N,N-Dimethylaniline and 1-(trifluoromethyl)benzene-functionalized tetrakis(ethynyl)pyrenes: Synthesis, photophysical, electrochemical and computational studies

Article abstract of DOI:10.1016/j.tet.2011.12.066

We have synthesized a series of tetrakis(ethynyl)pyrenes functionalized with N,N-dimethyaniline and 1-(trifluoromethyl)benzene as a peripheral electron-donor and electron-acceptor moiety, respectively. In solvatochromic studies, compounds with one periphe

Full text of DOI:10.1016/j.tet.2011.12.066

Tetrahedron 68 (2012) 1704e1711
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
N,N-Dimethylaniline and 1-(trifluoromethyl)benzene-functionalized
tetrakis(ethynyl)pyrenes: synthesis, photophysical, electrochemical
and computational studies
,
,
,
a,
Yeon Ok Lee a y, Tuhin Pradhan a y, Kwanghyun No b , Jong Seung Kim
*
*
a Department of Chemistry, Korea University, Seoul 136-701, Republic of Korea
b Department of Chemistry, Sookmyung Women’s University, Seoul 140-742, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized a series of tetrakis(ethynyl)pyrenes functionalized with N,N-dimethyaniline and 1-
(trifluoromethyl)benzene as a peripheral electron-donor and electron-acceptor moiety, respectively. In
solvatochromic studies, compounds with one peripheral donor and three peripheral acceptors (2), with
two donors and two acceptors (3 and 4), with three donors and one acceptor (5) show enhanced charge
transfer compared with tetra-donor (6) and tetra-acceptor (1) compounds. The redox peak reversibility
depends on the number of peripheral donors and acceptors appended to tetrakis(ethynyl)pyrenes as well
as on their substitution pattern as revealed by cyclic voltammetric studies. The photophysical and
electrochemical properties of compounds 1e5 have been compared with compound (6) reported re-
cently by J.-W. Oh et al. [Angew. Chem., Int. Ed. 2009, 48, 2522e2524]. The density functional theory (DFT)
based calculations such as spin density distribution (SDD) of cation/anion radicals, electrostatic potential
(ESP) density distribution, non-adiabatic reduction potentials (NRP) for cation radicals, and vertical
detachment energy (VDE) for anion radicals supported the experimental observations. The differences in
oxidation peak reversibility for different substitution pattern have been rationalized by calculated static
Received 16 November 2011
Received in revised form 21 December 2011
Accepted 21 December 2011
Available online 27 December 2011
Keywords:
Tetrakis(phenylethynyl)pyrene
Substitution pattern
Radical stability
DFT calculation
first hyperpolarizability (
b). Our observations would be helpful in designing new ECL-active materials,
where ECL (electrogenerated chemiluminescence) efficiency can be improved through improving radical
stability.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
applications of pyrene derivatives is based on the way of multifold
tuning of structureeproperty relationships. Subtle changes in
Pyrene is a polycyclic aromatic hydrocarbon (PAH).1 Pyrene-
based organic materials have been used for many purposes, espe-
cially for molecular electronic devices such as organic light emitting
diodes (OLEDs),2 electronic skin, etc. The fluorescence properties of
pyrene have made its derivatives suitable to be used as biological
probes for the investigation of structural properties of proteins and
peptides,3 DNA recognition,4 surfactant micelles and vesicles
properties.5 Both photophysical and electronic properties of pyr-
enes have been exploited in optoelectronic devices such as organic
photovoltaic cells (OPV),6 organic field-effect transistors (OFETs),7
organic lasers, solar cells, etc. More recently, authors have used
the cruciform-type8 structure of alkynylpyrene with peripheral
multidonors substitution to prepare very efficient electrogenerated
chemiluminescence (ECL) materials.9a The key of these versatile
structure can greatly alter not only the physical properties like
solubility and stability in ambient air, but also the optical and
electronic properties such as energy gap, electron affinity and
electron transfer efficiency; even stability of cation or anion pro-
duced after electron donation or acceptance depends on structural
changes at the molecular level.10 The electrochemically generated
cation and anion radical stabilities at the vicinity of electrode are
very important criteria for showing ECL, which is a light emission
from the excited-state molecules during electrochemical reac-
tions.9e11 There are very few examples9a,10 of improving radical
stability for improving ECL efficiency. Bard et al.10a have improved
the stability of oxidized fluorene compound for ECL by modifying
the fluorene ring to 9,90-spirobifluorene derivatives. Although
pyrene derivatives are well known for their poor ECL properties
because of the instability of cations produced electrochemically, we
observed, in our previous work,9a that ECL efficiencies of the pyrene
derivatives increase proportionally with the number of peripheral
donors, which correspond to their improved cation radical stability.
There is no report of using peripheral acceptors appended to
* Corresponding authors. E-mail addresses: hyun@sookmyung.ac.kr (K. No),
jongskim@korea.ac.kr (J.S. Kim).
y
Equally contributed to this work.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.12.066

Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
1705
alkynylpyrene unit for investigating cation or/and anion radical
stability for ECL.
Compounds 2e5 were obtained by Sonogashira coupling of 7e10
with 4-ethynyl-benzotrifluoride.
In this present work, we have prepared a series of alkynylpyrene
derivatives (Scheme 1), where pyrene acts as central acceptor
moiety,9 N,N-dimethylaniline and 1-(trifluoromethyl)benzene act,
respectively, as peripheral donor and peripheral acceptor moieties.
An ethynyl group acts as a bridge between central acceptor and
peripheral donor (D-
central acceptor and peripheral acceptor (cA-
p
-cA, cA¼central acceptor) and between
p
-A) as well. The
reason of using peripheral acceptor is that it may communicate
with peripheral donor through central acceptor, which can extend
the electronic conjugation for intramolecular charge transfer
(ICT).10b,11a,12 We have varied the number of peripheral donor and
acceptor groups appended to alkynylpyrene unit keeping the total
number of peripheral donor and acceptor groups fixed, as to
monitor the electrochemically produced radical stability. Keeping
this in mind, we have also changed the substitution pattern of the
peripheral donor and acceptor groups where the number of pe-
ripheral acceptors (or donors) is same. While the reported cruci-
form systems contain either peripheral donor or acceptor arms9a,b
only, the present systems contain both peripheral donor and ac-
ceptor arms. We then studied photophysical and electrochemical
properties of the synthesized compounds and compared them with
a standard compound of similar kind, which is already reported in
the literature.9a Finally, we have explained the observed cationic
and/or anionic radical stability at the molecular level by density
functional theory (DFT) based theoretical calculations.
Scheme 2. Synthesis of 2e5. Reagents and conditions: (a) PdCl2(PPh3)2, CuI, PPh3,
Et3N, toluene, 100 ꢀC, 2 h.
We investigated the optical properties of 1e6, and their selected
spectroscopic data are shown in Fig. 1 and summarized in Table 1.
The absorption of 1 peaked at 467 nm; however, this is bath-
ochromically shifted by 34e42 nm when any electron withdrawing
group (eCF3) is replaced by an electron donating group (eNMe2) in
2, implying that the HOMOeLUMO gap in the molecule is de-
creased due to the increased conjugation length from the periph-
eral donor (N,N-dimethyl aniline) to the peripheral acceptor (1-
(trifluoromethyl)benzene) moiety. It is noted that replacement of
two or more acceptor groups in 1 with donor groups does not make
a considerable change to the absorption peak position relative to
that of 2. Compounds 3 and 4 having same number of donor and
acceptor groups did not show significant differences in peak posi-
tion of the lowest-energy absorption band. In comparison to the
absorption spectra, emission spectra show some significant spec-
tral shifts depending on the number of acceptor and donor moieties
in the tetrakis(ethynyl)pyrenes. This may be related to the excited-
state dipole moment of the molecule as well as the solvent polarity.
Among 1e6, compound 2 shows the largest Stokes shift (steady
state) in dichloromethane, and 1 shows the smallest. If the Stokes
shifts for 1e6 are measured in same solvent (meaning that the
solvent polarization function in the LipperteMataga equation14
would be the same for 1e6), according to the LipperteMataga re-
N
CF3
CF3
F3C
1
CF3
CF3
F3C
N
2
CF3
CF3
F3C
N
lation,
experimentally
observed
Stokes
shift
order:
2>3z4>5>6>1 should follow the differences between ground-
and excited-state dipole moments (Dm) for the six compounds. The
value of Dm, in a D-p-cA-p-A system depends on how intra-
4
molecular charge transfer (ICT)10b,12 occurs from peripheral donor
to peripheral acceptor units.
F3C
N
N
N
3
N
N
CF3
N
6
N
N
F3C
N
5
Scheme 1. Schematic molecular structures of 1e6.
2. Results and discussion
The synthetic route for preparation of a series of 2e5 is depicted
in Scheme 2. Compounds 1 and 6 were prepared by adaptation of
procedures reported earlier.13 Sonogashira cross-coupling of
1,3,6,8-tetrabromopyrene with 4-ethynyl-N,N-dimethylaniline
gave a mixture of 7e10, which were able to be isolated as pure
compounds by silica mediated column chromatography.
Fig. 1. Steady-state absorption and fluorescence spectra of 2e6 in various solvents.

1706
Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
Table 1
Table 2
Parameters obtained from optical studies for 1e6
Parameters obtained from electrochemical, optical and theoretical studies for 1e6
[nm]a
l
[nm]
Stokes shift [cmꢁ1
]
Fb
Compd Epc [V] Epa [V]
D
E
D
E
DE
gap
HOMO
(eV) (calcd) (eV) (calcd)
LUMO
abs
em.
elec
opt
calcd
Compd
l
max
max
gap
gap
[eV]a [eV]b [eV]c
1
2
3
4
5
6
467
501
506
509
506
508
491
627
608
605
576
562
1047
4011
3315
3117
2401
1891
0.98
0.43
0.42
0.45
0.65
0.60
1
2
3
4
5
6
d
d
d
2.65
2.47
2.45
2.43
2.45
2.44
2.50
2.32
2.23
2.28
2.32
2.37
ꢁ5.44
ꢁ4.97
ꢁ4.65
ꢁ4.67
ꢁ4.42
ꢁ4.18
ꢁ2.94
ꢁ2.66
ꢁ2.42
ꢁ2.38
ꢁ2.10
ꢁ1.80
ꢁ1.81 0.28
ꢁ1.79 0.32
ꢁ1.76 0.24
ꢁ1.90 0.13
ꢁ1.95 0.12
2.09
2.11
2.10
2.03
2.07
a
Recorded at the lowest-energy wavelengths.
b
a
Using Rhodamine 6G in CH2Cl2. Ff¼0.95 in EtOH. The photophysical data were
Electrochemical band gap calculated from the difference between the two redox
obtained in CH2Cl2.
peak potentials.
b
HOMOeLUMO gap calculated from the lowest-energy UVevisible absorption
band maximum in CH2Cl2.
c
HOMOeLUMO gap calculated by DFT method at B3LYP/6-31G(d) level of theory.
From this viewpoint, we may predict that 2, with one periph-
eral donor and three peripheral acceptor arms, is the best com-
pound with the most ICT. Compound 5 with three peripheral
donors and one peripheral acceptor has weaker ICT than 2. Given
the two or three peripheral donor moieties in a molecule, the
effect of electronic delocalization due to cross-conjugation be-
tween the peripheral donor moieties is expected to be significant.
This may be a reason for the weaker ICT in 5 in comparison with 2.
Another possibility can also be discussed in this regard. N,N-Di-
methyl aniline unit is known as a stronger electron-donor while 1-
(trifluoromethyl)benzene unit is known as an weaker acceptor.
Therefore, adding more than one peripheral donor has little fur-
ther effect in 5, whereas in 2, three weaker acceptors plus the
pyrene system (which is also a weaker acceptor) translates into
a relatively strong acceptor, that is coupled to a strong NMe2 do-
The photophysical and electrochemical data were obtained in CH2Cl2.
cathodically shifted by w200 mV. In addition, the reversibility of
the oxidation peak increases with the number of peripheral donor
groups, indicating enhanced cation radical stability. Despite the
fact that 3 and 4 have same number of donor and acceptor groups,
they have different oxidation peak positions and reversibility,
implying, respectively, different ease of oxidation and different
cation radical stability (3 and 4 exhibit oxidation peaks, re-
spectively, at 0.32 and 0.24 V; 4 exhibits better reversibility).
Compounds 2e5 displayed reversible reduction peaks located
at ꢁ1.76 to ꢁ1.95 V. The reduction potential follows an opposite
trend to the potential, in which the more difficult reductions are
observed with increasing number of donor groups (2/6). In ad-
dition, reversibility of the reduction peaks diminished with in-
creasing donor groups. This means that anion radical stability
decreases with increasing number of donor groups (2/6). In
other words, anion radical stability increases with increasing
number of acceptor groups (6/2). However, compounds (2e4)
having one or two donor groups (conversely with three or two
acceptor groups, respectively) do not exhibit much change both in
reversibility and reduction potential. From the perspective of both
cation and anion radical stability, 4 and 5 are better candidates
than the others (even than 6),9a which may make them eligible for
ECL applications.
nor. Another notable finding is that the ICT in 6 (D-p-cA system) is
stronger than in 1 (A- -cA system). The quantum yields for fluo-
p
rescence, measured relative to Rhodamine 6G in ethanol as
a standard,15 were also determined for 1e6 in CH2Cl2 solution and
given in Table 1. All the compounds have high quantum yields,
which is a requirement for the compounds to be used as ECL-
active materials.
The electrochemical behaviours of 2e6 were investigated by
cyclic voltammetry (CV) with Bu4NPF6 in CH2Cl2 (0.1 M) on a Pt
electrode as summarized in Fig. 2 and Table 2. Oxidation peaks of
2e6, which may originate from the removal of one electron from
the amino segment in peripheral donor groups, appear at
0.12e0.32 V. Easier oxidations are observed with increasing
number of peripheral donor groups appended to the tetrakis(e-
thynyl)pyrenes. In comparison with 2 (one peripheral donor
group), oxidation peak of 6 (four peripheral donor groups) is
To get insight into radical stabilities at the molecular level,
computational studies were performed on compounds 1e6 by
using density functional theory (DFT) at B3LYP/6-31G(d) level of
theory in a suite of Gaussian 09 W programs.16 The HOMO
(highest occupied molecular orbital) energy level raises on going
from 1 to 6 (Table 2). This is consistent with literature reports for
D-p-A system, where HOMO energy level raised upon in-
3
troduction of donor groups.10b Interestingly, LUMO (lowest un-
occupied molecular orbital) energy level also follows the same
trend (Table 2). The HOMOeLUMO gaps calculated from compu-
tational studies, electrochemical measurements (the difference
between the oxidation and reduction potentials) and lowest-
energy absorption band maxima are listed in Table 2. The calcu-
lated band gaps from DFT and UVevisible spectral bands are in
good agreement, displaying almost same energy gaps for com-
pounds 2e5. The little differences in band gaps from DFT and
UVevisible spectral bands are associated with the interactive
mediums, where solvent contributions on the band gaps have
been neglected in theoretical calculations. The band gaps ob-
tained from electrochemical measurements are relatively smaller
than the values obtained from DFT and UVevisible spectral
bands.17 However, the electrochemically measured band gaps for
2e6 are, on an average, same and within experimental error limit
(ꢂ5%). For 2e6, the HOMO is localized in the peripheral donor
arms with some degree of orbital coefficient on pyrene core,
whereas LUMO is located mainly on peripheral acceptor arms
with some degree of orbital coefficient on pyrene core (Fig. S1).
2
0
-3
4
3
0
-4
4
4
0
-4
5
5
0
-5
5
6
0
-5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Potential / V vs. Ag/AgCl
Fig. 2. Cyclic voltammograms of 2e6 (0.5 mM) for a Pt electrode with Bu4NPF6 in
CH2Cl2 (0.1 M). Scan rate¼100 mV sꢁ1
.

Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
1707
Therefore, it is expected that probable intramolecular charge
transfer (ICT) occurs from peripheral donor arms to peripheral
acceptor arms through pyrene core (D-p-cA-p-A). We have the-
which can help to understand the geometry or electronic de-
formation of the molecules under external electronic perturbation.
The details of static first hyperpolarizability tensor components for
3 and 4 are listed in Table S1 (Supplementary data). We could not
oretically studied spin density distribution in radical cations/an-
ions of 1e6 to understand the radical stability at the molecular
level. We have considered the net spin, which leads to a differ-
ence between the electron densities for the spin up (alpha) and
spin down (beta) states. Fig. 3 gives the spin density isosurfaces of
singly occupied molecular orbitals (SOMO) of cations and anions
for compounds 1e6. In the case of cation radicals SOMOs corre-
spond to their HOMOs (Fig. S1, Supplementary data). As shown in
Fig. 3, the net spin density in the SOMOs of 2e5 resides on the
pyrene core as well as on the donor arms and the density de-
localization18 occurs with increasing number of donor groups
(2/6). This overall electron spin density delocalization in the
SOMO surfaces supports the enhanced cation radical stability in
going from 2 to 6, because electron-deficient cation radical pro-
duced after oxidation needs immediate electron density to be
thermodynamically stable and that can be supplied from other
electron-rich peripheral donor arms. It can also be supported
form calculated electrostatic potential (ESP) density distribution.
The electrostatic potential density surfaces of the neutral mole-
cule (centre), cation (left), anion (right) of compound 2 have been
shown in Fig. 4. In Fig. 4, it is evident that positive charge (blue) of
cation radicals resides mostly on donor arms along with pyrene
core, whereas negative charge (red) of anion radicals resides
mostly on acceptor arms along with pyrene core, implying that
positive charge distribution in cation radicals depends on number
of donor arms and negative charge distribution in anion radicals
depends on number of acceptor arms. It is interesting to notice
that although 3 and 4 have same number of donor groups, the
cation radical produced from 3 is not so stable (i.e., the oxidation
peak is not reversible, Fig. 2) whereas the cation radical produced
from 4 is very stable. In the case of anion radicals SOMOs corre-
spond to their LUMOs (Fig. S1, Supplementary data). The spin
density of anion is located basically on the pyrene core and in
acceptor arms. The pyrene core in 1e6 is known as electron-
deficient moiety.1,9a Therefore, the pyrene core together with
acceptor arms functionalized with electron withdrawing groups
(eCF3) will delocalize the excess electron density in the molecule
after it is being reduced. Consequently, the anion radical stability
increases with increasing number of acceptor groups (6/2). The
anion radical produced after reduction in 6 is the least stable
among 2e6 because there are no acceptor arms attached to pyr-
ene core. The calculated non-adiabatic reduction (cati-
on/neutral) potential (NRP)9a for the cation radicals of 1e6 are,
respectively, ꢁ6.31, ꢁ5.83, ꢁ5.46, ꢁ5.45, ꢁ5.17, and ꢁ4.90 eV,
which indicates that compounds with less number of peripheral
donor groups (1e4) are more stable upon addition of one electron
than the compounds with more number of peripheral donor
groups (5 and 6). Conversely, cation radicals with more number of
peripheral donor groups (5 and 6) are more stable than that with
less number of peripheral donor groups (1e4), which are con-
sistent with the analysis based on photophysical and electro-
chemical measurements. It is noted that cation radicals of 3 and 4
(with same number of peripheral donor groups), according to the
calculated non-adiabatic reduction potential, have little difference
in their stability. However, in cyclic voltammograms (Fig. 2), 3 and
4 have distinct differences in oxidation peak reversibility. On the
other hand, the calculated vertical detachment energy (VDE)9a
(anion/neutral) of anion radicals 1e6 are, respectively, 2.11,
1.84, 1.58, 1.58, 1.31, and 1.02 eV, which implies that anion radical
stability increases on going from 6 to 1, which are also consistent
with our experimental observations.
check the experimental b values, as we did not get any single crystal
for those compounds. However, we would find here the qualitative
understanding about the cation radical stabilities of 3 and 4 from
the calculated
polarizability (
b values. The calculated total static first hyper-
b
) of 3 is w56,515ꢃ10ꢁ30 esu, which is w974-fold
larger than that of 4 (58ꢃ10ꢁ30 esu). The non-centrosymmetric
geometry of 3 may be responsible for such large
b
value20 in 3.
The large
b in 3 suggests that electron density from the electron-
rich region (NMe2-funtionalized arms) can be highly deformed
towards electron-deficient region (eCF3 functionalized arms),
which may reduce the stability of cation radicals produced elec-
trochemically during oxidation process. This may be a possible
reason for the less stability of cation radical of 3 compared to 4. It is
noteworthy that the hyperpolarizability effect becomes less sig-
nificant in the present target molecules when the number of pe-
ripheral donor groups increases (or the number of peripheral
acceptor groups decreases). On the contrary, we observed very little
differences between 3 and 4 in the reduction region of the cyclic
voltammograms. The reduction peaks for both the compounds are
reversible. The peaks occur at almost same position, wꢁ1.78 V. The
reasons may be the presence of central acceptor unit (pyrene
moiety) along with the two peripheral acceptor groups in both the
compounds, where central acceptor unit and two peripheral ac-
ceptor groups simultaneously can participate to stabilize the anion
radicals, dominating over the effects of different substitution pat-
tern of the acceptor groups in tetrakis(ethynyl)pyrenes.
3. Conclusions
We have synthesized a series of donor-pyrene-acceptor (1e5) by
varying the substitution pattern and the number of functional
groups in tetrakis(ethynyl)pyrenes, and performed their photo-
physical, electrochemical and computational studies. The redox
potentials and radical stability of 2e5 have been compared with
a standard ECL-active material of the similar kind (compound 6 in
the present article) reported in Ref. 9a. From electrochemical re-
versibility, it is observed that cation radical stability enhances with
the number of peripheral donor groups and anion radical stability
enhances with the number of peripheral acceptor groups appended
to tetrakis(ethynyl)pyrenes, while the total number of peripheral
donor and acceptor groups is fixed (here the total number is 4).
These experimental observations are also supported by theoretical
calculations based on density functional theory (DFT). The net spin
density is mainly located in peripheral donor arms along with
pyrene core in case of cation radical, whereas it is located in pe-
ripheral acceptor arms along with pyrene core in case of anion
radical, which implies that cation and anion radical stability at the
molecular level depends, respectively, on number of peripheral
donor and acceptor arms. The predicted radical stability at the
molecular level from calculated non-adiabatic reduction potential
(NRP) and vertical detachment energy (VDE), respectively, for cat-
ions and anions of 1e6 are also consistent with the experimental
observations. In addition, differences in stability of cation radicals
in oxidation process for the different substitution pattern (3 and 4)
have been rationalized with the calculated static first hyper-
polarizability (
b). Therefore, we may conclude that electrochemical
properties of the materials can be controlled by varying the number
of functional groups, characteristics of functional groups (electron
withdrawing or donating) and substitution patterns, which, in turn,
may control the ECL efficiency of the materials. Studies of the ECL
properties for these compounds would be interesting as 4 and 5
have a possibility of being stronger ECL materials compared to 6.
To understand the differences between 3 and 4 in oxidation, we
have calculated the molecular static first hyperpolarizability (b
),19

1708
Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
Fig. 3. The spin density isosurfaces (at a value of 0.0004 a.u.) of singly occupied molecular orbitals (SOMO) of cation and anion radicals for compounds 1e6. Blue and green areas
refer to regions of positive and negative spin density, respectively.

Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
1709
hyperpolarizability
(b
) was calculated analytically by density
functional theory (DFT). The total static first hyperpolarizability
(
btot) was estimated by the following relations.19
ÂÀ
Á
À
Á
2
btot
¼
bxxx
þ
bxyy
þ
bxzz 2þ byyy
þ
byxx
þ
byzz
(3)
À
Á Ã
2
1=2
þ
bzzz
þ
bzxx
þ
bzyy
The details of static first hyperpolarizability tensor components
for 3 and 4 are listed in Table S1 (Supplementary data). The elec-
tronic excitation energies were calculated by using time-
dependent density functional theory (TDDFT) at B3LYP/6-31G(d)
level of theory. As we were interested only in qualitative results,
we did not use any other diffuse functions in the basis set for
calculating hyperpolarizability or electronic excitation energies.
All calculations were performed using the Gaussian 09 W program
package.16
Fig. 4. The calculated electrostatic potential (ESP) density of 2 (middle), after removing
one electron from 2 (left), and after adding one electron to 2 (right). The more blue and
more red, respectively, indicate more positive and more negative electrostatic poten-
tials. Isovalue of the isosurfaces is 0.0004 a.u.
4. Experimental section
4.1. Spectroscopic measurements
4.4. 1-[(4-N,N-Dimethylaminophenyl)ethynyl]-3,6,8-tris[(4-
trifluoromethylphenyl)ethynyl]pyrene (2)
Absorption spectra were recorded on a Hewlett-Packard 8453
diode array spectrophotometer with 20 M solution of 1e6 in CH2Cl2
and photoluminescence spectra were obtained with Hitachi F-7000
fluorescence spectrometer with a 1 cm standard quartz cell using
3 M solution conditions in various solvents, respectively. The fluo-
rescence quantum yields were determined by using Rhodamine 6G
as the reference by the literature method.15
Compound
7 (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 4-ethynyl-benzotrifluoride (116 mg, 0.688 mmol) were
added to a degassed solution of triethylamine (40 ml) and tol-
uene (60 ml) under Ar. The resulting mixture was stirred at
100 ꢀC for 2 h. The solvent was removed under vacuum to give
crude mixture. Compound 2 (32 mg) was obtained after column
chromatography (silica gel, hexane/dichloromethane, 7:3, v/v).
Mp 280e290 ꢀC. IR (KBr pellet, cmꢁ1): 2200 (C^C), 1609, 1522,
4.2. Electrochemistry measurements
1359 (CeN), 1323. 1H NMR (400 MHz, CDCl3):
d
8.62 (d, J¼9.4 Hz,
Cyclic voltammetry (CV) was carried out using an electro-
chemical analyzer (CH Instruments 624C); 1 Hz stepwise poten-
tials were generated for 20 s using a CHI 624C. Electrochemical
experiments were referenced with respect to the Ag/AgCl refer-
ence electrode. All potentials were measured by the addition of
ferrocene as an internal standard, where Eo(Fcþ/Fc)¼70 mV ver-
sus Ag/AgCl. A platinum disk (2 mm diameter) working electrode
1H), 8.59e8.54 (m, 3H), 8.34 (d, J¼3.8 Hz, 2H), 7.77 (d, J¼7.9 Hz,
6H), 7.71 (d, J¼8.3 Hz, 4H), 7.56 (d, J¼8.8 Hz, 4H), 6.70 (d,
J¼9.2 Hz, 4H), 3.05 (s, 6H). 13C NMR: spectrum could not be
recorded due to inadequate solubility. HRMS: calcd 849.2078,
found 849.2073.
was polished on a felt with 0.05 mM alumina (Buehler), rinsed
4.5. 1,8-Bis[(4-N,N-dimethylaminophenyl)ethynyl]-3,6-bis[(4-
trifluoromethylphenyl)ethynyl]pyrene (3)
with water and sonicated in absolute ethanol for 5 min. Then
it was dried with Ar gas flow before each experiment. Dichloro-
methane solutions for CV measurement contained 0.5 mM tetra-
kis(ethynyl)pyrenes, respectively, and 0.1 M TBAPF6 as an
electrolyte.
Compound
8 (80 mg, 0.124 mmol), PdCl2(PPh3)2 (20 mg,
0.028 mmol), CuI (11 mg, 0.058 mmol), PPh3 (70 mg, 0.267 mmol),
and 4-ethynyl-benzotrifluoride (105 mg, 0.62 mmol) were added to
a degassed solution of triethylamine (40 ml) and toluene (60 ml)
under Ar. The resulting mixture was stirred at 100 ꢀC for 2 h. The
solvent was removed under vacuum to give compound 3. The crude
product was then subjected to column chromatography (silica gel,
hexane/dichloromethane, 7:3, v/v) to yield 3 (55 mg) as a red
powder. Mp 271e280 ꢀC. IR (KBr pellet, cmꢁ1): 2194 (C^C), 1606,
4.3. Computational details
The geometries of compounds 1e6 and the geometries of their
corresponding cation/anion radical species were optimized at
B3LYP/6-31G(d) level of theory. The frontier molecular orbital en-
ergy and orbital surfaces, spin density distribution (SDD) surfaces,
electrostatic potential (ESP) density surfaces, non-adiabatic re-
duction potential (NRP), vertical electron detachment energy (VDE)
1522, 1358 (CeN), 1320. 1H NMR (300 MHz, CDCl3):
d 8.65 (s, 2H),
8.51 (s, 2H), 8.31 (s, 2H), 7.77 (d, J¼7.7 Hz, 4H), 7.64 (d, J¼8.3 Hz,
4H), 7.58 (d, J¼8.9 Hz, 4H), 6.72 (d, J¼8.3 Hz, 4H), 3.05 (s, 12H). 13C
NMR: spectrum could not be recorded due to inadequate solubility.
HRMS: calcd 824.2626, found 824.2626.
and static first hyperpolarizability (b) were also calculated at the
same level of theory using optimized geometries. The non-
adiabatic reduction potential (NRP) for cation radicals and vertical
electron detachment energy (VDE) for anion radicals were calcu-
lated by using the following relation.9a
4.6. 1,6-Bis[(4-N,N-dimethylaminophenyl)ethynyl]-3,8-bis[(4-
trifluoromethylphenyl)ethynyl]pyrene (4)
NRP for cation radical ¼ EcðneutralÞ ꢁ EcðcationÞ
(1)
Compound
9 (30 mg, 0.046 mmol), PdCl2(PPh3)2 (10 mg,
0.014 mmol), CuI (6 mg, 0.032 mmol), PPh3 (25 mg, 0.095 mmol),
and 4-ethynyl-benzotrifluoride (40 mg, 0.24 mmol) were added
to a degassed solution of triethylamine (15 ml) and toluene
(30 ml) under Ar. After stirring at 100 ꢀC for 2 h, the red pre-
cipitate was filtered and washed with toluene and then re-
crystallization from CHCl3 to afford the pure desired compound as
a red powder (38 mg). Mp >300 ꢀC. IR (KBr pellet, cmꢁ1): 2191
VDE for anion radical ¼ EaðneutralÞ ꢁ EaðanionÞ
(2)
where, Ec (cation) and Ea (anion) are, respectively, energy of the
cation and anion radical species. Ec (neutral) and Ea (neutral) rep-
resent the energy of the neutral system bearing, respectively, the
optimized structure of the cation and anion radicals. The static first

1710
Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
(C^C), 1606, 1522, 1362 (CeN), 1323. 1H NMR (300 MHz, CDCl3):
1525, 1362 (CeN), 1197. 1H NMR (300 MHz, CDCl3):
d 8.69 (q,
d
8.75 (d, J¼9.6 Hz, 2H), 8.68 (d, J¼8.9 Hz, 2H), 8.41 (s, 2H), 7.82 (d,
J¼9.0 Hz, 3H), 8.44 (d, J¼9.4 Hz, 1H), 8.38 (d, J¼12.9 Hz, 2H), 7.59 (d,
J¼7.9 Hz, 4H), 7.70 (d, J¼7.9 Hz, 4H), 7.60 (d, J¼8.3 Hz, 4H), 6.70 (d,
J¼8.9 Hz, 4H), 3.06 (s, 8H). 13C NMR: spectrum could not be
recorded due to inadequate solubility. HRMS: calcd 824.2626,
found 824.2631.
J¼8.8 Hz, 6H), 6.73 (d, J¼8.7 Hz, 6H), 3.06 (s, 18H). 13C NMR
(100 MHz, CDCl3):
d 150.58, 150.51, 133.44, 133.32, 133.21, 133.17,
131.16, 131.35, 131.04, 130.64, 127.59, 126.66, 125.57, 124.23, 120.56,
120.15, 120.01, 119.94, 112.11, 112.08, 110.21, 110.15, 109.92, 98.50,
97.78, 97.72, 86.39, 86.29, 85.95, 40.46, 40.45, HRMS: calcd
709.2093, found 710.2069.
4.7. 1,3,6-Tris[(4-N,N-dimethylaminophenyl)ethynyl]-8-[(4-
trifluoromethylphenyl)ethynyl]pyrene (5)
Acknowledgements
Compound 10 (250 mg, 0.352 mmol), PdCl2(PPh3)2 (20 mg,
0.03 mmol), CuI (13 mg, 0.071 mmol), PPh3 (77 mg, 0.290 mmol),
and 4-ethynyl-trifluoromethyl benzene (120 mg, 0.710 mmol) are
added to a degassed solution of triethylamine (50 ml) and toluene
(100 ml) under Ar. The resulting mixture was heated at 100 ꢀC with
stirring for 2 h. After the mixture was cooled, the red precipitate
was filtered and washed with toluene and then recrystallized from
CHCl3 to afford the pure desired compound as a red powder
(232 mg). Mp >300 ꢀC. IR (KBr pellet, cmꢁ1): 2191 (C^C), 1607,
This work was supported by Sookmyung Women’s University
Research Grant 2009.
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2011.12.066.
1528, 1362 (CeN), 1318. 1H NMR (400 MHz, CDCl3):
d 8.71 (q,
References and notes
J¼8.0 Hz, 3H), 8.61 (d, J¼9.2 Hz, 1H), 8.35 (d, J¼3.9 Hz, 2H), 7.82 (d,
J¼8.2 Hz, 4H), 7.69 (d, J¼8.9 Hz, 4H), 7.60 (d, J¼7.9 Hz, 6H), 6.73 (d,
J¼8.2 Hz, 6H), 3.06 (s, 18H). 13C NMR: spectrum could not be
recorded due to inadequate solubility. HRMS: calcd 799.3174, found
799.3175.
€
1. (a) Figueira-Duarte, T. M.; Mullen, K. Chem. Rev. 2011, 111, 7260e7314; (b)
€
€
Watson, M. D.; Fechtenkotter, A.; Mullen, K. Chem. Rev. 2001, 101, 1267e1300.
2. (a) Jiang, J. X.; Xu, Y. H.; Yang, W.; Guan, R.; Liu, Z. Q.; Zhen, H. Y.; Cao, Y. Adv. Mater.
2006, 18, 1769e1773; (b) Liu, J.; Zhou, Q. G.; Cheng, Y. X.; Geng, Y. H.; Wang, L. X.;
Ma, D. G.; Jing, X. B.; Wang, F. S. Adv. Mater. 2005, 17, 2974e2978; (c) Gong, X.;
Wang, S.; Moses, D.; Bazan, G. C.; Heeger, A. J. Adv. Mater. 2005,17, 2053e2058; (d)
Qiu, Y.; Wei, P.; Zhang, D. Q.; Qiao, J.; Duan, L.; Li, Y. K.; Gao, Y. D.; Wang, L. D. Adv.
Mater. 2006, 18, 1607e1611; (e) Shao, Y.; Yang, Y. Appl. Phys. Lett. 2005, 86,
073510(1)e073510(3); (f) Carlson, B.; Phelan, G. D.; Kaminsky, W.; Dalton, L.;
Jiang, X. Z.; Liu, S.; Jen, A. K. Y. J. Am. Chem. Soc. 2002, 124, 14162e14172.
3. (a) Goedeweeck, R.; Vanderauweraer, M.; Deschryver, F. C. J. Am. Chem. Soc.
1985, 107, 2334e2341; (b) Hammarstrom, P.; Kalman, P. B.; Jonsson, B. H.;
Carlsson, U. FEBS Lett. 1997, 420, 63e68; (c) Sahoo, D.; Weers, P. M. M.; Ryan,
R. O.; Narayanaswami, V. J. Mol. Biol. 2002, 321, 201e214; (d) Sahoo, D.; Nar-
ayanaswami, V.; Kay, C. M.; Ryan, R. O. Biochemistry 2000, 39, 6594e6601.
4. (a) Paris, P. L.; Langenhan, J. M.; Kool, E. T. Nucleic Acids Res. 1998, 26,
3789e3793; (b) Lewis, F. D.; Zhang, Y. F.; Letsinger, R. L. J. Am. Chem. Soc. 1997,
119, 5451e5452; (c) Yamana, K.; Iwai, T.; Ohtani, Y.; Sato, S.; Nakamura, M.;
Nakano, H. Bioconjugate Chem. 2002, 13, 1266e1273; (d) Tong, G.; Lawlor, J. M.;
Tregear, G. W.; Haralambidis, J. J. Am. Chem. Soc. 1995, 117, 12151e12158.
5. (a) Ollmann, M.; Schwarzmann, G.; Sandhoff, K.; Galla, H. J. Biochemistry 1987,
26, 5943e5952; (b) Pap, E. H. W.; Hanicak, A.; van Hoek, K. W. A.; Wirtz, A. J.
W.; Visser, G. Biochemistry 1995, 34, 9118e9125; (c) Somerharju, P. Chem. Phys.
Lipids 2002, 116, 57e74.
4.8. Compounds 7e10
1,3,6,8,-Tetrabromopyrene (10.0 g, 19.3 mmol), PdCl2(PPh3)2
(100 mg, 0.142 mmol), CuI (27 mg, 0.142 mmol), PPh3
(75 mg, 0.286 mmol), and 4-ethynyl-N,N-dimethylaniline (1 g,
6.89 mmol) were added to a degassed solution of triethylamine
(200 ml) and toluene (350 ml) under Ar. The resulting mixture
was stirred at 100 ꢀC for 2 h. The solvent was removed under
vacuum to give a mixture of compounds 7e10. Compounds 7
(201 mg, yellow solid), 8 (189 mg, yellow orange solid), 9 (38 mg,
yellow orange solid) and 10 (335 mg, red orange solid) were
separated by column chromatography (silica gel, hexane/
dichloromethane, 7:3, v/v).
6. Tang, C. W. Appl. Phys. Lett. 1986, 48, 183e185.
4.8.1. 1,6,8-Tribromo-3-[4-(N,N-dimethylamino)phenylethynyl]pyr-
7. (a) Chabinyc, M. L.; Salleo, A. Chem. Mater. 2004, 16, 4509e4521; (b) Veres, J.;
Ogier, S.;Lloyd, G.; de Leeuw, D. Chem. Mater. 2004,16, 4543e4555;(c) McCulloch,
I.; Heeney, M.; Bailey, C.; Genevicius, K.; MacDonald, I.; Shkunov, M.; Sparrowe,
D.; Tierney, S.; Wagner, R.; Zhang, W. M.; Chabinyc, M. L.; Kline, R. J.; McGehee,
M. D.; Toney, M. F. Nat. Mater. 2006, 5, 328e333; (d) Allard, S.; Forster, M.; Sou-
harce, B.; Thiem, H.; Scherf, U. Angew. Chem., Int. Ed. 2008, 47, 4070e4098.
8. (a) Marsden, J. A.; Miller, J. J.; Shirtcliff, L. D.; Haley, M. M. J. Am. Chem. Soc. 2005,
127, 2464e2476; (b) Spitler, E. L.; Shirtchliff, L. D.; Haley, M. M. J. Org. Chem.
2007, 72, 86e96; (c) Zucchero, A. J.; Wilson, J. N.; Bunz, U. H. F. J. Am. Chem. Soc.
2006, 128, 11872e11881.
9. (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, 2522e2524; (b) Fujimato, K.; Shimizu, H.; Furusuyo, M.;
Akiyama, S.; Ishida, M.; Furukawa, U.; Yokoo, T.; Inouye, M. Tetrahedron 2009,
65, 9357e9361.
10. (a) Rashidnadimi, S.; Hung, T. H.; Wong, K.-T.; Bard, A. J. J. Am. Chem. Soc. 2008,
130, 634e639; (b) Jiang, X.; Yang, X.; Zhao, C.; Jin, K.; Sun, L. J. Phys. Chem. C
2007, 111, 9595e9602.
11. (a) Yang, M.; Jacquemin, D.; Champagne, B. Phys. Chem. Chem. Phys. 2002, 4,
5566e5571; (b) Richter, M. M. Chem. Rev. 2004, 104, 3003e3036; (c) Miao, W.
Chem. Rev. 2008, 108, 2506e2553; (d) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.;
Jokisz, P. G.; Holmes, A. B. Chem. Rev. 2009, 109, 897e1091.
12. Yang, J.-S.; Liau, K.-L.; Wang, C.-M.; Hwang, C.-Y. J. Am. Chem. Soc. 2004, 126,
12325e12335.
13. (a) Maeda, H.; Maeda, T.; Mizuno, K.; Fujimoto, K.; Shimizu, H.; Inouye, M.
Chem.dEur. J. 2006, 12, 824e831; (b) Venkataramana, G.; Sankararaman, S. Eur.
J. Org. Chem. 2005, 4162e4166; (c) Yang, S.-W.; Elangovan, A.; Hwang, K.-C.; Ho,
T.-I. J. Phys. Chem. B 2005, 109, 16628e16635; (d) Shimizu, H.; Fujimoto, K.;
Furusyo, M.; Maeda, H.; Nanai, Y.; Mizuno, K.; Inouye, M. J. Org. Chem. 2007, 72,
1530e1533; (e) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42,
2586e2617; (f) Kim, H. M.; Lee, Y. O.; Lim, C. S.; Kim, J. S.; Cho, B. R. J. Org. Chem.
2008, 73, 5127e5130.
ene (7). Mp 252e260 ꢀC. IR (KBr pellet, cmꢁ1): 2185 (C^C), 1591,
1524, 1363 (CeN), 1062. 1H NMR (300 MHz, CDCl3):
d 8.75 (d,
J¼8.9 Hz, 1H), 8.56e8.43 (m, 5H), 7.60 (d, J¼8.5 Hz, 2H), 6.74 (d,
J¼8.6 Hz, 2H), 3.06 (s, 6H). 13C NMR: spectrum could not be
recorded due to inadequate solubility. HRMS: calcd 578.8833,
found 578.8833.
4.8.2. 1,8-Dibromo-3,6-bis[4-(N,N-dimethylamino)phenylethynyl]
pyrene (8). Mp >300 ꢀC. IR (KBr pellet, cmꢁ1): 2185 (C^C), 1606,
1522, 1358 (CeN), 1166. 1H NMR (300 MHz, CDCl3):
d
8.71 (s, 2H),
8.45 (d, J¼9.6 Hz, 4H), 7.61 (d, J¼8.9 Hz, 4H), 6.73 (d, J¼8.6 Hz, 4H),
3.05 (s, 12H). 13C NMR (100 MHz, CDCl3):
156.7, 133.8, 133.2, 131.2,
d
129.7, 127.7, 126.6, 125.2, 121.2, 120.2, 112.1, 109.8, 98.9, 85.7, 40.4.
HRMS: calcd 646.0463, found 646.0439.
4.8.3. 1,6-Dibromo-3,8-bis[4-(N,N-dimethylamino)phenylethynyl]
pyrene (9). Mp >300 ꢀC. IR (KBr pellet, cmꢁ1): 2190 (C^C), 1606,
1523, 1369 (CeN), 1197. 1H NMR (400 MHz, CDCl3):
d 8.71 (d,
J¼9.8 Hz, 2H), 8.50 (d, J¼9.3 Hz, 2H), 8.45 (s, 2H), 7.58 (d, J¼9.1 Hz,
4H), 6.74 (d, J¼8.9 Hz, 4H), 3.05 (s, 12H). 13C NMR: spectrum could
not be recorded due to inadequate solubility. HRMS: calcd
644.0463, found 647.0463.
4.8.4. 1-Bromo-3,6,8-tris[4-(N,N-dimethylamino)phenylethynyl]pyr-
14. Wang, S.; Cai, J.; Sadygov, R.; Lim, E. C. J. Phys. Chem. 1995, 99, 7416e7420.
15. Crosby, G. A.; Demas, J. N. J. Phys. Chem. 1971, 75, 991e1024.
ene (10). Mp >300 ꢀC. IR (KBr pellet, cmꢁ1): 2189 (C^C), 1608,

Y.O. Lee et al. / Tetrahedron 68 (2012) 1704e1711
17. Lin, J. H.; Elangovan, A.; Ho, T.-I. J. Org. Chem. 2005, 70, 7397e7407.
1711
16. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Car-
icato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg,
J. L.; Hada, M.; Ehara,M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.;
Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.;
Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.;
Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.;
Fox, D. J. Gaussian 09, Revision B.01; Gaussian: Wallingford, CT, 2010.
€
18. (a) Baumgarten, M.; Koch, K.-H.; Mullen, K. J. Am. Chem. Soc. 1994, 116,
7341e7348; (b) Palacio, F.; Anntorena, G.; Castro, M.; Burriel, R.; Rawson, J. M.;
Smith, J. N. B.; Bricklebank, N.; Novoa, J.; Ritter, C. Phys. Rev. Lett. 1997, 79,
2336e2339; (c) Veciana, J. In Molecular Magnetism: From Molecular Assemblies
to the Devices; Coronado, E., Delhaes, P., Gatteschi, D., Miller, J. S., Eds.; NATO ASI
Series; Kluwer Acad.: Dordrecht, 1996; Vol. 321, p 425.
19. (a) Hinchliffe, A.; Machado, H. J. S. Int. J. Mol. Sci. 2000, 1, 39e48; (b) Meyers, F.;
Bredas, J. L.; Zyss, J. J. Am. Chem. Soc. 1992, 114, 2914e2921; (c) Isborn, C. M.;
ꢀ
Leclercq, A.; Vila, F. D.; Dalton, L. R.; Bredas, J. L.; Eichinger, B. E.; Robinson, B. H.
J. Phys. Chem. A 2007, 111, 1319e1327.
20. Cardoso, C.; Abreu, P. E.; Nogueira, F. J. Chem. Theory Comput. 2009, 5,
850e852.