Light-Harvesting Organic Nanocrystals Capable of Photon Upconversion

Article abstract of DOI:10.1002/cssc.201701389

Harvesting and converting low energy photons into higher ones through upconversion have great potential in solar energy conversion. A light-harvesting nanocrystal assembled from 9,10-distyrylanthracene and palladium(II) meso-tetraphenyltetrabenzoporphyrin as the acceptor and the sensitizer, respectively effects red-to-green upconversion under incoherent excitation of low power density. An upconversion quantum yield of 0.29±0.02 % is obtained upon excitation with 640 nm laser of 120 mW cm^?2. The well-organized packing of acceptor molecules with aggregation-induced emission in the nanocrystals dramatically reduces the nonradiative decay of the excited acceptor, benefits the triplet–triplet annihilation (TTA) upconversion and guides the consequent upconverted emission. This work provides a straightforward strategy to develop light-harvesting nanocrystals based on TTA upconversion, which is attractive for energy conversion and photonic applications.

Full text of DOI:10.1002/cssc.201701389

Accepted Article
Title: Light-Harvesting Organic Nanocrystals Capable of Photon
Upconversion
Authors: Li Li, Yi Zeng, Tianjun Yu, Jinping Chen, Guoqiang Yang, and
Yi Li
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To be cited as: ChemSusChem 10.1002/cssc.201701389
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10.1002/cssc.201701389
ChemSusChem
FULL PAPER
Light-Harvesting Organic Nanocrystals Capable of Photon
Upconversion
Li Li, [a] Yi Zeng,*[a] Tianjun Yu,[a] Jinping Chen,[a] Guoqiang Yang,[b] and Yi Li*[a]
Abstract: Harvesting and converting low energy photons to higher
ones through upconversion have great potential in solar energy
conversion. Herein, we demonstrate a light-harvesting nanocrystal
assembled by 9,10-distyrylanthracene and palladium(II) meso-
tetraphenyltetrabenzoporphyrin as the acceptor and the sensitizer,
respectively, in which red-to-green upconversion is achieved under
incoherent excitation of low power density and the upconversion
quantum yield of 0.29  0.02% is obtained upon excitation with 640
nm laser of 120 mW cm−2. The well-organized packing of acceptor
molecules with aggregation-induced emission in the nanocrystals
dramatically reduces the nonradiative decay of the excited acceptor,
benefits the TTA upconversion and guides out the consequent
upconverted emission. This work provides a straightforward strategy
those low energy photons that do not meet bandgaps or
absorption thresholds of conventional light-harvesting materials.
A potential way to raise the efficiency of solar energy conversion
is employing photon upconversion, by which low energy photons
convert to higher energy photons allowing them to be used by
conventional solar converters. [5-8]
Photon upconversion has great potentials in solar energy
conversion and photonic techniques because it generates
higher-energy photons through absorbing lower energy photons
by excitation with low-power and noncoherent light source.
There are two distinct ways to achieve photon upconversion,
lanthanide
annihilation (TTA) upconversion.[9] Photon upconversion based
two-component system consisting of
ions-based
upconversion
and
triplet-triplet
to develop light-harvesting nanocrystals based on TTA upconversion, on TTA involves
which is attractive for energy conversion and photonic applications.
a
10, 11]
sensitizer and acceptor (or called annihilator).[5,
The
sensitizers capture lower-energy photons and undergo
intersystem crossing (ISC) forming the triplet excited sensitizers,
which give birth to triplet excited acceptors through triplet-triplet
energy transfer (TTET). Two triplet acceptors encounter within
their lifetime and the TTA process takes place, generating a
singlet excited acceptor and the consequent upconverted
fluorescence. TTA upconversion shows advantages over
lanthanide upconversion systems, such as potentially higher
upconversion efficiency, lower power density of excitation, and
broad spectral tunability. However, unlike the lanthanide
upconversion systems which have been widely produced as
lanthanide ion-doped nanomaterials with controlled size, shape,
and function, it is still a tough issue to achieve efficient TTA
upconversion of solid systems due to the requirement of
diffusion and proximity of photoactive components to guarantee
serial Dexter-type energy transfers during conventional TTA
upconversion. After continuous efforts in the past decade,
diversified strategies have been made in solidification or
immobilization of TTA upconversion by introducing inner
matrixes, such as polymeric backbone, gels, capsules and
vacuum deposition.[12-20] Those blending and encapsulation
approaches have made a step forward into a solid or quasi-
solid state, thus advancing the application of TTA
upconversion in practical devices. Nevertheless, it is still
challenging to achieve crystalline TTA upconversion systems,
and obstacle factors including microphase segregation, limited
Introduction
Solar energy has been considered as one of the most promising
renewable energy resources. Collection and conversion of solar
energy by mimicking photosynthesis is one major area of
endeavor in sustainable chemistry research, because
photosynthesis is the most elegant way to utilize solar energy
and has powdered live beings on earth for billions of years. The
photosynthesis is initiated with light absorption by light-
harvesting components, followed by series energy migration and
transfer and finally funneling into reaction centers.[1] The unique
function has stimulated chemists to created artificial ways to
harvest solar energy and a large number of artificial light-
harvesting systems based on molecular and supramolecular
complexes have been developed.[2-4] In order to meet the
increasing demands of solar energy conversion, it is desirable to
harvest as much energy from sunlight as possible, especially
[a]
[b]
L. Li, Dr Y. Zeng, T. J. Yu, J. P. Chen, Prof. Dr. Y. Li
Key Laboratory of Photochemical Conversion and Optoelectronic
Materials, Technical Institute of Physics and Chemistry
University of Chinese Academy of Sciences
Chinese Academy of Sciences
Beijing 100190, China
E-mail: zengyi@mail.ipc.ac.cn; yili@mail.ipc.ac.cn
Prof. Dr. G. Q. Yang
molecular
diffusion and self-quenching of
excited
chromophores in aggregate states still need to be addressed
for improving upconversion performance. [7,21,22]
Sensitized TTA upconversion in organic crystals and the
triplet exciton fusion therein as well as the magnetic field
effects have been studied theoretically and experimentally
decades ago.[23-25] More recently, metal-organic frameworks
(MOFs) architectures with well-aligned chromophores and
effective exciton diffusion have been applied to efficient TTA
upconversion under low power excitation,[26] however, there
Beijing National Laboratory for Molecular Sciences (BNLMS), Key
Laboratory of Photochemistry, Institute of Chemistry
University of Chinese Academy of Sciences
Chinese Academy of Sciences
Beijing 100190, China
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201701389
ChemSusChem
FULL PAPER
are still limited successes in crystals or nanocrystals for efficient
TTA upconversion.[26-28] Organic nanocrystals composed of
small molecules with special photophysical or optoelectronic
properties have attracted great interest because of their function
versatility in fundamental studies and practical applications
including bioimaging, nanophotonic and optoelectronic
devices.[29-32] By harnessing the flexibility of organic molecule
tailoring and assembling, organic nanocrystals capable of
efficient photon upconversion via TTA show great potential in
solar energy conversion, although the design and preparation is
still challenging.
bands of PdTPTBP, partially alleviating the energy transfer from
the excited singlet DSA to PdTPTBP.
a
N
N
N
N
Pd
DSA
Here, we present
a straightforward approach for TTA
upconversion nanocrystals based on acceptors nanocrystals
doping with sensitizer. The upconversion chromophore pair
consists of a porphyrin-type sensitizer, palladium(II) meso-
tetraphenyltetrabenzoporphyrin (PdTPTBP), and an acceptor,
9,10-distyrylanthracene (DSA), with aggregation-induced
emission (AIE) property. AIE chromophores, different from
traditional dyes with aggregation caused quenching, are non-
emissive or weakly emissive in molecularly dissolved solution
but highly emissive in aggregate or solid-state mainly due to the
restriction of intramolecular motions, which restrains
nonradiative decays and consequently benefits the aggregate or
solid-state emission.[33, 34] The doped nanocrystal is fabricated
through a single-step solution-based crystallization assisted by
sodium dodecyl sulfate (SDS). It is found that the nanocrystals
of DSA acceptor doped with PdTPTBP effectively upconvert red
photons to green ones. This study provides a versatile strategy
to develop upconversion nanocrystals based on TTA for energy
and photonic applications.
Pd TPTBP
PdTPTBP
DSA crystals
PdTPTBP
DSA
b
1.0
0.8
0.6
0.4
0.2
0.0
2.5
2.0
1.5
1.0
0.5
0.0
×5
300
400
500
600
700
800
900
Wavelength (nm)
Figure 1. (a) Structures of the sensitizer PdTPTBP and the acceptor DSA. (b)
Absorption spectra of PdTPTBP and DSA and normalized emission spectra of
PdTPTBP in deaerated toluene and DSA crystals. λ = 414 nm.
Results and Discussion
The phosphorescence of PdTPTBP can be readily quenched
by DSA. The free-energy change (∆G) involved in an electron
transfer process from the triplet PdTPTBP to DSA is determined
to be positive (+1.61 eV) according to Rehm-Weller equation,
indicating that the electron transfer process is endothermic and
thermodynamically unfavorable. It is proposed that triplet-triplet
energy transfer from PdTPTBP to DSA accounts for the
phosphorescence quenching upon addition of DSA into the
PdTPTBP solution. The efficiency of triplet-triplet energy transfer
is estimated to be near unity in toluene with a sensitizer/acceptor
ratio of 1/800, as verified by the steady-state and time-resolved
phosphorescence quenching (Figure S1 in Supporting
Information). However, no upconverted emission is detected in
solution-based systems upon selective excitation of PdTPTBP
using 640 nm laser of up to 120 mW cm−2. It can be rationalized
by the severe nonradiative decay caused by intramolecular
rotations of DSA in solution (the fluorescence quantum yield of
DSA in toluene is determined to be 1.1%), which deactivate
either triplet excited DSA or the possible singlet DSA formed
from TTA.
PdTPTBP and DSA (Figure 1a) are prepared according to
previous reports and the structures are characterized by NMR
and MS.[35-38] The acceptor DSA and its analogues exhibit typical
AIE behaviors with high fluorescence quantum yield at solid-
state and have been used as aggregate or solid-state emitters
for bioimaging, sensing, and mechanochromism applications.[39-
41]
DSA molecules in crystals adopt a slipped-cofacial packing
structure due to the non-coplanar conformation of the styryl
substituent and anthracene core, which endows DSA crystals
with high emission quantum yield and waveguide function,
making them as promising photonic materials.[39] The absorption
and emission spectra of PdTPTBP and DSA are shown in Figure
1b. PdTPTBP shows strong absorption in the region of 400‒460
and 600‒650 nm with peaks at 441 (Soret-band) and 628 nm
(Q-band), respectively. It emits phosphorescence with maximum
at about 800 nm at room temperature and its reported ISC
efficiency is near unity.[36] PdTPTBP has been applied as the
sensitizers in various TTA upconversion systems and the
photophysical process therein have also been investigated in
depth.[42-45] The absorption of DSA lies below 500 nm with
smaller extinction coefficient compared to that of PdTPTBP. The
crystalline DSA displays narrow emission around 514 nm mostly
located at the transmission window between the Soret- and Q-
To obtain nanocrystals for TTA upconversion, we apply an
approach employing solution-based self-assembly of organic
compounds which is a mild and facile technique to prepare
organic nanocrystals with various morphologies and doping
compositions. In this work, the TTA upconversion nanocrystals
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10.1002/cssc.201701389
ChemSusChem
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are prepared by SDS assisted assembly of PdTPTBP and DSA
in aqueous solution. A THF solution of PdTPTBP (5 μM) and
DSA (4 mM) is rapidly injected into a SDS aqueous solution (10
mM), which is stirred vigorously for 10 mins and then stabilized
for 24 hours. The obtained colloidal solution is subjected to
centrifugation giving the doped self-assembly sample as light
yellow solids. Scanning electron microscopy (SEM)
measurement demonstrates that these compounds self-
assembly into nanorods of about 150-200 nm in average width
and 1‒3 µm in length, which possess rectangular cross-section
and good morphological purity (Figure 2a). Transmission
electron microscopy and selected area electron diffraction
(SAED) pattern (Figure 2b) reveal that the doped nanorods
possess uniform crystal structures growing along the [001]
direction. X-ray diffraction (XRD) patterns were also recorded to
further investigate the crystal structure of these nanorods
(Figure 2c). The evident diffraction peaks from the doped
nanorods confirm the highly crystalline structure of the nanorods
and the similar patterns to that of the DSA single crystals,
verifying that the doping of such amount of the photosensitizer
has little effect on the crystalline structure of DSA in nanorods.
chromophores. To characterize the TTA upconversion property,
the doped nanorods from co-assembly of PdTPTBP and DSA is
sandwiched between two quartz coverslips in a glove box filled
with argon (O2 concentration < 0.1 ppm) and sealed by epoxy
adhesive. Upconversion luminescence imaging of the nanorods
was performed on a confocal microscope with continuous wave
(CW) laser of 640 nm as the excitation source. All of the
nanorods show evident upconversion emission, indicating that
sensitizers are well distributed in DSA-based nanorods (Figure
S5). Furthermore, the upconverted emission spectra were
collected by using an integrating sphere coupled to
a
spectrometer with a liquid-nitrogen cooled CCD upon excitation
with different intensities of 640 nm laser and the double
logarithmic plots of the upconversion emission intensity as a
function of the incident light power are presented in Figure 3a.
The intensity of upconverted green emission shows dependence
on the incident power from quadratic to linear as increasing the
excitation laser power, which strengthens that the upconverted
emission originates from the TTA upconversion.[46,47] Two linear
regions fitted to the slopes of 1.9 and 1.2 have been
demonstrated, which correspond to the low- and high-power
density regimes, respectively. The threshold excitation intensity
Ith, defined as the slope transition point,[47] is evaluated to be
35.9 mW cm−2 for 640 nm excitation light. After Ith the TTA
process of excited triplet acceptors surpasses the spontaneous
decay and the upconversion emission intensity starts to be
linearly dependent to the incident power.
a
2
Ith = 35.9 mW cm
c
1
PdTPTBP-doped DSA nanorods
DSA single crystal
Slope = 1.2
0.1
Slope = 1.9
5
10
15
20
25
30
0.01
2θ (degree)
10
100
Excitation Intensity (
mW cm )
2
Figure 2. (a) SEM image of PdTPTBP-doped DSA nanorods. Inset shows the
cross section of a nanorod. (b) TEM image and SAD pattern of DSA. (c) XRD
patterns of DSA single crystal (reference no. CCDC 688692) and the doped
nanorods from bottom to top.
b
0.3
0.2
0.1
The nanorods show clear green emission with a fluorescence
characteristic of the DSA crystal with a maximum at 514 nm
upon excitation with 640 nm laser. The observation of
upconverted emission implies the occurrence of TTA
upconversion in the nanorods, which is indicated further by the
control experiments that neat DSA or PdTPTBP crystals show
no detectable luminescence with wavelength shorter than the
excitation light under the same experimental conditions.
Apparent upconversion emission from the nanocrystals under air
can also be observed as the impeded diffusion of oxygen into
the crystals, however, the upconversion intensity decreases
gradually upon irradiation which may be due to the oxidation of
the nanocrystals by singlet oxygen generated by the triplet
1.0
@ 120 mW cm2
0.5

0
20
40
60
Irradiation Time (min)
0
30
60
90
120
Excitation Intensity
(
mW cm2
)
Figure 3. (a) Upconversion emission intensity of the doped nanorods changes
with the excitation intensity of 640 nm laser. The two linear fitting with slops of
1.9 (red) and 1.2 (green) are presented and the extrapolated intersection of
the two fitting lines indicates the threshold excitation intensity (Ith). Inset shows
a photo of the nanorods sealed between coverslips taken behind a 500‒520
nm bandpass filter under irradiation with a 640 nm CW laser. (b) Upconversion
quantum yields of the doped nanorods as a function of the excitation intensity.
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10.1002/cssc.201701389
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Inset shows time-dependent upconversion emission intensity of the nanorods
transient absorption measurements. To estimate the triplet
lifetime of the acceptor (τT), which affects the TTA upconversion
efficiency, we use the following approximation function. When
the triplet-triplet annihilation rate is much smaller or negligible
compared with the spontaneous decay of the acceptor triplet in
the longer time region, there is an approximation IUC(t) 
exp(−t/τUC) = exp(−2t/τT), where τUC is the upconversion emission
lifetime and τT is the lifetime of the acceptor triplet[27, 49]. Based
on this relationship, a τT value of 5.2 µs is estimated for the
triplet DSA by fitting the tail of the kinetic trace of the
upconverted emission. The relatively short lifetime of the
acceptor triplet limits the triplet diffusion distance and encounter
probability. The triplet lifetime of acceptors needs to be extended
to improve the upconversion efficiency and may be improved by
new molecular design or introducing rigid framework
confinement.[50]
under continuous irradiation with 640 nm laser at 120 mW cm−2
.
The upconversion efficiency is described by upconversion
quantum yield (ΦUC) which is defined as the ratio of emitted
upconversion photons to absorbed photons with a theoretical
maximum of 50%. The absolute upconversion quantum yield of
the nanorods is quantified by using an integrating sphere
coupled to a spectrometer with a liquid-nitrogen cooled CCD and
following the reported method in the literature.[48] ΦUC of the
nanorods are measured at various excitation intensities and an
average ΦUC of (0.29  0.02)% is obtained at the incident laser
intensity of 120 mW cm−2. The upconversion emission in the
nanorods is likely attributed to the blockage of nonradiative
relaxation of the excited DSA state caused by the restraint of
free intramolecular torsional motions in solid-state. Adjacent
packing of the acceptor molecules in the crystalline material
makes the triplet exciton diffusion and thus the subsequent TTA
upconversion possible in molecular diffusion-free environment.
The waveguide property may help to guide out the upconverted
emission within the nanocrystals[39] Furthermore, the TTA
upconversion nanorods show steady upconversion emission
under continuous irradiation at 120 mW cm−2 for 60 minutes
(Figure 3b), indicating the good photostability. The air-stability of
the epoxy-sealed sample was also examined and the result
showed that the upconversion efficiency of the sample can be
maintained at ambient conditions for more than 28 days
indicating of the good gas proofness of the epoxy-sealed device
(Figure S3 in Supporting Information).
0.1
0.01

UCs
1E-3
0
2000
4000
6000
8000
10000
Time (ns)
Figure 4. Kinetic profile of the delayed fluorescence observed in the nanorods
excited with 635 nm pulse laser (7 ns pulse from OPO laser). The solid red
line indicates the exponential fit of the tail of decay trace.
The photophysical processes within the upconversion
nanomaterial are further investigated by steady-state and time-
resolved spectroscopy. The phosphorescence of PdTPTBP
nanoaggregates dispersed in SDS (~ 110 nm diameter) shows a
mono-exponential decay with a lifetime of τ0 = 367 µs, while in
the PdTPTBP-doped DSA nanorods, the phosphorescence of
PdTPTBP decays rapidly and the dynamic trace almost overlaps
with the instrument response function (IRF, 9 µs), which is
consistent with the observation of phosphorescence quenching
of PdTPTBP by DSA in toluene solution. A TTET efficiency
(ΦTTET) of about 97% was estimated by considering these two
lifetimes. The phosphorescence quantum yields of PdTPTBP
nanoaggregates dispersed in SDS and PdTPTBP doped DSA
nanomaterials are measured to be 2.6% and 0.06%,
respectively, providing the same TTET efficiency as those
estimated by phosphorescence lifetime measurements. The
fluorescence quantum yield (ΦF) of neat DSA crystals is
measured to be 39%. Thus, the triplet-triplet annihilation
efficiency ΦTTA of about 0.76% is obtained for the upconversion
nanocrystal according to the relationship ΦUC = ΦISCΦTTETΦTTAΦF.
The time-resolved upconversion emission of the doped
nanocrystal was also measured. The fluorescence lifetime of the
acceptor extends into the microsecond region as depicted in
Figure 4, demonstrating a delayed fluorescence feature and
strengthening the occurrence of the TTA upconversion. The
generation of upconversion emission is prompt and no rising
dynamics is observed under the experiment condition. No
transient absorption of the acceptor could be detected in
Conclusion
In summary,
a
promising approach for light-harvesting
nanomaterials capable of photon upconversion based on
acceptors nanocrystals doped with sensitizers has been
demonstrated. An acceptor with aggregation-induced emission
is adopted in combination with a porphyrin-type sensitizer to
construct the sensitizer-acceptor pair of TTA upconversion
system. The doped nanocrystal is fabricated through a single-
step solution-based crystallization assisted by surfactant. The
doped-nanocrystals upconvert red excitation photons into green
emission with an upconversion quantum yield of about 0.29% on
account of the well-defined alignment of AIE acceptor molecules
in the nanocrystals which dramatically reduce the nonradiative
decay of the excited acceptor and benefit the consequent TTA
upconversion. The fluorescence quantum yield of DSA crystals
is about 0.4 and there are still plenty rooms to improve the TTA
upconversion by developing AIE acceptors with higher
fluorescence quantum yields, since a lot of AIE compounds
show near 100% fluorescence quantum yields. In addition, it is a
potential way to incorporate classic chromophore units with high
TTA efficiency into AIE acceptors, and enhance the triplet
diffusion and TTA process. Rigid frameworks or environmental
effects can be introduced into the AIE systems to extend the
triplet lifetime which is also a feasible way to improve the TTA
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10.1002/cssc.201701389
ChemSusChem
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μs FWHM). The decay dynamics of the upconverted fluorescence was
monitored on an Edinburgh LP920 spectrometer equipped with
nanosecond pulse laser (7 ns FWHM) provided by the combination of
Nd:YAG laser and OPO.
Upconversion emission spectra and emission quantum yields were
recorded in an integrating sphere (Labsphere) combining to a Princeton
Instrument Acton SP2500 spectrograph and a SPEC-10 liquid nitrogen-
cooled CCD. The upconversion quantum yields of nanocrystals and the
fluorescence quantum yield of DSA crystals were measured by excitation
with 640 and 405 nm CW lasers (PicoQuant LDH-D-C-series),
respectively, following the method reported in literature.[19]
upconversion. This study provides
a potential strategy to
develop light-harvesting nanocrystals based on TTA
upconversion, which is attractive for solar energy conversion
and photonic applications by harnessing the modification and
tunability of morphology, size, surface functionality from organic
nanocrystals.
Experimental Section
The free-energy change (∆G) of a electron transfer process was
calculated according to Rehm-Weller equation:
Materials
ꢄ
ꢄ
Reagents were purchased from Aldrich or Innochem or J&K chemical
and were used without further purification, unless otherwise noted.
Palladium(II) tetraphenyltetrabenzoporphyrin (PdTPTBP)[32] and 9,10-
distyrylanthracene (DSA)[33] were prepared according to literature reports.
PdTPTBP is obtained as dark green powder with a total yield of 3%. 1H
NMR (400 MHz, DMSO-d6) δ 8.25 (d, J = 7.1 Hz, 8H), 8.03 (d, J = 7.4 Hz,
4H), 7.96 (t, J = 7.5 Hz, 8H), 7.31-7.29 (m, 8H), 7.07-7.04 (m, 8H).
MS(MALDI/TOF) calcd. m/z for M+ 918.2, found 918.2.
ꢃ
ꢍ
ꢍ
∆G ꢀ ꢁ[EOX-ERED]ꢂE0,0ꢂ ꢅꢆꢇ
ꢂ ꢌꢃꢆ
(
ꢏ ꢊꢍ ꢑꢒꢇ ꢂ ꢇꢍ ꢑ
ꢇ
ꢉ
ꢊ
ꢋꢋ
ꢊ
ꢎ
ꢈ
ꢐ
ꢓꢔꢕ
ꢉ
EOX and ERED are the oxidation potential of electron donor (PdTPTBP)
and the reduction potential of electron acceptor (DSA), respectively,
which are 0.61 V and -2.07 V in THF with reference to Fc/Fc+. E0,0
represents the triplet excited state energy of PdTPTBP, which is 1.56 eV.
εS = static dielectric constant of the solvent, RD is the radius of the donor,
RA is the radius of the electron acceptor, εREF is the static dielectric
constant of the solvent used for the electrochemical studies(7.58 for
THF), ε0 permittivity of free space. The solvents used in the calculation of
free energy of the electron transfer is toluene (εS = 2.38). The distance
between the donor and the acceptor (rcc) is about 55 Å. To estimate the
Born correction to the solvation energy, we set RD and RA equal to 8.3
and 5.9 Å, respectively, by assuming that both donor and acceptor are
spherical. The value of ∆G in toluene is calculated to be +1.61 eV.
DSA is prepared by Heck coupling of styrene and 9,10-
dibromoanthracene and obtained as yellow solid (yield 55%). mp: 276.7–
278.4 ºC. 1H NMR (400 MHz, CDCl3) δ 8.41 (dd, J = 6.7, 3.1 Hz, 8H),
7.94 (d, J = 16.5 Hz, 2H), 7.70 (d, J = 7.4 Hz, 4H), 7.48 (dd, J = 10.2, 5.1
Hz, 8H), 7.37 (t, J = 7.3 Hz, 2H), 6.95 (m, J = 16.5 Hz, 2H). 13C NMR
(101 MHz, CDCl3) δ 137.50, 137.35, 132.72, 129.61, 128.86, 128.05,
126.62, 126.48, 125.26, 125.21. MS(EI-TOF) calcd. m/z for M+ 382.1722,
found 382.1723.
Acknowledgements
Preparation of samples for upconversion
Quartz coverslips (φ 25 mm × 25 mm × 0.2 mm) were washed by
continuous sonication in detergent solution for 30 mins, cleaned by
deionized water, ethanol and dichloromethane, and then dried by a
stream of compressed nitrogen.
Financial support from the 973 program (2013CB834703 and
2013CB834505), the National Natural Science Foundation of
China (Nos. 21233011, 21673264, 21573266, 21472201 and
21672226), and the Strategic Priority Research Program
(XDB17030300) and Youth Innovation Promotion Association
(2017032) of Chinese Academy of Sciences is gratefully
acknowledged.
The PdTPTBP-doped DSA nanocrystals were prepared by a solution-
based nanocrystallization process.
A 4mL THF solution containing
PdTPTBP (0.005 mM) and DSA (4 mM) was rapidly injected into 25 mL
sodium dodecyl sulfate (SDS, 10 mM) aqueous solution under vigorous
stirring. After being stirred for 10 mins and standing for 24h at 25 ºC, the
obtained colloidal solution was subjected to centrifugation at 3,000 rpm
for 3 mins to remove large precipitates. The doped nanocrystals were
collected by centrifugation at 9,000 rpm for 10 mins. The nanocrystals
were dried under vacuum and sealed between two quartz coverslips
using two-component epoxy adhesive (Ergo 7300) in a glovebox charged
with argon (O2 concentration < 0.1 ppm).
Keywords: light harvesting • photochemistry • nanoparticles •
photon upconversion • aggregation
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Entry for the Table of Contents
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A light-harveting nanocrystal
Li Li, Yi Zeng,* Tianjun Yu, Jinping
assembled by 9,10-distyrylanthracene
and palladium(II) meso-
Chen, Guoqiang Yang, Yi Li*
Page No. – Page No.
tetraphenyltetrabenzoporphyrin in
which red light is harvested and
converted to green emission under
incoherent excitation of low power
density and the upconversion
quantum yield of 0.29  0.02% is
obtained on account of the well-
defined alignment of the molecules
with aggregation-induced emission in
the nanocrystals.
Light-Harvesting Organic
Nanocrystals Capable of Photon
Upconversion
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