Efficient solid emitters with aggregation-induced emission and intramolecular charge transfer characteristics: Molecular design, synthesis, photophysical behaviors, and OLED application

Article abstract of DOI:10.1021/cm300416y

Emissive electron donor-acceptor (D-A) conjugates have a wide variety of applications in biophotonics, two-photon absorption materials, organic lasers, long wavelength emitters, and so forth. However, it is still a challenge to synthesize high solid-state efficiency D-A structured emitters due to the notorious aggregation-caused quenching (ACQ) effect. Though some D-A systems are reported to show aggregation-induced emission (AIE) behaviors, most are only selectively AIE-active in highly polar solvents, showing decreased solid-sate emission efficiencies compared to those in nonpolar solvents. Here we report the triphenylamine (TPA) and 2,3,3-triphenylacrylonitrile (TPAN) based D-A architectures, namely, TPA3TPAN and DTPA4TPAN. Decoration of arylamines with TPAN changes their emission behaviors from ACQ to AIE, making resulting TPA3TPAN and DTPA4TPAN nonluminescent in common solvents but highly emissive when aggregated as nanoparticles, solid powders, and thin films owing to their highly twisted configurations. Both compounds also display a bathochromic effect due to their intramolecular charge transfer (ICT) attribute. Combined ICT and AIE features render TPA3TPAN and DTPA4TPAN intense solid yellow emitters with quantum efficiencies of 33.2% and 38.2%, respectively. They are also thermally and morphologically stable, with decomposition and glass transition temperatures (T_d/T_g) being 365/127 and 377/141 °C, respectively. Multilayer electroluminescence (EL) devices are constructed, which emit yellow EL with maximum luminance, current, power, and external quantum efficiencies up to 3101 cd/m², 6.16 cd/A, 2.64 lm/W, and 2.18%, respectively. These results indicate that it is promising to fabricate high efficiency AIE-ICT luminogens with tunable emissions through rational combination and modulation of propeller-like donors and/or acceptors, thus paving the way for their biophotonic and optoelectronic applications.

Full text of DOI:10.1021/cm300416y

Article
pubs.acs.org/cm
Efficient Solid Emitters with Aggregation-Induced Emission and
Intramolecular Charge Transfer Characteristics: Molecular Design,
Synthesis, Photophysical Behaviors, and OLED Application
Wang Zhang Yuan,†,‡ Yongyang Gong,‡ Shuming Chen,§ Xiao Yuan Shen,∥ Jacky W. Y. Lam,† Ping Lu,⊥
Yawei Lu,‡ Zhiming Wang,⊥ Rongrong Hu,† Ni Xie,† Hoi Sing Kwok,§ Yongming Zhang,‡ Jing Zhi Sun,∥
and Ben Zhong Tang*,†,∥
†Department of Chemistry and State Key Laboratory of Molecular Neuroscience, Institute for Advanced Study, The Hong Kong
University of Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, China
‡School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
§Center for Display Research, The Hong Kong University of Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong
Kong, China
∥Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China
⊥State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130023, China
S
* Supporting Information
ABSTRACT: Emissive electron donor−acceptor (D−A)
conjugates have a wide variety of applications in biophotonics,
two-photon absorption materials, organic lasers, long wave-
length emitters, and so forth. However, it is still a challenge to
synthesize high solid-state efficiency D−A structured emitters
due to the notorious aggregation-caused quenching (ACQ)
effect. Though some D−A systems are reported to show
aggregation-induced emission (AIE) behaviors, most are only
selectively AIE-active in highly polar solvents, showing
decreased solid-sate emission efficiencies compared to those
in nonpolar solvents. Here we report the triphenylamine
(TPA) and 2,3,3-triphenylacrylonitrile (TPAN) based D−A
architectures, namely, TPA3TPAN and DTPA4TPAN. Deco-
ration of arylamines with TPAN changes their emission behaviors from ACQ to AIE, making resulting TPA3TPAN and
DTPA4TPAN nonluminescent in common solvents but highly emissive when aggregated as nanoparticles, solid powders, and
thin films owing to their highly twisted configurations. Both compounds also display a bathochromic effect due to their
intramolecular charge transfer (ICT) attribute. Combined ICT and AIE features render TPA3TPAN and DTPA4TPAN intense
solid yellow emitters with quantum efficiencies of 33.2% and 38.2%, respectively. They are also thermally and morphologically
stable, with decomposition and glass transition temperatures (Td/Tg) being 365/127 and 377/141 °C, respectively. Multilayer
electroluminescence (EL) devices are constructed, which emit yellow EL with maximum luminance, current, power, and external
quantum efficiencies up to 3101 cd/m2, 6.16 cd/A, 2.64 lm/W, and 2.18%, respectively. These results indicate that it is promising
to fabricate high efficiency AIE-ICT luminogens with tunable emissions through rational combination and modulation of
propeller-like donors and/or acceptors, thus paving the way for their biophotonic and optoelectronic applications.
KEYWORDS: aggregation-induced emission, intramolecular charge transfer, high solid-state efficiency
changes detection,9 optoelectronic devices,5,7,10−12 cellular
INTRODUCTION
Conjugated molecules with electron donor−acceptor (D−A)
architectures are of growing interest for optoelectronic
■
imaging,13 and so on. Particularly, emissive D−A conjugates
are promising candidates for biophotonics and optoelectronics,
such as fluorescent molecular rotors,14 chemo- and bio-
applications due to their unique photochemical and intra-
sensors,13b,15 upconverting fluorophores,6b,c,16 low band gap
molecular charge transfer (ICT) properties.1−7 The independ-
ent and diverse selections of donor and acceptor groups allow
for facile modulation of the electronic structure and thus
electronic and optoelectronic properties of the resulting
conjugates, making them suitable for a wide variety of
applications in solar energy conversion,5,8 microenvironmental
emitters,17 organic lasers,18 optical power limiting materials,19
Received: February 7, 2012
Revised: April 5, 2012
Published: April 6, 2012
© 2012 American Chemical Society
1518
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
Chart 1. Chemical Structures of TPA3TPAN and DTPA4TPAN
optical data storage media,20 light-emitting diodes (LEDs),4,21
and field-effect transistors (FETs).3d,22
We are wondering whether we can create such D−A
conjugates as normal AIE luminogens that are weakly or
nonluminescent in common solvents but become strong
emitters when aggregated. If so, it will be instructive to
fabricate such highly fluorescent solid emitters as red and near-
IR luminogens with tunable emissions, which have important
applications in optoelectronic devices and biophotonics.32 In
the present paper, we endeavored to develop such D−A
systems consisting of electron-donating triphenylamine (TPA)
or N4,N4,N4′,N4′-tetraphenylbiphenyl-4,4′-diamine (a TPA
dimer, DTPA) cores and electron-accepting 2,3,3-triphenyla-
crylonitrile (TPAN) peripherals, and the resulting TPA3TPAN
and DTPA4TPAN (Chart 1) molecules exhibit typical AIE and
ICT characteristics as expected.
Normally, strong fluorescence in the aggregated state is
highly desired for most applications of emissive D−A
conjugates, particularly for the biophotonic and electro-
luminescent cases.4,13a,21 However, many conventional lumino-
phores suffer from the notorious aggregation-caused quenching
(ACQ) effect due to the formation of such detrimental species
as excimers and exciplexes in the aggregated state.23,24 Various
chemical, physical, and engineering methods were exploited to
prevent the formation of luminophore aggregates with the aim
of mitigating the ACQ effect.25 Such efforts, however, have met
with only limited success, because they are basically working
against a natural process: it is well-known that luminophore
molecules inherently aggregate in the condensed phase.
Contrary to the ACQ effect, we have recently discovered a
novel phenomenon of aggregation-induced emission (AIE).26
In sharp contrast to traditional luminophores, the AIE
luminogens are nonemissive when dissolved in good solvents
but become highly emissive upon aggregation in poor solvents
or in the solid state.26−28
Meanwhile, traditional D−A structured luminogens are
weakly or even nonemissive in highly polar solvents like
DMF due to the presence of dark ICT state but normally
exhibit high luminescence in nonpolar solvents (hexane,
toluene, 1,4-dioxane, etc.) from the local excited (LE) state.3c,29
This is the expected effect of ICT on solution quantum
efficiency; namely, fluorescence efficiency should decrease with
increasing charge transfer strength. The solid state emissions,
however, depend on the molecular configurations despite the
restricted ICT process: while distorted geometry diminishes the
intermolecular interactions and thus favors efficient fluores-
cence,30,31 planar structure induces strong π−π interactions and
thereby quenches the emission.29
EXPERIMENTAL SECTION
■
Materials. THF and toluene were distilled under normal pressure
from sodium benzophenone ketyl under nitrogen immediately prior to
use. Dichloromethane (DCM) was distilled under normal pressure
over calcium hydride under nitrogen before use. Benzene,
dimethylformamide (DMF), dimethylacetamide (DMA), 4-bromo-
benzylnitrile (1), benzophenone (2), sodium hydride (NaH),
bis(pinacolato)diborane (4), 1,1′-bis(diphenylphosphino)ferrocene]-
dichloropalladium(II) ((dppf)PdCl2), diphenylamine (6), 4,4′-diiodo-
biphenyl (7), potassium iodide (KI), potassium iodate (KIO3), and
sodium carbonate (Na2CO3) were purchased from Aldrich and used as
received. Tris(4-iodophenyl)amine (10) was synthesized according to
reference procedures.33
Instruments. 1H and 13C NMR spectra were measured on a
Bruker ARX 400 spectrometer using CDCl3 as solvent and
tetramethylsilane (TMS, δ = 0) as internal standard. Matrix-assisted
laser desorption/ionization time-of-flight (MALDI-TOF) high-reso-
lution mass spectra (HRMS) were recorded on a GCT premier
CAB048 mass spectrometer. Absorption spectra were taken on a
Milton Roy Spectronic 3000 Array spectrometer. Emission spectra
were taken on a Perkin-Elmer spectrofluorometer LS 55. Emission
quantum yields (ΦF's) of TPA3TPAN and DTPA4TPAN in different
solvents were estimated by using 9,10-diphenylanthracene (ΦF = 90%
in cyclohexane, for TPA3TPAN and DTPA4TPAN) or 2-amino-
prydine (ΦF = 60% in 0.1 N H2SO4, for TPAN) as standard, while
solid-state efficiencies of the thin films were determined using an
integrating sphere. Thermal stability of the compounds was evaluated
on a Perkin-Elmer TGA 7 under nitrogen at a heating rate of 20 °C/
min. A Perkin-Elmer DSC 7 was employed to measure the phase
transition thermograms at a scan rate of 10 °C/min. The ground-state
Some works reported the D−A systems showing AIE
characteristic in highly polar aqueous media. However, the
solid-state efficiencies are still lower than those of molecularly
dissolved species in nonpolar solvents;31 namely, these
molecules are only selectively AIE-active in specific solvents.
Steady and transient absorption and emission studies revealed
that the transition from emissive LE state to dark ICT state is
the main cause for such selective AIE phenomena.31
1519
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
Scheme 1. Synthetic Routes to TPA3TPAN and DTPA4TPAN
geometries were optimized using the density functional with B3LYP
hybrid functional at the basis set level of 6-31G(d). All calculations
were performed using the Gaussian 09 package. Cyclic voltammo-
grams were recorded on a Zahner IM6e Electrochemical Workstation
with Pt, glassy carbon, and Ag/AgCl electrodes as counter, working,
and reference electrodes, respectively, at a scan rate of 100 mV/s, with
0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) as the
supporting electrolyte in anhydrous dichloromethane (DCM) purged
with nitrogen. The HOMO energy levels are derived from the onset
oxidation potentials (Eonset‑ox) according to the equation HOMO =
−(Eonset‑ox + 4.8 eV − Eferrocene). Optical band gaps (Egopt) of the
compounds were derived from the absorption edges in DCM, thereby
giving the LUMO levels of (HOMO + Egopt).
OLED Device Fabrication. The devices were fabricated on an 80
nm-ITO coated glass with a sheet resistance of 25 Ω □−1. Prior to
loading into the pretreatment chamber, the ITO-coated glass was
soaked in ultrasonic detergent for 30 min, followed by spraying with
deionized water for 10 min, soaking in ultrasonic deionized water for
30 min, and oven-baking for 1 h. The cleaned samples were treated by
perfluoromethane plasma with a power of 100 W, gas flow of 50 sccm,
and pressure of 0.2 Torr for 10 s in the pretreatment chamber. The
samples were transferred to the organic chamber with a base pressure
of 7 × 10−7 Torr for the deposition of 1,4-bis[(1-naphthylphenyl)-
amino]biphenyl (NPB), emitter, and 1,3,5-tris(N-phenylbenzimidazol-
2-yl)benzene (TPBi), which served as hole-transport, light-emitting,
and electron-transport layers, respectively. The samples were then
transferred to the metal chamber for cathode deposition to lithium
fluoride (LiF) capped with aluminum (Al). The light-emitting area was
4 mm2. The current density−voltage characteristics of the devices were
measured by a HP4145B semiconductor parameter analyzer. The
forward direction photons emitted from the devices were detected by a
calibrated UDT PIN-25D silicon photodiode. The luminance and
external quantum efficiencies of the devices were inferred from the
photocurrent of the photodiode. The electroluminescence spectra
were obtained by a PR650 spectrophotometer. All measurements were
carried out under air at room temperature without device
encapsulation. Due to the high molecular weight (Mw = 1606) and
dipole−dipole interactions, DTPA4TPAN needs high evaporation
temperature (320−370 °C) to deposit, which might damage the
molecules.
RESULTS AND DISCUSSION
■
Synthesis. The synthetic routes to TPA3TPAN and
DTPA4TPAN are depicted in Scheme 1. Briefly, the important
intermediate 5 was synthesized by coupling between 4-
bromobenzylnitrile (1) and benzophenone (2), followed by
metathesis of the bromine atom for boronpinacolate.34 While
10 was prepared according to our previous procedures,33
another key reactant 9 was obtained by Ullmann reaction
between diphenylamine (6) and 4,4′-diiodobiphenyl (7) and
then followed by iodination. Suzuki couplings of the aromatic
boron reagent 5 with 10 and 9 catalyzed by (dppf)PdCl2 in
basic media give the desirable compounds of TPA3TPAN and
DTPA4TPAN, respectively. All compounds were characterized
by standard spectroscopic methods, from which satisfactory
analysis data corresponding to their molecular structures were
obtained (see Supporting Information for detail). The final
products give [M + H]+ and M+ peaks at m/z 1083.4620
(calcd: 1083.4427) and 1605.6542 (calcd: 1605.6478) in the
HRMS spectra for TPA3TPAN and DTPA4TPAN (Figures S3
and S4, Supporting Information), confirming the formation of
the expected adducts.
Intramolecular Charge Transfer. Combination of typical
electron-donating TPA and electron-accepting cyano groups
offers ready ICT process in TPA3TPAN and DTPA4TPAN.
Since photophysics of the D−A conjugates in solutions are
strongly dependent on the solvent polarity,29 we thus examined
the absorption and emission properties of both compounds in
varying solvents.
As depicted in Figure 1A,B, both compounds exhibit two
characteristic absorption bands in varying solvents, with
shorter/longer-wavelength absorptions of ∼318/390 and
∼326/390 nm for TPA3TPAN and DTPA4TPAN, respec-
tively, irrespective of the solvent polarity. The former band can
be ascribed to the π−π* transitions, whereas the latter is
assignable to the ICT between electron rich arylamine and
electron deficient cyano segments. Much longer π−π*
transition absorption wavelength of DTPA4TPAN than
TPA3TPAN suggests its longer effective conjugation length.
Luminogen Preparation. TPA-TPAN adducts were synthesized
according to the synthetic routes shown in Scheme 1. Detailed
synthetic procedures and characterization data are given in Supporting
Information.
1520
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
and DTPA4TPAN in varying solvents were calculated, and
their solvatochromic behaviors were quantitatively described by
the Lippert−Mataga equation:35
2Δf
Δν = ν − ν =
(μE − μG)2 + constant
a
e
hca3
(1)
where νa and νe represent the maximum absorbance and
emission wavenumbers, μG and μE are the dipole moments in
the ground and excited states, and h, c, a, and n are the Planck
constant, the speed of light, the Onsager solvent cavity radius,
and the refractive index of the solvent, respectively.
The orientational polarizability, Δf, described in eq 2, is
chosen as the measure of polarity.
ε − 1
2ε + 1
n2 − 1
Δf =
−
2n2 + 1
(2)
where ε is the static dielectric constant and n is the optical
refractive index of the solvent.
The linear dependence of Δν on Δf together with the large
slope of the Δν versus Δf plot (Figure 2) suggest that the ICT
Figure 1. Normalized (A, B) absorption and (C, D) emission spectra
of (A, C) TPA3TPAN and (B, D) DTPA4TPAN in varying solvents.
Concentration = 5 μM; excitation wavelength = 410 nm.
Their ICT absorptions, however, are similar due to almost
identical electron donating and accepting strengths.
The absorption profile and maxima of both compounds are
almost identical in varying solvents, suggesting their solvent
polarity independent ground state electronic structures and
small dipole moments associated with the ICT transitions.
Additionally, the optical band gaps (Egopt) deduced from the
onset absorptions in DCM are 2.6 and 2.5 eV for TPA3TPAN
and DTPA4TPAN, respectively, which are much narrower than
those of 2.84 and 2.82 eV for their 3TPETPA and 4TPEDTPA
congeners without cyano groups due to much stronger ICT
effect.27b
Emission spectra of TPA3TPAN and DTPA4TPAN
solutions are shown in Figure 1C,D. As the solvent polarity
increased from nonpolar toluene to moderately polar THF and
DCM and to highly polar DMF, the emission peaks are
gradually red-shifted (also see Table 1), exhibiting an obvious
bathochromic effect. The Stokes shifts (Δν) of TPA3TPAN
Figure 2. Plots of Stokes shift (Δν) of TPA3TPAN and
DTPA4TPAN vs solvent polarity parameter (Δf).
excited state has a larger dipolar moment than the ground state
due to the substantial charge redistribution, which is probably
derived from the relaxation of the initially formed Franck−
Condon excited state, instead of the direct transition from the
ground state. Meanwhile, according to Roncali and co-workers’
work, a stronger ICT effect might be achieved if more powerful
donor and acceptor moieties are adopted.5e,8d,e
Table 1. Photophysical Properties of TPA3TPAN and
a
DTPA4TPAN
solvent
Δf
λab (nm)
λem (nm)
Δν (cm−1
)
ΦF,s (%)
TPA3TPAN
The quantum efficiencies of the compounds in different
solvents are also determined. As summarized in Table 1, neither
of them emits effectively in solutions, which is similar to their
3TPETPA and 4TPEDTPA counterparts27b but distinctly
different from traditional D−A structured molecules. Normally,
D−A conjugates show weak or nonfluorescence in highly polar
solvents due to the fast interconversion from the emissive local
excited (LE) state to the low emissive ICT state; however, they
exhibit much stronger emission in nonpolar solvents or in the
solid state due to restricted ICT transitions.26,36 Herein,
TPA3TPAN and DTPA4TPAN are almost nonemissive in
varying solvents, regardless of the solvent polarity. Such
phenomenon should be ascribed to their strikingly twisted
molecular configurations, which undergo active rotations and
toluene
THF
0.014
0.210
0.218
0.275
318, 392
316, 388
318, 389
317, 389
529
598
614
651
6606.6
9050.8
9420.3
10346.0
0.061
0.225
0.232
0.041
DCM
DMF
DTPA4TPAN
toluene
THF
0.014
0.210
0.218
0.275
326, 391
325, 389
328, 389
329, 386
540
611
626
683
7056.9
9340.3
9732.5
11265.4
0.044
0.478
0.003
0.014
DCM
DMF
a
Abbreviation: Δf = solvent polarity parameters, λab = absorption
maximum, λem = emission maximum, ΦF,s = solution fluorescence
quantum yield estimated by using 9,10-diphenylanthracen as standard
(ΦF = 90% in cyclohexane).
1521
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
vibrations in solutions, thus resulting in fast nonradiative
relaxations and low emission quantum yields.26
aqueous media were conducted. Water is used because it is a
nonsolvent for the compounds: the luminogens must aggregate
in the aqueous mixtures with high water fractions (fw). As
shown in Figure 3, the PL intensities of TPA3TPAN and
DTPA4TPAN in THF are so low that only weak signals are
recorded with maxima at 598 and 611 nm, respectively. With
increasing fw, the PL intensities initially decrease due to the
increased solvent polarity37 and then start to increase at the fw
of 50% and 40% for TPA3TPAN and DTPA4TPAN,
respectively, at which solvating powers of the mixtures are
worsened to such an extent that the luminogen molecules begin
to aggregate. At a high fw of 90%, nanoaggregates are formed,
from which the PL peak intensities are increased by ∼19- and
∼14-fold when compared to their molecularly dispersed species
in THF for TPA3TPAN and DTPA4TPAN, respectively, thus
testifying to their AIE nature.
Aggregation-Induced Emission. As discussed above,
both TPA3TPAN and DTPA4TPAN are practically non-
emissive when molecularly dissolved in solvents due to active
intramolecular rotations and vibrations. It is known that TPE
derivatives display AIE behaviors through a restricted intra-
molecular rotation (RIR) mechanism.26 As a congener of TPE,
TPAN (Chart 2) is nonemissive in solvents, amorphous
Chart 2. Chemical Structures of TPE and TPAN
It is noticeable that both TPA and DTPA are ACQ
chromophores, whose emission efficiencies in solution and
thin film states are 13.0%/10.2% and 75.6%/13.7%, respecti-
vely.27b Decoration with TPAN changed their emission
behaviors from ACQ to AIE, which is of crucial importance
for the fabrication of high efficiency solid emitters.
Such an AIE attribute is also confirmed by the vivid image
contrast of the luminogens in varying solvents and as solid
powders. As depicted in Figure 4, neither TPA3TPAN nor
DTPA4TPAN is emissive in toluene, THF, DCM, and DMF,
but both emit intensely as aggregated solid powders. To
quantitatively evaluate the AIE effect of the luminogens, the
nanosuspensions, and as a solid solution on TLC plate but
highly fluorescent in the crystalline state (Figure S7, Supporting
Information), exhibiting crystallization-induced emission (CIE)
behaviors. The ΦF values of TPAN in THF and as crystalline
powders are 1.08% and 43.4%, respectively, giving a CIE factor
(αCIE = ΦF,c/ΦF,s) of 40.2 (Chart 2). Therefore, TPAN
decorated TPA3TPAN and DTPA4TPAN are expected to be
AIE- or CIE-active. To check it, emission spectra of
TPA3TPAN and DTPA4TPAN in THF and THF/water
Figure 3. PL spectra of (A) TPA3TPAN and (C) DTPA4TPAN in THF and THF/water mixtures. Plots of PL peak location and intensity vs water
fraction (fw) for (B) TPA3TPAN and (D) DTPA4TPAN. Concentration = 5 μM; excitation wavelength = 380 nm. The inset graphs in (B) and (D)
are the solutions of TPA3TPAN and DTPA4TPAN in THF (fw = 0%) and their suspensions in THF/water mixture with fw = 90% under UV
illumination.
1522
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
reversely giving blue-shifted emissions. DTPA4TPAN behaves
similarly to TPA3TPAN. As shown in Figure 4B, when fw is
increased from 0 to 30% and then to 90%, the emission peak is
first slightly red-shifted from 611 to 620 nm and then greatly
blue-shifted to 576 nm.
To better understand the AIE nature of TPA3TPAN and
DTPA4TPAN, quantum chemical optimization on their energy
levels based on DFT/B3LYP/6-31G(d) using Gaussian 09 was
conducted. The optimized geometries and HOMO/LUMO
plots of TPA3TPAN and DTPA4TPAN are illustrated in
Figure 6. Both molecules adopt highly twisted propeller-like
Figure 4. Photographs of (upper) TPA3TPAN and (lower)
DTPA4TPAN in toluene, THF, DCM, and DMF and as solid
powders under 365 nm UV light illumination.
thin-film emission spectra and quantum efficiencies (ΦF,f) were
determined. While TPA3TPAN displays a broad emission with
the maximum at 563 nm, DTPA4TPAN exhibits the shoulder
and peak emissions at 546 and 581 nm (Figure 5). The ΦF,f
Figure 6. Optimized geometries and molecular orbital amplitude plots
of HOMO and LUMO energy levels of TPA3TPAN and
DTPA4TPAN.
nonplanar conformations, which are favorable for active
intramolecular rotations of multiple phenyls and cyano groups
in solutions, thereby powerfully dissipating the excitons energy
and making them nonemissive in all solvents. Such emission
behavior is strikingly different from that of conventional ICT
systems, which are normally nonfluorescent in highly polar
solvents but intensely emissive in nonpolar solvents. When
aggregated as nanosuspensions, solid powders, or thin films, on
one hand, the intramolecular rotations are impeded; on the
other hand, the propeller-like configurations prevent the
formation of detrimental excimers or exciplexes, thus endowing
the aggregates with intense emission. Meanwhile, in polar
solvents such as THF, DCM, and DMF, aggregation also
partially restrains the ICT process, which is also helpful for the
light emission.
Notably, the electron clouds of the HOMO levels for both
luminogens are mainly located on the electron-donating TPA
and DTPA units; however, those of LUMO levels are
dominated by orbitals from the electron-accepting TPAN
peripheries. Generally, such electron distribution imparts the
dye molecules with an intrinsic intramolecular charge transfer
property, which is consistent with the experimental data.
Meanwhile, despite different molecular structures and HOMO
levels, TPA3TPAN and DTPA4TPAN have almost identical
LUMO levels with electron clouds distributed on two TPAN
units connecting with one TPA moiety, indicative that their
differences in ICT property inherently lies in the electron
donor segments.
Figure 5. Film emission spectra of TPA3TPAN and DTPA4TPAN.
Excitation wavelength = 390 nm. The inset graph is the TPA3TPAN
thin film under 365 nm UV light illumination.
values are determined to be 33.2% and 38.2% for TPA3TPAN
and DTPA4TPAN, respectively, which are considerably
boosted compared to those in solutions, giving AIE factors
(α = ΦF,f/ΦF,s) of 147.6 and 79.7 with respect to those in THF.
It is also noted that the emission peak varies with fw. For
example, with increasing fw, the emission peak of TPA3TPAN
is initially red-shifted until fw reaches 40%, then remarkably
blue-shifted, giving the emission peak from 598 to 622 nm,
then to 558 nm when fw is increased from 0 to 40%, and finally
to 90% (Figure 3B). Such spectral shift can be explained as
follows: when fw is no more than 40%, TPA3TPAN molecules
are still genuinely dissolved in the mixtures, and increasing fw
enhances the mixture polarity, consequently generating red-
shifted emission due to the ICT effect; however, as fw reaches
50%, owing to the decreased mixture solvating power,
TPA3TPAN molecules start to aggregate, resulting in less
polar microenvironment for the luminogens due to self-
wrapping. The microenvironment gets less and less polar
with more serious aggregation caused by increased fw, thus
Electrochemical Property. Electrochemical properties of
TPA3TPAN and DTPA4TPAN are investigated by cyclic
voltammetry in 0.1 M solution of (Bu4N)PF6 in DCM with a
1523
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
glassy carbon electrode as the working electrode. As shown in
Figure 7, both compounds show reversible p-doping processes.
Figure 8. TGA and DSC (inset) thermograms of TPA3TPAN and
DTPA4TPAN recorded under nitrogen at the scan rates of 20 and 10
°C/min, respectively.
Figure 7. Cyclic voltammograms of TPA3TPAN and DTPA4TPAN in
DCM with 0.1 M Bu4NPF6 as a supporting electrolyte at a scan rate of
100 mV/s.
V, emits at 556 and 575 nm, and exhibits maximum luminance
(Lmax), current, power, and external quantum efficiencies
(CEmax, PEmax, EQE) of 1867 cd/m2, 2.45 cd/A, 0.48 lm/W,
and 0.79%, respectively. Though the result is fair, it already
demonstrates the potential applications of TPA3TPAN in
OLEDs. Since the cyano group is a strong electron withdrawing
group, it is suspected that TPA3TPAN may have good
electron-transporting property. Therefore, we fabricated a
double-layer EL devices without electron-transporting TPBi
with the configuration of ITO/NPB (60 nm)/TPA3TPAN (60
nm)/LiF (1 nm)/Al (100 nm) (device II). While the EL
spectrum profile of the device is almost identical to that of
device I (Figure 9A), its performance gets even worse with the
turn-on voltage (Von), Lmax, CEmax, PEmax, and EQE being 8.0 V,
572 cd/m2, 0.35 cd/A, 0.12 lm/W, and 0.13%, respectively. It is
understandable that the device without the TPBi layer is not
efficient because of quenching at the cathode. The result
strongly suggests that an additional electron-transporting layer
is beneficial to the device performance of TPA3TPAN, though
electron deficient cyano groups are incorporated.
TPA derivatives are well-known hole-transporting materi-
als.39 Our previous studies have shown that TPA-containing
AIE luminogens exhibit excellent hole-transporting property,
whose EL devices without the hole-transporting NPB layer
perform even better than those with.27b,40 To improve the
device performance, we thus newly fabricated a device without
NPB with a configuration of ITO/TPA3TPAN (80 nm)/TPBi
(40 nm)/LiF (1 nm)/Al (100 nm) (device III). The EL results
are displayed in Figure 9 and are summarized in Table 2.
Apparently, device III performs best, whose maximal luminance
and efficiencies are remarkably improved when compared to
devices I and II, giving Lmax, CEmax, PEmax, and EQE of 3101
cd/m2, 6.16 cd/A, 2.64 lm/W, and 2.78%, respectively. Such
good result indicates that TPA3TPAN is not only a good EL
emitter but also an excellent hole-transporting material. The
use of NPB as an additional hole-transporting layer is thus not
necessary and could be even harmful because it increases the
contact impedance and also may break the charge balance in
the EL device.
While TPA3TPAN exhibits only one oxidation peak,
DTPA4TPAN shows two peaks associated to the formation
of radical cations and dications. The onset oxidation potentials
(Eonset‑ox) for TPA3TPAN, DTPA4TPAN, and ferrocene are
0.75, 0.66, and 0.33 eV, giving corresponding HOMO levels for
the luminogens of −5.2 and −5.1 eV, respectively. The slightly
lower Eonset‑ox of DTPA4TPAN compared to TPA3TPAN is
presumably due to the more extensively delocalized HOMO
structure (Figure 6). Together with the optical band gaps
(Egopt) deduced from the onset absorptions in DCM, the same
LUMO energy levels of −2.6 eV are derived for both
luminogens, which is in good agreement with the above
calculation result.
Thermal Properties. Excellent thermal stability is highly
desired for the device fabrication and optoelectronic
applications for molecular conjugates. Particularly, Tg of an
organic luminophore is one of the most important factors
influencing the device stability and lifetime.38 Once a device is
heated above Tg of the organic luminophores, irreversible
failure can occur. Therefore, we checked the thermal property
of TPA3TPAN and DTPA4TPAN by thermogravimetric
analysis (TGA) and differential scanning calorimetry (DSC)
measurements. As shown in Figure 8, both TPA3TPAN and
DTPA4TPAN enjoy high thermal stability with Td (defined as
the temperature at which a sample loses its 5% weight) values
of 365 and 377 °C, respectively. DSC analysis reveals the Tg’s
for TPA3TPAN and DTPA4TPAN are 127 and 141 °C,
respectively, indicating excellent morphological stability of both
compounds. Coupled with their efficient solid-state emissions,
the dye molecules thus are promising candidates for such
optoelectronic applications as EL emitters.
Electroluminescence. The high solid-state emission
efficiency and good thermal and morphological stability of
TPA3TPAN and DTPA4TPAN promoted us to investigate
their EL performances. We first constructed a typical three-
layer EL device with the configuration of ITO/NPB (60 nm)/
TPA3TPAN (20 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100
nm) (device I) using TPA3TPAN as a light-emitting layer
(LEL). As illustrated in Figure 9, the device is turned on at 8.9
Herein, without an additional NPB layer, the contact
resistance and energy barrier are lowered (Figure S8,
Supporting Information). Moreover, excessive hole-injection
1524
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
Figure 9. (A) EL spectra of TPA3TPAN and DTPA4TPAN, (B) current density−voltage−luminance plots, (C) current efficiency−voltage−power
efficiency plots, and (D) external quantum efficiency−voltage plots of their multilayer LEDs with a general device configuration of ITO/X/LiF/Al.
As an analogue of TPA3TPAN, DTPA4TPAN may have
similar optoelectronic properties; we thus fabricated device IV
using DTPA4TPAN as the emitting layer without NPB with
the architecture of ITO/DTPA4TPAN (20 nm)/TPBi (40
nm)/LiF (1 nm)/Al (100 nm). The EL spectrum of device IV
peaks at 558 and 582 nm. However, the device performance is
far from ideal; the CEmax, PEmax, and EQE are merely 0.35 cd/
A, 0.06 lm/W, and 0.14%, respectively, presumably caused by
the high evaporation temperature induced destruction of
DTPA4TPAN (high evaporation temperature of 320−370
°C). Notably, DTPA4TPAN shows good film-forming ability;
thus, its solution casting OLED devices may achieve better
performances. And we will try such solution processable
molecular devices in future.
Table 2. Performance of the EL Devices of TPA3TPAN and
DTPA4TPAN
a
λmax
(nm)
Von
(V)
Lmax (cd/ PEmax (lm/ CEmax (cd/
EQE
(%)
device
m2)
W)
A)
I
556, 575
561, 579
580
8.9
8.0
7.4
1867
572
0.48
0.12
2.64
0.06
2.45
0.35
6.16
0.35
0.79
0.13
2.18
0.14
II
III
IV
3101
387
558, 582 11.0
a
Device configuration: ITO/X/LiF (1 nm)/Al (100 nm); X = NPB
(60 nm)/TPA3TPAN (20 nm)/TPBi (40 nm) (device I), NPB (60
nm)/TPA3TPAN (60 nm) (device II), TPA3TPAN (80 nm)/TPBi
(40 nm) (device III), DTPA4TPAN (20 nm)/TPBi (40 nm) (device
IV); abbreviations: λ = EL peak, Von = turn on voltage, Lmax
=
maximum luminance, PEmax = maximum power efficiency, CEmax
=
maximum current efficiency, and EQE = maximum external quantum
efficiency.
CONCLUSIONS
■
A combination of electron-donating arylamines (TPA, DTPA)
and electron-accepting TPAN with propeller-like configurations
yields TPA3TPAN and DTPA4TPAN with typical D−A
architectures. Both compounds show bathochromic shift in
varying solvents due to the ICT effect. Moreover, decoration of
TPA and DTPA with TPAN changed their emission behaviors
from ACQ to AIE: while TPA and DTPA are subject to an
ACQ problem in the solid state, the resulting TPA3TPAN and
DTPA4TPAN are practically nonluminescent when molecu-
larly dissolved in solvents but emit intensely upon aggregate
formation, demonstrating a typical AIE feature. Owing to the
combined ICT and AIE attributes, their nanoaggregates, solid
powders, and thin films emit yellow light intensely, with the
thin film quantum efficiencies of 33.2% and 38.2% for
TPA3TPAN and DTPA4TPAN, respectively. Both luminogens
is eliminated to reach a much better charge balance in the
emitting layers, thus giving excellent EL performance. There-
fore, TPA3TPAN can serve as an emissive component as well
as hole-transport material in the EL devices. The multifunc-
tional property of TPA3TPAN helps to simplify the device
structure, shorten the fabrication process, reduce the
production cost, and moreover enhance the device perform-
ance.21a,27b,41 It is also notable that the EL devices of
TPA3TPAN are unoptimized; thus, much better performance
including the brightness and efficiency could be achieved
through further optimizations as interlayer and anode
modifications, tuning drift mobility, charge balance, and other
engineering efforts.42
1525
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
2011, 23, 3805. (c) Jenekhe, S. A.; Lu, L.; Alam, M. M. Macromolecules
2001, 34, 7315. (d) Zhu, Y.; Champion, R. D.; Samson, A.
Macromolecules 2006, 39, 8712.
(4) (a) Shirota, Y. J. Mater. Chem. 2005, 15, 75. (b) Justin Thomas,
K. R.; Lin, J. T.; Tao, Y.-T.; Chuen, C.-H. Chem. Mater. 2004, 16,
5437. (c) Thomas, K. R.; Lin, J. R.; Velusamy, M.; Tao, Y.-T.; Chuen,
C.-H. Adv. Funct. Mater. 2004, 14, 83.
enjoy high thermal stability (Td ≥ 365 °C) and are
morphologically stable (Tg ≥ 127 °C). An unoptimized EL
device with the configuration of ITO/TPA3TPAN/TPBi/LiF/
Al is constructed, which gives efficient yellow EL with
maximum luminance and efficiencies of 3101 cd/m2, 6.16 cd/
A, 2.64 lm/W, and 2.18%.
Unlike traditional D−A structured ICT systems, which are
either subjected to a serious ACQ problem or only selectively
AIE-active in highly polar solvents, TPA3TPAN and
DTPA4TPAN exhibit typical AIE behaviors in all solvents.
The present results indicate that the combination of electron
donors and propeller TPAN acceptors is a promising approach
to generate AIE-ICT luminogens with efficient solid emissions
and tunable emission colors. Further modulation of the donor
and acceptor strengths is expected to generate more AIE
luminogens with tunable emissions and multifunctional proper-
ties.
(5) (a) Cremer, J.; Bauerle, P. J. Mater. Chem. 2006, 16, 874.
(b) Roquet, S.; Cravino, A.; Leriche, P.; Aleveque, O.; Frere, P.;
́ ̂ ̀
̈
Roncali, J. J. Am. Chem. Soc. 2006, 128, 3459. (c) Esteban, S. G.; de la
Cruz, P.; Aljarilla, A.; Arellano, L. M.; Langa, F. Org. Lett. 2011, 13,
5362. (d) Lin, L.-Y.; Chen, Y.-H.; Huang, Z.-Y.; Lin, H.-W.; Chou, S.-
H.; Lin, F.; Chen, C.-W.; Liu, Y.-H.; Wong, K.-T. J. Am. Chem. Soc.
2011, 133, 15822. (e) Roncali, J. Adv. Energy Mater. 2011, 1, 147.
(f) Zhang, X.; Shim, J. W.; Tiwari, S. P.; Zhang, Q.; Norton, J. E.; Wu,
P.-T.; Barlow, S.; Jenekhe, S. A.; Kippelen, B.; Bred
́
as, J.-L.; Marder, S.
R. J. Mater. Chem. 2011, 21, 4971.
(6) (a) Noh, S. B.; Kim, R. H.; Kim, W. J.; Kim, S.; Lee, K.-S.; Cho,
N. S.; Shim, H.-K.; Pudavar, H. E.; Prasad, P. N. J. Mater. Chem. 2010,
20, 7422. (b) Jiang, Y.; Wang, Y.; Hua, J.; Tang, J.; Li, B.; Qian, S.;
Tian, H. Chem. Commun. 2010, 46, 4689. (c) Wang, B.; Wang, Y.;
Hua, J.; Jiang, Y.; Huang, J.; Qian, S.; Tian, H. Chem.Eur. J. 2011,
17, 2647.
(7) (a) He, G. S.; Xu, G. C.; Prasad, P. N.; Reinhardt, B. A.; Bhatt, J.
C.; Dillard, A. G. Opt. Lett. 1995, 20, 435. (b) Lin, T.-C.; He, G. S.;
Zheng, Q.; Prasad, P. N. J. Mater. Chem. 2006, 16, 2490.
(8) (a) Blouin, N.; Michaud, M.; Gendron, D.; Wakim, S.; Blair, E.;
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthetic procedures and characterization data, HRMS spectra
of important intermediates (5 and 9), TPA3TPAN, and
DTPA4TPAN, absorption and emission spectra of TPA,
DTPA, and TPAN, emission spectra of TPAN in THF and
THF/water aqueous mixtures, photographs and XRD pattern
of TPAN, time-resolved fluorescence plots, and energy level
diagrams of the EL devices (PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
̂
Neagu-Plesu, R.; Belletete, M.; Durocher, G.; Tao, Y.; Leclerc, M. J.
Am. Chem. Soc. 2008, 130, 732. (b) Zhang, Q. T.; Tour, J. M. J. Am.
Chem. Soc. 1998, 120, 5355. (c) Ajayaghosh, A. Chem. Soc. Rev. 2003,
32, 181. (d) Cravino, A.; Leriche, P.; Alev
Roncali, J. Adv. Mater. 2006, 18, 3033. (e) Roquet, S.; Cravino, A.;
Leriche, P.; Aleveque, O.; Frere, P.; Roncali, J. J. Am. Chem. Soc. 2006,
128, 3459.
́ ̂
eque, O.; Roquet, S.;
AUTHOR INFORMATION
Corresponding Author
*E-mail: tangbenz@ust.hk. Phone: +852-2358-7375. Fax:
+852-2358-1594.
■
́
̂
̀
(9) (a) Mallick, A.; Haldar, B.; Chattopadhyay, N. J. Phys. Chem. B
2005, 109, 14683. (b) Singh, R. B.; Mahanta, S.; Guchhait, N.
Spectrochim. Acta, Part A 2009, 72, 1103.
Notes
(10) (a) Thompson, B. C.; Frechet, J. M. J. Angew. Chem., Int. Ed.
2008, 47, 58. (b) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev.
2009, 109, 5868. (c) Kim, F. S.; Ren, G.; Jenekhe, S. A. Chem. Mater.
2011, 23, 682. (d) Osaka, I.; Sauve, G.; Zhang, R.; Kowalewski, T.;
McCullough, R. D. Adv. Mater. 2007, 19, 4160. (e) Osaka, I.;
Takimiya, K.; McCullough, R. D. Adv. Mater. 2010, 22, 4993.
(11) (a) Peumans, P.; Forrest, S. R. Appl. Phys. Lett. 2001, 79, 126.
(b) Peumans, P.; Yakimov, A.; Forrest, S. R. J. Appl. Phys. 2003, 93,
3693. (c) Roquet, S.; Cravino, A.; Leriche, P.; Aleveque, O.; Frere, P.;
Roncali, J. J. Am. Chem. Soc. 2006, 128, 3459.
(12) (a) Belfield, K. D.; Liu, Y.; Negres, R. A.; Fan, M.; Pan, G.;
Hagan, D. J.; Hernandez, F. E. Chem. Mater. 2002, 14, 3663.
(b) Bhawalkar, J. D.; He, G. S.; Park, C. K.; Zhao, C. F.; Ruland, G.;
Prasad, P. N. Opt. Commun. 1996, 124, 33. (c) He, G. S.; Helgeson, R.;
Lin, T. C.; Zheng, Q.; Wudl, F.; Prasad, P. N. IEEE J. Quantum
Electron. 2003, 39, 1003. (d) He, G. S.; Bhawalkar, J. D.; Zhao, C. F.;
Prasad, P. N. Appl. Phys. Lett. 1995, 67, 2433.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work reported in this paper was partially supported by the
National Science Foundation of China (21104044, 20974028),
the RPC and SRFI Grants of HKUST (RPC10SC13,
RPC11SC09, and SRFI11SC03PG), the Research Grants
Council of Hong Kong (604711, 603509, HKUST2/CRF/10,
and N_HKUST620/11), the Innovation and Technology
Commission (ITCPD/17-9), and the University Grants
Committee of Hong Kong (AoE/P-03/08 and T23-713/11-
1). B.Z.T. thanks the support from the Cao Guangbiao
Foundation of Zhejiang University. W.Z.Y. thanks the support
from Ph.D. Programs Foundation of Ministry of Education of
China (20110073120040) and the Start-up Foundation for
New Faculties of Shanghai Jiao Tong University.
(13) (a) Kim, E.; Park, S. B. Chem. Asian J. 2009, 4, 1646. (b) Qian,
F.; Zhang, C.; Zhang, Y.; He, W.; Gao, X.; Hu, P.; Guo, Z. J. Am.
Chem. Soc. 2009, 131, 1460.
REFERENCES
■
(14) (a) Benjelloun, A.; Brembilla, A.; Lochon, P.; Adibnejad, M.;
(1) (a) Bryce, M. R. Adv. Mater. 1999, 11, 11. (b) Grabowski, Z. R.;
Rotkiewicz, K. Chem. Rev. 2003, 103, 3899.
Viriot, M.-L.; Carre,
P.; Mely, Y.; Duportail, G.; Klymchenko, A. S. Biophys. J. 2009, 96,
3461.
́
M.-C. Polymer 1996, 37, 879. (b) Demchenko, A.
́
(2) (a) Wu, P.-T.; Kim, F. S.; Jenekhe, S. A. Chem. Mater. 2011, 23,
4618. (b) Ahmed, E.; Subramaniyan, S.; Kim, F. S.; Xin, H.; Jenekhe,
S. A. Macromolecules 2011, 44, 7207. (c) Kim, F. S.; Guo, X.; Watson,
M. D.; Jenekhe, S. A. Adv. Mater. 2010, 22, 478.
(3) (a) Ahmed, J. E.; Ren, G.; Kim, F. S.; Emily C. Hollenbeck, E. C.;
Jenekhe, S. A. Chem. Mater. 2011, 23, 4563. (b) Ellinger, S.; Graham,
K. R.; Shi, P.; Farley, R. T.; Steckler, T. T.; Brookins, R. N.; Taranekar,
P.; Mei, J.; Padilha, L. A.; Ensley, T. R.; Hu, H.; Webster, S.; Hagan, D.
J.; Van Stryland, E. W.; Schanze, K. S.; Reynolds, J. R. Chem. Mater.
(15) (a) Sauer, M. Angew. Chem., Int. Ed. 2003, 42, 1790. (b) Wilson,
J. N.; Bunz, U. H. F. J. Am. Chem. Soc. 2005, 127, 4124. (c) Aoki, S.;
Kagata, D.; Shiro, M.; Takeda, K.; Kimura, E. J. Am. Chem. Soc. 2004,
126, 13377. (d) Suzuki, Y.; Yokoyama, K. J. Am. Chem. Soc. 2005, 127,
17799. (e) Das, R.; Guha, D.; Mitra, S.; Kar, S.; Lahiri, S.; Mukherjee,
S. J. Phys. Chem. A 1997, 101, 4042. (f) Valeura, B.; Leraya, I. Coord.
Chem. Rev. 2000, 205, 3.
1526
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
(16) (a) Fang, H. H.; Chen, Q. D.; Yang, J.; Xia, H.; Gao, B. R.; Feng,
J.; Ma, Y.; Sun, H. B. J. Phys. Chem. C 2010, 114, 11958. (b) Fang, H.
H.; Chen, Q. D.; Yang, J.; Xia, H.; Ma, Y.; Wang, H. Y.; Sun, H. B. Opt.
Lett. 2010, 35, 441. (c) Kim, S.; Zheng, Q.; He, G. S.; Bharali, D. J.;
Pudavar, H. E.; Baev, A.; Prasad, P. N. Adv. Funct. Mater. 2006, 16,
2317.
(17) (a) Qian, G.; Zhong, Z.; Luo, M.; Yu, D.; Zhang, Z.; Wang, Z.
Y.; Ma, D. Adv. Mater. 2009, 21, 111. (b) Velusamy, M.; Justin
Thomas, K. R.; Lin, J. T.; Wen, Y. S. Tetrahedron Lett. 2005, 46, 7647.
(c) Kato, S.; Matsumoto, T.; Ishi, T.; Thiemann, T.; Shigeiwa, M.;
Gorohmaru, H.; Maeda, S.; Yamashita, Y.; Mataka, S. Chem. Commun.
2004, 2342.
(18) (a) Chen, Q. D.; Fang, H. H.; Xu, B.; Yang, J.; Xia, H.; Chen, F.
P.; Tian, W. J.; Sun, H. B. Appl. Phys. Lett. 2009, 94, 201113. (b) He,
G. S.; Lin, T. C.; Hsiao, V. K. S.; Cartwright, A. N.; Prasad, P. N.;
Natarajan, L. V.; Tondiglia, V. P.; Jakubiak, R.; Vaia, R. A.; Bunning, T.
J. Appl. Phys. Lett. 2003, 83, 2733. (c) Tang, X. J.; Wu, L. Z.; Zhang, L.
P.; Tung, C. H. Chem. Phys. Lett. 2002, 356, 573. (d) Fang, H.-H.;
Chen, Q.-D.; Yang, J.; Xia, H.; Ma, Y.-G.; Wang, H.-Y.; Sun, H.-B. Opt.
Lett. 2010, 35, 441.
(19) (a) Jiang, Y.; Wang, Y.; Wang, B.; Yang, J.; He, N.; Qian, S.;
Hua, J. Chem. Asian J. 2011, 6, 157. (b) He, G. S.; Lin, T. C.; Prasad, P.
N.; Cho, C. C.; Yu, L. J. Appl. Phys. Lett. 2003, 82, 4717.
(20) (a) Parthenopoulos, D. A.; Rentzepis, P. M. Science 1989, 245,
843. (b) Strickler, J. H.; Webb, W. W. Opt. Lett. 1991, 16, 1780.
(c) Belfield, K. D.; Schafer, K. J. Chem. Mater. 2002, 14, 3656.
(d) Belfield, K. D.; Liu, Y.; Negres, R. A.; Fan, M.; Pan, G.; Hagan, D.
J.; Hernandez, F. E. Chem. Mater. 2002, 14, 3663.
(21) (a) Tao, S.; Li, L.; Yu, J.; Jiang, Y.; Zhou, Y.; Lee, C.-S.; Lee, S.-
T.; Zhang, X.; Kwon, O. Chem. Mater. 2009, 21, 1284. (b) Patra, A.;
Pan, M.; Friend, C. S.; Lin, T.-C.; Cartwright, A. N.; Prasad, P. N.;
Burzynski, R. Chem. Mater. 2002, 14, 4044. (c) Hancock, J. M.;
Gifford, A. P.; Zhu, Y.; Lou, Y.; Jenekhe, S. A. Chem. Mater. 2006, 18,
4924. (d) Kulkarni, A. P.; Zhu, Y.; Babel, A.; Wu, P.-T.; Jenekhe, S. A.
Chem. Mater. 2008, 20, 4212. (e) Thomas, K. R. J.; Lin, J. T.; Tao, Y.-
T.; Chuen, C.-H. Chem. Mater. 2002, 14, 3852. (f) Huang, J.; Su, J.-H.;
Li, X.; Lam, M.-K.; Fung, K.-M.; Fan, H.-H.; Kok-Wai Cheah, K.-W.;
Chen, C. H.; Tian, H. J. Mater. Chem. 2011, 21, 2957.
F.; Lam, J. W. Y.; Sun, J. Z.; Tang, B. Z. Macromolecules 2009, 42,
9400.
(27) (a) Zhao, Z.; Wang, Z.; Lu, P.; Chan, C. Y. K.; Liu, D.; Lam, J.
W. Y.; Sung, H. H. Y.; Williams, I. D.; Ma, Y.; Tang, B. Z. Angew.
Chem., Int. Ed. 2009, 48, 7608. (b) Yuan, W. Z.; Lu, P.; Chen, S.; Lam,
J. W. Y.; Wang, Z.; Liu, Y.; Kowk, H. S.; Ma, Y.; Tang, B. Z. Adv.
Mater. 2010, 22, 2159. (c) Zeng, Q.; Li, Z.; Dong, Y.; Di, C.; Qin, A.;
Hong, Y.; Ji, L.; Zhu, Z.; Jim, C. K. W.; Yu, G.; Li, Q.; Li, Z.; Liu, Y.;
Qin, J.; Tang, B. Z. Chem. Commun. 2007, 70. (d) Dong, S.; Li, Z.;
Qin, J. J. Phys. Chem. B 2009, 113, 434. (e) Yuan, W. Z.; Chen, S.;
Lam, J. W. Y.; Deng, C.; Lu, P.; Sung, H. H-Y.; Williams, I. D.; Kwok,
H. S.; Zhang, Y.; Tang, B. Z. Chem. Commun. 2011, 47, 11216.
(f) Yuan, W. Z.; Yu, Z.-Q.; Tang, Y.; Lam, J. W. Y.; Xie, N.; Lu, P.;
Chen, E.-Q.; Tang., B. Z. Macromolecules 2011, 44, 9618.
(28) (a) Yuan, W. Z.; Mahtab, F.; Gong, Y.; Yu, Z.; Lu, P.; Tang, Y.;
Lam, J. W. Y.; Zhu, C.; Tang, B. Z. J. Mater. Chem. 2012,
DOI: 10.1039/c2jm30620d. (b) Yang, Z.; Chi, Z.; Yu, T.; Zhang,
X.; Chen, M.; Xu, B.; Liu, S.; Zhang, Y.; Xu, J. J. Mater. Chem. 2009,
19, 5541. (c) An, B.-K.; Gihm, S. H.; Chung, J. W.; Park, C. R.; Kwon,
S.-K.; Park, S. Y. J. Am. Chem. Soc. 2009, 131, 3950. (d) Yoon, S.-J.;
Park, S. Y. J. Mater. Chem. 2011, 21, 8338. (e) Wang, M.; Zhang, G.;
Zhang, D.; Zhu, D.; Tang, B. Z. J. Mater. Chem. 2010, 20, 1858.
(f) Wang, M.; Zhang, D.; Zhang, G. X.; Zhu, D. B. Chem. Commun.
2008, 4469. (g) Han, T.; Feng, X.; Tong, B.; Shi, J.; Chen, L.; Zhi, J.;
Dong, Y. Chem. Commun. 2012, 48, 416. (h) Yuan, W. Z.; Yu, Z.-Q.;
Lu, P.; Deng, C.; Lam, J. W. Y.; Wang, Z.; Chen, E.-Q.; Ma, Y.; Tang,
B. Z. J. Mater. Chem. 2012, 22, 3323. (i) Yuan, W. Z.; Shen, X. Y.;
Zhao, H.; Lam, J. W. Y.; Tang, L.; Lu, P.; Wang, C.; Liu, Y.; Wang, Z.;
Zheng, Q.; Sun, J. Z.; Ma, Y.; Tang, B. Z. J. Phys. Chem. C 2010, 114,
6090.
(29) (a) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.;
Springer: New York, U.S.A., 2006; Chapter 6, pp 205−235. (b) Jones,
G., II; Jackson, W. R.; Choi, C. Y.; Bergmark, W. R. J. Phys. Chem.
1985, 89, 294. (c) Kosower, E. M.; Dodiuk, H.; Kanety, H. J. Am.
Chem. Soc 1978, 100, 4179.
(30) (a) Palayangoda, S. S.; Cai, X.; Adhikari, R. M.; Neckers, D. C.
Org. Lett. 2008, 10, 281. (b) Liu, Y.; Tao, X.; Wang, F.; Dang, X.; Zou,
D.; Ren, Y.; Jiang, M. J. Phys. Chem. C 2008, 112, 3975. (c) Xu, J.; Liu,
X.; Lv, J.; Zhu, M.; Huang, C.; Zhou, W.; Yin, X.; Liu, H.; Li, Y.; Ye, J.
Langmuir 2008, 24, 4231. (d) Yeh, H.-C.; Yeh, S.-J.; Chen, C.-T.
Chem. Commun. 2003, 2632.
(31) (a) Gao, B.-R.; Wang, H.-Y.; Yang, Z.-Y.; Wang, H.; Wang, L.;
Jiang, Y.; Hao, Y.-W.; Chen, Q.-D.; Li, Y.-P.; Ma, Y.-G.; Sun, H.-B. J.
Phys. Chem. C 2011, 115, 16150. (b) Gao, B.-R.; Wang, H.-Y.; Hao, Y.-
W.; Fu, L.-M.; Fang, H.-H.; Jiang, Y.; Wang, L.; Chen, Q.-D.; Xia, H.;
Pan, L.-Y.; Ma, Y.-G.; Sun, H.-B. J. Phys. Chem. B 2010, 114, 128.
(32) (a) Peng, X.; Song, F.; Lu, E.; Wang, Y.; Zhou, W.; Fan, J.; Gao,
Y. J. Am. Chem. Soc. 2005, 127, 4170. (b) Zaheer, A.; Lenkinskl, R. E.;
Mahmood, A.; Jones, A. G.; Cantley, L. C.; Frangioni, J. V. Nat.
Biotechnol. 2001, 19, 1148.
(22) Lee, W.-Y.; Wang, T.-F.; Chueh, C.-C.; Chen, W.-C.; Tuan, C.-
S.; Lin, J.-J. Macromol. Chem. Phys. 2007, 208, 1919.
(23) (a) Birks, J. B. Photophysics of Aromatic Molecules; Wiley:
London, U.K., 1970. (b) Capek, I. Adv. Colloid Interface Sci. 2002, 97,
91. (c) Mancin, F.; Scrimin, P.; Tecilla, P.; Tonellato, U. Coord. Chem.
Rev. 2009, 253, 2150.
(24) (a) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. Rev.
2007, 107, 1339. (b) Shih, P.-I.; Chiang, C.-L.; Dixit, A. K.; Chen, C.-
K.; Yuan, M.-C.; Lee, R.-Y.; Chen, C.-T.; Diau, E. W.-G.; Shu, C.-F.
Org. Lett. 2006, 8, 2799. (c) Chen, C.-T. Chem. Mater. 2004, 16, 4389.
(25) (a) Swager, T. M. Acc. Chem. Res. 2008, 41, 1181. (b) Grimsdale,
A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B. Chem.
Rev. 2009, 109, 897. (c) Lee, S. H.; Jang, B. B.; Kafafi, Z. H. J. Am.
Chem. Soc. 2005, 127, 9071. (d) Marsitzky, D.; Vestberg, R.; Blainey,
P.; Tang, B. T.; Hawker, C. J.; Carter, K. R. J. Am. Chem. Soc. 2001,
123, 6965. (e) Setayesh, S.; Grimsdale, A. C.; Weil, T.; Enkelmann, V.;
Muellen, K.; Meghdadi, F.; List, E. J. W.; Leising, G. J. Am. Chem. Soc.
2001, 123, 946. (f) Chiang, C.-L.; Tseng, S.-M.; Chen, C.-T.; Hsu, C.-
P.; Shu, C.-F. Adv. Funct. Mater. 2008, 18, 248. (g) Hecht, S.; Frechet,
J. M. J. Angew. Chem., Int. Ed. 2001, 40, 74. (h) Tang, C. W.; Vanslyke,
S. A.; Chen, C. H. J. Appl. Phys. 1989, 65, 3610. (i) Bulovic, V.;
Shoustikov, A.; Baldo, M. A.; Bose, E.; Kozlov, V. G.; Thompson, M.
E.; Forrest, S. R. Chem. Phys. Lett. 1998, 287, 455. (j) Xia, Z.-Y.; Su, J.-
H.; Fan, H.-H.; Cheah, K.-W.; Tian, H.; Chen, C. H. J. Phys. Chem. C
2010, 114, 11602.
(33) Haussler, M.; Liu, J.; Zheng, R.; Lam, J. W. Y.; Qin, A.; Tang, B.
̈
Z. Macromolecules 2007, 40, 1914.
(34) (a) Wang, S.; Oldham, W. J., Jr.; Hudack, R. A., Jr.; Bazan, G. C.
J. Am. Chem. Soc. 2000, 122, 5695. (b) Gilbert, J.; Miquel, J.-F.;
Precigoux, G.; Haospital, M.; Raynaud, J.-P.; Michel, F.; de Paulet, A.
́
C. J. Med. Chem. 1983, 26, 693.
(35) (a) Lippert, E. Z. Naturforsch. A: Phys. Sci. 1955, 10, 541.
(b) Mataga, N.; Kaifu, Y.; Koizumi, M. Bull. Chem. Soc. Jpn. 1956, 29,
465.
(36) Hu, R.; Lager, E.; Aguilar-Aguilar, A.; Liu, J.; Lam, J. W. Y.;
Sung, H. H.-Y.; Williams, I. D.; Zhong, Y.; Wong, K. S.; Pena-Cabrera,
̃
E.; Tang, B. Z. J. Phys. Chem. C 2009, 113, 15845.
(37) Addition of water into THF increases the solvent polarity and
decreases the solvating power. The former decreases the emission
intensity of an ICT luminogen, whereas the latter promotes aggregate
formation and activates the AIE process. The emission of TPA3TPAN
and DTPA4TPAN molecules is thus determined by the competition
between these two antagonistic effects.
(26) (a) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.;
Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem. Commun.
2001, 1740. (b) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Commun.
2009, 4332. (c) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev.
2011, 40, 5361. (d) Zhao, Z.; Lam, J. W. Y.; Tang, B. Z. Curr. Org.
Chem. 2010, 14, 2109. (e) Yuan, W. Z.; Zhao, H.; Shen, X. Y.; Mahtab,
1527
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528

Chemistry of Materials
Article
(38) (a) Ko, C.-W.; Tao, Y.-T. Synth. Met. 2002, 126, 37. (b) Naito,
K.; Miura, A. J. Phys. Chem. 1993, 97, 6240. (c) Ham, E.; Do, L.;
Niidome, Y.; Fujihira, M. Chem. Lett. 1994, 969.
(39) (a) Zhao, H.; Tanjutco, C.; Thayumanavan, S. Tetrahedron Lett.
2001, 42, 4421. (b) Low, P. J.; Paterson, M. A. J.; Yufit, D. S.; Howard,
J. A. K.; Cherryman, J. C.; Tackley, D. R.; Brook, R.; Brow, B. J. Mater.
Chem. 2005, 15, 2304.
(40) Liu, Y.; Chen, S.; Lam, J. W. Y.; Lu, P.; Kwok, R. T. K.; Mahtab,
F.; Kwok, H. S.; Tang, B. Z. Chem. Mater. 2011, 23, 2536.
(41) (a) Tao, S. L.; Lee, C. S.; Lee, S. T.; Zhang, X. H. Appl. Phys.
Lett. 2007, 91, 013507. (b) Tong, Q.-X.; Lai, S.-L.; Chan, M.-Y.; Zhou,
Y.-C.; Kwong, H.-L.; Lee, C.-S.; Lee, S.-T. Chem. Mater. 2008, 20,
6310.
(42) (a) Yan, H.; Huang, Q.; Cui, J.; Veinot, J. G. C.; Kern, M. M.;
Marks, T. J. Adv. Mater. 2003, 15, 835. (b) Chin, B. D.; Suh, M. C.;
Lee, S. T.; Chung, H. K.; Lee, C. H. Appl. Phys. Lett. 2004, 84, 1777.
(c) Veinot, J. G. C.; Marks, T. J. Acc. Chem. Res. 2005, 38, 632.
1528
dx.doi.org/10.1021/cm300416y | Chem. Mater. 2012, 24, 1518−1528