Electrogenerated chemiluminescence of N,N-dimethylamino functionalized tetrakis(phenylethynyl)pyrenes

Article abstract of DOI:10.1016/j.tet.2013.05.010

The synthesis of star-shaped molecules, comprising a pyrene core with tetrakis(phenylethynyl) arms substituted with N,N-dimethylamino and propyl groups (1-5), is reported. The electrochemical and photophysical properties of 1-5 depend on the number of N,N-dimethylamino groups on the tetrakis(phenylethynyl)pyrene framework. In electrogenerated chemiluminescence (ECL) studies, the spectra of 4 and 5 show red-shifts and band broadening; in contrast, 1 exhibits a typical high-intensity pyrene ECL emission. It was confirmed that the ECL spectra arise from the intramolecular charge transfer (ICT) induced by the annihilation of radical ions owing to the presence of a strong donor.

Full text of DOI:10.1016/j.tet.2013.05.010

Tetrahedron 69 (2013) 5908e5912
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Electrogenerated chemiluminescence of N,N-dimethylamino
functionalized tetrakis(phenylethynyl)pyrenes
,
,
,
,
*
Yeon Ok Lee a, Tuhin Pradhan a b, Kihang Choi a b, Dong Hoon Choi a b, Joung Hae Lee c
,
,
Jong Seung Kim a
*
a Department of Chemistry, Korea University, Seoul 136-701, Republic of Korea
b Research Institute for Natural Sciences, Korea University, Seoul 136-701, Republic of Korea
c Korea Research Institute of Standards and Science, Daejon 305-600, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of star-shaped molecules, comprising a pyrene core with tetrakis(phenylethynyl) arms
substituted with N,N-dimethylamino and propyl groups (1e5), is reported. The electrochemical and
photophysical properties of 1e5 depend on the number of N,N-dimethylamino groups on the tetraki-
s(phenylethynyl)pyrene framework. In electrogenerated chemiluminescence (ECL) studies, the spectra of
4 and 5 show red-shifts and band broadening; in contrast, 1 exhibits a typical high-intensity pyrene ECL
emission. It was confirmed that the ECL spectra arise from the intramolecular charge transfer (ICT)
induced by the annihilation of radical ions owing to the presence of a strong donor.
Received 23 March 2013
Received in revised form 2 May 2013
Accepted 7 May 2013
Available online 10 May 2013
Keywords:
Tetrakis(phenylethynyl)pyrene
Substitution N,N-dimethylamino group
Radical stability
Ó 2013 Elsevier Ltd. All rights reserved.
Intramolecular charge transfer (ICT)
1. Introduction
However, to date, it has not been determined why the ECL band is
affected by changing the functionalization of pyrenes, such as by
In electrogenerated chemiluminescence (ECL), a radical species
generated at an electrode undergoes a high-energy electron-
transfer reaction to form an excited species, which then emits
light.1 The ECL efficiency of luminophores is one of the most im-
portant criteria for the evaluating the performance of light-
emitting materials.2 For the ECL systems of optoelectronic de-
vices, pyrene is a possible radical candidate because of its prom-
inent photophysical properties.3 However, the pyrene molecule has
a serious disadvantage as well; the pyrenyl cation radical, which
forms in an ECL process, is unstable owing to its intrinsic electron
deficiency.4
using electron-donating groups.
Introduction of certain functional groups to
p-conjugation
systems can induce different ECL patterns, presumably because
their annihilation mechanisms are intrinsically different. In par-
ticular, in the presence of strong acceptors or donors in the parent
molecule, an excited intramolecular charge transfer (ICT) occurs
by the collision of radical anions with radical cations to provide
ECL, as seen in Scheme 1.8,9 The ICT generally quenches the fluo-
rescence because of a nonradiative pathway; therefore, it could be
considered as a factor to change ECL efficiency in optoelectronic
materials.1b,9
In order to improve the stability of the pyrenyl cation so
that they could be used in ECL applications, many pyrene de-
rivatives have been exploited. It has been reported that the
ECL efficiency of pyrene is markedly enhanced by increasing
p
eelectron conjugation using specific functional groups on the
pyrene framework.5e7 Among the various pyrene derivatives, the
tetrakis(phenylethynyl)pyrene framework shows high ECL activity
because of its considerably developed
peelectron networks com-
pared to the mono-, bis-, and tris-substituted pyrene molecules.5,7
Scheme 1. ECL emission of donor (D)eacceptor (A)-type luminophores. (1) Radical
cation formation. (2) Radical anion formation. (3) ICT formation by direct annihilation.
(4) ECL emission.
* Corresponding authors. E-mail addresses: ecljh@kriss.re.kr (J.H. Lee), jong-
skim@korea.ac.kr (J.S. Kim).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.05.010

Y.O. Lee et al. / Tetrahedron 69 (2013) 5908e5912
5909
In this study, various electrochemical and photophysical ex-
periments were performed to investigate the possibility that when
tetrakis(phenylethynyl)pyrene molecules with different dimethy-
lamino groups (electron donors) are used, the ECL changes so
produced are closely related to ICT. This phenomenon has not been
exploited before in the ECL studies of the tetrakis-substituted
pyrene derivatives. For this purpose, we synthesized tetraki-
s(phenylethynyl)pyrene derivatives whose structures are depicted
in Scheme 2.
Fig. 1. Cyclic voltammograms of 1e5 (0.5 mM) with a Pt electrode using Bu4NPF6 in
CH2Cl2 (0.1 M). Scan rate¼100 mV sꢀ1
.
Finally, although the oxidation peaks for 1, 4, and 5 showed good
reversibility, the peaks had considerable differences in the current
magnitudes. The magnitudes of the anodic peak currents (ipa w17
and ipa w12 A) for 4 and 5 were three times higher than the anodic
current of 1 (ipa w4 A). This implies that with one electron per
mA
m
Scheme 2. Molecular structures of 1e5.
m
donor atom, more than three electrons were involved in the oxida-
tion process in 4 and 5. The oxidation and reduction phenomena
observed above show that the dimethylamino substituents in a tet-
rakis(phenylethynyl)pyrene molecule play a crucial role in the redox
process, i.e., the cation radical formed by oxidation is very sensitive
to the dimethylamino groups. Therefore, it was concluded that in the
pyrenyl derivatives, oxidation and reduction take place on the
electron-donor atom (AeDꢁþ) and pyrene core (AꢁꢀeD), respectively.
Absorption and fluorescence behaviors of all the synthesized
compounds were determined in the same solvent used for elec-
trochemistry and ECL experiments and are shown in Fig. 2a and b,
respectively. Table 1 summarizes the photophysical parameters of
1e5. As the number of donating peripheral substituents increases,
the corresponding wave bands red-shifted. These results are in
agreement with a previous report, which states that an electron-
donating group allows the HOMO energy level of certain mole-
cules to effectively upshift, causing a red-shift in the absorption
spectra.11
2. Results and discussion
Pyrene derivatives (2e4) were synthesized by Sonogashira
coupling reactions of 6e8 with 4-ethynylpropylbenzene as shown
in Scheme 3. Compounds 1, 5, and 6e8 were prepared by adapting
the procedures reported earlier.5e7
Scheme 3. Syntheses of 2e4. Reagents and conditions: (a) PdCl2(PPh3)2, CuI, PPh3,
Et3N, toluene, 100 ꢂC, 3 h.
Table 1
Parameters obtained from the electrochemical, optical, and theoretical studies for
1e5
To gain an insight on the influence of a dimethylamino group on
the electrochemical properties of tetrakis(phenylethynylpyrene),
cyclic voltammetry (CV) was performed using Bu4NPF6 in CH2Cl2
(0.1 M) with a Pt electrode. These results are summarized in Fig. 1
and Table 1. Each compound, 1e4, showed one reversible re-
duction peak at ꢀ1.93, ꢀ1.87, 1.89, and 1.91 V versus SCE, re-
spectively, in contrast, no reverse peak was observed for 5 at 1.91 V.
Similar reduction potentials were observed in 1e5, which indicates
that the formation of radical anions can be ascribed, not to the
nature of the functional groups on the phenyl rings, but to the
pyrenyl core.5,7
Compound
1
2
3
4
5
abs
l
l
l
[nm]a
[nm]
[nm]
470
473
488
508
509
max
em
494
612
596
d
591
d
603
633
556
624
max
ECL
max
Stokes shift [nm]
24
118
123
d
103
d
123
28
47
68
ECL
em
max
l
ꢀ
l
[nm]
max
Fb
0.78
ꢀ1.938
0.543
2.48
2.52
2.50
ꢀ4.79
ꢀ2.29
0.44
ꢀ1.877
0.321
2.20
2.36
2.43
ꢀ4.59
ꢀ2.16
0.22
ꢀ1.899
0.269
2.17
2.30
2.39
ꢀ4.43
ꢀ2.04
0.47
ꢀ1.910
0.159
2.06
2.29
2.37
ꢀ4.29
ꢀ1.92
0.60
ꢀ1.910
0.082
1.99
2.27
2.37
ꢀ4.17
ꢀ1.80
Epc [V]
Epa [V]
[eV]c
[eV]d
[eV]e
elec
D
D
D
E
E
E
gap
opt
gap
calc
gap
In contrast, the oxidation peaks of 1e5 showed a trend different
from the reduction peaks. First, as the number of donating peripheral
substituents increase (from 1 to 5), the compounds are more easily
oxidized in the order 0.543)0.321)0.269)0.159)0.082 V versus
SCE. Second, the reversibility of the oxidation peaks varied on in-
creasing the number of donor atoms. Reversibility in the oxidation
peaks was observed for compounds 1, 4, and 5, but not for 2 and 3.
These results suggest that electronic communication between the
peripheral donor groups and the central acceptors occurs in 2 and 3.
HOMO (eV) (calcd)
LUMO (eV) (calcd)
a
Recorded at the maximum of the longest spectra in absorption.
Using Rhodamine 6G in CH2Cl2. Ff¼0.95 in EtOH. Photophysical data was ob-
b
tained in CH2Cl2.10
c
Electrochemical band gap calculated from the difference between the two redox
peak potentials.
d
HOMOeLUMO gap calculated from the lowest-energy UV/vis absorption value
in CH2Cl2. The photophysical and electrochemical data were obtained in CH2Cl2.
e
HOMOeLUMO gap calculated by DFT method at B2LYP/6-31G(d) level of theory.

5910
Y.O. Lee et al. / Tetrahedron 69 (2013) 5908e5912
Fig. 2. Steady-state absorption (a) and fluorescence spectra (b) of 1e5 in CH2Cl2. (c)
Fluorescence spectra of 1e5 in toluene and CH2Cl2.
Compounds 2e4 exhibited broad emission bands centered at
w600 nm, while the maxima of 5 is seen at 556 nm with a narrower
band. Compound 1 shows a band at 494 nm with a shoulder peak at
525 nm, which is a typical pyrene emission pattern. A relatively
large Stokes shift of 115 nm was observed in 2e4; in contrast, only
a small Stokes shift of 47 nm was seen for 5. However, the Stokes
shift observed in 5 was still greater than that in 1 (24 nm). To gain
an insight into this distinctive difference, the emission spectra for
all compounds were compared using different solvents (Fig. 2c). In
toluene, compounds 2e5 showed almost the same fluorescence
patterns as 1. This reflects that the fluorescence spectra in toluene
originate from the FrankeCondon (FC) excited state (or LE state),
suggesting negligible CT character. In CH2Cl2 (a more polar solvent),
the emission bands of 1e5 are different: 494, 596, 591, 603, and
556 nm, respectively. For 2e4, the fluorescence difference in tolu-
ene from CH2Cl2 is 64 nm, whereas for 5, it is only 19 nm, obviously
because of 5’s nonpolar property as verified in previous studies.5c
This confirms that in a more polar solvent (CH2Cl2), the more de-
veloped ICT band gives a larger Stokes shift. Because the degree of
ICT character of 2e5 in CH2Cl2 is rather weak and revealed mod-
erate fluorescence quantum yields (0.44, 0.22, 0.47, and 0.60, re-
spectively), they should be worthy of application for ECL.
Fig. 3. Profiles of frontier molecular orbitals (highest occupied and lowest unoccupied
of 1e5). Green and red correspond to the different phase of the molecular wave
functions for the HOMOs and LUMOs, and the isovalue is 0.02 au.
To get insight into the electronic structures, calculation based on
density functional theory (DFT) at B3LYP/6-31G(d) level of theory
was performed on compounds 1e5. From the HOMO-LUMO gaps,
electrochemical measurements (the difference between oxidation
and reduction potentials) and lowest-energy absorption band max-
ima are listed in Table 1. We noticed that there is a good agreement
between computed and experimental results. The HOMO energy
increases in going from 1 to 5 (Table 1), which is well correlated with
easier oxidation with increasing number of donor groups (2)5) as
the electrons of donor groups can be released more easily. Frontier
molecular orbital surfaces of 1e5 are depicted in Fig. 3. The electron
density in HOMOs of 2e5 resides on the pyrene core as well as on the
donor arms and electron density delocalization increases with in-
creasing number of donor groups (2)5). This overall electron
density delocalization in HOMO surfaces could explain the enhanced
radical stability in going from 2 to 5, because upon oxidation the
electron-deficient cation radical could be stabilized by other
electron-rich donor arms. On the other hand, LUMO is mainly lo-
cated on pyrene core with some degree of orbital coefficient on triple
bond bridges. In this reason, the reduction peaks show little changes
among 1e5. In addition, the intramolecular charge transfer (ICT)
from peripheral donor arms to pyrene core occurs.
showed a strong ECL emission at 612 nm because of an excimer
band formed by radical ion annihilation, caused by its planar
nature.1b,7 It was then found that the ECL intensity of 5 at 624 nm is
five times smaller than that of 1 and also that 4 shows a much
weaker ECL band. However, no ECL activities were observed in 2 or
3, which is mostly because of instability of the cation radicals. It is
notable that the ECL emission of 4 is very weak, despite its elec-
trochemical stability in both oxidation and reduction processes. To
understand the quenching behaviors of 4 and 5 in ECL spectra, their
fluorescence spectra were compared. The ECL bands of 4 and 5
exhibited red-shifts of 30 and 68 nm, respectively, compared to
their fluorescence bands. This undoubtedly implies that the ICT
behaviors in 4 and 5 are more developed in electrochemical lumi-
nescence than in conventional fluorescence. This is in agreement
with the fact that a compound, having both donor and acceptor
units and, which shows oxidation and reduction independently in
each part, tends to exhibit longer wavelength emission in ECL than
in excited state-driven fluorescence, as depicted in Scheme 1.1b As
a result, it is concluded that compounds 2 and 3 have an ICT
character but negligible ECL intensity because of their radical in-
stability. On the other hand, compounds 4 and 5 reveal more de-
veloped ICT as well as stable radical formation for annihilation and
give a red-shifted and quenched ECL intensity.
The ECL spectra of 1e5 (0.5 mM/CH2Cl2) were recorded with
0.1 M Bu4NPF6 as a supporting electrolyte (Fig. 4). Compound 1

Y.O. Lee et al. / Tetrahedron 69 (2013) 5908e5912
5911
water (200 mL). The organic layer was separated and dried over
anhydrous MgSO4 followed by solvent removal under vacuum. Col-
umn chromatography (silica gel, hexane/dichloromethane, 8/2, v/v)
gave 45 mg (34%) of an orange red powder. Mp 240e248 ꢂC. IR (KBr
pellet, cmꢀ1): 2200 (C^C), 1594, 1511. 1H NMR (300 MHz, CD2Cl2):
d
8.74 (m, 4H), 8.42 (s,1H), 8.39 (s,1H), 7.68 (d, J¼7.9 Hz, 6H), 7.62 (d,
J¼8.8 Hz, 2H), 7.30 (d, J¼8.1 Hz, 6H), 6.75 (d, J¼8.8 Hz, 2H), 3.06 (s,
6H), 2.68 (t, J¼7.6 Hz, 6H),1.77e1.65 (m, 6H),1.00 (t, J¼7.3 Hz, 9H).13C
NMR (100 MHz, CDCl3): d 150.5,143.8,133.7,133.2,132.4,132.3,131.9,
128.9,128.8,128.7,127.2,127.0,126.7,126.6,124.3,120.7,120.2,119.2,
118.9, 97.9, 96.4, 87.6, 86.3, 40.5, 38.3, 24.6, 14.0. MS (FAB) m/z: [M]þ
calcd for C59H49N 771.4; found 771.4.
Fig. 4. ECL spectra of 0.5 mM 1e5 with 0.1 M Bu4NPF6 in CH2Cl2 by pulsing (10 Hz)
between peak potentials for reduction and oxidation of the compounds, respectively.
4.3.2. 1,8-Bis[(4-N,N-dimethylaminophenyl)ethynyl]-3,6-bis(4-
propylphenylethynyl)pyrene (3). Compound 7 (200 mg, 0.56 mmol),
PdCl2(PPh3)2 (40 mg, 0.056 mmol), CuI (2.7 mg, 0.056 mmol), PPh3
(3.7 mg, 0.056 mmol), and 1-ethynyl-4-propylbenzene (242 mg,
1.68 mmol) were added to a gassed solution of triethylamine
(50 mL) and toluene (200 mL) under Ar. After stirring for 3 h at
100 ꢂC, the reaction mixture was poured into CH2Cl2 (200 mL) and
water (200 mL). The organic layer was separated and dried over
anhydrous MgSO4 followed by solvent removal in a vacuum. The
crude product was then subjected to column chromatography
(silica gel, hexane/dichloromethane, 7/3, v/v) to give 177 mg (41%)
of 3 as an orange red powder. Mp 242e260 ꢂC. IR (KBr pellet, cmꢀ1):
3. Conclusions
In conclusion, a series of tetrakis(phenylethynyl)pyrene de-
rivatives, compounds 1e5, bearing N,N-dimethyl and propyl groups
on their para-positions were synthesized, and their electrochemical
and photophysical properties were determined. In ECL studies, the
spectra of 4 and 5 show red-shifts with band broadening while 1
exhibits a typical high-intensity pyrene ECL emission. These ECL
spectra arise from the ICT induced by the annihilation of radical
ions because of the presence of a strong donor. It was shown that
compounds 2 and 3 show a good ICT pattern but negligible ECL
intensity, attributed to their radical instability. However, for com-
pounds 4 and 5, a more developed ICT followed by stable radical
formation for annihilation was demonstrated, and hence, a red-
shifted and quenched ECL intensity was observed.
2200 (C^C), 1597, 1511. 1H NMR (300 MHz, CD2Cl2):
d 8.75 (d,
J¼7.5 Hz, 4H), 8.38 (s, 2H), 7.68 (d, J¼7.9 Hz, 4H), 7.62 (d, J¼8.9 Hz,
4H), 7.30 (d, J¼8.0 Hz, 4H), 6.78 (d, J¼8.8 Hz, 4H), 3.06 (s, 12H), 2.68
(t, J¼7.73 Hz, 4H), 1.71 (m, 4H), 0.99 (t, J¼7.4 Hz, 6H). 13C NMR
(100 MHz, CD2Cl2): 150.6, 143.8, 133.3, 133.16, 131.9, 131.5, 128.9,
128.4, 126.9, 126.6, 124.4, 120.7, 119.9, 118.9, 112.1, 110.0, 97.9, 96.2,
87.6, 86.3, 40.4, 38.3, 24.6, 13.9. MS (FAB) m/z: [M]þ calcd for
C58H48N2 772.4; found 772.5.
4. Experimental section
4.1. Spectroscopic measurements
4.3.3. 1,3,6-Tris[(4-N,N-dimethylaminophenyl)ethynyl]-8-tris(4-
propylphenylethynyl)pyrene (4). Compound8(300mg, 0.422mmol),
PdCl2(PPh3)2 (30 mg, 0.042 mmol), CuI (10.5 mg, 0.042 mmol), PPh3
(11.4 mg, 0.042 mmol), and 1-ethynyl-4-propylbenzene (122 mg,
0.844 mmol) were added to a degassed solution of triethylamine
(20 mL) and toluene (100 mL) under Ar. The resulting mixture was
stirred at 100 ꢂC for 3 h. The solvent was removed under vacuum to
give 4. The crude product was then subjected to column chroma-
tography (silica gel, hexane/dichloromethane, 6/4, v/v) to yield 4
(137 mg, 42%) as a red powder. Mp 264e276 ꢂC. IR (KBr pellet, cmꢀ1):
Absorption spectra were recorded on a HewlettePackard 8453
diode array spectrophotometer with 20
mM solution of 1e5 in
CH2Cl2, while photoluminescence spectra were obtained with
a Hitachi F-7000 fluorescence spectrometer with a 1.0-cm standard
quartz cell using 3.0 M solutions in various solvents. The fluores-
cence quantum yields were determined using Rhodamine 6G as the
reference using the literature method.10
4.2. Electrochemistry measurements
2202 (C^C), 1596, 1513. 1H NMR (300 MHz, CD2Cl2):
d 8.74 (m, 4H),
CV was carried out using an electrochemical analyzer (CH In-
struments 624C). One-Hertz stepwise potentials were generated for
20 s using a CHI 624C. Electrochemical experiments were referenced
with respect to the Ag/AgCl reference electrode. All the potentials
were measured using ferrocene as an internal standard, where
Eo(Fcþ/Fc)¼70 mV versus Ag/AgCl. A platinum disk (2 mm di-
8.37 (s, 1H), 8.34 (s, 1H), 7.68 (d, J¼8.2 Hz, 2H), 7.61 (d, J¼8.9 Hz, 6H),
7.30 (d, J¼8.0 Hz, 2H), 6.78 (d, J¼8.9 Hz, 6H), 3.06 (s, 18H), 2.68 (t,
J¼7.6 Hz, 2H), 1.71 (m, 2H), 0.98 (t, J¼7.3 Hz, 3H). 13C NMR (100 MHz,
CDCl3):
d 150.0, 143.7, 133.3, 133.2, 133.1, 132.4, 132.3, 131.9, 128.9,
128.7, 127.0, 126.9, 126.6, 126.4, 127.5, 119.9, 119.6, 118.7, 112.1, 110.3,
97.6, 96.0, 87.8, 86.5, 40.5, 38.3, 24.6,14.0. MS(FAB)m/z: [M]þ calcd for
C57H47N3 773.4, found 773.4.
ameter) working electrode was polished on felt with 0.05 mM alu-
mina (Buehler), rinsed with water, and sonicated in absolute ethanol
for 5 min. Next, it was dried with Ar gas before each experiment.
Dichloromethane solutions for CV measurement contained 0.5 mM
tetrakis(ethynyl)pyrene and 0.1 M TBAPF6 as an electrolyte.
Acknowledgements
This work was supported by the CRI project (20120000243)
(J.S.K.) and Priority Research Centers Program (20120005860) of
Research Institute for Natural Sciences from NRF of Korea (K.C. and
D.H.C.).
4.3. Syntheses
4.3.1. 1-[(4-N,N-Dimethylaminophenyl)ethynyl]-3,6,8-tris(4-
propylphenylethynyl)pyrene (2). Compound 6 (100 mg, 0.172 mmol),
PdCl2(PPh3)2 (21 mg, 0.03 mmol), CuI (12 mg, 0.063 mmol), PPh3
(76 mg, 0.288 mmol), and 1-ethynyl-4-propylbenzene (100 mg,
0.688 mmol) were added to a degassed solution of triethylamine
(10 mL) and toluene (50 mL) under Ar. After the mixture was stirred
for 3 h at 100 ꢂC, the product was poured into CH2Cl2 (200 mL) and
Supplementary data
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.05.010.
These data include MOL files and InChiKeys of the most important
compounds described in this article.

5912
Y.O. Lee et al. / Tetrahedron 69 (2013) 5908e5912
4. Lai, R. Y.; Fleming, J. J.; Merner, B. L.; Vermeji, R. J.; Bodwell, G. J.; Bard, A. J. J.
References and notes
Phys. Chem. A 2004, 108, 376.
5. (a) Oh, J.-W.; Lee, Y. O.; Kim, T. H.; Ko, K. C.; Lee, J. Y.; Kim, H.; Kim, J. S. Angew.
Chem., Int. Ed. 2009, 48, 2522; (b) Kim, H. M.; Lee, Y. O.; Lim, C. S.; Kim, J. S.; Cho,
B. R. J. Org. Chem. 2008, 73, 5127; (c) Sung, J.; Kim, P.; Lee, Y. O.; Kim, J. S.; Kim,
D. J. Phys. Chem. Lett. 2011, 2, 818.
6. Lee, Y. O.; Pradhan, T.; No, K.; Kim, J. S. Tetrahedron 2012, 68, 1704.
7. Lee, Y. O.; Pradhan, T.; Yoo, S.; Kim, T. H.; Kim, J.; Kim, J. S. J. Org. Chem. 2012, 77,
11007.
8. (a) Lai, R. Y.; Fabrizio, E. F.; Jenekhe, S. A.; Bard, A. J. J. Am. Chem. Soc. 2001, 123,
9112; (b) Rashidnadimi, S.; Hung, T.-H.; Wong, K.-T.; Bard, A. J. J. Am. Chem. Soc.
2008, 130, 634.
9. (a) Kosower, E. M.; Dodiuk, H.; Kanety, H. J. Am. Chem. Soc. 1978, 100, 4179; (b)
Elangovan, A.; Lin, J.-H.; Yang, S.-W.; Hsu, H.-Y.; Ho, T.-I. J. Org. Chem. 2004, 69,
8086; (c) Elangovan, A.; Lin, J.-H.; Yang, S.-W.; Hsu, H.-Y.; Ho, T.-I. J. Org. Chem.
2005, 70, 1104.
10. (a) Crosby, G. A.; Demas, J. N. Phys. Chem. 1971, 75, 991; (b) Yang, W. J.; Kim, C.
H.; Jeong, M. Y.; Lee, S. K.; Piao, M. J.; Jeon, S. J.; Cho, B. R. J. Org. Chem. 2004, 16,
2783.
11. (a) Cocchi, C.; Prezzi, D.; Ruini, A.; Caldas, M. J.; Molinari, E. J. Phys. Chem. Lett.
2011, 2, 1315; (b) Cocchi, C.; Ruini, A.; Prezzi, D.; Caldas, M. J.; Molinari, E. J. Phys.
Chem. C 2011, 115, 2969.
1. (a) Richter, M. M. Chem. Rev. 2004, 104, 3003; (b) Miao, W. Chem. Rev. 2008, 108,
2506; (c) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B.
Chem. Rev. 2009, 109, 897; (d) Armstrong, N. R.; Wightman, R. M.; Gross, E. M.
Annu. Rev. Phys. Chem. 2001, 52, 391; (e) Fahnrich, K. A.; Pravda, M.; Guilbault,
G. G. Talanta 2001, 54, 531.
€
2. (a) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913; (b) Burroughes, J.
H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Bums,
P. L.; Homes, A. B. Nature 1990, 347, 539; (c) Adachi, C.; Baldo, M.; Thompson,
M. E.; Forrest, S. R. J. Appl. Phys. 2001, 90, 5048; (d) Kido, J.; Lizumi, Y. Appl. Phys.
Lett. 1987, 73, 2721; (e) Tessler, N.; Harrison, N.; Friend, R. Adv. Mater. 1998, 10,
64; (f) Vaeth, R. Inf. Disp. 2003, 19, 16; (g) Friend, R. H.; Gymer, R. W.; Holmes, A.
B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; DosSantos, D. A.;
Bredas, J. L.; Logdlund, M.; Salaneck, W. R. Nature 1999, 397, 121; (h) Guo, Z.;
Song, N. R.; Moon, J. H.; Kim, M.; Jun, E. J.; Choi, J.; Lee, J. Y.; Bielaswki, C. W.;
Sesseler, J. L.; Yoon, J. J. Am. Chem. Soc. 2012, 134, 17846; (i) Song, N. R.; Moon, J.
H.; Jun, E. J.; Choi, J.; Kim, S.-J.; Lee, J. Y.; Yoon, J. Chem. Sci. 2013, 4, 1765.
€
3. (a) Figueira-Duarte, T. M.; Mullen, K. Chem. Rev. 2011, 111, 7260; (b) Antony,
J. E. Angew. Chem., Int. Ed. 2008, 46, 452; (c) Shirota, Y.; Kageyama, H. Chem.
€
Rev. 2007, 107, 953; (d) Wu, J. S.; Pisula, W.; Mullen, K. Chem. Rev. 2007,
107, 718.