A fluorene-based material containing triple azacrown ether groups: Synthesis, characterization and application in chemosensors and electroluminescent devices

Article abstract of DOI:10.1039/c3ob42054j

We design a novel multifunctional fluorene-based material containing triple azacrown ether (FTC) not only for application in aqueous solution as a chemosensor towards Fe³⁺ but also to enhance the electroluminescence of PLEDs using an environmentally stable aluminum cathode. The photo-physical and sensing properties were investigated by absorption and photoluminescence (PL) spectroscopy. The FTC exhibited specific selectivity and high sensitivity toward Fe³⁺, with the Stern-Volmer coefficients (K_sv) being 1.59 × 10⁵ M^-1 in a solvent mixture of tetrahydrofuran and water (THF-H₂O = 9/1, v/v). The FTC maintained high selectivity toward Fe³⁺ in the presence of ten interfering metal cations. The HOMO and LUMO levels were estimated to be -5.88 eV and -2.88 eV, respectively. The FTC significantly enhances the emission performance of PLEDs [ITO/PEDOT:PSS/MEH-PPV/EIL/Al] when used as an electron injection layer (EIL), especially in the presence of metal carbonates. Particularly, the device using K₂CO₃ doped FTC as the electron-injection layer (EIL) exhibited significantly enhanced performance compared to the one without EIL. The performance was significantly enhanced to 11630 cd m^-2 and 1.47 cd A^-1, respectively, from 230 cd m^-2 and 0.03 cd A ^-1 of the non-FTC device. Current results indicate that multifunctional fluorene-based material FTC is a potential candidate for selective detection of Fe³⁺ and as an effective electron injection layer to enhance the performance of MEH-PPV.

Full text of DOI:10.1039/c3ob42054j

View Article Online
View Journal
Organic &
Biomolecular
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. Wu, Y. Lin and
Y. Chen, Org. Biomol. Chem., 2013, DOI: 10.1039/C3OB42054J.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/obc

View Article Online
DOI: 10.1039/C3OB42054J
Introduction
Organic conjugated materials have attracted a great deal of attention because of their potential
applications light-emitting diodes (LEDs),1,2 chemical sensors,3,4 organic solar cells,5,6 and
field-effect transistors.7,8 Recently, there has been a growing need for developing highly sensitive
and selective probes for the detection of metal ions in biological and environmental samples.
Analytical techniques based on fluorescence detection are very popular because fluorescence
measurements are usually very sensitive, easy to perform, and inexpensive.9,10 Therefore, a large
number of papers involving fluorescent chemical sensors have been reoprted.11 Some heavy metal
ions, such as Fe3+, Zn2+, Cu2+, Co2+, Mn2+, and Mo4+, are essential for the maintenance of human
metabolism. However, high concentrations of these ions can lead to many adverse health effects.12
Therefore, the development of selective and sensitive methods for the determination of heavy metal
ions is currently receiving considerable attention.9
On the other hand, to achieve highly electroluminescent efficiency it is necessary that both
electrons and holes are efficiently injected/transported and balanced.13,14 However, for conventional
electroluminescent MEH-PPV {poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene]},
holes are more readily injected and transported than electrons, leading to imbalanced carriers
currents in PLEDs.15-19 Moreover, for development of the PLEDs industrialization, the cathode
must be stable to environment, the environmentally stable high-work-function metals such as Al,
Cu, Ag, and Au as the cathode has recently attracted extensive attention. Use of a water- or
alcohol-soluble electron injection layer (EIL) based on a conjugated polymer grafted with amino,
ammonium salt, or diethanolamino groups has been demonstrated to allow the use of a
high-work-function metal as the cathode.20-23 This is because interfacial dipole or space charge is
formed between the emitting layer (EML) and the cathode that reduces the electron injection
barrier.
Among the typical fluorescent materials, fluorene-based derivatives show good thermal and
chemical stabilities, exhibit wide energy band gap, and high photoluminescence (PL) efficiency
(60~80%) in solution and solid states. 24-26 Moreover, relatively high reactivity of the protons at C-9
position of fluorene unit renders the chemical modification of polyfluorene easy without perturbing
its electrochemical properties. Accordingly, the fluorene-based derivatives are widely used in
2

View Article Online
DOI: 10.1039/C3OB42054J
electroluminescent (EL) devices, solar cells and chemical sensory applications. In additional, crown
ethers are designed as molecular hosts able to complex alkali and alkaline earth cations, transition
metal cations and ammonium cations.27 The stability of the crown ether-metal ion complex is
dependent on the number of ether donor atoms. Of particular importance is the size and shape of the
cavity relative to the cation size.28 The crown ether-metal ion complex forms in a 1:1 ratio when the
ion is able to fit within the cavity. However, the ion is larger than that of the crown cavity, there is a
tendency for the crown ether moieties to ‘‘sandwich’’ the metal ions between adjacent crown
units.29
An azacrown ether is a crown ether that has nitrogen donor atoms as well as oxygen donor
atoms to coordinate to the metal iron. The nitrogen atoms in azacrown ether should play important
role in coordination with metal cations. To our best knowledge, a few researches focus on small
molecule which could be not only applied as chemosensor for cations but also as electron injection
layer to enhance electroluminescence. In particular, small-molecular-weight materials have received
interest due to their easy purification by re-crystallization or column chromatographic techniques,
and mono-disperse with well-defined chemical structures, and synthetically well-reproducibility.
In this study, we report the synthesis and characterization of a novel and small-molecule
fluorene-based material containing triple azacrown ether groups FTC. The azacrown ether groups
attached on FTC are expected not only to coordinate with certain metal ions to result in
fluorescence quenching but also to be applied as electron injection layer to enhance significantly the
electroluminescence of MEH-PPV. Moreover, vinyl groups also have been introduced between
fluorene-cored and triple azacrown ethers to extend the conjugation of mono-fluorene part. This is
not only to make the PL emission of FTC locate visible region but also achieve more suitable
LUMO and HOMO energy levels. The PL quenching is caused by the energy transfer from fluorene
moiety to the adjacent coordinated metal ions. The electroluminescent enhancement is attributable
to reduce the electron injection barrier to obtain more balance of charges in MEH-PPV. The results
indicate that the FTC is potentially not only applicable in chemical sensors if high selectivity and
sensitivity are realized but also in enhancing device performance of PPV derivatives.
Experimental Section
1
All new synthesized compounds were identified by H NMR and elemental analysis (EA).
The 1H NMR spectra were recorded on a Bruker AMX-400 MHz FT-NMR, and the chemical shifts
3

View Article Online
DOI: 10.1039/C3OB42054J
are reported in ppm using tetramethylsilane (TMS) as an internal standard. The elemental analysis
was carried out on a Heraus CHN-Rapid elemental analyzer. Absorption and photoluminescence
(PL) spectra were measured on a Jasco V-550 spectrophotometer and a Hitachi F-4500
spectrofluorometer, respectively. Cyclic voltammograms were measured with a voltammetric
apparatus (model CV-50W from BAS) equipped with a three-electrode cell. The cell was made up
of an oligomer-coated glassy carbon as the working electrode, an Ag/AgCl electrode as the
reference electrode, and a platinum wire as the auxiliary electrode. The electrodes were immersed in
acetonitrile containing 0.1 M (n-Bu)4NClO4. The energy levels were calculated using the ferrocene
(FOC) value of -4.8 eV with respect to vacuum level, which is defined as zero.30
Synthesis and Characterization
N,N-Bis(acetoxyethyl)phenylamine (1)
A mixture of N-phenyldiethanolamine (8.0 g, 44 mmol), triethylamine (13.3 g, 132 mmol)
and THF (40 mL) was added to a solution of acetyl chloride (9.3 mL, 132 mmol) in THF (40 mL).
o
The mixture was stirred at 35 C for 20 h. Then, 40 mL water was added dropwise to the mixture
slowly. After removal of THF by rotary evaporation, the mixture was extracted with chloroform and
the organic layer was dried (MgSO4) and concentrated under reduced pressure. The residue was
distillated in vacuo (210 oC, 7 torr ) to obtain 1 (9.7 g , 82.9 %). 1H NMR (400 MHz, CDCl3, TMS,
25 oC): δ 7.20-7.24 (t, 2H, J = 16 Hz, Ar-H), 6.70-6.76 (m, 3H, Ar-H), 4.21-4.24 (t, 4H, J = 12.5 Hz
, -CH2-), 3.59-3.63 (t, 4H, J = 12.6 Hz, -CH2-), 2.04 (s, 6H, -CH3).Anal. Calcd. for C14H19NO4 (%):
C, 63.38; H, 7.22; N, 5.28. Found: C, 62.98 7.18; N, 5.22.
FT-IR (KBr, cm-1): ν 1735 (C=O stretch), 2963 (-CH stretch).
4-(Bis(2-acetoxylethyl)amino)benzaldehyde (2)
Phosphoryl trichloride (6.9 g, 45 mmol) was added slowly to N,N-dimethylformamide (13.8
o
g, 188 mmol) under ice bath and stirred at room temperature for 1 h, and then reacted at 75 C for
additional 12 hr after adding compound 1. Chloroform and sodium acetate solution (24.7 g, 0.3
mol) was added slowly under ice bath and stirred at room temperature overnight. The mixture was
extracted with chloroform and the organic layer was dried (MgSO4) and concentrated under reduced
pressure to give 2 (12.2 g, 92.8 %). 1H NMR (400 MHz, CDCl3, TMS, 25 oC): δ 9.74 (s, H, -CHO)
6.81-6.83.(d, 2H, J = 8.6 Hz, Ar-H), 7.73-7.75 (d, 2H, J = 8.7 Hz, Ar-H), 4.26-4.29 (t, 4H, J = 12.2
Hz, -CH2-), 3.71-3.74 (t, 4H, J = 12.3 Hz, -CH2-), 2.04 (s, 6H, -CH3). Anal. Calcd. for C15H19NO5
4

View Article Online
DOI: 10.1039/C3OB42054J
(%): C, 61.42; H, 6.53; N, 4.78. Found: C, 61.09; H, 6.56; N, 4.65. FT-IR (KBr, cm-1): ν 1676
(-CHO stretch), 1739 (C=O stretch), 2815 (-CH aldehyde), 2963 (-CH stretch).
4-Bis(2-hydroxyethyl)amino)benzaldehyde (3)
A mixture of 2 (10 g, 34 mmol), methanol (150 mL) and sodium carbonate solution (10.9 g,
102 mmol) was stirred at room temperature overnight. Few drops of 1N HCl were added to the
mixture; and then the methanol was removed by rotary evaporation. The mixture was extracted with
chloroform and the organic layer was dried (MgSO4) and concentrated under reduced pressure. The
residue was purified by column chromatography eluted with ethyl acetate to give 3 (4.9 g, 69.5 %).
1H NMR (300 MHz, CDCl3, TMS, 25 oC): δ 9.62 (s, H, -CHO) 7.63-7.66 (d, 2H, J = 9.0 Hz, Ar-H),
6.68-6.71 (d, 2H, J = 9.0 Hz, Ar-H), 3.86-3.89 (t, 4H, J = 9.8 Hz, -CH2-), 3.65-3.68 (t, 4H, J = 9.7
Hz, -CH2-), 3.40-3.45 (d, 2H, J = 16.4 Hz, -OH). Anal. Calcd. for C11H15NO3 (%): C, 63.14; H,
7.23; N, 6.69. Found: C, 63.07; H, 7.28; N, 6.59. FT-IR (KBr, cm-1): ν 1667 (-CHO stretch),
2753(-CH aldehyde), 3352 (-OH stretch).
Triethyleneglycol Ditosylate (4)
Mixture of p-toluenesulfonyl chloride (5.75 g, 0.03 mol), triethylene glycol (1.5 g, 0.01 mol)
o
and THF (15 mL) was mechanically stirred at 0 C. Aqueous solution of KOH (16 M, 4 mL) was
added portion wise to the mixture within 1 h and then stirred at room temperature for 7 h. The
mixture was poured into ice water, the appearing white precipitate was collected by filtration and
re-crystallized from methanol/water to afford white crystal of 4 (3.214 g, 70 %, m.p. 81-83 oC). 1H
o
NMR (400 MHz, CDCl3, TMS, 25 C): 7.25-7.79 (m, 8H, aromatic region), 4.1 (m, 4H), 3.6 (m,
4H), 3.5 (s, 4H), 2.4 (s, 6H). FT-IR (KBr, cm-1): ν 1600 (aromatic ring), 1129 (C-O-C), 1175
(sulfonate). Anal. Calc. for C20H26O8S2: C, 52.39; H, 5.72. Found: C, 52.37; H, 5.72.
4-(Monoaza-15-crown-5)benzaldehyde (5)
A mixture of compound 3 (0.4 g, 2.09 mmol) and NaH (0.8 g, 60 % in mineral oil, 20 mmol)
in dried THF (300 mL) was refluxed under nitrogen atmosphere for 30 min. The mixture was added
dropwise with a solution of compound 4 (1.0 g, 2.1 mmol) in THF (200 mL) and then stirred at 70
oC for 2 days. After adding an aqueous solution of H2SO4 (2 M, 50 mL), the THF was removed by
rotary evaporation. The mixture was then extracted with chloroform and the organic layer was dried
(MgSO4) and concentrated under reduced pressure. The crude product was purified by column
5

View Article Online
DOI: 10.1039/C3OB42054J
1
chromatography (eluent: acetone/n-hexane = 3/2) to give 5 (0.3 g, 44.49 %). H NMR (400 MHz,
CDCl3, TMS, 25 oC): δ 9.73 (s, H, -CHO) 7.70-7.73 (d, 2H, J = 8.8 Hz, Ar-H), 6.71-6.74 (d, 2H, J
= 8.7 Hz), 3.52 (m, 4H, crown ether), 3.77-3.80 (m, 16H, crown ether). Anal. Calcd. for C17H25NO5
(%): C, 63.14; H, 7.79; N, 4.33. Found: C, 62.68; H, 7.77; N, 4.14. FT-IR (KBr, cm-1): ν 2798 (-CH
aldehyde), 1667 (-CHO stretch), 1124 (C-O stretch).
2,4,7-Tri(bromomethyl)-9,9-dihexylfluorene (6)
Into the mixture of 9,9-dihexylfluorene (3.25 g, 9.5 mmol) and paraformaldehyde (9.3g, 0.31
mole) under ice bath was added drop-wise with HBr aqueous solution (33 wt%). The mixture was
o
stirred at 70 C for 2 day under nitrogen atmosphere, poured into ice water and extracted with
CH2Cl2. After removal of CH2Cl2 by a rotary evaporator, the residues were purified by column
chromatography using n-hexane/toluene (10/1, v/v) as eluent to afford colorless liquid of 6. (4.19 g,
1
o
72%) H NMR (400 MHz, CDCl3, TMS, 25 C): δ 7.87-7.89 (d, 1H, J = 8 Hz), 7.3-7.4 (m, 2H
,ArH), 7.30-7.35 (m, 2H, ArH), 4.8 (s, 2H, -CH2-), 4.5 (s, 2H, -CH2-), 4.6 (s, 2H, -CH2-), 1.93-1.97
(m, 4H, -CH2-), 0.56-1.25 (m, 22H, -CH2-). Anal. Calc. for C28H37Br3: C, 54.83; H, 6.08. Found: C,
54.41; H, 6.01.
2,4,7-Tri[methylene(triphenylphosphonium bromide)]-9,9-dihexylfluorene (7)
To a mixture of compound 6 (4.3 g, 7.5 mmol) and triphenylphosphine (15.7 g, 59.8 mmol)
o
and DMF (60 mL) was stirred at 100 C for 2 days under nitrogen atmosphere. The mixture was
poured into excess of benzene and the appearing solid was collected by filtration, which was dried
in vacuo at 100 oC to get the desired product 7 (8.7 g, 82.5 %). 1H NMR (400 MHz, CDCl3, TMS,
o
25 C): δ 7.84~7.52 (m, 45H, Ar-H), 7.12 (s, 1H, Ar-H), 6.96 (s, 2H, Ar-H), 6.87 (s, 1H, Ar-H),
6.71 (s, 1H, Ar-H), 5.56~5.52 (d, 2H, J = 16Hz, -CH2Br), 5.35~5.31 (d, 2H, J = 16 Hz, -CH2Br),
5.16~5.12 (d, 2H, J = 16Hz, -CH2Br), 1.43~1.33 (m, 4H, -CH2-), 1.15~1.1 (m, 4H, -CH2-),
0.95~0.79 (m, 14H, -CH3- and -CH2-), 0.046 (m, 4H, -CH2-). Anal. Calc. forC82H82Br3P3: C, 70.3;
H, 5.9. Found: C, 70.1; H, 5.99.
2,4,7-Tri[4-(monoaza-15-crown-5)styryl]-9,9-dihexylfluorene (FTC)
A mixture of compound 5 (3.36 g, 10.4 mmol) and compound 7 (1.6 g, 1.1 mmol) in dried
ethanol (20 mL) was added dropwise with sodium ethoxide (3.4 g, 10.4 mmol) and stirred at room
temperature overnight under nitrogen atmosphere. The mixture was extracted with chloroform and
6

View Article Online
DOI: 10.1039/C3OB42054J
the organic layer was dried (MgSO4) and concentrated under reduced pressure. The crude product
was purified by column chromatography (eluent: acetone/n-hexane = 1/1, EA) (0.51 g, 34.5 %).1H
NMR (400 MHz, CD2Cl2, TMS, 25 oC): δ 7.88~7.86 (d, 1H, Ar-H), 7.70~7.66 (d, 1H, Ar-H), 7.6 (s,
1H, Ar-H),7.54~7.42 (m, 8H, Ar-H), 7.38 (s, 1H, Ar-H), 7.20~6.98 (m, 5H, Ar-H), 6.76~6.68 (m,
6H, Ar-H), 3.80~3.53 (m, 60H, crown ether), 2.06~2.02 (t, 4H, -CH2-), 1.16~1.03 (m, 12H, -CH2-),
0.79~0.75 (m, 6H, -CH3-), 0.67~0.65 (m, 4H, -CH2-). Anal. Calc. for C79H109N3O12: C, 73.40; H,
8.50; N, 3.25. Found: C, 73.42; H, 8.72; N, 3.11.
Results and Discussion
The FTC was synthesized from monoaza-15-crown-5 derivative (5) and
2,4,7-tri[methylene(triphenylphosphonium-bromide)]-9,9-dihexylfluorene (7) by the Wittig reaction
1
(Scheme 1). The chemical structure of FTC was characterized by H NMR, COSY and NOESY
spectra and elemental analysis. The optical properties of FTC were investigated using absorption
spectroscopy (UV/Vis) and photoluminescence spectroscopy (PL). Cyclic voltammetry (CV) was
used to measure onset reduction and oxidation potentials of FTC film, which in turn were used to
estimate the LUMO and HOMO levels respectively.
7

View Article Online
DOI: 10.1039/C3OB42054J
O
C
O
C
OH
OH
OAc
OAc
POCl3
DMF
OAc
H3C
Cl
N
N
H
N
TEA
OAc
1
2
O
O
O S O
O
O
O S O
4
O
C
O
O
O
C
sodium carbonate
methanol
OH
OH
O
CH3
CH3
H
N
H
N
O
NaH, THF
3
5
Br
1-bromohexane
t-BuOK, DMF
paraformaldehyde
HBr
Br
6
Br
O
O
O
H
C
N
P+Ph3Br-
O
O
5
PPh3
-BrPh3+P
-BrPh3+P
DMF
Sodium ethoxide, Ethanol
7
O
O
O
O
N
O
O
O
N
O
N
O
O
O
O
FTC
Scheme 1. Synthetic procedures of FTC.
8

View Article Online
DOI: 10.1039/C3OB42054J
Characterization of Fluorene-Based Material FTC
1
Figure S1-S3 (Supporting Information) shows the H NMR, COSY and NOESY spectra of
FTC. Assignments of each proton were assisted by the two-dimensional NMR spectra (Figure
S2-S3), which agree well with the proposed molecular structure of FTC. Thermal decomposition
temperatures (Td) (at 5 wt% loss) and glass transition temperatures (Tg) of of FTC were evaluated
with thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively.
The Td at 5% weight loss, glass transition temperature (Tg) and melting point (Tm) of FTC was
observed at 394 oC, 49 °C and 64 °C, respectively [Figure S4 (SI)], but no obvious Tc was detected
between 30°C and 150°C. The asymmetric structure of FTC and the twist of 4-azacrown ether
moiety relative to the fluorene plane effectively prevent close packing between the molecules.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
FTC in film state
FTC in CHCl
3
300
400
500
600
Wavelength (nm)
Figure 1. Absorption spectra and photoluminescence spectra of FTC in the film state and CHCl3
solution.
Optical Properties
Figure 1 illustrates the absorption and photoluminescence (PL) spectra of FTC in solution
(CHCl3) and as film spin-coated from CHCl3 solution. The absorption spectra of FTC in solution
and film state are peaked at ca. 416 nm and 424 nm, respectively. The absorption could be
attributed to the n-π* and π-π* electronic transitions of crown ether and conjugated fluorenyl vinyl
phenyl moiety. The PL spectra of FTC in solution and solid state locate at ca. 470 nm and ca. 535
nm, respectively. Solid state PL maximum of FTC is greatly red-shifted (65 nm) relative to solution
9

View Article Online
DOI: 10.1039/C3OB42054J
state, probably due to excimer formation via inter-molecular interactions. The interactions are
attributed to π-π stacking in solid state.
Acetonitrile
Chloroform
1.0
Methanol
Toluene
Ethanol
DMF
Acetone
THF
0.8
0.6
0.4
0.2
0.0
Ethyl acetate
350
400
450
500
550
Wavelength (nm)
Figure 2. Absorption spectra of FTC in various solvent. The concentration of FTC was fixed at
10-5 M.
Acetonitrile
Chloroform
1.0
Methanol
Toluene
Ethanol
DMF
0.8
Acetone
THF
Ethyl acetate
0.6
0.4
0.2
0.0
450
500
550
600
650
700
Wavelength (nm)
Figure 3. Photoluminescence spectra of FTC in various solvent. The concentration of FTC was
fixed at 10-5 M.
10

View Article Online
DOI: 10.1039/C3OB42054J
Figure 2 and Figure 3 show the absorption and photoluminescence (PL) spectra of FTC in
various solvents with the characteristic optical data summarized in Table 1. In general, the
fluorophore has a larger dipole moment in the excited state (μE) than in the ground state (μG). The
solvent dipoles can reorient or relax around μE, which lowers the energy of the excited state via
excitation. This means that the absorption and PL emission are red-shifted with increasing the
solvent polarities. Therefore, FTC showed red-shifts in absorption and PL emission with gradually
increasing the polarity of solvent.31 However, absorption maximum are slightly red-shifted (ca. 10
nm) relative to PL emission (ca. 40 nm) due to the fluorescence lifetimes (1–10 ns) are usually
much longer than the time required for solvent relaxation (10–100 ps).
Table 1. Absorption and photoluminescence maximum wavelength of FTC in various solvents.
Wavelength
Solvent
λabs,max (nm)
λfluo,max (nm)
468, 489s
488
Toluene
THF
396s, 418, 442s
389s, 417, 440s
391s, 416, 440s
390s, 414, 438s
389s, 411, 433s
391s, 415, 440s
388s, 412, 434s
392s, 414, 438s
395s, 421, 445s
Chloroform
Ethyl acetate
Methanol
Acetone
Ethanol
473, 491s
475
497
501
496
Acetonitrile
DMF
504
508
Chemosensory Properties of FTC
To investigate the applications of FTC as chemical sensor for cations, the chemosensory
characteristics of FTC were investigated in two aqueous mixture solvent systems (THF/H2O = 9/1
and methanol/H2O = 9/1). The chloride salts of Li+, Na+, K+, Ca2+, Ba2+, Co2+, Ni2+, Pb2+, Zn2+,
Co2+, Fe2+ and Fe3+ were dissolved in a mixture solvent of THF/H2O (9/1, v/v), methanol/H2O (9/1,
v/v), or ethanol/H2O (9/1, v/v) to prepare their corresponding stock solutions (10-4 M). In the
11

View Article Online
DOI: 10.1039/C3OB42054J
presence of Fe2+, the absorption and PL spectra slightly diminished intensities. However, the
absorption spectral intensity and wavelength remain almost unchanged in the presence of other
cations tested as shown in Figure 4 and Figure 5. However, the absorption spectra demonstrated
obviously blue-shift from 419 nm to 376 nm as well as the PL intensity significantly decreased in
the presence of Fe3+.
1.2
FTC
Li+
1.0
Na+
K+
Ca2+
Ba2+
0.8
Co2+
Ni2+
Pb2+
0.6
Zn2+
Cd2+
Fe2+
0.4
Fe3+
0.2
0.0
300
350
400
450
500
550
Wavelength (nm)
Figure 4. Absorption spectra of FTC with various metal ions in solution (THF/H2O = 9/1, v/v).The
concentration of FTC and metal ions were fixed at 10-5 M and 10-4 M, respectively.
140
FTC
Li+
120
Na+
K+
Ca2+
100
Ba2+
Co2+
Ni2+
80
Pb2+
Zn2+
60
Cd2+
Fe2+
Fe3+
40
20
0
450
500
550
600
650
Wavelength (nm)
12

View Article Online
DOI: 10.1039/C3OB42054J
Figure 5. Photoluminescence spectra of FTC with various metal ions in solution (THF/H2O = 9/1,
v/v).The concentration of FTC and metal ions were fixed at 10-5 M and 10-4 M, respectively.
Excitation wavelength was 418 nm.
Similarly, the same tendency also could be found in methanol/H2O = 9/1 system (Figure S5 and
Figure S6 in SI). The addition of Fe3+ caused obvious blue-shift from 412 nm to 367 nm in
absorption spectrum with decreasing PL intensity concomitantly.
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
Metal ions
Fe3+ Li+ Ni2+ Co2+ Zn2+ Fe2+ Na+ Cd2+ Ca2+ Pb2+ Ba2+ K+
Diameter (Å) 1.28 1.36 1.44 1.48 1.48 1.52 1.90 1.94 1.98 2.66 2.98 3.04
Figure 6. Fluorescence emission response profile of FTC upon addition of various metal ions in
solution (THF/H2O = 9/1, v/v). The concentration of FTC and metal ions were fixed at 10-5 M and
10-4 M, respectively. Excitation wavelength was 418 nm.
Figure 6 and Figure S7 (in SI) shows the fluorescence responses [(I-I0)/I0] of FTC toward
various metal ions in two systems. The quenching ability of FTC showed great sensitivity towards
Fe3+, suggesting it is a potential chemosensor to detect Fe3+. The quenching response towards Fe3+
is mainly governed by the interaction between metal ion and the lone pair electrons of nitrogen
atom on the azacrown ether. The interaction is mainly depends on : (1) charge density of metal ions,
(2) size of metal ions relative to that of crown ether, and (3) solvent in the system.32 Moreover,
quenched fluorescence intensities also depends partially on the charge density of the complexed
metal ion.33
The obvious blue-shift of absorption spectra and the quenching effect of fluorescence spectra
towards Fe3+ have been further discussed. For instance, the photo-excited energy may relax via
13

View Article Online
DOI: 10.1039/C3OB42054J
three possible ways after exciting the mixed solution of FTC with Fe3+. Three types of molecules
probably coexisted in solution, which are Q, M, and [MQ]. Those symbols Q, M, and [MQ] mean
the free Fe3+ metal ion, vacant FTC, the complex of FTC with Fe3+, respectively.
The first way is the excitation of M resulted in the immediately energy transfer to Q. It is well
known that Fe3+ is d block metal. The d block metals are per se inclined towards easy and reversible
electron-transfer processes and have access to different and consecutive oxidation states. Such an
access can be typically controlled by varying the coordinative environment around the metal.
Therefore, quenching can be induced from the transfer of an electron from the excited state of the
fluorophore directly to the metal center.34 Also the quenching efficiency depends on the degree of
overlap between the absorption spectrum of metal ion (Fe3+) and fluorescence spectrum of the
fluorophore.35,36 As shown in Figure S8 and Figure S9 (SI), the overlap leads to the possibility of
energy transfer in both two systems.
The second is the excited M* which did not collide and energy transfer with Q, so light
emission would be detected. The final possibility is the formation of complex [MQ] which leads to
the photoinduced charge transfer (PCT) phenomenon. When the cation interacts with the donor
group (azacrown ether), the excited state is more strongly destabilized by the cation than the ground
state, results in a blue-shift of the absorption and PL emission spectra. Therefore, the blue-shifted
absorption and PL emission spectra were induced by PCT. However, the blue-shift of PL emission
is much smaller than absorption. The electron density of the nitrogen atom is reduced when the
cation interacts with the fluorophore. This nitrogen atom becomes a non-coordinating atom due to
the positive polarization of nitrogen atom. Therefore, excitation induces a photo-disruption of the
interaction between the cation and the nitrogen atom of the azacrown. Only slight shift is found in
the PL emission spectra, because most of the fluorescence is emitted from the fluorophore which
does not interact with cation anymore or the interaction is much weaker. Also the formation of
non-fluorescent complex is the characteristic of static quenching, resulting in the reduction of
fluorescence.37
Therefore, in our case those three possible ways contributed to the blue-shift of absorption
spectra and the quenching effect of fluorescence spectra towards Fe3+. And the slight changes in
spectra of FTC towards Fe2+ were found which was attributed to the partially oxidation of Fe2+ in
the presence of H2O. These results indicate the selectivity of FTC towards Fe3+.
14

View Article Online
DOI: 10.1039/C3OB42054J
Response Sensitivity towards Fe3+
In order to further investigate the sensitivity of FTC with Fe3+, the absorption and
fluorescence spectra of FTC with various concentration of Fe3+ were investigated in two mixture
solvent systems (THF/H2O = 9/1 and ethanol/H2O = 9/1). In addition, the solvent composition was
changed to ethanol/H2O (9/1) when the solubility was poor due to high concentration. As a
quantitative measure of fluorescence quenching, the Stern-Volmer equation (Equation 1) is a useful
method, where [Q] is the concentration of the quencher, Ksv is the Stern-Volmer constant which is
proportional to sensitivity, F0 and F are the fluorescence intensity in the absence and presence of the
quencher, respectively.38
F0/F = 1 + Ksv [Q]
(Eq. 1)
FTC
1.0x10-6
5.0x10-6
1.0x10-5
1.5x10-5
2.0x10-5
2.5x10-5
3.0x10-5
3.5x10-5
4.0x10-5
5.0x10-5
7.5x10-5
1.0x10-4
2.5x10-4
5.0x10-4
7.5x10-4
1.0x10-3
1.0x10-2
M
M
M
M
M
M
M
140
120
100
80
M
M
M
M
M
M
M
M
M
M
60
40
20
0
450
500
550
600
650
700
Wavelength (nm)
Figure 7. Photoluminescence spectra of FTC with varying concentration of Fe3+in solution
(THF/H2O = 9/1, v/v). The concentration of FTC was fixed at 10-5 M. Excitation wavelength was
418 nm.
As shown in Figure 7 and Figure S10 (in SI), the PL emission intensity of FTC decreased
gradually with increasing concentration of Fe3+ from 1.0×10-6 M to 1.0×10-2 M in two solvent
systems. Figure S11 and Figure S12 (in SI) demonstrated the Stern-Volmer plots of FTC. From the
Stern-Volmer plot, it was an upward curvature and concaved towards y-axis. The slopes increased
gradually at the beginning and rose dramatically as the concentration of Fe3+ was more than
15

View Article Online
DOI: 10.1039/C3OB42054J
1.0×10-4 M. It is well known that the upward curvature is the characteristic of combination of
dynamic and static quenching. 38 Therefore, the Stern-Volmer constants (Ksv) of FTC toward Fe3+
were 2.90×103 M-1 and 1.54×104 M-1 in ethanol/H2O (v/v = 9/1) and 1.15×104 M-1 and 1.59×105
M-1 in THF/H2O (v/v = 9/1) for the static and dynamic quenching regions, respectively. As the
concentration of quencher (cation) increases, the possibility of collision raises as well as the
distance between quencher and fluorophore is shortened which leads to the immediately energy
transfer from fluorophore to quencher.
Table 2. Stern-Volmer constants of ethanol and THF systems.
Ksv(1)
Ksv(2)
ethanol/H2O = 9/1
THF/H2O = 9/1
2.90 ×103
1.15×104
1.54×104
1.59×105
Further comparison of the Ksv values between two mixture solvent systems (THF/H2O = 9/1
and ethanol/H2O = 9/1). Table 2 reveals that the Ksv values of THF system were almost one order
magnitude larger than those of the ethanol system. The Ksv value can be estimated by equation (2),
where kq is bimolecular quenching constant, τ0 was the lifetime of fluorophore in the absence of
quencher, fQ is the quenching efficiency, k0 is diffusion controlled bimolecular rate constant, R is
the collision radius which is generally assumed to be the sum of the molecular radii of the
fluorophore (Rf) and quencher (Rq), and D is the sum of the diffusion coefficients of the fluorophore
(Df) and quencher (Dq), and N was Avogadro's number. And equation 3 is used to calculate D
(diffusion coefficient), where κ is Boltzmann's constant, T is temperature, η is the solvent viscosity,
and R is the molecular radius.38
Ksv  k
q
0  ( fQk0 )0  fQ0 (4RDN /1000)
(Eq. 2)
(Eq. 3)
D  T /6R
Accordingly, the Ksv value is inversely proportional to viscosity. Moreover, the viscosity of
THF (0.48 cps) is much lower than that of ethanol (1.07 cp), which leads to the larger Ksv value in
THF/H2O mixture. Furthermore, it has long been known that conjugated polymers-based
fluorescent sensors possess high sensitivity, which is due to the signal is transformed and amplified
16

View Article Online
DOI: 10.1039/C3OB42054J
by the highly conjugated backbone.39,40 Comparing to small molecules, conjugated polymers is
more sensitive towards analytes. However, FTC which is a small molecular, possesses triple
azacrown ether as the recognition moieties; the Ksv are comparable with our previously conjugated
polymer sensors PFC (Ksv =1.1 ×103 M-1).41 In addition, color variations of the solutions in both
THF/H2O and ethanol/H2O are detectable by naked eye (Figure 8). These results suggest that FTC
is a promising candidate for sensing Fe3+.
(b)
(a)
Figure 8. Color variations of FTC added with various concentrations of Fe3+ in solution. (a)
ethanol/H2O = 9/1 and (b) THF/H2O = 9/1. (bottom images: excited with 365 nm wavelength)
140
FTC
FTC + metal ions
FTC + metal ions +Fe3+
120
100
80
60
40
20
0
450
500
550
600
650
Wavelength (nm)
Figure 9. Fluorescence spectral quenching of FTC by Fe3+ interfered by various metal ions (Li+ + Na+ +
K+ + Ca2+ + Ba2+ + Co2+ + Ni2+ + Pb2+ + Zn2+ + Co2+) (THF/H2O = 9/1, v/v). The concentration of
FTC and metal ions were fixed at 10-5 M and 10-3 M, respectively. Excitation wavelength was 419
nm.
Selectivity of FTC towards Fe3+
17

View Article Online
DOI: 10.1039/C3OB42054J
In the real applications, various metal ions often coexist in the contaminated solution.
Therefore, it is important to investigate the selectivity of FTC towards Fe3+ in the stock solution.
The fluorescence spectral intensity of FTC diminishes only slightly in the presence of ten metal
ions (Figure 9). However, further addition of Fe3+ quenches the fluorescence significantly.
Therefore, FTC shows very high selectivity to Fe3+ against the interfering cations.
Influence of pH on Absorption and Fluorescence Spectra of FTC
The azacrown ether (monoaza-15-crown-5) in FTC is directly linked to the conjugated
fluorenyl core via nitrogen atom. There is one lone pair within the nitrogen atom which might be
protonated by the addition of acid.42 The absorption and PL spectra of FTC with hydrochloric acid
in mixture solvent system (THF/H2O = 9/1) had been investigated (Figure S13 and Figure S14 in
SI). As the concentration of hydrochloric acid reached 1.0×10-2 M, the absorption and fluorescence
spectra of FTC started to blue-shift and decrease emission intensity. This is probably attributed to
THF was also protonated by hydrochloric acid, the start point of spectra change was 1.0×10-2 M
which was larger than the concentration of FTC (1.0×10-5 M). The remarkable blue-shift was
attributed to the protonation of nitrogen atom, which resulted in PCT phenomenon. The proton (H+)
readily interacted with the lone pair electrons. The excited state was more strongly destabilized by
the H+ than the ground state, resulting in a blue-shift of the absorption and emission spectra.
Therefore, FTC was not only applicable as a Fe3+ sensor but also as a pH sensor.
Electrochemical properties
Cyclic voltammetry (CV) was employed to investigate the electrochemical properties of FTC.
The cyclic voltammograms are shown in Figure S15 in (SI), with the representative electrochemical
data summarized in Table 3. HOMO and LUMO energy levels were estimated by the equations:
EHOMO (eV) = − (Eox,FOC + 4.8) and ELUMO (eV) = − (Ered,FOC + 4.8), where Eox,FOC and Ered,FOC are
the onset oxidation and onset reduction potentials, respectively, relative to the
ferrocene/ferrocenium couple whose energy level is already known (-4.8 eV). The HOMO and
LUMO energy levels of FTC were estimated to be -5.88 eV and -2.88 eV, respectively as well as
el
its electrochemical band-gap (Eg ) was 3.0 eV.
On the other hand, the optical band gap (Egopt.) was estimated to 2.55 eV from the onset
absorption wavelength 486 nm obtained from the absorption spectrum of FTC in the film state
18

View Article Online
DOI: 10.1039/C3OB42054J
(Figure 1). The energy band gaps obtained by optical method and cyclic voltammetry were 2.55 eV
el
el
and 3 eV, respectively. Electrochemically-estimated band-gap (Eg ), calculated using Eg
=
LUMO − HOMO, is slightly different from optical band-gap (Egopt) obtained from onset
el
absorption. The electrochemical band-gap (Eg ) is the energy difference between the LUMO and
HOMO levels, which in turn are estimated from the onset oxidation and reduction potentials,
respectively. However, oxidation and reduction may start from different parts of a molecule which
is composed of electron-donating and electron-withdrawing groups. Therefore, the discrepancy
el
between the band-gaps determined electrochemically (Eg ) and optically (Egopt) is probably due to
their different estimating bases. Due to FTC is comprised of conjugated fluorene core and three
crown ethers, oxidation may start from the electron-donating crown ether parts, and reduction may
start from the conjugated core of FTC.
Table 3. Electrochemical properties of FTC
Eonset(ox)
Eonset(red)
EHOMO
(eV)b
-5.88
ELUMO
(eV)b
-2.88
Egel
(eV)c
3.00
Compound
vs. FOC(V)a vs. FOC(V)a
FTC
1.08
-1.92
a EFOC= 0.49 V vs. Ag/AgCl.
b EHOMO= -(Eonset(ox)
FOC +4.8) eV; ELUMO = -(Eonset(red)
c Eg = |LUMO – HOMO|
,
, FOC + 4.8 ) eV.
Electroluminescent Enhancement of PLEDs by inserting FTC
According to the energy band diagrams depicted in Figure 10, the energy barrier between
aluminum (A1) and MEH-PPV (1.60 eV) is larger than that between PEDOT:PSS and MEH-PPV
(0.02 eV). Moreover, holes are usually more readily transported than electrons in conjugated
materials, leading to reduced recombination ratio of holes and electrons. However, the charge
injection/transport imbalance in MEH-PPV can be alleviated by inserting the electron injection and
hole-blocking layer FTC in which both LUMO and HOMO energy levels are lower than those of
MEH-PPV. The lowered LUMO and HOMO levels give rise to enhanced electron
injection/transport and hole-blocking, respectively, in MEH-PPV based devices, resulting in more
balanced charges recombination.
19

View Article Online
DOI: 10.1039/C3OB42054J
-2.70
-2.88
FTC
-5.88
MEH-PPV
Al
-4.3
ITO
PEDOT
-4.8
-5.0
-5.02
Figure 10. The energy band diagrams of MEH-PPV, with those of FTC, PEDOT:PSS, and
electrodes.
Multi-layer polymer light-emitting diodes (PLEDs) with
a
configuration of
ITO/PEDOT:PSS/MEH-PPV(90~100 nm)/EIL/Al(80 nm) were fabricated to investigate their
electroluminescent characteristics. In this work, we propose the use of a water/alcohol-soluble FTC
blended with M2CO3 (M = Na, K, Cs) as electron injection layer (EIL) in a PLED with MEH-PPV
as the emitting layer (EML), the optimal condition for processing the EIL materials in PLEDs was
to use water and alcohol (v/v = 1/5) as solvent for spin-coating. The ratio of FTC/M+ was fixed at
1:9 (azacrown/M+
=
1:3) and the concentration was
1
mg FTC/ml. Current
density–luminance–voltage (J–L–V) and luminous efficiency–current density (LE–J) characteristics
of the devices are shown in Figure 11 and Figure 12, with the corresponding optoelectronic data
summarized in Table 4. Electroluminescent performances are significantly enhanced by inserting
the electron-injection layer (FTC or doped FTC) between emitting layer (MEH-PPV) and Al
cathode.
The turn-on voltages are slightly decreased from 4.8 V to 4.6 V by inserting the
electron-injection layer (EIL: neat FTC) between emitting layer (MEH-PPV) and Al cathode (Table
4). This is mainly attributed to effectively promoted electron injection/transport with FTC as EIL.
20

View Article Online
DOI: 10.1039/C3OB42054J
104
103
102
101
Non EIL
FTC
FTC + Na2CO3
FTC + K2CO3
FTC + Cs2CO3
0
2
4
6
8
10
12
Voltage (V)
1000
800
600
400
200
0
Non EIL
FTC
FTC + Na2CO3
FTC + K2CO3
FTC + Cs2CO3
0
2
4
6
8
10
12
Voltage (V)
Figure 11. Luminance versus voltage and current density versus voltage characteristics of PLEDs.
Device structure: ITO/PEDOT:PSS/MEH-PPV(90~100 nm)/EIL/Al(80 nm).
Moreover, maximum luminance and current efficiency of devices were greatly increased from 230
cd/m2 and 0.03 cd/A to 1990 cd/m2 and 0.65 cd/A, respectively, by inserting the electron-injection
layer (EIL: neat FTC). The performance enhancement is attributable to the hole-blocking and
electron injection effect of FTC that raises charges recombination ratio. The lower HOMO level of
21

View Article Online
DOI: 10.1039/C3OB42054J
FTC (-5.88 eV) than emitting layer MEH-PPV (-5.02 eV) results in the accumulation of holes in
the interface between emitting and FTC layers. Moreover, the lower LUMO level of FTC (-2.88
eV) than emitting layer MEH-PPV (-2.70 eV) promotes electron injection (Figure 10). Therefore,
holes will readily combine with electrons passing through the interface to increase the
recombination ratio.
1.6
1.4
1.2
1.0
0.8
Non EIL
FTC
FTC + Na2CO3
0.6
0.4
0.2
0.0
FTC + K2CO3
FTC + Cs2CO3
0
200
400
600
800
Current density (mA/cm2)
Figure 12. Luminous efficiency versus current density characteristics of PLEDs. Device structure:
ITO/PEDOT:PSS/MEH-PPV(90~100 nm)/EIL/Al(80 nm).
The device performances using MEH-PPV as emitting layer were further significantly
enhanced in the presence of metal carbonates M2CO3 (M = Na, K, Cs) (Table 4). The turn-on
voltages with doped-FTC are greatly decreased from 4.8 V to 3.1 V due to abundant
azacrown-chelated M+. The chelated metal cation (M+) can further reduce the electron-injection
barrier through the formation of an interfacial dipole and the establishment of an intermediate step
for electron injection.43 The devices using K2CO3-doped FTC as EIL reveal the best performance,
i.e., the maximum luninance and current efficiencies of the device based on MEH-PPV were further
promoted to 11630 cd/m2 and 1.47 cd/A, respectively (Table 4). Moreover, these performances are
superior to those obtained with conventional Ca/Al cathode (3230 cd/m2 and 0.29 cd/A) (Table 4).
In addition, The 1931 CIE coordinates (x, y) of the EL emission shift slightly from (0.51, 0.49) to
22

View Article Online
DOI: 10.1039/C3OB42054J
(0.57, 0.43) with non-FTC, FTC and doped-FTC, which originated from MEH-PPV emission
(Figure 13). Consequently, the potassium carbonate-doped FTC as EIL effectively promoted
electron injection/transport to significantly enhance the device performance.
Table 4. Optoelectronic Properties of the Light-emitting Diodes Based on MEH-PPVa
Von
(V)b
L max
(cd/m2)c
CE max
(cd/A)d
CIE
(x, y)f
EIL
None
Ca26e
4.8
3.3
4.6
3.6
3.1
3.6
230
3230
1990
5190
11630
7240
0.03
0.29
0.65
1.13
1.47
1.42
(0.51, 0.49)
(0.54, 0.46)
(0.57, 0.43)
(0.56, 0.43)
(0.54, 0.46)
(0.55, 0.45)
FTC
FTC + Na2CO3
FTC + K2CO3
FTC + Cs2CO3
a [ITO/PEDOT:PSS/MEH-PPV (90~100 nm)/EIL/Al (80nm)].
b Turn-on voltage at 10 cd/m2.
c Maximum luminance.
d Maximum current efficiency.
e Maximum luminous power efficiency.
f The 1931 CIE coordinate at Maximum luminance.
1.2
non-EIL
FTC
FTC + Na2CO3
1.0
0.8
0.6
0.4
0.2
0.0
FTC + K2CO3
FTC + Cs2CO3
250 300 350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Figure
13.
Emission
spectra
of
PLEDs.
Device
configuration:
ITO/PEDOT:PSS/MEH-PPV(90~100 nm)/EIL/Al(80 nm).
23

View Article Online
DOI: 10.1039/C3OB42054J
Conclusions
We have successfully synthesized the multi-functional FTC comprising of tiple
monoaza-15-crown-5 ether and fluorene-based moiety. The FTC was satisfactorily characterized by
1H NMR, COSY, NOESY, FT-IR and elemental analysis. The absorption and fluorescence spectra
of FTC red shifted with gradually increasing the polarity of solvents. Fluorescence of FTC solution
was selectively quenched by Fe3+ cation, with static (dynamic) Stern-Volmer constants (Ksv) being
1.15×104 M-1 (1.59×105 M-1) in THF/H2O and 2.90×103 M-1 (1.54×104 M-1) in ethanol/H2O
mixtures. The selective recognition of FTC toward Fe3+ was still maintained in the presence of ten
interfering metal cations. The absorption and fluorescence spectra of FTC were blue-shifted and
quenched in the presence of hydrochloric acid, respectively. The HOMO and LUMO energy levels
of FTC were estimated to be -5.88 eV and -2.88 eV, respectively. The FTC was a highly efficient
EIL, especially after addition with metal carbonates M2CO3 (M = Na, K, Cs). The maximum
luminance and current efficiency of devices were greatly increased from 230 cd/m2 and 0.03 cd/A
to 1990 cd/m2 and 0.65 cd/A, respectively, by inserting the electron-injection layer (EIL: neat FTC).
Furthermore, the device performance based on MEH-PPV with K2CO3-doped FTC as EIL were
further promoted to 11630 cd/m2 and 1.47 cd/A, respectively which are superior to those obtained
with conventional Ca/Al cathode (3230 cd/m2 and 0.29 cd/A). Current results demonstrate that FTC
is not only a promising chemical sensor for the detection of Fe3+ but also applied as electron
injection layer effectively promoted electron injection/transport to significantly enhance the device
performance of MEH-PPV.
References
(1) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.;
Bruns, P. L.; Holmes, A. B. Nature 1990, 347, 539.
(2) Akcelrud, L. Prog. Polym. Sci. 2003, 28, 875.
(3) (a) Satrijo, A.; Swager, T. M. J. Am. Chem. Soc. 2007, 129, 16020. (b) Kim, J.; McQuade, D. T.;
McHugh, S. K.; Swager, T. M. Angew. Chem. Int. Ed. 2000, 39, 3868.
(4) Pu, K. Y.; Pan, S. Y. H.; Liu, B. J. Phys. Chem. B 2008, 112, 9295.
(5) Colladet, K.; Fourier, S.; Cleij, T. J.; Lutsen, L.; Gelan, J.; Vanderzande, D.; Nguyen, L. H.;
Neugebauer, H.; Sariciftci, S.; Aguirre, A.; Janssen, G.; Goovaerts, E. Macromolecules 2007, 40,
24

View Article Online
DOI: 10.1039/C3OB42054J
65.
(6) Liu, C. L.; Tsai, J. H.; Lee, W. Y.; Chen, W. C.; Jenekhe, S. A. Macromolecules 2008, 41, 6952.
(7) Horowitz, G. Adv. Mater. 1998, 10, 365.
(8) Baek, N. S.; Hau, S. K.; Yip, H. L.; Acton, O.; Chen, K. S.; Jen, A. K. Y. Chem. Mater. 2008,
20, 5734.
(9) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.;
Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97, 1515.
(10) Butler, O. T.; Cook, J. M.; Harrington, C. F.; Hill, S. J.; Rieuwerts, J.; Miles, D. L. J. Anal. At.
Spectrom. 2006, 21, 217.
(11) Quang, D. T.; Kim, J. S. Chem. Rev. 2010, 110, 6280.
(12) Lee, J. W.; Jung, H. S.; Kwon, P. S.; Kim, J. W.; Bartsch, R. A.; Kim, Y.; Kim, S.-J.; Kim, J. S.
Org. Lett. 2008, 10, 3801.
(13) Lee, Y. Z.; Chen, X.; Chen, S. A.; Wei, P. K.; Fann, W. S. J. Am. Chem. Soc. 2001, 123, 2296.
(14) Garten, F.; Hilberer, A.; Cacialli, F.; Esselink, E.; Dam, Y. V.; Schlatmann, B.; Friend, R. H.;
Klapwijk,T. M.; Hadziioannou, G. Adv. Mater. 1997, 9, 127.
(15) (a) Takiguchi, T.; Park, D. H.; Ueno, H.; Yoshino, K.; Sugimoto, R. Synth Met 1987, 17, 657.
(b) Braun, D.; Heeger, A. J. Appl Phys Lett 1991, 58, 1982.
(16) (a) Kraft, A.; Burn, P. L.; Holmes, A. B.; Bradley, D. D. C.; Friend, R. H.; Martens, J. H. F.
Synth Met 1993, 57, 4163. (b) Antoniadis, H.; Abkowitz, M. A.; Hsieh, B. R. Appl Phys Lett
1994, 65, 2030.
(17) (a) Meyer, H.; Haarer, D.; Naarmann, H.; Hörhold, H. H. Phys Rev B 1995, 52, 2587. (b)
Blom, P. W. M.; de John, M. J. M.; Vleggaar, J. J. M. Appl Phys Lett 1996, 68, 3308.
(18) (a) Yang, Y.; Pei, Q.; Heeger, A. J. J Appl Phys 1996, 79, 934. (b) Wang, Y. Z.; Gebler, D. D.;
Spry, D. J.; Fu, D. K.; Swager, T. M.; MacDiarmid, A. G.; Epstein, A. J. IEEE Trans Electron
Devices 1997, 44, 1263.
(19) (a) Li, X.-C.; Grimsdale, A. C.; Cervini, R.; Holmes, A. B.; Moratti, S. C.; Yong, T. M.;
Grüner, J.; Friend, R. H. ACS Symp Ser 1997, 672, 322. (b) Meng, H.; Yu, W. L.; Huang, W.
Macromolecules 1999, 32, 8841. (c) Martens, H. C. F.; Huiberts, J. N.; Blom, P. W. M. Appl
25

View Article Online
DOI: 10.1039/C3OB42054J
Phys Lett 2000, 77, 1852.
(20) (a) Huang, F.; Wu, H. B.; Wang, D. L.; Yang, W.; Cao, Y. Chem. Mater. 2004, 16, 708. (b)
Huang, F.; Niu, Y. H.; Zhang,Y.; Ka, J. W.; Liu, M. S.; Jen, A. K. Y. Adv. Mater. 2007, 19,
2010. (c) Huang, F.; Zhang,Y.; Liu, M. S.; Jen, A. K. Y. Adv. Funct. Mater. 2009, 19, 2457. (d)
Huang, F.; Shih, P. I.; Shu, C. F.; Chi, Y.; Jen, A. K. Y. Adv. Mater. 2009, 21, 361.
(21) Oh, S. H.; Vak, D.; Na, S. I.; Lee, T. W.; Kim, D. Y. Adv. Mater. 2008, 20, 1624.
(22) Hoven, C. V.; Garcia, A.; Bazan, G. C.; Nguyen, T. Q. Adv. Mater. 2008, 20, 1.
(23) (a) Yang, R.; Wu, H.; Cao, Y.; Bazan, G. C. J. Am. Chem. Soc. 2006, 128, 14422.(b) Xu, X.;
Han, B.; Chen, J.; Peng, J.; Wu, H.; Cao, Y. Macromolecules 2011, 44, 4204.
(24) (a) Kreyenschmidt, M.; Klaerner, G.; Fuhrer, T.; Ashenhurst, J.; Karg, S.; Chen, W. D.; Lee, V.
Y.; Scoot, J. C.; Miller, R. D. Macromolecules, 1998, 31, 1099. (b) Grice, A. W.; Bradley, D. D.
C.; Bernius, M. T.; Inbasekaran, M.; Wu, W. W.; Woo, E. P. Appl. Phys. Lett., 1998, 73, 629.
(25) (a) Scherf, U.; List, E. J. W. Adv. Mater., 2002, 14, 477. (b) Becker, S.; Ego, C.; Grimsdale, A.
C.; List, E. J. W.; Marsitzky, D.; Pogantsch, A.; Setayesh, S.; Leising, G.; Müllen, K. Synth. Met.,
2002, 125, 73. (c) Babel, A.; Jenekhe, S. A. Macromolecules, 2003, 36, 7759. (d) Cho, N. S.;
Hwang, D.-H.; Jung, B.-J.; Lim, E.; Lee, J.; Shim, H.-K. Macromolecules, 2004, 37, 5265.
(26) (a) Wu, C.-S.; Chen, Y. Macromolecules, 2009, 42, 3729. (b) Wu, C.-S.; Chen, Y. J. Mater.
Chem., 2010, 20, 7700. (c) Wu, C.-S.; Chen, Y. J. Polym. Sci. Part A Polym. Chem., 2010, 48,
5727. (d) Wu, C.-S.; Lee, S.-L.; Chen, Y. J. Polym. Sci. Part A Polym. Chem., 2011, 49, 3099. (e)
Wu, C.-S.; Chen, Y. J. Polym. Sci. Part A Polym. Chem., 2011, 49, 3928. (f) Wu, C.-S.; Yang,
Y.-J.; Fang, S.-W.; Chen, Y. J. Polym. Sci. Part A Polym. Chem., 2012, 50, 3875 (g) Wu, C.-S.;
Lee, Y.-T.; Chen, Y. Polym. Chem., 2012, 3, 2776. (h) Wu, C.-S.; Liu, C.-T.; Chen, Y. Polym.
Chem., 2012, 3, 3308. (i) Wu, C.-S.; Wu, J.-W.; Chen, Y. J. Mater. Chem., 2012, 22, 23877. (j)
Wu, C.-S.; Chen, C.-P.; Chen, Y. J. Polym. Sci. Part A Polym. Chem., 2013, 51, 3975. (k) Wu,
C.-S.; Fang, S.-W.; Chen, Y. Phys. Chem. Chem. Phys., 2013, 15, 15121. (l) Wu, C.-S.; Lu,
H.-A.; Lin, Y.-J.; Chen, Y. J. Mater. Chem. C 2013, 1, 6850. (m) Wu, C.-S.; Lu, H.-A.; Chen,
C.-P.; Kuo, T.-F.; Chen, Y. Org. Biomol. Chem. 2014, 12, .
26

View Article Online
DOI: 10.1039/C3OB42054J
(27) Fabre, B.; Simonet, J. Coord. Chem. Rev. 1998, 178-180, 1211.
(28) Greenwood, N. N., Earnshaw, A. , Chemistry of the Elements. Pergamon Press Inc.: Tarrytown,
1984; p 105–110.
(29) Saalfrank, R. W.; Löw, N.; Kareth, S.; Seitz, V.; Hampel, F.; Stalke, D.; Teichert, M. Angew.
Chem. Int. Ed. 1998, 37, 172.
(30) Coulson, D. R.; Satek, L. C.; Grim, S. O. Inorg. Synth. 1972, 13, 121.
(31) Lakowicz, J. R., Solvent and Evironmental Effects. In Principles of Fluorescence
Spectroscopy, 3rd ed.; springer: 2006; Vol. chapter 6.
(32) Létard, J.-F., Lapouyade, R., Rettig, W. Pure Appl. Chem. 1993, 65, 1705.
(33) Xia, W.-S.; Schmehl, R. H.; Li, C.-J. J. Am. Chem. Soc. 1999, 121, 5599.
(34) Fabbrizzi, L.; Poggi, A. Chem. Soc. Rev. 1995, 24, 197.
(35) Callan, J. F.; de Silva, A. P.; Magri, D. C. Tetrahedron 2005, 61, 8551.
(36) Lakowicz, J. R., Introduction to Fluorescence. In Principles of Fluorescence Spectroscopy, 3rd
ed.; springer: 2006; Vol. chapter 1, p 13.
(37) Valeur, B.; Leray, I. Coord. Chem. Rev. 2000, 205, 3.
(38) Lakowicz, J. R., Quenching of Fluorescence. In Principles of Fluorescence Spectroscopy, 3rd
ed.; springer: 2006; Vol. chapter 8.
(39) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537.
(40) Thomas, S. W.; Joly, G. D.; Swager, T. M. Chem. Rev. 2007, 107, 1339.
(41) Yu, J.-M.; Chen, Y. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 2985.
(42) Skoog, D. A., Holler, F. J., Nieman, T. A. , Principles of Instrumental Analysis. In 5th ed.;
Harcourt Brace & Co.: 1998; Vol. chapter 15.
(43) Lu, H. H.; Ma, Y. S.; Yang, N. J.; Lin, G. H.; Wu, Y. C.; Chen, S. A. J. Am. Chem. Soc. 2011,
133, 9634.
27