Oil-in-water microemulsion: An effective medium for triplet-triplet annihilated upconversion with efficient triplet acceptors

Article abstract of DOI:10.1039/c4tc00791c

The oil-in-water (o/w) microemulsion containing bimolecular system of acceptor (9,10-dinaphthylanthracene) and sensitizer (Pd(ii)tetratolylporphyrin), i.e., upconverted o/w microemulsion, was firstly reported for the triplet-triplet annihilated upconversion (TTA-UC) by temperature effects. The correlation between structure/up-conversion performance of three 9,10-dinaphthylanthracenes doped with Pd(ii)tetratolylporphyrin were investigated. Under excitation at an ultralow power density at 60 mW cm^-2, the up-converted o/w microemulsion emits green-to-blue upconversion and an efficiency (Φ_UC) increase is accompanied by an increase in temperature. The maximum Φ_UCvalue for the upconverted o/w microemulsion obtained was as high as 33.12%, which is comparable to its counterpart in a pure organic solvent. Very importantly, there is no need for the upconverted o/w microemulsion to deaerate, which is of critical importance for applications such as upconversion-powered photoelectrochemistry. To the best of our knowledge, the current study represents a simple approach to obtain high TTA-UC without degassing.

Full text of DOI:10.1039/c4tc00791c

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DOI: 10.1039/C4TC00791C
Journal Name
RSCPublishing
ARTICLE
O/w microemulsion: An effective medium for
triplet-triplet annihilated upconversion with
efficient triplet acceptors
Cite this: DOI: 10.1039/x0xx00000x
Changqing Ye,a,§ Bao Wang,a,§ Xiaomei Wang,a,* Ping Ding,a Xutang Tao,b
Zhigang Chen,a Zuoqing Liang,a Yuyang Zhoua
Received 00th January 20144,
Accepted 00th January 2012
The oilꢀinꢀwater (o/w) microemulsion containing bimolecular system of acceptor (9,10ꢀ
dinaphthylanthracene) and sensitizer (Pd(II)tetratolylporphyrin), i.e., upconverted o/w microemulsion,
was firstly reported for the tripletꢀtriplet annihilated upconversion (TTAꢀUC) by temperature effect. The
correlations between structure/upconversion performance of three 9,10ꢀdinaphthylanthracenes doped
with Pd(II)tetratolylporphyrin were investigated. Under the excitation of ultralow power density at 60
mW⋅cmꢀ2, the upconverted o/w microemulsion emits greenꢀtoꢀblue upconversion and the efficiency
(ΦUC) increase is accompanied by the temperature increase. The maximum ΦUC value for the
upconverted o/w microemulsion was obtained as high as 33.12% that is comparable to the counterpart in
pure organic solvent. Very importantly, it is no need for the upconverted o/w microemulsion to deaerate,
which is of critical importance for the application such as upconversionꢀpowered photoelectrochemistry.
To the best of our knowledge, the current study represents the simple approach to obtain high TTAꢀUC
without degassing anymore.
DOI: 10.1039/x0xx00000x
www.rsc.org/
the tripletꢀtriplet annihilation (TTA) with the result that the photonꢀ
Introduction
Twoꢀphoton absorption (TPA) is a nonlinear optical process1ꢀ3
that a molecule simultaneously absorbs two photons via virtual state
toward the excited state and usually results in photonꢀupconversion.
Although such TPAꢀbased upconversion exhibits valuable potential
applications such as upconversion lasing,4 twoꢀphoton
polymerization5 and photodynamic therapy,6, 7 it always needs very
high excitation intensity as high as hundreds of MW~GM⋅cmꢀ2 (one
million times as large as solar energy)8 that leads to the serious
application limitation. Alternatively, another photonꢀupconversion
upconversion produces. The most important thing is that such TTA
upconversion can be obtained at very low excitation intensity (less
than 100 mW⋅cmꢀ2, solar energy is enough),13, 14 which would bring
about many practical applications such as photovoltaics,15
photocatalysis,16 photodynamic therapy of cancer17 and display18 as
well as the solar cells.19 For example, in the singleꢀjunction solar
cell the unabsorbed longꢀwavelength transmission light can be
efficiently upconverted into absorbable photons through
upconversion materials which makes its theoretical efficiency reach
1.33ꢀfolds increase in comparison with that without upconversion
mechanism has already been paid much attention recently, which is
20
materials.19,
However, the TTA upconversion materials work
10
called tripletꢀtriplet annihilation (TTA) upconversion.9,
TTA
efficiently only to shorter wavelengths ≤ 750 nm,21 Moreover, since
upconversion (TTAꢀUC) is also a nonlinear optical process11 which
involves in a bimolecular system (i.e., sensitizer/acceptor). TTAꢀ
UC undergoes a series of multiple quantum processes:12 that is, i)
the sensitizer firstly absorbs one photon to the excited singlet state
and goes across its triplet excited state by intersystem crossing
(ISC); ii) then the tripletꢀtriplet energy transfer (TTT) occurs from
the sensitizer to acceptor; and then two triplet acceptors actualize
TTAꢀUC relies exclusively on the efficient generation of the triplet
excited states of both sensitizer and acceptor, dissolved O2 can
strongly annihilate these formed triplets.22, 23 So, the medium for
upconversion must be devoid of oxygen to prevent tripletꢀstate
quenching, which is absolutely not ideal for the most TTAꢀUC
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VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C4TC00791C
applications. Although lots of efforts have been made to achieve
TTAꢀUC in the aerated enviroment by embedding chromophores in
rubbery polymeric matrixs,24~26 encapsulating chromophores with
rigid polymer shell,27~30 loading chromophores into silica
nanoparticles31 as well as even incorporating the upconverting dyes
in micellar carriers,32 all of these have shown some intrinsic
limitations of either the complicated preparation processes or very
low UCꢀefficiency (less than 6% at the excitation intensity of 100
mW⋅cmꢀ2). Of the mentioned techniques, microꢀemulsification is a
simple method, widely used for encapsulation in micelles by
surfactants to produce nanoparticles including metals,33
semiconductor nanoparticles34 and polymerꢀbased TTA upꢀ
conversion nanoparticles.35 However, few reports have published to
obtain high TTAꢀUC efficiency in o/w microemulsion with
temperature effect to our knowledge.
Sensitizer (0.12 mM) and acceptor (1.2~ 48 mM) stock solutions
were prepared prior to the experiment by dissolving in toluene and
kept in dark prior to use.
To get the transparent upconverted oilꢀinꢀwater (o/w)
microemulsion, 2 mL of stock solutions were added into the
deionized water (18 mL) in the presence of Tweenꢀ20 (10 mL) at
room temperature under stirred condition and N2 atmosphere. Thus,
a series of the upconverted o/w microemulsions were obtained with
diameters of 40~60 nm in size (Figure S1 in supporting
information section).
2.2 Characterization and measurements
Melting points (m.p.) were recorded on an Xꢀ5 melting
point measurement instrument (Gongyi City Yuhua Instrument
1
Co., Ltd). H NMR and 13C NMR spectra were recorded at 25
oC using a Bruker Avance 300 MHz spectrometer. Elemental
analyses were performed on an Elementar Vario ELꢀIII
instrument. UVꢀVis absorption spectra have been measured
with Hitachi Uꢀ3500 recording spectrophotometer from quartz
cuvettes of 1 cm path.
In this paper, we have demonstrated for the first time that o/w
microemulsion can act as an effective medium for the TTAꢀUC
performance by temperature tuning. This o/w (oilꢀinꢀwater)
microemulsion using nonionic surfactant as emulsifier can be
reversibly converted into w/o (waterꢀinꢀoil) microemulsion with a
phase inversion temperature (PIT).36, 37 That is, in the upconverted
o/w microemulsion, the nanometerꢀsized droplets of oil containing
sensitizer/acceptor pair can disperse in waterꢀrich continuous phase
at room temperature. When the temperature is increased, the
nanometerꢀsized droplets of water conversely dispersed in oilꢀrich
continuous phase wherein the soluble sensitizer/acceptor would
Steadyꢀstate emission and timeꢀresolved decay curves were
measured on an Edinburgh FLS 920 fluorophotometer equipped
with timeꢀcorrelated singleꢀphoton counting (TCSPC) card. With
the aid of nF 900 soft ware, the prompt fluorescence lifetime (τF)
was measured under detection of nF lamp at room temperature;
while the phosphorescence lifetime (τP) and delayed fluorescence
lifetime (τDF) were measured at room temperature and nitrogen
atmosphere, under detection of microsecond xenon flash lamp
(Edinburgh Analytical Instruments, ꢁF 900). The monoexponential
fit for prompt fluorescence decay and diexponential fits for
phosphorescence and delayed fluorescence decays give acceptable
statistics parameters of χ2 < 1.1. χ2 is the “reduced chiꢀsquare”.
Fluorescence quantum yields (Φf) were measured using quinine
sulfate (in 0.1 mol·dm3 aqueous NaOH, Φr= 0.53) as the standard
according to literature.38
freely collide with each other. As
a result, the enhanced
upconversion efficiency (ΦUC) in microemulsion medium could be
comparable to the counterpart in pure organic solvent. Besides the
obvious advantages offered by upconverted o/w microemulsion
such as absence of toxic solutions, easy to fabricate, being
inexpensive and stable; the most important thing is that it presents
high upconversion effieicncy (e.g., ΦUC =33.12 % at the excitation
intensity of 60 mW⋅cmꢀ2) without the need of deaerating, which is
of critical importance from a practical point of view.
Diode solid laser (532 nm, 60 mW·cmꢀ2) was used as the
excitation source for TTA upconversion that was observed with
Experimental
PR655 SpectraScan colorimeter. Upconversion efficiency (ΦUC
)
All chemicals were purchased from Aldrich or Acros Chemical
Co. and were used without any further purification. The
synthesis details of three 9,10ꢀdinaphthylanthracenes (DNAMe,
DNACl and DNACN) (Figure 1) are found in the supporting
information section.
was obtained relative to rhodamine 6G in ethanol according to Eq
(1).24

  2
A
F η
r  r  s  s 
Φ =2Φ
(1)
UC
A
F
η
 

s

r
r
2.1 Preparation of o/w microemulsion
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C4TC00791C
Herein, the factor 2 accounts for the fact that two absorbed
photons are required to produce one upconverted photon. Φr is the
fluorescence quantum yield of rhodamine 6G as the reference
standard (in ethanol, 0.5 ꢁM, Φr = 0.88).39 As and Ar are the
absorbency of sensitizer and rhodamine 6G under the excitation
wavelength, respectively. Fs and Fr are the integrated emission of
acceptor and rhodamine 6G under the excitation wavelength,
respectively. ηs and ηr are the refractive index of solvent used in
sample and reference measurements, respectively.
2.3 Upconversionꢀpowered photoelectrochemistry
Upconversionꢀpowered
photoelectrochemistry40,41
was
achieved in a threeꢀelectrode cell (electrolyte: 1.0 M H2SO4 in
H2O) with WO3 film (Eg =2.7 eV) deposited on ITO glass as
working electrode, platinum rod as counter electrode and
Ag/AgCl (0.1 M) as reference electrode. Firstly, diodeꢀpumped
solidꢀstate laser (532 nm, 60 mW·cm−2) irradiates our
upconverted o/w microemulsion to obtain greenꢀtoꢀblue
upconversion. Then, the blue upconversion photoꢀactivates
Figure 1 Molecular structures of 9,10ꢀdinaphthylanthracenes (DNAMe, DNACl
and DNACN) and triplet sensitizer PdMeTPP.
9,10ꢀDinaphthylanthracenes show the characteristic vibronic
absorption bands in the range of 350~450 nm and the emission
spectra present the peaks at ~430 nm for DNAMe and DNACl,
while DNACN extends out to long wavelength at 452 nm due to its
increasing molecular conjugation (Figure 2a). Calculated
fluorescence quantum yields (Φf, %) are in order of DNAMe (0.78)
> DNACl (0.69) > DNACN (0.63), with concomitant of their
fluorescence lifetime (τF, ns) increase from 3.81 ns (DNAMe) to
3.98 ns (DNACl) till to 5.31 ns (DNACN) (see Table 1 and Figure
2b). These show that 9,10ꢀdinaphthylanthracene with donating
group (such as CH3ꢀ) on 2ꢀposition exhibits large radiation
probability in comparison with those containing accepting group
(such as ꢀCl and ꢀCN). We noticed that the absorption and emission
spectra of 9,10ꢀdinaphthylanthracenes in o/w microemulsion
medium show similar to those in DMF solvent (see Figure 2a and
Figure S2).
the
WO3
working
electrode
and
induce
the
photoelectrochemistry. The upconverted o/w microemulsion is
filled inside a quartz cuvette of 1 cm path under air atmosphere,
which is placed near the working electrode. Thus, the shuttered
current/time response of the WO3 photoanode biased to +0.33
V vs. Ag/AgCl was recorded by a computer controlled
electrochemistry station.
Results and discussion
3.1 Absorption and emission
Very interested in enhancement TTAꢀUC efficiency (ΦUC), we
designed a series of new 9,10ꢀdinaphthylanthracenes (Figure. 1),
topꢀendꢀcapped with naphthyl group on 9,10ꢀposition and flanked
with different groups (such as ꢀCH3, ꢀCl and ꢀCN) on 2ꢀposition of
the anthracene, whose names are abbreviated as DNAMe, DNACl
and
DNACN,
respectively.
Triplet
sensitizer
Table 1 Absorption and emission data of acceptors in DMF (1ꢀM)
Pd(II)tetratolylporphyrin, abbreviated as PdMeTPP, is also
presented.
λ
ab (nm)
τF (ns)
Acceptor
λem (nm)
Φf (%)
DNAMe
362, 378, 399
364, 381, 402
431
0.78
3.81
DNACl
434
452
0.69
0.63
3.98
5.31
DNACN
353, 373, 396, 416
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Table 2 Absorption and emission data of PdMeTPP in different mediums
medium
λab, nm
in DMF solvent
418, 524
in o/w microemulsion
420, 526
λfluo., nm
λphos., nm
569, 611
569, 611
676, 750
680, 752
9.8 (13.87%), 19.1 (86.13%)
418, 524
5.8 (17.63%), 19.5 (82.37%)
420, 526
τ
F, ns
λab, nm
τF and τP are fluorescence lifetime and phosphorescence lifetime, respectively.
Figure 3 Absorption and emission spectra of PdMeTPP in DMF and o/w
microemualsion (8 ꢀM, the emission spectra are obtained under the excitation of
Qꢀband).
3.2 Structure/ TTAꢀUC performances in DMF
Under the excitation of diode laser (532 nm, 60 mW⋅cmꢀ2), the
greenꢀtoꢀblue upconversion from DNAMe was recorded (Figure 4),
where the upconverted intensities exhibit almost quadratic integral
enhancement (insert) as a function of incident power intensity at
10.89~55.97 mW⋅cmꢀ2. These strongly suggest that the TTAꢀUC
was a nonlinear optical process (As expressed in Eq. (1): two
absorbed photons are required to produce one upconverted photon,
that is quasi twoꢀphoton process).
Figure 2 (a) Absorption and emission spectra of 9,10ꢀdinaphthylanthracenes (in
DMF, 1 ꢀM); (b) fluorescence timeꢀresolved decay curves.
As shown in Table 2 and Figure 3, the absorption spectrum of
sensitizer PdMeTPP in o/w microemulsion shows 2ꢀnm redꢀshift in
comparison with that in DMF. Meanwhile, the emission bands
located at 569 and 611 nm with nanosecond lifetimes are confirmed
to be fluorescence decays while the bands located at ~680 and ~750
nm with microsecond lifetimes to be phosphorescence decays .
Noted that both fluorescence and phorsphorescence maxima of
PdMeTPP are very similar in DMF and o/w microemulsion, but
the particular decay times are quite different. Relative to those in
DMF, the lifetimes of fluorescence and phorsphorescence are
decreased in the o/w microemulsion (Table 2), accompanying by
dramatical decrease in fluorescence intensity (Figure 3). The
reason for these observed differences in emission decay can be
interpretd that the confined space and unfree collision between
droplets in the o/w microemulsion could open the triplet state
radiative relaxation pathway, which would have influence on
tripletꢀtriplet annihilated upconversion.
Since twoꢀphoton process can occur in concentrated solution, the
dependence of upconversion intensity on the concentration of 9,10ꢀ
dinaphthylanthracenes (acceptor) is shown in Figure 5 (a~c). With
the increasing of acceptor’ concentration from 0.08 to 3.6 mM
(doped with PdMeTPP at 8ꢀM), the upconveted intensities of three
9,10ꢀdinaphthylanthracenes are remarkably increased, showing
14.2ꢀfolds (DNAMe), 7.4ꢀfolds (DNACl) and 4ꢀfolds (DNACN)
enhancements, respectively. Correspondingly, the efficiencies
(ΦUC) give the maximum values at 34.68% (DNAMe), 24.57%
(DNACl) and 21.03% (DNACN), respectively (Figure 6), which is
correlative with TTT efficiency (ΦTTT) and TTA efficiency (ΦTTA
as well as the acceptor’ fluorescence quantum yield (Φf), that is,
UC= ΦTTT⋅ΦTTA⋅Φf.42
)
Φ
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DOI: 10.1039/C4TC00791C
decreased delayed fluorescence lifetime from DNACN (2.68, 13.37
ꢀs), DNACl (2.28, 11.64 ꢀs) to DNAMe (0.93, 10.11 ꢀs), which
have positive contribution to tripletꢀtriplet annihilated upconversion
efficiency (see Table 3).
Figure 4 Upconverted intensity of DNAMe following excitation of
PdMeTPP (λex=532 nm) measured as a function of incident power intensity
(Inset: nearly double logarithm plot of the normalized upconverted
emission of DNAMe as a function of the normalized incident power
intensity of the laser).
Tripletꢀtriplet energy transfer (TTT) efficiency (ΦTTT) can be
evaluated according to SternꢀVolmer equation (2), where Po/P is
the phosphorescence intensity of sensitizer without and with
acceptor. τP and [Q] are the phosphorescence lifetime of sensitizer
and the concentration of acceptor, respectively. KQ is the triplet
quenching constant that can stand for the tripletꢀtriplet energy
transfer efficiency (ΦTTT).
Po
(2)
= KQτ p[Q]+1
P
Thus, the relationship of Po/P and [Q] for 9,10ꢀ
dinaphthylanthracenes were plotted (Figure 7) and the calculated
triplet quenching constants (KQ) are in the order of DNAMe
(7.65×108 Mꢀ1⋅sꢀ1)
> > DNACN
DNACl (3.89×108 Mꢀ1⋅sꢀ1)
(0.74×108 Mꢀ1⋅sꢀ1), which approach the diffusion limit of the DMF
o
solvent (8.3 × 109 Mꢀ1 sꢀ1 at 25 C).43 These indicate that TTT is a
diffusion controlled process in the present experimental system.
Based on the KQ values, one can see that the TTT efficiency (ΦTTT
)
are in the order of DNAMe > DNACl > DNACN.
Delayed
fluorescence
decay
curves
of
9,10ꢀ
dinaphthylanthracenes doped with PdMeTPP indicate that they have
dual delayed fluorescence lifetimes (τDF1, τDF1) (Figure 8a and
Table 3), which attributed to the dual phosphorescence of
PdMeTPP (see Table 2). We noticed that the unconverted (residual)
phosphorescence of PdMeTPP presents almost reduced
phosphorescence lifetime (τunp) in the presence of acceptor (Figure
8b). Furthermore, for the sensitizer of PdMeTPP the unconverted
(residual) phosphorescence lifetime increase is accompanied by the
Figure 5 Dependence of upconversion intensity on concentration of (a) DNAMe,
(b) DNACl and (c) DNACN in degassed DMF, at fixed concentration of
sensitizer (8 ꢁM) under the excitation of 532 nm (60 mW⋅cmꢀ2).
Based on the discussion of structure/TTAꢀUC performance
correlations, it was found that 9,10ꢀdinaphthylanthracene flanked
with donating group (CH3ꢀ) on 2ꢀposition exhibit higher
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fluorescence quantum yield (Φf) (see Table 1), larger triplet
quenching constant (KQ) and decreased delayed fluorescence
lifetime (τDF), relative to those with accepting group (CNꢀ and Clꢀ).
As a result, the efficient upconversion efficiency (ΦUC) was
obtained as high as 34.68% in DMF.
Figure 7 SternꢀVolmer curves of PdMeTPP quenched by DNAMe (a),
DNACl (b) and DNACN (c), upon excitation at 532 nm (60 mW⋅
cmꢀ2).
Figure 6 Dependence of upconversion efficiency on concentration of (a)
DNAMe, (b) DNACl and (c) DNACN in degassed DMF, at fixed concentration
of sensitizer (8 ꢁM) under the excitation of 532 nm (60 mW⋅cmꢀ2).
Table 3 Upconversion properties of acceptors doped with PdMeTPP and
unconverted phorphorescence lifetime of PdMeTPP in the prescence of acceptors
λUC
(nm)
ΦUC
(%)
KQ
Acceptor
DNAMe
τ
DF1, τDF1 (ꢀs)
(108Mꢀ1sꢀ1)
τ
unp (ꢀs)
0.93 (1.45%)
10.11 (98.55%)
11.23 (52.55)
4.11 (47.45)
446
34.68
7.65
2.28 (23.50%)
10.48 (78.90)
DNACl
448
464
24.57
21.03
3.89
0.74
11.64 (76.50%) 0.80 (21.10)
2.68 (17.36%) 9.35 (72.07)
13.37 (82.64%) 1.43 (27.93)
DNACN
τ
DF is the lifetimes of delayed fluorescence of dinaphthylanthracenes and τunp is
the unconverted phorphorescence lifetime of PdMeTPP.
3.3 TTAꢀUC performances in o/w microemulsion
TTAꢀupconversion performances in o/w microemulsion
containing DNAMe and PdMeTPP are conducted without the need
of deaerating anymore. These transparent upconverted o/w
microemulsion are stable at the environment for several months and
exhibit not only the concentrationꢀdependent upconverted intensity
that shows the similar to those in pure organic medium (Figure S3),
but also the temperatureꢀdependent upconverted intensity (Figure
S4). It is interpreted36 that the o/w (oilꢀinꢀwater) microemulsion
using nonionic surfactant as emulsifier can be reversibly converted
Figure 8 (a) Delay fluorescence curves of three 9,10ꢀdinaphthylanthracenes
doped with PdMeTPP, upon excitation at 532 nm and detection at ~440 nm); (b)
Unconverted phosphorescence decay curves of PdMeTPP in the presence of
different 9,10ꢀdinaphthylanthracenes, upon excitation at 532 nm and detection at
~680 nm ).
into w/o (waterꢀinꢀoil) microemulsion with the phase inversion
temperature (PIT). Below PIT the nonionic surfactant forming the
microemulsion prefers a high curvature surface around oil; and
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DOI: 10.1039/C4TC00791C
above the PIT the surfactant prefers a high curvature surface around
water.37 O/w microemulsion possesses the confined spaces that
block the collision between sensitizers and acceptors, which is
deleterious to upconversion performance. On the contrary, w/o
microemulsion with oil continuous phase, the soluble sensitizer and
acceptor are prone to diffusion and collision. Finally, not only TTT
process but also TTA process are promoted, which make the ΦUC
value reach to the counterpart in pure organic solvent.
3.4 Upconversionꢀpowered photoelectrochemistry
Upconverted o/w microemulsion can be employed as the
desired light used in photoelectrochemistry. As shown in
Figure 11a, the greenꢀtoꢀblue upconversion irradiates WO3
film deposited on ITO that acts as the working electrode. Since
WO3 photoanode (Eg = 2.7 eV,
λ
ab= 459 nm)44 is able to
absorb the blue illumination produced by our upconverted o/w
microemulsion, the oxidation of water can take place on the
WO3 photoanode, meanwhile the hydrogen can be obtained at
the platinum rod electrode. As a result, shuttered current/time
response of a WO3 photoanode biased to +0.33 V vs. Ag/AgCl
was recorded by a computer controlled electrochemistry
station.
Measurement data (Figure 11b) show that larger photocurrent (Ii=
0.046 ꢀA⋅cmꢀ2) was obtained under the irradiation by larger
upconverted
o/w
microemulsion
(DTAMe/PdMeTPP,
Φ
UC=33.12%), while smaller photocurrent (Ii=0.035ꢀA⋅cmꢀ2) was
recorded from small upconverted o/w microemulsion
(DTACl/PdMeTPP, ΦUC = 23.43%), strongly confirming that
upconversionꢀdriven photoelectrochemitry was indeed responsible
for the generated photocurrent. In order to eliminate the
photocurrent resulting from the excitation of diode pumped solid
state laser, the contrastive experiments were conducted under the
identical conditions excepting for using the quartz cuvette
containing only blank solvent. Considering that the upconverted
o/w microemulsion possesses absence of toxicity, easy to fabricate
and unnecessary to deaerate, the o/w microemulsion can be a
suitable medium for tripletꢀtriplet annihilation upconversion.
Figure
9 Concentrationꢀdependent upconverted efficiencies of DNAMe
combined with PdMeTPP (fixed at 8 ꢁM) in o/w microemulsion (70 oC) and
o
DMF (25 C), respectively. Insert is the photographs of blue upconversion from
the systems above (The excitation source is diode laser at 532 nm and 60
mW⋅cmꢀ2).
As shown in Figure 9, the enhanced upconversion efficiency
(ΦUC) in o/w microemulsion is almost the same as that in DMF
(insert presenting the photographs of greenꢀtoꢀblue upconversion
obtained from DNAMe/PdMeTPP in o/w micromulsions and in
DMF). Very importantly, this upconverted o/w microemulsion can
keep high efficiency (ΦUC=33.12%) without degassing for several
days. Contrarily, the efficiency (ΦUC) of counterpart in DMF
decreases to naught within 1.2 hour without degassing (Figure 10).
Moreover, a comparison experiment of DNAMe/ PdMeTPP using
o/w microemulsion, both with deaeration and without deaeration,
has further confirmed that the upconverted o/w microemulsion is no
need of deaerating anymore (Figure S5). These imply that the
upconveted o/w microemulsion is not sensitive to the oxygen,
which is of great significance. What’s more, the temperatureꢀ
dependent upconversion shows that the system with high
upconverted efficiency (ΦUC) is more sensitive to the temperature,
which is probably used as the temperature sensor (Figure S6).
Figure 10 Timeꢀdependent upconversion efficiency for DNAMe/PdMeTPP
(3.2 mM/8 ꢁM) in o/w microemulsion (70 oC) and DMF (25 oC),
respectively, under the air atmosphere. (The excitation source is diode laser
at 532 nm and 60 mW⋅
cmꢀ2).
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

Journal of Materials Chemistry C
Page 8 of 9
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C4TC00791C
promote the TTT and TTA processes with the result that the
upconveted efficiency is enhanced. These demonstrated that
thermalꢀdriven upconversion mechanism is functioned. The
maximum upconverted efficiency in o/w microemulsion was
obtained as high as 33.12% that is comparable to the counterpart in
DMF solvent (34.68%).
More importantly, it is no need for upconverted o/w
microemulsion to deaerate any more, which is of critical importance
for the application in photoelectrochemistry. The importance in this
study suggests that the upconverted o/w microemulsion provides
the simple approach to obtain high TTAꢀUC efficiency without
degassing at all.
Acknowledgements
The authors are grateful to National Natural Science (Grant No.51273141,
51303122), Natural Science Foundation of Jiangsu Province
(BK20130262), Natural Science Foundation of Jiangsu Provincial
Department of Education (11KJA430003), the Opening Project (No.
SJHG1311) of the Jiangsu Key Laboratory for Environment Functional
Materials, Project of Person with Ability of Jiangsu Province (2010ꢀxclꢀ
015), Excellent Innovation Team in Science and Technology of Jiangsu
Provincial Department of Education, and Project of Science and
Technology of Suzhou (SYG201204) for financial supports.
Figure 11 (a) Photograph of the upconversionꢀdriven photoelectrochemical
cell biased to +0.33 V vs. Ag/AgCl; (b) the corresponding recorded
photocurrent curves illumined by greenꢀtoꢀblue upconversion coming from
the upconverted o/w microemulsions (70oC) under air atmosphere (The
Author Contributions
§These authors contributed equally to this work.
excitation source is diode laser at 532 nm and 60 mW
⋅
cmꢀ2).
* The corresponding author.
Notes and references
Conclusions
aJiangsu Key Laboratory for Environmental Functional Materials, School of
Chemistry, Biology and Materials Engineering, Suzhou University of
Science and Technology, Suzhou, 215009, P. R. China.
bState Key Laboratory of Crystal Materials, Shandong University, Jinan,
250100, China.
An effective medium for tripletꢀtriplet annihilated upconversion
was
firstly
reported
and
the
correlations
of three
between
9,10ꢀ
structure/upconversion
performance
dinaphthylanthracenes doped with sensitizer (PdMeTPP) were
discussed. It was found that 9,10ꢀdinaphthylanthracene (DNAMe)
with donating group exhibits high fluorescence quantum yield
(Φf=78%) and larger TTT efficiency (KQ, 7.65×108 Mꢀ1sꢀ1), in
comparison with DNACl (Φf=69%, KQ=3.89×108 Mꢀ1sꢀ1) and
DNACN (Φf=63%, KQ=0.74×108 Mꢀ1⋅sꢀ1), resulting in the
efficiency (ΦUC) in the order of DNAMe (34.68 %) > DNACl
(24.57 %) > DNACN (21.03 %) in DMF solvent.
†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See DOI:
10.1039/b000000x/
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