−Triplet Annihilation Assisted Upconversion
Xiaoneng Cui,† Azzam Charaf-Eddin,‡ Junsi Wang,† Boris Le Guennic,§ Jianzhang Zhao,*,†
and Denis Jacquemin*,‡,∥
†State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, E-208 West Campus, 2
Ling-Gong Road, Dalian 116024, P. R. China
‡CEISAM UMR CNRS 6230, Universite
́ ̀
de Nantes, 2 rue de la Houssiniere, BP 92208,44322Nantes Cedex 3, France
§Institut Universitaire de France (IUF), 103, Boulevard Saint-Michel, 75005 Paris Cedex 05, France
∥Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite
Cedex, France
́
de Rennes 1, 263 Av. du General Leclerc, 35042 Rennes
S
* Supporting Information
ABSTRACT: A series of perylene derivatives are prepared as triplet
energy acceptors for triplet−triplet annihilation (TTA) assisted
upconversion. The aim is to optimize the energy levels of the T1 and S1
states of the triplet acceptors, so that the prerequisite for TTA (2ET1
>
ES1) can be better satisfied, and eventually to increase the upconversion
efficiency. Tuning of the energy levels of the excited states of the triplet
acceptors is realized either by attaching aryl groups to perylene (via single
or triple carbon−carbon bonds), or by assembling a perylene-BODIPY
dyad, in which the components present complementary S1 and T1 state
energy levels. The S1 state energy levels of the perylene derivatives are
generally decreased compared to perylene. The anti-Stokes shift, TTA, and upconversion efficiencies of the new triplet acceptors
are improved with respect to the perylene hallmark. For the perylene-BODIPY dyads, the fluorescence emission was substantially
quenched in polar solvents. Moreover, we found that extension of the π-conjugation of BODIPY energy donor significantly
reduces the energy level of the S1 state. Low S1 state energy level and high T1 state energy level are beneficial for triplet
photosensitizers.
The photophysical properties of triplet photosensitizers and
triplet acceptors/emitters are crucial for TTA assisted
upconversion. An ideal triplet photosensitizer should show
strong visible light absorption, long-lived triplet excited state,
and appropriate T1 state energy level.25−27 For the triplet
acceptor, the desired photophysical properties include high
fluorescence quantum yield, appropriate T1 state energy level
(lower than the T1 state energy level of the triplet photo-
sensitizers), but higher S1 state energy level than the triplet
photosensitizer, to ensure the TTA assisted upconversion, i.e.,
upconverted fluorescence with anti-Stokes shift against the
incident excitation light. Furthermore, the crucial photophysical
property for triplet energy acceptor is 2ET1 > ES1, which is
required for efficient TTA process.25,26,28
Currently, most studies devoted to TTA assisted upconver-
sion have been focused on the application in different inert
matrixes, such as nanoparticles or polymeric microcapsules, or
focus on development of new triplet photosensitizers, but the
triplet acceptors are rarely investigated.29−43 However, the
selection of an appropriate triplet acceptor is crucial and far
INTRODUCTION
■
Triplet−triplet-annihilation (TTA) assisted upconversion has
attracted much attention, due to its advantages over the
conventional upconversion methods: strong absorption of the
excitation, low excitation power threshold (noncoherent, solar
light is sufficient), and high upconversion quantum yields (up
to 20%).1−12 Moreover, the TTA assisted upconversion is
based on supramolecular features, i.e., intermolecular energy
transfer between the triplet photosensitizer and the triplet
acceptor. The triplet photosensitizer (energy donor) and the
triplet energy acceptor/emitter involved in TTA assisted
upconversion can be selected independently. Consequently,
both the excitation and emission wavelengths of a TTA assisted
upconversion protocol can be readily changed by combining
different triplet photosensitizers and triplet acceptors (emit-
ters).2 This feature differs from other upconversion methods,
such as those based on rare earth materials, for which the
excitation/emission wavelengths are not easily tunable.13−17
Recently, TTA assisted upconversion has been widely used in
luminescent bioimaging or oxygen (O2) sensing,18−20 solar
cells,21−23 and photocatalysis including hydrogen (H2)
production by water photolysis.24
Received: December 7, 2013
Published: February 11, 2014
© 2014 American Chemical Society
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a
Scheme 1. Synthesis of the Organic Triplet Acceptor
a
Triplet acceptors A-1−A-6, 1-chloro-bis-phenyl ethynylanthracene (1CPBEA), BDP (A-3′), and the triplet sensitizers B-6, PdTPTBP are
presented. Compound 1,46 2,47 and 342 were reported previously. (a) NBS, DMF, r.t., 20 h; yield: 84%; (b) Phenylboronic Acid, K2CO3, Pd(pph3)4,
toluene/ethanol/H2O (2:2:1 v/v/v), 80 °C, under Ar, reflux, 8 h; yield: 72%; (c) compound 2, K2CO3, Pd(pph3)4, toluene/ethanol/H2O (2:2:1 v/
v/v), 80 °C, under Ar, reflux, 8 h; yield: 40%; (d) phenylacetylene, (pph3)2PdCl2, pph3, CuI, Et3N, 90 °C, under Ar, reflux, 8 h; yield: 55%; (e) 9-
butyl-3-ethynyl-carbazole (3), (pph3)2PdCl2, pph3, CuI, Et3N, 90 °C, under Ar, reflux, 8 h; yield: 47%.
from being a trivial task, due to the desired photophysical
properties mentioned above, one of the major concerns being
to satisfy the 2ET1 > ES1 prerequisite.5 Unfortunately the vast
majority of available triplet acceptors only satisfy this
requirement marginally. For example, perylene is a versatile
chromophore and has been widely used as triplet acceptor for
TTA assisted upconversion.2,5 However, the S1 and T1 state
energy levels of perylene are 2.78 and 1.53 eV, respectively.
Therefore, the TTA of perylene is assumed to be poor. In order
to overcome this limitation, a hetero BODIPY-perylene dimer
triplet acceptor was reported recently, in which the perylene
unit acts as the triplet energy acceptor, but the BODIPY part
allowed a reduction of the S1 state energy.28 As a result, the
TTA of the dyad acceptor was improved compared to the
unsubstituted perylene because the 2ET1 > ES1 requirement
could be better satisfied. As a result, improved TTA assisted
upconversion efficiency was observed with this hetero
chromophore dimer.28 However, much room is left to fully
explore this novel strategy for designing more efficient triplet
energy acceptors. For example, although intramolecular energy
transfer may be dominant for the hetero chromophore dimer,
intramolecular electron transfer cannot be excluded. Intra-
molecular electron transfer could be detrimental for the
fluorescence of the dyad triplet acceptor. Moreover, with a
significantly red-shifted upconverted emission, the anti-Stokes
shifts of the TTA assisted upconversion that has been obtained
with the previously reported perylene-BODIPY dyad was
largely compromised compared with its single perylene
counterpart.28 Normally large anti-Stokes shift is desired for
TTA assisted upconversion.44 Therefore, it is interesting to
explore new triplet acceptors with balanced upconversion
performances, such as improved TTA efficiency, and at the
same time, fairly large anti-Stokes shift.
Herein, a series of perylene-based triplet acceptor/emitters
has been prepared by attaching aryl groups to perylene (via
single or triple carbon−carbon bonds) or constructing
BODIPY-perylene dyads. The fluorescence emission of these
perylene derivatives is red-shifted as compared to perylene and
the energy of the S1 state is decreased compared to perylene,
which is beneficial for TTA. For the TTA assisted
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upconversion, we obtained generally improved TTA efficiency
with these new triplet acceptors. We demonstrated that for the
perylene-BODIPY dimers, the fluorescence was substantially
quenched in polar solvents. This property was not found for the
respective components of the dyads, i.e., the perylene or
BODIPY chromophores. Furthermore, the energy level of the
S1 state of BODIPY triplet photosensitizer was substantially
decreased by extension of the π-conjugation framework (the
fluorescence emission wavelength is red-shifted), whereas the
T1 energy did not decrease substantially. These results are
useful for the design of new triplet photosensitizers and
acceptors for TTA assisted upconversion, as well as for the
study of photochemistry and photophysics of organic
chromophores.
RESULTS AND DISCUSSION
■
2.1. Design and Synthesis of the Perylene/Bodipy
Based Dyad Triplet Acceptors. Two strategies were used for
designing perylene-based triplet acceptors with the aim to
improve the TTA efficiency by optimization of the S1 and T1
state energy levels. First, the π-conjugation framework of
perylene was extended by introducing aryl moieties, which are
linked to the perylene framework by CC triple bond (A-4, A-
5, Scheme 1). The fluorescence emission wavelength of these
perylene derivatives is expected to be red-shifted as compared
to perylene;45 in other words, the S1 state energy level of these
derivatives will be lower than that of perylene. As a result, the
2ET1 > ES1 relation can be better satisfied and the TTA can be
improved compared to perylene.28 Second, with the prepara-
tion of a new perylene-BODIPY dimer triplet acceptor,
BODIPY was selected as the fluorescence emitter due to its
satisfactory photophysical properties, e.g., high fluorescence
quantum yields and environmentally independent fluorescence
emission.48−52 The fluorescence emission property of the
hetero chromophore dimers is more complex than the
respective components of the dyads; for example, the
fluorescence emission intensity of the dyads is highly sensitive
to the polarity of the solvents, which is different from the
property of the perylene or the BODIPY chromophores alone.
The reactions were carried out with 1-bromoperylene as the
starting material (Scheme 1). Pd(0)-catalyzed Suzuki crossing
coupling and Sonogashira coupling reactions were used. All the
compounds were obtained with satisfactory yields.
Figure 1. UV−vis absorption spectra of the compounds. In toluene. c
= 1.0 × 10−5 M, 20 °C.
2.2. UV−vis Absorption and Fluorescence Emission
Spectra. The UV−vis absorption spectra of the compounds
were studied (Figure 1). Auxochromic groups have a noticeable
impact on the perylene spectra. For example, attaching the
phenylethynyl moiety to the perylene (A-4) induces a red-
shifted absorption maximum at 467 nm (439 nm for perylene).
Similar bathochromic shifts were observed for other derivatives.
For the perylene-BODIPY dimer, A-3, besides the absorption
bands of the perylene core, a distinct absorption band at 504
nm was observed, which is attributed to the BODIPY moiety.
The absorption profile indicates weak electronic interaction
between the perylene and the BODIPY part at the ground state
(see also the later calculations second).53,54 With 2,6-diethyl
substituent on the BODIPY core, A-6, the absorption is further
red-shifted. Clearly in both A-3 and A-6, the S1 energy level is
lower than that of perylene.
Figure 2. Normalized fluorescence emission spectra of (a) A-1 (λex
=
400 nm), A-2 (λex = 400 nm), A-4 (λex = 435 nm), and A-5 (λex = 444
nm); and (b) A-1 (λex = 400 nm), A-3 (λex = 480 nm), A-6 (λex = 449
nm), and BDP (λex = 480 nm). c = 1.0 × 10−5 M in toluene, 20 °C.
enhancement. With the introduction of the carbazole moiety
through the CC triple bond linker (A-5), a strongly red-
shifted emission at 490 nm is obtained, and we attribute this
feature to the charge-transfer (CT) nature of the compound.
All the new perylene derivatives show blue-shifted fluorescence
emission compared to the previously reported BODIPY-
perylene dimer (A-6) and the same holds for A-3 that emits
at 517 nm (25 nm blue shift). These increased S1 state energy
levels are beneficial for reaching larger anti-Stokes shift.28
The solvent dependency of the UV−vis absorption and the
fluorescence emission spectra were also assessed (Figure 3). A-
3 shows similar UV−vis absorption in solvents of different
polarity (hexane, toluene, THF, and MeCN), indicating that
the ground state of A-3 is not affected by the polarity of the
The fluorescence emission spectra were recorded (Figure 2).
All the perylene derivatives show red-shifted fluorescence
emission compared to perylene, confirming that the S1 energy
level of the derivatives is decreased, a beneficial shift for TTA
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Figure 3. UV−vis absorption spectra of (a) A-3, (b) A-5, and (c) A-6 in different solvents. c = 1.0 × 10−5 M, 20 °C. Emission spectra of (d) A-3 (λex
= 480 nm), (e) A-5 (λex = 444 nm), (f) A-6 (λex = 449 nm) in different solvents. c = 1.0 × 10−5 M, 20 °C.
Table 1. Photophysical Parameters of the Organic Triplet Acceptor
a
b
c
d
λabs (nm)
503
ε
λex (nm)
λem (nm)
516
Φ
τF (ns)
g
e
f
f
f
BDP (A-3′)
A-1
8.30
480
400
400
480
435
444
449
0.72
0.98
0.94
0.58
0.68
0.64
3.73\3.30 \3.42
412\439
2.87\3.82
445\471\504
462\490
517
3.80
3.26
A-2
421\447
1.61\0.20
e
A-3
423\449\504
440\467
2.16\2.86\6.28
0.88\1.09
2.97\3.80 \3.64
A-4
478\511\546
490\526
542
2.35
2.17
A-5
450\478
1.68\1.93
e
A-6
442\449\527
2.88\3.53\7.07
0.75
4.86\4.83 \5.16
a
b
c
In toluene (1.0 × 10−5 M), 20 °C. Molar extinction coefficient at the absorption maxima. ε: 104 M−1 cm−1. Fluorescence quantum yields in
toluene, with perylene as the standard (ΦF = 98% in n-hexane). Fluorescence lifetimes in toluene. In THF. In EtOAc. Literature value.43
d
e
f
g
solvent. Similar results were observed for other compounds,
such as A-5 and A-6.
quenching was observed by excitation of either the perylene
part or the BODIPY part (Figure S18). We measured the
nanosecond time-resolved transient difference absorption of
both A-3 and A-6, but no signal was detected, hinting that
triplet excited state was produced by neither the charge transfer
nor the charge recombination, or that the charge separated state
is short-lived (less than 10 ns, based on the time-resolution of
the transient absorption spectrometer).55
The photophysical properties of the compounds were listed
in Table 1. All the perylene derivatives show smaller
fluorescence quantum yields than perylene. The fluorescence
lifetimes in toluene are close to that of perylene. In polar
solvent such as THF, however, the fluorescence lifetime of A-3
and A-6 does not decrease. Thus, static quenching or formation
of ground state complex in polar solvents are responsible for
the quenching.
2.3. DFT Calculations. Time-dependent density functional
theory (TD-DFT) simulations have been performed on the two
dyads, as well as on model systems for the BODIPY and
perylene moieties. Details of the computational models can be
found in the Experimental Section.56−65 The obtained energetic
diagram, together with representation of the excited states, can
be found in Figure 4. Consistently with experiments, one
notices that the lowest excited-state, ES1, is clearly BODIPY-
centered, whereas the second, ES2, that lies slightly higher in
energy is characteristic of the perylene group. Following
Kasha’s rule (the process can also be considered as intra-
molecular energy transfer) and considering that ES1 and ES2
Interestingly, the emission shows a drastically different
response to the solvent polarity, e.g., the emission intensity
decreases in polar solvents, such as DMSO and MeCN
compared with that in less polar solvents, such as toluene and
THF. For A-5, this effect is moderate and can be attributed to
the CT feature. Contrary to A-5, the fluorescence intensity of
dyad A-3 is highly dependent on the solvent polarity (Figure
3d): it fluoresces intensively in nonpolar solvents, such as
hexane and toluene, but the emission is much weaker in THF
and ethyl acetate. The emission band shape remains the same.
In polar solvents (MeCN, DMF, and DMSO), the fluorescence
emission is almost completely quenched. The quenched
fluorescence of A-3 in polar solvents is not related to solubility,
as normal UV−vis absorption spectra were observed for A-3 in
these solvents. We tentatively attribute the quenching to the
photoinduced intramolecular electron transfer, which is known
to be more efficient in highly polar solvents.54,55 This
interpretation is confirmed by the fluorescence emission of
BODIPY in different solvents, for which no polarity-dependent
fluorescence emission was observed (Figure S16).
For A-6, similar solvent polarity-dependent fluorescence
emission was observed (Figure 3f), but with a more distinct
ON−OFF character, that is, the fluorescence emission is hardly
affected when going from nonpolar and slightly polar solvents,
but is completely switched off in highly polar media. We
emphasize that similar solvent-polarity induced fluorescence
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Figure 4. Energetic diagram obtained at the SS-PCM M06-2X/6-
31G(d) level for the two BODIPY-perylene dyads. For the vertical
absorption, representation of density difference plots (contour
thresholds of 0.0004 a.u., blue/red regions: decrease/increase of
density upon transition) are also given. Energies represented are not
corrected for vibrational effects; see Experimental Section for more
details.
are close in energy, it is therefore expected that only the
emission signature of the BODIPY can be detected, and this is
consistent with the experiments. This was further confirmed by
additional calculations. First, the computations performed on
the compounds yield vertical absorption energies of 3.04, 2.94,
and 3.23 eV for A-3′, A-6′, and A-2, respectively, which
obviously correspond to the 3.04, 2.91, and 3.20 eV values
reported in Figure 4. Second, we have determined the
vibrationally resolved spectra with TD-DFT and it turns out
that the hallmark BODIPY/perylene band topologies are
restored, so that it is obvious that the experimental absorption
spectra of A-3 is the addition of A-3′ and A-2, whereas its
emission is similar to that of A-3′ (Figure 5). Third, we have
computed 0−0 energies for A-3 and A-6 using a reliable TD-
DFT protocol that accounts for both state-specific solvation
and vibrational effects.57 The obtained values of 2.86 and 2.72
eV, that after simple linear corrections (see Section 3.1 in ref
56) yield 2.46 and 2.33 eV, which fit experimental values of
2.43 and 2.32 eV very well.
2.4. Electrochemical Properties. The electrochemical
properties of the dyad triplet acceptors were studied with
cyclovoltametry (CV, Figure 6). A reversible oxidation was
observed at E1/2 = +0.89 V, which is anodically shifted by 0.04
V compared with perylene (+0.93 V) for A-2. This result
indicates that attachment of the phenyl ring to the perylene
section perturbs the electronic property of the latter. The CV of
the A-6 was also studied (Figure 6). Beside the reversible
oxidation peak at +0.98 V, a pseudoreversible reductive band at
E1/2 = −1.40 V was observed, which can be attributed to the
reduction of the BODIPY section in A-6, a postulate supported
by electrochemical data of reference compounds (Table 2).
The free energy changes of the PET were calculated
according to the Rehm−Weller equation (Table 2; for the
computational details, please refer to the Supporting
Information). They are small, which indicates that the PET is
weakly allowed. This interpretation is in agreement with the
Figure 5. Vibronic spectra computed for A-3′ (left) and A-2 (right).
Figure 6. Cyclic voltammogram of the triplet acceptor (a) A-2 and (b)
A-6. Ferrocene (Fc) was used as reference E1/2 = +0.38 V (Fc+/Fc) vs
SCE (saturated calomel electrode). Inset: (b) Note there is no
apparent oxidation peak of 2-ethyl-BDP. In deaerated CH2Cl2
solutions containing 1.0 mM acceptor alone, or with ferrocene, 0.10
M Bu4N[PF6] as supporting electrolyte, Ag/AgNO3 reference
electrode, scan rates: 100 mV/s.
experimental fact that the fluorescence of the dyad triplet
acceptors is only quenched in highly polar solvents, especially
for A-6 (Figure 3f). PET is more efficient in polar solvents
because of the increased free energy changes.
2.5. TTA Assisted Upconversion with the Perylene
Derivatives as the Triplet Acceptor. The perylene
derivatives were used as triplet acceptors for TTA assisted
upconversion. B-6 was used as triplet photosensitizer, for which
the absorption is red-shifted compared with the perylene
derivatives, but the T1 state energy level of B-6 is higher than
that in perylene derivatives. This energy level profile ensures
the triplet−triplet energy transfer (TTET) from the triplet
photosensitizer to the triplet acceptors.43
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the new triplet acceptors can be attributed to their lower S1
energy. It should be pointed out that the TTA is dependent on
the excitation power; therefore, the TTA efficiencies reported
in this paper cannot be compared directly with that reported
previously.28
Table 2. Redox Potentials of Acceptors and the of Free-
Energy Changes (ΔGET, PET) for the Potential
Intramolecular Electron Transfer (with Perylene Unit as
Electron Donor and BODIPY Unit as Electron Acceptor in
a
A-3 and A-6)
Next, the TTA assisted upconversion bands with A-1, A-3,
and BODIPY (A-3′) as the triplet acceptor were compared
(Figure 7c). For A-3 and BODIPY (A-3′), the upconverted
emission bands have the same shape and wavelength, which are
red-shifted compared to perylene. This result indicates that the
emissive singlet excited state of A-3 is localized on the BODIPY
part, not on perylene part. Furthermore, the TTA assisted
upconversion with A-3 is much larger than that obtained using
BODIPY as the triplet acceptor. This enhanced TTA assisted
upconversion with the dyad (A-3) is due to the improved
TTET because the T1 state energy level of perylene is lower
than that of BODIPY. The upconversion emission intensity
with A-3 is comparable to that of perylene. However, it should
be pointed out that the anti-Stokes shift of the TTA assisted
upconversion with the new perylene-based triplet acceptor is
smaller than that with perylene as the triplet acceptor; this is
within expectation since the S1 state energy level is lower than
that of perylene.
Previously it was reported that TTA can be improved using
A-6 as triplet acceptor/emitter rather than perylene.28
However, the anti-Stokes shift with A-6 is smaller than that
with perylene. With A-3 as the triplet acceptor, the anti-Stokes
shift (74 nm) is increased with respect to A-6 (46 nm).
We noted that the upconversion quantum yield of B-6 with
perylene as acceptor is up to 17%. In our previous report, the
upconversion quantum yield with 1CPBEA (Scheme 1) as
triplet acceptor was 1%.43 Our selection of 1CPBEA as triplet
acceptor was based on the assumption that the extended π-
conjugation framework of BODIPY in B-6 will yield a T1 state
with decreased energy level than BODIPY (A-3′). However,
the present higher upconversion quantum yield with perylene
as the triplet acceptor indicates that this may not be the case.
That is, the T1 triplet state energy level of B-6 may be not
significantly reduced compared with that of BODIPY, although
the S1 singlet state energy level of B-6 is much lower than that
of BODIPY (i.e., the fluorescence emission wavelength of B-6
is 623 nm whereas that of BODIPY is 516 nm). This
information is helpful for designing new triplet photo-
sensitizers, since the current knowledge on the relationship
between molecular structure and T1 state energy level is very
limited, at least for organic chromophores.27
E(OX) (V)
E(RED) (V)
ΔGcs(eV)
b
b
b
BDP
A-1
A-2
A-3
A-6
+1.14
+0.89
+0.93
+0.90
+0.98
−1.66
b
b
c
d
e
f
−1.49
−1.40
0.18 /0.11 /−0.077 /−0.37
c
d
e
f
0.69 /0.19 /0.003 /−0.29
a
Anodic and cathodic peak potential were presented. The potential
values of the compounds are vs standard hydrogen electrode (with Fc
as internal reference, for which E1/2 (Fc+/Fc) = +0.38 V vs SCE
(saturated calomel electrode)). Cyclic voltammetry in Ar saturated
CH2Cl2 containing a 0.10 M Bu4NPF6 supporting electrolyte; Counter
electrode is Pt electrode; working electrode is glassy carbon electrode;
Ag/AgNO3 couple as the reference electrode. c[Ag+] = 0.1 M. 1.0 mM
dyad photosensitizers in DCM, 20 °C. Conditions: 1.0 mM dyad
photosensitizers and 1.0 mM ferrocene in DCM, 293 K, and calculated
b
relative to SCE (saturated calomel electrode). No reduction potential
c
were observed, or no ΔGcs values were calculated. Value of ΔGcs in
d
toluene, with perylene unit as electron donor. Value of ΔGcs in
e
CHCl3, with perylene unit as electron donor. Value of ΔGcs in DCM,
f
with perylene unit as electron donor. Value of ΔGcs in MeCN, with
perylene unit as electron donor.
The TTA assisted upconversion with different triplet
acceptors is given in Figure 7. With perylene as triplet acceptor
In order to demonstrate the versatility of the triplet
acceptors, a red light-excitable triplet photosensitizer PdTPTBP
was also used for TTA assisted upconversion. A 635 nm red
laser was used as the excitation source (Figure 8).29 Similar
upconversion results were observed (see parameters in Table
3). Notably all the new triplet acceptors show higher TTA
efficiency than that with perylene.
Figure 7. Upconversions with B-6 as triplet photosensitizer and
different triplet acceptors. (a) A-1 and 1CPBEA, (b) A-1, A-2, A-4,
and A-5, (c) A-1, A-3, and A-3′. Excited with 589 nm continuous laser
(4.8 mW, 24.5 mW cm−2). (d) Emission of the sensitizers in the
presence of triplet acceptor A-1, A-3, and A-6. Excited with 589 nm
continuous laser (2.8 mW, 14.3 mW cm−2). c [B-6] = 2.0 × 10−6 M; c
[Acceptor] = 4.0 × 10−5 M. In deaerated toluene, 20 °C.
In order to prove that the emission observed in the TTA
assisted upconversion is genuine upconverted delayed
fluorescence, the time-resolved emission spectra of the TTA
assisted upconversion was studied (Figure 9).66,67 The
luminescence lifetime is much longer than the prompt
fluorescence lifetime of the perylene-based triplet acceptors,
therefore the TTA assisted upconversion was verified (Figure
10). For example, the prompt fluorescence lifetime of A-3
attains 3.27 ns. In the TTA assisted upconversion experiments,
the lifetime of the delayed fluorescence is up to 292.2 μs.
(A-1), intense upconverted fluorescence emission was
observed, whereas with A-2, A-4, and A-5, a red-shifted
emission was observed but with a weaker upconversion
emission intensity than A-1. However, we have shown that
the fluorescence quantum yields of the new perylene derivatives
are smaller than their perylene counterpart. Considering this
result, the TTA efficiency of the new triplet acceptors is actually
exceeding the perylene (Table 3). The higher TTA efficiency of
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Table 3. Upconversion Parameters of B-6, PdTPTBP with Triplet Acceptor A-1−A-6 and A-3′
A-1
A-2
A-3
A-4
7.9
A-5
A-6
A-3′
a
b
c
g
g
B-6
ΦUC (%)
TTA(%)
17.8
4.7
11.1
5.9
10.9
9.8
10.5
9.4
15.1
6.0
6.3
8.7
Φ
6.4
221.3
257.3
5.0
d
Ksv
465.9
230.7
7.2
240.8
207.6
10.4
5.8
233.6
292.2
8.1
245.7
217.1
5.3
396.8
330.2
11.7
8.2
117.6
211.6
-
e
τDF (μs)
ΦUC
f
PdTPTBP
ΦTTA
3.3
7.0
6.0
4.3
-
a
Excited with 589 nm laser (4.8 mW), with the prompt fluorescence of B-6 as the inner standard (Φ = 10.6% in toluene) and the concentration of
b
c
sensitizers (B-6) is 2.0 × 10−6 M. c [Acceptor] = 4.0 × 10−5 M. Upconversion quantum yield (ΦUC). Relative triplet−triplet annihilation yield
d
(ΦTTA) of B-6 and PdTPTBP, the triplet−triplet-energy-transfer (TTET) efficient of BDP is approximated as 100%. Stern−Volmer constants. In
e
f
103 M−1. Lifetimes of the delayed fluorescence (upconverted fluorescence). ΦUC = ΦISC × ΦTTET × ΦTTA × ΦF. Excited with 635 nm laser, with the
prompt fluorescence of H2TPTBP as the standard (Φ = 0.28% in toluene) and the concentration of sensitizers (PdTPTBP) is 2.0 × 10−6 M. c
g
[Acceptor] = 4.0 × 10−5 M; in deaerated toluene, 20 °C. Using A-3 as TTA upconversion quantum yield reference, calculated with the upconverted
fluorescence emission peak area upon excitation with laser at power of 2.8 mW.
process and the TTA assisted upconversion efficiency, a series
of perylene derivatives were prepared as triplet energy
acceptors. To this end, approaches of attaching aryl groups to
perylene (via single or triple carbon−carbon bonds) or
assembling perylene-BODIPY dyads were used. It was found
that the S1 state energy levels are generally decreased. As a
result the TTA was improved compared to perylene, the
benchmark triplet acceptor widely used for TTA assisted
upconversion. The photophysical properties of the triplet
acceptors (anti-Stokes shift, TTA efficiency, and TTA assisted
upconversion efficiency) are generally improved compared to
that of perylene. Interestingly, we observed that the
Figure 8. Upconversions with photosensitizer PdTPTBP. Emission of
the sensitizer in the presence of triplet acceptor A-1, A-2, A-3, A-4, A-
5, A-6, and BDP. Excited with 635 nm laser (4.8 mW, 17.0 mW cm−2).
(c [PdTPTBP] = 2.0 × 10−6 M; c [acceptor] = 4.0 × 10−5 M; in
deaerated toluene, 20 °C).
fluorescence of the perylene-BODIPY dyad triplet acceptors
was diminished in polar solvents. Furthermore, we found that
with extension of the π-conjugation framework of BODIPY, the
S1 state energy level decreases more substantially compared
with the T1 state energy level, which is ideal for BODIPY
derivatives to be used as triplet photosensitizers. These results
will be useful for the future molecular structural design of triplet
photosensitizers and acceptors and for the study of the
photochemistry of organic chromophores.
In order to study the TTET efficiency between the triplet
photosensitizer B-6 and the proposed triplet acceptors, the
Stern−Volmer quenching curves were plotted (Figure 11). The
quenching results clearly indicate that the perylene based triplet
acceptors are all more efficient than BODIPY as triplet
quencher, presumably due to the lower T1 state energy level
of the new perylene based triplet acceptors compared with
BODIPY. Among the perylene based triplet acceptors, A-1 and
A-6 are the most efficient. The other perylene based triplet
acceptors give similar quenching constants. We tentatively
attribute these results to the bulkiness of the different
derivatives (diffusion limited bimolecular quenching ability
may be affected) and the different redox potentials (Dexter
triplet energy transfer may be affected). A more detailed study
is underway.
The TTA assisted upconversion with the perylene-based
triplet acceptors is visible to unaided eyes (Figure 12). For the
triplet photosensitizer B-6 alone, red emission was observed,
which is attributed to the fluorescence of B-6 at 623 nm. In the
presence of triplet acceptors such as A-1, A-2, A-4, A-5, and so
forth, a panel of emission colors from purple, pink to yellow
could be observed (Figure 12). These different emission colors
are due to the different delayed fluorescence emission
wavelength of the triplet acceptors, i.e., the different anti-
Stokes shifts of the TTA assisted upconversion. Such a
tuneability of the TTA assisted upconversion wavelength with
a library of triplet acceptor is reported here for the first time.
2.6. Conclusions. In summary, aiming to optimize the
relevant energy levels of the T1 and the S1 states of triplet
acceptors to enhance the triplet−triplet annihilation (TTA)
EXPERIMENTAL SECTION
■
3.1. Analytical Measurements. All the chemicals used in
synthesis are analytically pure and were used as received. Solvents
were dried and distilled before use for synthesis. Luminescence
lifetimes were measured on a OB 920 fluorescence/phosphorescence
lifetime spectrofluorometer (Edinburgh Instruments, UK). Lumines-
cence quantum yields of the compounds were measured with A-1 as
the standard (ΦF = 0.98 in n-hexane).
3.2. Synthesis of 1. Compound 1 was prepared by the reported
method.46 A-1 (1.51 g, 6.0 mmol) and DMF (180 mL) were mixed,
and the mixture was stirred at room temperature until all perylene
solid was dissolved. Then DMF (20 mL) solution of N-
bromosuccinimide (1.05 g, 6.0 mmol) was slowly added, and the
solution was stirred for 24 h at room temperature. H2O was added to
the reaction mixture to give a golden solid, which was collected by
filtration. The crude solid is 3-bromoperylene (1.75 g, yield 84%). This
compound was used directly for the next reaction. TOF HRMS ESI−:
Calcd ([C20H11Br]+), m/z = 330.0044, found, m/z = 330.0053.
3.3. Synthesis of A-2. Under Ar atmosphere, 3-bromoperylene
(230.0 mg, 0.70 mmol), phenylboronic acid (85.4 mg, 0.70 mmol),
K2CO3 (290.0 mg, 2.1 mmol), and EtOH/toluene/water (v/v/v =
2:2:1, 50 mL) were mixed together. Then Pd(PPh3)4 (40.4 mg, 0.035
mmol, 5.0 mol %) was added. The reaction mixture were refluxed and
stirred under Ar for 8 h. After completion of the reaction, the mixture
was cooled to room temperature. The reaction mixture was extracted
with CH2Cl2, and the organic layer was washed with water (2 × 100
mL) and dried over Na2SO4. The solution was evaporated to dryness
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Figure 9. Time-resolved emission spectra (TRES) of the TTA assisted upconversion A-1, A-2, and A-3 as the triplet acceptor. (a) B-6 alone. τF =
92.0 μs (λem = 630 nm). (b) B-6/A-1, τDF = 241.2 μs (λem = 450 nm). (c) B-6/A-2, τDF = 195.7 μs (λem = 460 nm). (d) B-6/A-3, τDF = 284.1 μs (λem
= 520 nm). The samples were excited using nanosecond pulsed OPO laser (589 nm). c [B-6] = 2.0 × 10−6 M. c [Acceptor] = 4.0 × 10−5 M. In
deaerated toluene, 20 °C.
Figure 11. Stern−Volmer plot of quenching of the triplet state of (a)
B-6 and (b) PdTPTBP with different triplet acceptor. c[triplet
photosensitizer] = 2.0 × 10−6 M. In deaerated toluene, 20 °C.
(m, 4H), 7.78 (d, 1H, J = 12.0 Hz), 7.71 (d, 2H, J = 8.0 Hz), 7.53−
7.48 (m, 6H), 7.45 (t, 3H, J = 12.0 Hz). 13C NMR (100 MHz, CDCl3)
δ 140.9, 140.2, 134.9, 133.1, 131.6, 131.4, 130.8, 130.1, 129.3, 128.9,
128.6, 127.9, 127.5, 126.8, 126.7, 126.3, 120.5, 120.3, 120.1. TOF
Figure 10. Delayed fluorescence observed in the TTA assisted
upconversion with B-6 as the triplet photosensitizer and (a) A-1, (b)
A-3 as the triplet acceptor. Excited at 589 nm (nanosecond pulsed
HRMS ESI−: Calcd ([C26H16]+), m/z = 328.1252, found, m/z =
328.1261.
3.4. Synthesis of A-3. A-3 was obtained following procedure
OPO laser, synchronized with FLS 920 spectrofluorometer), the
similar to that of A-2. 3-Bromoperylene (100.0 mg, 0.30 mmol), 2
emission was monitored at 445 nm (A-1) and 520 nm (A-3). The
decay trace of the prompt fluorescence of (c) A-1 and (d) A-3
determined in a different experiment. Excited with picosecond pulsed
(135.4 mg, 0.30 mmol) instead of phenylboronic acid, K2CO3 (124.2
mg, 0.9 mmol), and Pd(PPh3)4 (17.3 mg, 0.015 mmol, 5 mol %) were
mixed in EtOH/toluene/water (v/v/v = 2:2:1, 50 mL). After the
reaction finished, the crude product was further purified with column
405 nm laser; the decay of the emission was monitored at 445 nm (A-
1) and 520 nm (A-3). In deaerated toluene; c [B-6] = 2.0 × 10−6 M; c
chromatography (silica gel, CH2Cl2/petroleum ether = 1:2, v/v) to
[Acceptor] = 4.0 × 10−5 M, 20 °C.
give red solid (70.2 mg, Yield: 40%). Mp > 250 °C. 1H NMR (CDCl3,
400 MHz): δ 8.28 (d, 2H, J = 8.0 Hz), 8.25 (d, 2H, J = 8.0 Hz), 7.73
(d, 3H, J = 6.4 Hz), 7.67 (d, 2H, J = 7.6 Hz), 7.52−7.43 (m, 6H), 6.05
(s, 2H), 2.59 (s, 6H), 1.58 (s, 6H). 13C NMR (100 MHz, CDCl3): δ
155.8, 143.2, 141.8, 141.7, 139.0, 131.4, 130.9, 129.0, 128.8, 128.7,
128.3, 127.0, 126.9, 125.6, 121.5, 120.7, 120.6, 120.5, 120.0, 19.4, 14.8.
under reduced pressure to obtain a crude solid. The crude product was
further purified with column chromatography (silica gel, CH2Cl2/
petroleum ether = 1:10, v/v) to give orange solid (164.1 mg, Yield:
1
72%). Mp, 196−199 °C. H NMR (CDCl3, 400 MHz): δ 8.26−8.21
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Figure 12. Photographs of the emission of triplet photosensitizer (B-6) alone and the TTA assisted upconversion. Excited with 589 nm laser (4.8
mW). The use of different triplet acceptors is marked. c [B-6] = 2.0 × 10−6 M; c [acceptor] = 4.0 × 10−5 M; in deaerated toluene, 20 °C.
TOF HRMS ESI−: Calcd ([C39H29BF2N2]+), m/z = 574.2392, found,
m/z = 574.2407.
the following equation, where ΦUC, Asam, Isam, and ηsam represent the
quantum yield, absorbance, integrated photoluminescence intensity,
and the refractive index of the samples and the solvents (eq 1, where
the subscript “std” is for the standard used in the measurement of the
quantum yield and “sam” for the samples to be measured). The
equation is multiplied by a factor of 2 in order to make the maximum
quantum yield unity.
3.5. Synthesis of A-4. 3-Bromoperylene (60.0 mg, 0.18 mmol), 1-
ethynylbenzene (0.19 mL, 1.8 mmol), toluene (10 mL), and
triethylamine (10 mL) were mixed together. Then Pd(PPh3)2Cl2
(12.6 mg, 0.018 mmol, 10 mol %), PPh3 (4.7 mg, 0.018 mmol 10
mol %), and CuI (3.4 mg, 0.018 mmol, 10 mol %) were added. The
reaction mixture was refluxed at 90 °C and stirred under Ar for 8 h.
After completion of the reaction, the mixture was cooled to rt and the
yellow precipitate was collected by filtration. Then the crude product
was purified with column chromatography (silica gel, CH2Cl2/
petroleum ether = 1:10, v/v) to give 35.0 mg yellow solid (Yield:
55%). Mp > 250 °C. 1H NMR (CDCl3, 400 MHz): δ 8.33 (d, 1H, J =
8.0 Hz), 8.28 (d, 1H, J = 7.2 Hz), 8.24 (t, 2H, J = 14.4 Hz), 8.19 (d,
1H, J = 8.0 Hz), 7.77 (d, 1H, J = 7.6 Hz), 7.73−7.65 (m, 4H), 7.63 (t,
1H, J = 8.0 Hz), 7.53 (t, 2H, J = 12.0 Hz), 7.42−7.38 (m, 3H). 13C
NMR (100 MHz, CDCl3) δ 134.8, 132.0, 131.8, 131.2, 131.0, 130.8,
128.6, 127.4, 126.8, 126.4, 121.1, 120.5, 119.9, 95.6, 88.2. TOF HRMS
ESI−: Calcd ([C28H16]+), m/z = 352.1252, found, m/z = 352.1248.
3.6. Synthesis of A-5. A-5 was obtained following a procedure
similar to that of A-4 except 9-butyl-3-ethynyl-carbazole (3) (60.0 mg,
0.24 mmol) was used. The crude product was purified with column
chromatography (silica gel, CH2Cl2/petroleum ether = 1:3, v/v) to
2
⎛
⎝
⎞
⎠
⎛
⎜
⎝
⎞⎛
⎞
⎟
⎠
η
η
Astd Isam
sam
⎜
⎜
⎟
⎟
ΦUC = 2Φ
⎟⎜
std
A
I
sam ⎠⎝
std
(1)
std
The TTET efficiency was obtained through the Stern−Volmer
quenching constants, the concentration of the photosensitizer was
fixed, the lifetime of the photosensitizers was measured by LP920 laser
flash photolysis spectrometer with increasing perylene concentration
in the solution.
3.8. Nanosecond Time-Resolved Transient Difference
Absorption Spectra. The nanosecond time-resolved transient
difference absorption spectra were measured on LP920 laser flash
photolysis spectrometer (Edinburgh Instruments, UK) and recorded
on a Tektronix TDS 3012B oscilloscope. The lifetime values (by
monitoring the decay trace of the transients) were obtained with the
LP900 software. All samples in flash photolysis experiments were
deaerated with N2 for ca. 15 min before measurement and the gas flow
is kept during the measurement.
3.9. Delayed Fluorescence of the Upconversion. The spectra
were measured with a nanosecond pulsed laser (OpoletteTM 355II
+UV nanosecond pulsed laser, typical pulse length: 7 ns. Pulse
repetition: 20 Hz. Peak OPO energy: 4 mJ. The wavelength is tunable
in the range of 210−355 nm and 410−2200 nm. OPOTEK, USA),
which is synchronized to FLS 920 spectrofluorometer (Edinburgh
Instruments, UK). The decay kinetics of the upconverted fluorescence
(delayed fluorescence) was monitored with an FLS920 spectrofluor-
ometer (synchronized to the OPO nanosecond pulse laser). The
prompt fluorescence lifetime of the triplet acceptor was measured with
EPL picosecond pulsed laser (405 nm, 405 10 nm, pulse width: 66.9
ps, maximum average power: 5 mW; Edinburgh Instrument Ltd., UK)
which was synchronized to the FLS 920 spectrofluorometer.
3.10. Cyclic Voltammetry. Cyclic voltammetry was performed
using a CHI610D Electrochemical workstation (Shanghai, China).
Cyclic voltammograms were recorded at scan rates of 0.1 V/s. The
electrolytic cell used was a three electrodes cell. Electrochemical
measurements were performed at RT using 0.1 M tetrabutylammo-
nium hexafluorophosphate (Bu4N[PF6]) as supporting electrolyte,
after purging with N2. The working electrode was a glassy carbon
electrode, and the counter electrode was platinum electrode. A
nonaqueous Ag/AgNO3 (0.1 M in acetonitrile) reference electrode
was contained in a separate compartment connected to the solution
via frit. DCM was used as the solvent. Ferrocene was added as the
internal reference.
1
give 42.3 mg yellow solid (Yield: 47%). Mp, 241−244 °C. H NMR
(CDCl3, 400 MHz): δ 8.44 (d, 2H, J = 8.0 Hz), 8.29−8.15 (m, 5H),
7.80 (t, 2H, J = 19.2 Hz), 7.72 (d, 2H, J = 8.0 Hz), 7.66 (t, 1H, J = 8.0
Hz), 7.53 (t, 3H, J = 15.2 Hz), 7.45−7.42 (m, 2H), 7.29 (s, 1H), 4.36
(t, 2H, J = 14.0 Hz), 1.91 (t, 2H, J = 14.4 Hz), 1.46 (q, 2H, J = 22.8
Hz), 0.99 (t, 3H, J = 14.8 Hz). 13C NMR (100 MHz, CDCl3) δ 141.0,
140.4, 134.8, 126.8, 126.6, 126.3, 124.2, 123.1, 122.7, 121.3, 120.9,
120.8, 120.7, 120.0, 119.6, 113.5, 109.2, 109.0, 97.3, 86.5, 43.2, 31.3,
20.8, 14.1. TOF HRMS ESI−: Calcd ([C38H27N]+), m/z = 497.2143,
found, m/z = 497.2144.
3.7. Triplet−Triplet Annihilation Assisted Upconversions.
Diode pumped solid state (DPSS) continuous lasers with 589 nm
(type MGL-III, laser power is tunable in the range of 1−50 mW.
Changchun New Industries Optoelectronics Tech. Co., Ltd., China)
and 635 nm (type T635D500, laser power is tunable in the range of
1−500 mW. Xi’an Minghui Optoelectronic Technology Co., Ltd.,
China) output were used for the upconversion. The diameter of the
589 nm laser spot is ca. 5 mm, and for the 635 nm laser, it is ca. 6 mm.
The power of the laser beam was measured with VLP-2000
pyroelectric laser power meter. For the upconversion experiments,
the mixed solution (with different triplet sensitizer and acceptor) was
degassed for at least 15 min with N2 before measurement, and the gas
flow is maintained during the measurement. Then, the solution was
excited with laser. The upconverted fluorescence was recorded with a
RF 5301PC spectrofluorometer. In order to reduce the scattered laser,
a black box was put behind the fluorescent cuvette to damp the laser
beam.
The upconversion quantum yields (ΦUC) of B-6 and PdTPTBP
were determined with the prompt fluorescence of compound B-6 (ΦF
= 10.5%, in toluene) and H2TPTBP (ΦF = 0.28%, in toluene) as the
inner standard. The upconversion quantum yields were calculated with
3.11. DFT Calculations. TD-DFT was used to probe the nature of
the excited states of the dyads. All calculations have been performed
with the Gaussian 09 program,56 without performing any structural
simplification. We have applied the computational protocol recently
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optimized for BODIPY derivatives,57a and we redirect the interested
reader to that earlier contribution for a complete discussion of
methodological aspects. Our protocol relies on the M06-2X58
exchange-correlation functional for all computational steps, as it is
known that this hybrid meta-GGA is adequate for excited-state
calculations.59 The 6-31G(d) atomic basis set is used to determine
geometrical and vibrational parameters, whereas a much more
extended basis set, 6-311+G(2d,p), is used to correct the computed
0−0 energies. This basis set combination yields nearly converged
transition energies for BODIPY derivatives.60 The ground and excited-
state structures have been optimized using analytic DFT and TD-DFT
gradients, respectively. These force minimizations have been
performed until the residual mean square force is smaller than 1 ×
10−5 a.u. (tight threshold in Gaussian09). The harmonic vibrational
frequencies of the optimized structures have been computed on the
optimal geometries using analytic and numerical differentiation for
ground and excited states, respectively. This allowed us to ascertain the
nature of the minima. In our calculations, the electrostatic interactions
between the compound and the environment have been modeled
thanks to the PCM method that restores valid solvent effect, as long as
no specific solute−solvent interactions take place.61 For this reason, we
have modeled the results in toluene here. Both absorption and
fluorescence maxima have been evaluated using the state-specific (SS)
PCM model that allows correct polarization of the excited-state
cavity.62 Therefore, the reported 0−0 energies account for both state-
specific solvation and vibrational effects. The vibrationally resolved
spectrawithin the harmonic approximationwere computed using
the FCclasses program.63,64 The reported spectra have been simulated
using a convoluting Gaussian function presenting a full width at half-
maximum (fwhm) of 0.07 eV. A maximal number of 25 overtones for
each mode and 20 combination bands on each pair of modes were
included in the calculation. The maximum number of integrals to be
computed for each class was set to 1 × 1010, and it was checked that
such numbers provide converged FC factors (>0.9; see discussion in
ref 64 and references therein).
REFERENCES
■
(1) Baluschev, S.; Miteva, T.; Yakutkin, V.; Avlasevich, Y.; Nelles, G.;
Cheprakov, A.; Yasuda, A.; Wegner, G. Phys. Rev. Lett. 2006, 97,
143903.
(2) Singh-Rachford, T. N.; Castellano, F. N. Coord. Chem. Rev. 2010,
254, 2560−2573.
(3) Zhang, C.; Zheng, J.; Zhao, Y.; Yao, J. Adv. Mater. 2011, 23,
1380−1384.
(4) Chow, P. K.; Ma, C.; To, W. P.; Tong, G. S. M.; Lai, S. L.; Kui, S.
C. F.; Kwok, W. M.; Che, C. M. Angew. Chem., Int. Ed. 2013, 52,
6648−6652.
(5) Zhao, J.; Ji, S.; Guo, H. RSC Adv. 2011, 1, 937−950.
(6) Cerono, P. Chem.Eur. J. 2011, 17, 9560−9564.
(7) Monguzzi, A.; Tubino, R.; Hoseinkhani, S.; Campione, M.;
Meinardi, F. Phys. Chem. Chem. Phys. 2012, 14, 4322−4332.
(8) Simon, Y. C.; Weder, C. J. Mater. Chem. 2012, 22, 20817−20830.
(9) Mani, T.; Vinogradov, S. A. J. Phys. Chem. Lett. 2013, 4, 2799−
2804.
(10) Ji, S.; Guo, H.; Wu, W.; Wu, W.; Zhao, J. Angew. Chem., Int. Ed.
2011, 50, 8283−8286.
(11) Ji, S.; Wu, W.; Wu, W.; Guo, H.; Zhao, J. Angew. Chem., Int. Ed.
2011, 50, 1626−1629.
(12) Monguzzi, A.; Tubino, R.; Meinardi, F. Phys. Rev. B 2008, 77,
155122/1−155122/4.
(13) Haase, M.; Schafer, H. Angew. Chem., Int. Ed. 2011, 50, 5808−
̈
5829.
́ ́
(14) Adikaari, A. A. D.; Etchart, I.; Guering, P.-H.; Berard, M.; Silva,
S. R. P.; Cheetham, A. K.; Curry, R. J. J. Appl. Phys. 2012, 111, 094502.
(15) Liu, Q.; Sun, Y.; Yang, T.; Feng, W.; Li, C.; Li, F. J. Am. Chem.
Soc. 2011, 133, 17122−17125.
(16) Wenger, O. S.; Gudel, H. U. Inorg. Chem. 2001, 40, 5747−5753.
̈
(17) Luthi, S. R.; Pollnau, M.; Gudel, H. U.; Hehlen, M. P. Phys. Rev.
̈
̈
B 1999, 60, 162−178.
(18) Kim, J.-H.; Kim, J.-H. J. Am. Chem. Soc. 2012, 134, 17478−
17481.
(19) Liu, Q.; Yang, T.; Feng, W.; Li, F. J. Am. Chem. Soc. 2012, 134,
5390−5397.
ASSOCIATED CONTENT
■
(20) Borisov, S. M.; Larndorfer, C.; Klimant, I. Adv. Funct. Mater.
2012, 22, 4360−4368.
S
* Supporting Information
Free energy calculations, molecular structure characterization
data (NMR, HRMS spectra) and UV−vis spectra, cyclo-
voltammetric graph, TTA assisted upconversion graphs, and
tables of atom coordinates and absolute energies. This material
is available free of charge via the Internet at http://pubs.acs.org.
(21) Cheng, Y. Y.; Fuckel, B.; MacQueen, R. W.; Khoury, T.; Clady,
̈
R. G. C. R.; Schulze, T. F.; Ekins-Daukes, N. J.; Crossley, M. J.;
Stannowski, B.; Lips, K. Energy Environ. Sci. 2012, 5, 6953−6959.
(22) Schulze, T. F.; Czolk, J.; Cheng, Y.-Y.; Fuckel, B.; MacQueen, R.
̈
W.; Khoury, T.; Crossley, M. J.; Stannowski, B.; Lips, K.; Lemmer, U.
J. Phys. Chem. C 2012, 116, 22794−22801.
(23) Borjesson, K.; Dzebo, D.; Albinsson, B.; Moth-Poulsen, K. J.
Mater. Chem. A 2013, 1, 8521−8524.
(24) Khnayzer, R. S.; Blumhoff, J.; Harrington, J. A.; Haefele, A.;
Deng, F.; Castellano, F. N. Chem. Commun. 2011, 48 (2), 209−211.
(25) Moor, K.; Kim, J.-H.; Snow, S.; Kim, J.-H. Chem. Commun.
2013, 49, 10829−10831.
(26) Liang, Z.-Q.; Sun, B.; Ye, C.-Q.; Wang, X.-M.; Tao, X.-T.; Wang,
Q.-H.; Ding, P.; Wang, B.; Wang, J.-J. ChemPhysChem 2013, 14,
3517−3522.
(27) Zhao, J.; Wu, W.; Sun, J.; Guo, S. Chem. Soc. Rev. 2013, 42,
5323−5351.
̈
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: zhaojzh@dlut.edu.cn. Web: http://finechem.dlut.edu.
cn/photochem.
*E-mail: Denis.Jacquemin@univ-nantes.fr. Fax: (+33) 251 125
40.
Notes
The authors declare no competing financial interest.
(28) Turshatov, A.; Busko, D.; Avlasevich, Y.; Miteva, T.; Landfester,
K.; Baluschev, S. ChemPhysChem 2012, 13, 3112−3115.
(29) Singh-Rachford, T. N.; Haefele, A.; Ziessel, R.; Castellano, F. N.
J. Am. Chem. Soc. 2008, 130, 16164−16165.
ACKNOWLEDGMENTS
■
J. Z. thanks the NSFC (21073028 and 21273028), the Royal
Society (UK) and NSFC (China-UK Cost-Share Science
Networks, 21011130154), Ministry of Education (NCET-08-
0077 and SRFDP-20120041130005) and Dalian University of
Technology for financial support. A. C. E. and D. J.
acknowledge the European Research Council (ERC) for
financial support in the framework of Starting Grant
(Marches-278845). This research used resources of the
GENCI-CINES/IDRIS, of the CCIPL (Centre de Calcul Intensif
des Pays de Loire) and of a local Troy cluster.
(30) Cao, X.; Hu, B.; Zhang, P. J. Phys. Chem. Lett. 2013, 4, 2334−
2338.
(31) Chen, H.-C.; Hung, C.-Y.; Wang, K.-H.; Chen, H.-L.; Fann, W.
S.; Chien, F.-C.; Chen, P.; Chow, T. J.; Hsu, C.-P.; Sun, S.-S. Chem.
Commun. 2009, 4064−4066.
(32) Bergamini, G.; Ceroni, P.; Fabbrizi, P.; Cicchi, S. Chem.
Commun. 2011, 47, 12780−12782.
(33) Moor, K.; Kim, J.-H.; Snow, S.; Kim, J. Chem. Commun. 2013,
49, 3537−3539.
2047
dx.doi.org/10.1021/jo402718e | J. Org. Chem. 2014, 79, 2038−2048

The Journal of Organic Chemistry
Article
(34) Du, P.; Eisenberg, R. Chem. Sci. 2010, 1, 502−506.
(35) Dayan, S.; Ozpozan Kalaycioglu, N.; Daran, J. C.; Labande, A.;
Poli, R. Inorg. Chem. 2013, 52, 1206−1216.
(36) Deng, F.; Sommer, J.; Myahkostupov, M.; Schanze, K.;
Castellano, F. N. Chem. Commun. 2013, 49, 7406−7408.
(37) Huang, D.; Sun, J.; Ma, L.; Zhang, C.; Zhao, J. Photochem.
Photobiol. Sci. 2013, 12, 872−882.
(61) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999−3094.
(62) Improta, R.; Barone, V.; Scalmani, G.; Frisch, M. J. J. Chem.
Phys. 2006, 125, 054103−054109.
(63) Santoro, F.; Improta, R.; Lami, A.; Bloino, J.; Barone, V. J. Chem.
Phys. 2007, 126, 084509.
(64) Santoro, F.; Lami, A.; Improta, R.; Barone, V. J. Chem. Phys.
2007, 126, 184102.
(38) Cortijo, M.; Gonzal
́ ́
ez-Prieto, R.; Herrero, S.; Jimenez-Aparicio,
(65) Charaf-Eddin, A.; Planchat, A.; Mennucci, B.; Adamo, C.;
Jacquemin, D. J. Chem. Theory Comput. 2013, 9, 2749−2760.
(66) Cheng, Y. Y.; Khoury, T.; Clady, R. G. C. R.; Tayebjee, M. J. Y.;
Ekins-Daukes, N. J.; Crossley, M. J.; Schmidt, T. W. Phys. Chem. Chem.
Phys. 2010, 12, 66−71.
R.; San
́
chez Rivera, P. Inorg. Chem. 2013, 52, 6299−6310.
(39) Wu, W.; Zhao, J.; Sun, J.; Huang, L.; Yi, X. J. Mater. Chem. C
2013, 1, 705−716.
(40) Guo, S.; Sun, J.; Ma, L.; You, W.; Yang, P.; Zhao, J. Dyes Pigm.
2013, 96, 449−458.
(67) Kim, J.-H.; Deng, F.; Castellano, F. N.; Kim, J.-H. Chem. Mater.
2012, 24, 2250.
(41) Huang, D.; Zhao, J.; Wu, W.; Yi, X.; Yang, P.; Ma, J. Asian J. Org.
Chem. 2012, 1, 264−273.
(42) Yang, P.; Wu, W.; Zhao, J.; Huang, D.; Yi, X. J. Mater. Chem.
2012, 22, 20273−20283.
(43) Wu, W.; Zhao, J.; Sun, J.; Guo, S. J. Org. Chem. 2012, 77, 5305−
5312.
(44) Singh-Rachford, T. N.; Nayak, A.; Muro-Small, M. L.; Goeb, S.;
Therien, M. J.; Castellano, F. N. J. Am. Chem. Soc. 2010, 132, 14203−
14211.
(45) Adachi, M.; Nagao, Y. Chem. Mater. 2001, 13, 662−669.
(46) Yamaji, M.; Maeda, H.; Nanai, Y.; Mizuno, K. Chem. Phy. Let.
2012, 536, 72−76.
(47) Shao, J.; Guo, H.; Ji, S.; Zhao, J. Biosensors Bioelectron. 2011, 26,
3012−3017.
(48) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008,
47, 1184−1201.
(49) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891−4932.
(50) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L. Y.;
Burgess, K. Chem. Soc. Rev. 2013, 42, 77−88.
(51) Benniston, A. C.; Copley, G. Phys. Chem. Chem. Phys. 2009, 11,
4124−4131.
(52) Coskun, A.; Akkaya, E. U. J. Am. Chem. Soc. 2006, 128, 14474−
14475.
(53) Kostereli, Z.; Ozdemir, T.; Buyukcakir, O.; Akkaya, E. U. Org.
Lett. 2012, 14, 3636−3639.
(54) Brizet, B.; Eggenspiller, A.; Gros, C. P.; Barbe, J.-M.; Goze, C.;
Denat, F.; Harvey, P. D. J. Org. Chem. 2012, 77, 3646−3650.
(55) Dance, Z. E. X.; Mickley, S. M.; Wilson, T. M.; Ricks, A. B.;
Scott, A. M.; Ratner, M. A.; Wasielewski, M. R. J. Phys. Chem. A 2008,
112, 4194−4201.
(56) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
̈
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; O. Farkas, Foresman,
J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J., Gaussian 09, revision D.01;
Gaussian Inc., Wallingford, CT, 2009.
(57) (a) Chibani, S.; Le Guennic, B.; Charaf-Eddin, A.; Laurent, A.
D.; Jacquemin, D. Chem. Sci. 2013, 4, 1950−1963. (b) Quartarolo, A.
D.; Russo, N.; Sicilia., E. Chem.Eur. J. 2006, 12, 6797−6803.
(58) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241.
(59) See a recent review Laurent, A. D.; Jacquemin, D. Int. J.
Quantum Chem. 2013, 113, 2019−2039 and refs therein.
(60) Chibani, S.; Le Guennic, B.; Charaf-Eddin, A.; Maury, O.;
Andraud, C.; Jacquemin, D. J. Chem. Theory Comput. 2012, 8, 3303−
3313.
2048
dx.doi.org/10.1021/jo402718e | J. Org. Chem. 2014, 79, 2038−2048