BODIPY-bridged push-pull chromophores: Optical and electrochemical properties

Article abstract of DOI:10.1016/j.tetlet.2011.07.028

A series of BODIPY bridged push-pull chromophores were prepared by a sequence of reactions involving: i) cross-coupling reactions promoted by palladium complexes; ii) Knoevenagel condensation leading to dicyano derivatives; iii) [2+2] cycloaddition. The l

Full text of DOI:10.1016/j.tetlet.2011.07.028

Tetrahedron Letters 52 (2011) 4848–4853
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
BODIPY-bridged push–pull chromophores: optical
and electrochemical properties
Songlin Niu a, Gilles Ulrich a, , Pascal Retailleau b, Raymond Ziessel a,
⇑
⇑
a Laboratoire de Chimie Organique et Spectroscopies Avancées (LCOSA), UMR7515, ECPM, 25 rue Becquerel, 67087 Strasbourg, Cedex 02, France
b Laboratoire de Cristallochimie, ICSN-CNRS, Bat 27-1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of BODIPY bridged push–pull chromophores were prepared by a sequence of reactions involving:
i) cross-coupling reactions promoted by palladium complexes; ii) Knoevenagel condensation leading to
dicyano derivatives; iii) [2+2] cycloaddition. The last reaction is regioselective, providing mono-deriva-
tives with anisole substituents. With dimethylaminophenyl donor groups, double addition is feasible,
providing highly colored dyes displaying remarkable electrochemical properties.
Received 30 June 2011
Accepted 6 July 2011
Available online 22 July 2011
Keywords:
BODIPY
Ó 2011 Elsevier Ltd. All rights reserved.
Push–pull
Cycloaddition
Tetracyano
Fluorescence
Electrochemistry
The term ‘push–pull’ has been used to describe conjugated com-
pounds that have an electron donor group (D) and an electron
withdrawing (A) group that exhibit intramolecular charge transfer
push–pull system based on the BODIPY scaffold should provide
materials with new optical and electronic properties and thus
might offer new opportunities for advanced optoelectronic
devices.9,20
(ICT) through the
p-conjugated bridge (also called a D–p–A sys-
tem). ICT character derives from the molecular push–pull structure
and has been largely investigated for optical–electrical applica-
tions, such as in light-emitting devices,1,2 optical imaging of living
tissues,3,4 nonlinear optical devices (NLO),5,6 and solar cell materi-
als.7–10 It has been demonstrated that the combination of electron
donor and electron withdrawing groups can efficiently modify the
electronic signatures and chemical properties of the conjugated
chromophore7,11–13 such as seen in its optical absorption and elec-
tronic states (HOMO/LUMO). Over the last decade, most interest in
push–pull systems has been focused on understanding structure–
property relationships and the engineering of molecular materials
with strong NLO responses.
BODIPY dyes are well known for their strong absorption, high
solubility in common organic solvents, high fluorescence quantum
yield, and their good chemical and photochemical stability.14 Al-
ready known as laser dyes,14 BODIPY derivatives are promising
candidates for NLO applications. To date, however, only a few func-
tionalised BODIPY based chromophores have been described for
use in the field of two photon absorption for cell imaging or tele-
communications12–19 and overall the study of BODIPY based
push–pull systems is rather limited.7,11 The construction of a
Here, we present a series of BODIPY bridged push–pull chro-
mophores in which an electron donor group and an electron with-
drawing group have been successively conjugated to the BODIPY
core at the 2 and 6 positions. The optical and electrochemical prop-
erties have been investigated in detail. The introduction of anisole
or benzaldehyde groups onto the BODIPY 1 at the 2,6 positions was
performed by two successive Sonogashira coupling reactions under
standard conditions (Scheme 1).21 The ethynyl groups were se-
lected not only as a means to attach the D/A groups to the chromo-
phore, but also to extend the conjugation between the donor and
the acceptor.6 The dicyanomethylene group intended to function
as an electron withdrawing entity was generated by a Knoevenagel
condensation22 on the aldehyde 3 with malononitrile in dichloro-
methane at reflux, leading to the purple compound 4 (Scheme 1).
Some difficulties in the purification and identification of compound
4 were encountered due to its poor solubility in common solvents.
Intermolecular aromatic p–p stacking and anti-parallel dipole–di-
pole interactions in solution favor molecular aggregation. This is a
common practical problem that has been widely discussed in re-
gard to push–pull chromophore synthesis.23–25 The strategy often
applied is to introduce bulky substituents onto the push–pull chro-
mophore scaffold in order to increase the steric hindrance and pre-
vent aggregation, therefore providing better solubility.23,25 We
have previously shown that introduction of diethynyl-groups on
⇑
Corresponding authors. Tel.: +33 3 68 85 26 89; fax: +33 3 68 85 27 61 (R.Z.).
E-mail addresses: ziessel@unistra.fr, ziessel@chimie.u-strasbg.fr (R. Ziessel).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.07.028

S. Niu et al. / Tetrahedron Letters 52 (2011) 4848–4853
4849
O
[Pd(PPh3)2Cl2], CuI
O
I
I
I
N
N
N
N
B
B
Benzene, NEt3
60°C
F
F
Y Y
2, 32%
5, 74%
1
Y = F
Y =
N
EtMgBr
N
H
O
O
O
N
N
[Pd(PPh3)2Cl2], CuI
H
B
Y
Y
Benzene, NEt3
60°C
Y = F
Y =
3, 47%
6, 39%
N
CN
NC
CH2(CN)2, Al2O3
CH2Cl2, Reflux
O
N
N
B
Y
H
Y
Y = F
Y =
4, 47%
7, 54%
N
Scheme 1. Synthesis of BODIPY derivatives 2–7.
the boron atom of the BODIPY core by using the appropriate Grig-
nard reagents can indeed efficiently prevent the formation of
aggregates and increase the solubility.26,27 After the replacement
of the fluorides of dye 2 using the Grignard reagent of dim-
ethylaminopropyne to give 5, the same procedure as used to obtain
4 gave the dicyanomethylene derivative 7 (Scheme 1). Compound
9 was synthesized similarly in order to compare its optical proper-
ties with those of compounds 4 and 7 (Scheme 2). Dye 9 is less con-
jugated than 4 and therefore has a better solubility in common
organic solvents.
O
H
O
H
[Pd(PPh3)2Cl2], CuI
I
N
N
N
N
Benzene, NEt3
60°C
B
B
F
F
F
F
8, 95%
Al2O3, CH2(CN)2
CH2Cl2, Reflux
CN
NC
In order to improve the dipole moment strength along the BOD-
IPY molecular axis, more powerful electron donor and electron
withdrawing groups are required. This must, however, be associ-
ated with good solubility of the new dyes and a means of achieving
this desirable combination was suggested by the recent work of
Diederich and co-workers on the reaction of tetracyanoethene
(TCNE) with electron rich alkyne derivatives.28–31 The donor-
substituted alkyne groups undergo a [2+2] cycloaddition reaction
with TCNE, followed by the formation of an intermediate cyclobu-
tene which subsequently undergoes ring opening leading to the
1,1,4,4-tetracyanobuta-1,3-diene (TCBD) derivatives (Scheme 3).
N
N
H
B
F
F
9, 51%
Scheme 2. Synthesis of BODIPY derivative 9
The TCBD unit exhibits a strong acceptor character and imports a
good solubility in common solvents due to the non-planarity of
the molecule which efficiently prevents the formation of
aggregates.28,32
Scheme 3. ORTEP view of dye 11. Displacement ellipsoids are drawn at 30% probability level.

4850
S. Niu et al. / Tetrahedron Letters 52 (2011) 4848–4853
CH2Cl2
TCNE, RT
C4H9
C4H9
N
N
N
N
C4H9
C4H9
B
F
F
14
CN
NC
NC
NC
CN
C4H9
N
C4H9
CN
C4H9
N
C4H9
C4H9
C4H9
C4H9
C4H9
N
N
N
N
N
N
B
B
F
F
F
F
NC
CN
NC
CN
NC
CN
15, 55%
16, 36%
Scheme 4. Synthesis of dyes 15 and 16.
CN
NC
O
TCNE
R
R
O
N
N
N
N
CN
CH2Cl2, RT
B
B
NC
R = H
R =
F
F
F
F
10
12
R = H
R =
11, 51%
13, 77%
O
O
Figure 1. Synthesis of BODIPY derivatives 11 and 13.
planar. The two dicyanovinyl (DCV) residues project in opposite
directions, with an interplanar dihedral angle (C24–C13–C12–
C21) of 38.2° (Fig. 1). The DCV moiety adjacent to the BODIPY
twists out of the BODIPY plane with a torsion angle (C5–C6–
C12–C21) of 43.7°, while the other DCV moiety twists in the oppo-
site sense, with a torsion angle (C7–C6–C12–C13) of 43.5°. The tor-
sion angle between the anisole ring and the adjacent DCV (C24–
C13–C14–C19) is 47.1° and that with the other DCV (C12–C13–
C14–C15) is 46.7°. Due to the strongly electron withdrawing TCBD
groups, the C7–C6 bond (1.41 Å) is significantly longer than the
C2–C3 bond (1.36 Å).
Molecules of compound 11 are all aligned in the crystalline
state along the longest dimension of the unit cell, that is, the b axis,
but without developing efficient
p–p stacking interactions,
whereas TCBD moieties are segregated into layers along the glide
planes at positions y = 1 4 and 3 4 (Fig. 2). Among the numerous weak
interactions which mediate the crystal packing of these molecules,
for example, CH3(methoxy-)Á Á ÁO(methoxy at Àx, Ày, Àz), C–HÁ Á ÁF
making molecular chains along the [1 0 0] direction, C–H
Figure 2. Packing view of dye 11 in cyan at general position x, y, z. In gold,
molecules related by a center of inversion, in magenta, by c-glide planes (in
transparency) and in green by a two-fold screw axis. Dashed lines indicate non-
conventional hydrogen bonds.
(methoxybenzyl groupÁ Á Á
p (BODIPY) hydrogen bonds between
molecules related by the c glide planes, three out of the four TCBD
nitrogen accept Csp2 or 3-H bonds from close neighbors with dis-
tances ranging between 2.4 and 2.7 Å.
The BODIPYs 10 and 12 containing ethynyl donor groups at the
2,6 positions were selected to react with TCNE in dichloromethane
at room temperature, leading to the substituted TCBDs 11 and 13
in good yields (Fig. 3). Interestingly, the reaction of dye 12 with
TCNE in a proportion of 1:2.2 gives the mono substituted deriva-
tive 13 in 77% yield. Despite the use of an excess of TCNE, the
mono-insertion was principally observed, whereas no selectivity
was observed during reaction of dye 14 with TCNE (Scheme 4).
Compound 14 was synthesized according to the literature21 then
reacted with TCNE in a proportion of 1:1.3 under the standard
reaction conditions. This gave the mono and di-substituted deriva-
tives 15 and 16 in 55% and 36% isolated yields, respectively. The
TCNE was totally consumed in the reaction, indicating that the dib-
utylamino moiety of 14 reacts more readily with TCNE than the
anisole unit of 12.
The optical properties of the push–pull chromophores were
evaluated in different solvents. Table 1 contains selected data for
species other than the TCBD derivatives (see ahead). In solution,
all these compounds show a strong S0–S1 transition between
k ꢀ 540–570 nm with an absorption coefficient in the 60,000–
90,000 MÀ1 cmÀ1 range, unambiguously assigned to the boradiaza-
indacene chromophore.33 In EtOH, a decrease of the extinction
coefficient for both formyl derivatives 3 and 6 were observed. This
fact may be attributed to the poor solubility of the compounds in
EtOH. At higher energy, two weak broad bands centered around
410 nm and 350 nm, can be attributed to a charge transfer absorp-
tion33 and the S0–S2 transition of the BODIPY moiety, respec-
tively.34
p–
p⁄ transitions with vibronic structure are observed at
The molecular structure of compound 11 was determined by
X-ray diffraction on a single crystal. The BODIPY core remains
230–320 nm for the phenyl groups. In CH2Cl2, the BODIPY
dyes show emission maximum in the 561–611 nm range. The

S. Niu et al. / Tetrahedron Letters 52 (2011) 4848–4853
4851
Table 1
Optical properties of selected BODIPY derivatives
b
b
Compounds
kabs (nm)
e
(MÀ1 cmÀ1
)
kem (nm)
Ua (%)
s
(ns)
kr
knr
2 (CH2Cl2)
3 (Dioxan)
3 (CH2Cl2)
3 (EtOH)
4 (Dioxan)
4 (CH2Cl2)
4 (EtOH)
5 (CH2Cl2)
6 (Dioxan)
6 (CH2Cl2)
6 (EtOH)
7 (Dioxan)
7 (CH2Cl2)
7 (EtOH)
543
561
563
556
565
569
563
539
555
559
555
562
567
562
535
526
57,000
80,000
36,000
12,000
73,000
82,000
74,000
52,000
57,000
65,000
36,000
75,000
85,000
75,000
94,000
55,100
606
604
611
614
610
616
612
600
591
603
598
597
606
600
561
591
6
0.7
2.6
1.7
0.9
2.4
1.7
1.1
1.4
3.2
2.7
2.5
3.1
1.5
1.1
2.3
1.7
8.6
134.3
22.3
42.4
93.3
22.5
42.4
76.4
69.3
7.5
23.7
23.6
8.7
45.3
77.3
20.4
48.8
42
28
16
46
28
16
3
76
36
41
73
32
15
53
17
16.2
16.5
17.8
19.2
16.5
14.5
2.1
23.8
13.3
16.4
23.5
21.3
13.6
23.0
10.0
9 (CH2Cl2)
10(CH2Cl2)
a
Quantum yield determined in dilute solution (1 Â 10À6 M) using rhodamine 6G as reference (
u
F = 0.78 in water, kexc = 488 nm).38
b
All uF are corrected for changes in refractive index. kr (107 sÀ1) and knr (107 sÀ1) were calculated using the following equations: kr =
u
F/s, knr = (1 À uF)/s.
fluorescence quantum yields are in the 28–53% range, with the
exception of the intermediate iodo-substituted compounds 2 and
5, for which the fluorescence is dramatically reduced due to a fas-
ter nonradiative decay, suggesting a fast intersystem crossing from
the singlet excited state to the triplet state.21
1
0.8
0.6
0.4
0.2
0
4
7
9
The absorption spectra of the dicyanomethylene derivatives 4, 7
and 9 in dichloromethane show intense absorption around 480–
630 nm with molar absorption coefficients in the 75,000–
94,000 MÀ1 cmÀ1 range (Fig. 3). In the absence of the anisole group,
compound 9 shows hypsochromic shifts relative to compound 4 of
34 and 55 nm in absorption and emission, respectively. In addition,
9 has a relatively small Stokes shift (866 cmÀ1) with a higher quan-
tum yield (53%) and longer decay time (2.3 ns). The absorption
band centered at 420 nm with absorption coefficients in the
15,000–20,000 MÀ1 cmÀ1 range can be attributed to a charge trans-
fer absorption band. The absorption centered on 350 nm can be
attributed to the S0–S2 transition with absorption coefficients in
the range of 15,000–18,000 MÀ1 cmÀ1. This transition is also more
intense than in common BODIPYs.33 Surprisingly, no significant
solvatochromism is observed for any of the push–pull dyes, with
variation of less than 6 nm from solvents with weak dipole mo-
ments to solvents with a stronger dipole.
230
330
430
Wavelength (nm)
530
630
Figure 3. Normalized absorption spectra of 4 (dark blue), 7 (red) and 9 (green) in
CH2Cl2.
1
13
15
16
0.8
The influence of the solvent is more important on the fluores-
cence with a strong decrease of the quantum yields (
lifetime ( ) when the dipole moment of the solvent increases. Con-
versely, the Stokes shifts increase slightly in more polar solvents.
For 7, the quantum yield ( ) and lifetime ( ) decrease when the
solvent changes from dioxane (0.73, 3.1 ns) to EtOH (0.15,
1.1 ns). The rate of non-radiative decay knr increases (about nine
times) while that of radiative decay kn remains similar. The small
changes in Stokes shift in solvents with various dipole moments
may indicate that the difference in dipole moments between the
excited state and the ground state is small.33,35
U) and the
0.6
0.4
0.2
0
s
u
s
260
360
460
560
660
760
Wavelength (nm)
The TCBD BODIPY dyes 13, 15 and 16 show high solubility in
common solvents. The UV/Vis absorption spectra of all three mol-
ecules display a similar broad, less band between 450 and 700 nm,
with molar absorption coefficients in the 35,000–80,000 MÀ1 cmÀ1
range (Fig. 4). In comparison with the parent BODIPY 12, the lowest
energy absorption maximum of 13 shows a bathochromic shift of
25 nm. For 15 and 16, the formation of mono- and di-TCBD moie-
ties leads to bathochromic shifts of 25 and 40 nm, respectively,
compared with 14. The broad absorption band may be due to an
inhomogeneous distribution of the solvation sphere. Interestingly,
for 15 at shorter wavelengths, two overlapping absorption bands
are observed between 260 and 400 nm, corresponding to CT
Figure 4. Normalized absorption spectra of 13 (green), 15 (red), and 16 (dark blue)
in dioxane.
between the amino group and the adjacent TCBD, and to the
p–
p⁄ transition of the free alkylaminophenylethylene group, the lat-
ter being absent in the case of 16. The fluorescence of the TCBD
dyes 13, 15, and 16 is completely quenched.
The electrochemical properties of selected dyes were evaluated
by cyclic voltammetry (Table 2). Compound 12 was used as refer-
ence to compare with dyes 4 and 13. For dyes 4 and 12, both are

4852
S. Niu et al. / Tetrahedron Letters 52 (2011) 4848–4853
Table 2
Electrochemical data of selected BODIPYsa
14
15
16
Compounds E°ox [V] (
D
E [mV])
E°red [V] (DE [mV])
4
+1.09 (irrev)
+1.01 (irrev)
+1.27 (irrev)
+0.65 (irrev), +0.75
(irrev), +1.15 (76)
+0.76 (irrev), +1.26 (71)
À1.05 (irrev), À1.12 (90)
À1.10 (96)
12
13
14
Fc/Fc+
À0.25 (64), À0.73 (69), À1.48 (78)
À1.16 (106)
1700
1200
700
200
-300
-800
-1300
-1800
15
16
À0.41 (83), À0.80 (144), À1.57
(irrev)
Potential (mV)/vs SCE
+1.27 (80)
À0.29 (76), À0.42 (85), À0.81
(120), À0.95 (164)
a
Cyclic voltammetry carried out in deoxygenated CH2Cl2 solutions, containing
0.1 M TBAPF6, at a solute concentration range of 1.5 Â 10À3 M, at 20 °C. Potentials
were standardized using added ferrocene (Fc) as internal reference and converted
to SCE assuming that E1/2 (Fc/Fc+) = +0.38 V (
DEp = 70 mV) versus SCE. Error in half-
Figure 6. Cyclic voltammetry of TCBDs dyes 14 + ferrocene (dark blue), 15 + fer-
rocene (red), and 16 + ferrocene (green).
wave potentials is 15 mV. When the redox process is irreversible the peak
potential (Eap or Ecp) is quoted.
For dye 15, the first irreversible wave at +0.76 V can be unambig-
uously assigned to the one-electron oxidation of the free amino
group at the opposite side of the TCBDs residue (Fig. 6). The TCBD
group clearly renders the oxidation of the adjacent amino group
more difficult due to a pronounced electron withdrawing effect.
The second reversible but not well resolved oxidation wave at
+1.26 V is more difficult to assign. In comparison with 14, the peak
can be attributed either to the amino group adjacent to the TCBD,
or to the BODIPY oxidation to form the radical cation. For 13, two
well resolved reversible reduction steps at À0.41, À0.80 V, and a
third quasi-reversible reduction step at À1.57 V can be attributed
to the successive one-electron reductions of the dicyanovinyl
(DCV) groups and the BODIPY moiety, respectively. The reduction
of BODIPY core is made more difficult by the TCBD residue by
410 mV.
More interestingly, for dye 16 a single reversible oxidation peak
is observed at +1.27 V. The fact that the current integration of this
peak is double that for the first reduction peak at À0.29 V, indicates
that both amino groups oxidize at the same potential due to the
sterically enforced deconjugation induced by the TCBD residues.
Furthermore, in comparison with 15, the oxidation of the BODIPY
core will be shifted to a higher potential due to the presence of
two TCBDs residues. It is likely that the potential falls outside the
accessible electrochemical window (+1.6 V vs SCE). The remark-
able three reversible and fourth quasi-reversible reductions steps
observed at À0.29, À0.42, À0.81, and À0.95 V, respectively, corre-
spond to the successive one electron reductions of the four DCV
moieties. The reduction of the BODIPY core is obviously made more
difficult by the double TCBD residues, and is probably outside the
accessible electrochemical window (À1.6 V vs SCE).
4
12
Fc/Fc+
13
1500
1000
500
0
-500
-1000
-1500
-2000
Potential (mV)/vs SCE
Figure 5. Cyclic voltammetry of 4 + ferrocene (dark blue), 12 + ferrocene (green),
and 13 + ferrocene (red).
characterized by an irreversible oxidation wave at +1.09 and
+1.01 V, respectively, corresponding to the one-electron oxidation
of the BODIPY moiety to the radical cation (Fig. 5). On the reduction
scans, a single reversible peak is observed at À1.10 V for dye 12
and À1.12 V for 4 and can be unambiguously attributed to the for-
mation of the
p
-radical anion of the BODIPY core.11,29,36 For 4, an
additional irreversible reduction of the dicyanovinyl group was ob-
served at À1.05 V, this being in the expected potential range for a
dicyanovinyl residue.37
For dye 13, on the oxidation scans, an irreversible wave was ob-
served at +1.27 V and can be attributed to the BODIPY moiety
undergoing one-electron oxidation. Compared with dye 12, it is
clear that the TCBD residue makes the BODIPY moiety more diffi-
cult to oxidize by 250 mV. On the reduction scans, interestingly,
three reversible peaks are observed at À0.25, À0.73, and À1.48 V,
corresponding to the successive one-electron reductions of the
dicyanovinyl (DCV) groups and the BODIPY moiety, respectively.
Due to the electrostatic effect, the second reduction of the DCV
moiety is made more difficult by 480 mV and the reduction of
the BODIPY moiety is more difficult by 380 mV.
In summary, a series of BODIPY based push–pull chromophores
have been prepared and their optical and electrochemical proper-
ties have been investigated. Interesting electrochemical properties
of the TCBD BODIPY dyes were observed due to the strong electron
withdrawing groups. There appears to be an effective electronic
conjugation along the 2,6-molecular axis. Further investigations
of the nonlinear optical properties of these push–pull dyes are cur-
rently in process.
The electrochemical properties of dye 14 are shown in Fig. 6.
Three oxidation waves are observed at +0.65, +0.75 and +1.15 V.
The first two close but resolvable irreversible one-electron oxidation
waves can be attributed to the successive oxidation of the two dib-
utylamino moieties, indicating an effective electronic interaction
Acknowledgments
We acknowledge the CNRS for providing research facilities and
financial support and Professor Jack Harrowfield (ISIS in Stras-
bourg) for commenting on the manuscript before publication.
between both groups through the p-conjugated BODIPY core. The
third oxidation wave can be attributed to the formation of the BOD-
IPY radical cation. The reversible reductionpeak observed at À1.16 V
corresponds to the formation of the BODIPY radical anion.
References and notes
1. Zhou, Y.; Xiao, Y.; Chi, S.; Qian, X. Org. Lett. 2008, 10, 633–636.

S. Niu et al. / Tetrahedron Letters 52 (2011) 4848–4853
4853
2. Dong, Y.; Bolduc, A. a.; McGregor, N.; Skene, W. G. Org. Lett. 2011, 13, 1844–
21. Bonardi, L.; Ulrich, G.; Ziessel, R. Org. Lett. 2008, 10, 2183–2186.
22. Knoevenagel, E. Ber. Der. Deut. Chem. Gesell. 1898, 31, 2596–2619.
1847.
3. Barsu, C.; Cheaib, R.; Chambert, S.; Queneau, Y.; Maury, O.; Cottet, D.; Wege, H.;
Douady, J.; Bretonniere, Y.; Andraud, C. Org. Biomol. Chem. 2010, 8, 142–150.
4. Lord, S. J.; Conley, N. R.; Lee, H.-l. D.; Samuel, R.; Liu, N.; Twieg, R. J.; Moerner,
W. E. J. Am. Chem. Soc. 2008, 130, 9204–9205.
5. Marder, S. R.; Kippelen, B.; Jen, A. K. Y.; Peyghammbarian, N. Nature (London)
1997, 388, 845–851.
6. LeCours, S. M.; Guan, H.-W.; DiMagno, S. G.; Wang, C. H.; Therien, M. J. J. Am.
Chem. Soc. 1996, 118, 1497–1503.
7. Collado, D.; Casado, J.; González, S. R.; Navarrete, J. T. L.; Suau, R.; Perez-
Inestrosa, E.; Pappenfus, T. M.; Raposo, M. M. M. Chem. Eur. J. 2011, 17, 498–
507.
23. Würthner, F.; Wortmann, R.; Meerholz, K. ChemPhysChem 2002, 3, 17–31.
24. Moore, A. J.; Chesney, A.; Bryce, M. R.; Batsanov, A. S.; Kelly, J. F.; Howard, J. A.
K.; Perepichka, I. F.; Perepichka, D. F.; Meshulam, G.; Berkovic, G.; Kotler, Z.;
Mazor, R.; Khodorkovsky, V. Eur. J. Org. Chem. 2001, 2671–2687.
25. Würthner, F.; Yao, S. Angew. Chem., Int. Ed. 2000, 112, 2054–2057.
26. Goze, C.; Ulrich, G.; Ziessel, R. J. Org. Chem. 2007, 72, 313–322.
27. (a) Rousseau, T.; Cravino, A.; Bura, T.; Ulrich, G.; Ziessel, R.; Roncali, J. Chem.
Commun. 2009, 1673–1675; (b) Rousseau, T.; Cravino, A.; Bura, T.; Ulrich, G.;
Ziessel, R.; Roncali, J. J. J. Mater. Chem. 2009, 19, 2298–2300; (c) Niu, S. L.;
Massif, C.; Ulrich, G.; Ziessel, R.; Renard, P.-Y.; Romieu, A. Org. Biomol. Chem.
2010, 9, 66–69.
8. Burckstummer, H.; Kronenberg, N. M.; Meerholz, K.; Würthner, F. Org. Lett.
2010, 12, 3666–3669.
9. Erten-Ela, S.; Yilmaz, M. D.; Icli, B.; Dede, Y.; Icli, S.; Akkaya, E. U. Org. Lett. 2008,
10, 3299–3302.
10. Chu, T.-Y.; Lu, J.; Beaupre´, S. .; Zhang, Y.; Pouliot, J.-R. m.; Wakim, S.; Zhou, J.;
Leclerc, M.; Li, Z.; Ding, J.; Tao, Y. J. Am. Chem. Soc. 2011, 133, 4250–4253.
11. Ziessel, R.; Retailleau, P.; Elliott, K. J.; Harriman, A. Chem. Eur. J. 2009, 15,
10369–10374.
12. Zhou, E.; Tan, Z. a.; Yang, Y.; Huo, L.; Zou, Y.; Yang, C.; Li, Y. Macromolecules
2007, 40, 1831–1837.
13. Wakatsuki, Y.; Yamazaki, H.; Kobayashi, T.; Sugawara, Y. Organometallics 1987,
6, 1191–1196.
14. (a) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891–4932; (b) Ulrich, G.;
Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008, 47, 1184–1201.
15. Bouit, P. A.; Kamada, K.; Feneyrou, P.; Berginc, G.; Toupet, L.; Maury, O.;
Andraud, C. Adv. Mater. 2009, 21, 1151–1154.
16. Didier, P.; Ulrich, G.; Mely, Y.; Ziessel, R. Org. Biomol. Chem. 2009, 7, 3639–3642.
17. Zheng, Q.; Xu, G.; Prasad, P. Chem. Eur. J. 2008, 14, 5812–5819.
18. Zhang, D.; Wang, Y.; Xiao, Y.; Qian, S.; Qian, X. Tetrahedron 2009, 65, 8099–
8103.
19. Zheng, Q.; He, G. S.; Prasad, P. N. Chem. Phys. Lett. 2009, 475, 250–255.
20. Kolemen, S.; Cakmak, Y.; Erten-Ela, S.; Altay, Y.; Brendel, J.; Thelakkat, M.;
Akkaya, E. U. Org. Lett. 2010, 12, 3812–3815.
28. Kato, S.-I.; Diederich, F. Chem. Commun. 2010, 46, 1994–2006.
29. Kato, S. I.; Kivala, M.; Schweizer, W.; Boudon, C.; Gisselbrecht, J. P.; Diederich, F.
Chem. Eur. J. 2009, 15, 8687–8691.
30. Jarowski, P. D.; Wu, Y.-L.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M.; Schweizer,
W. B.; Diederich, F. Org. Biomol. Chem. 2009, 7, 1312–1322.
31. Reutenauer, P.; Kivala, M.; Jarowski, P. D.; Boudon, C.; Gisselbrecht, J.-P.; Gross,
M.; Diederich, F. Chem. Commun. 2007, 4898–4900.
32. Esembeson, B.; Scimeca, M. L.; Michinobu, T.; Diederich, F.; Biaggio, I. Adv.
Mater. 2008, 20, 4584–4587.
33. Qin, W.; Baruah, M.; Van der Auweraer, M.; De Schryver, F. C.; Boens, N. J. Phys.
Chem. A 2005, 109, 7371–7384.
34. Karolin, J.; Johansson, L. B. A.; Strandberg, L.; Ny, T. J. Am. Chem. Soc. 1994, 116,
7801–7806.
35. (a) Demeter, A.; Berces, T.; Zachariasse, K. A. J. Phys. Chem. A 2001, 105, 4611–
4621; (b) Druzhinin, S. I.; Kovalenko, S. A.; Senyushkina, T. A.; Demeter, A.;
Januskevicius, R.; Mayer, P.; Stalke, D.; Machinek, R.; Zachariasse, K. A. J. Phys.
Chem. A 2009, 113, 9304–9320.
36. Nepomnyashchii, A. B.; Cho, S.; Rossky, P. J.; Bard, A. J. J. Am. Chem. Soc. 2010,
132, 17550–17559.
37. Liu, Y.; Zhou, J.; Wan, X.; Chen, Y. Tetrahedron 2009, 65, 5209–5215.
38. Olmsted, J. J. Phys. Chem. 1979, 83, 2581–2584.