Triindolo-Truxene Derivatives: Design, Synthesis, and Fine-Tuning of Electronic Properties and Molecular Assembly through Molecular Engineering

Article abstract of DOI:10.1002/chem.201804457

Triindolo-truxene, a C₃-symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms that can be facilely functionalized. Herein, butyl, carbonyl, cyano, and/or malononitrile groups were int

Full text of DOI:10.1002/chem.201804457

A Journal of
Accepted Article
Title: Novel Triindolo-Truxene Derivatives: Design, Synthesis, and
Fine-Tuning of Electronic Properties and Molecular Assembly
through Molecular Engineering
Authors: Jun-Bo Chen, Cen Zhou, Ru-Qiang Lu, Xin-Chang Wang,
Hang Qu, Mithu Saha, Hao-Liang Liu, Hui Zhang, and Xiao-
Yu Cao
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Novel Triindolo-Truxene Derivatives: Design, Synthesis, and Fine-
Tuning of Electronic Properties and Molecular Assembly through
Molecular Engineering
Jun-Bo Chen, Cen Zhou, Ru-Qiang Lu, Xin-Chang Wang, Hang Qu, Mithu Saha, Hao-Liang Liu, Hui
Zhang and Xiao-Yu Cao*[a]
Abstract: Triindolo-truxene, a C3-symmetric molecule with a large
π-conjugated plane, has six methylene carbon atoms and three
aromatic carbon atoms which can be facilely functionalized. Herein,
we introduce butyl, carbonyl, cyano, and/or malononitrile groups into
six methylene carbon atoms (6-, 14-, 22-, or 8-, 16-, 24-positions)
and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of
triindolo-truxene to produce eight derivatives. Their photophysical
and electrochemical properties, and molecular assembly can be
effectively modulated by substituents and substitution patterns.
Incorporation of electron-deficient groups led to red shifts in both the
absorption and the emission of these derivatives, and also lowered
their HOMO and LUMO levels. Different substitution patterns
resulted in the different intramolecular donor-acceptor interactions.
The substitutions of electron-deficient groups at 6-, 14-, and 22-
methylene carbon atoms led to the intramolecular charge transfer
from the fluorene arms to the truxene core, whereas the
corresponding substitutions at 8-, 16-, and 24-methylene carbon
atoms resulted in the converse intramolecular charge transfer from
the truxene core to the fluorene arms. Their molecular packing in
single crystals and molecular aggregation in solutions are also
manipulated by their substituents and substitution patterns. This
work provides a straightforward strategy to alter the properties of
triindolo-truxene.
Truxene, a well-performed and widely used building block in
light-emitting[28-32] and hole-transporting[32-38] materials, features
its adjustable properties through facile functionalizations.[39-40]
Truxene possesses six aromatic carbon atoms in 2-, 3-, 7-, 8-,
12-, and 13-positions provided by three fluorene subunits
(Figure 1), which can be functionalized by bromination,[41]
acetylation,[42] nitration,[43] etc. In addition, the other three
methylene carbon atoms in 5-, 10-, and 15-positions can also be
substituted by alkyl groups,[39] carbonyl groups[44] or
malononitrile groups[45]. Nonetheless, in most cases, these
methylene carbon atoms can only be substituted by one type of
functional groups that are usually alkyl chains to improve the
solubility of truxene, thus limiting control over the properties of
truxene. Triindolo-truxene,
a favoured alternative structure
synthesized by Pei et al.,[46] maintains the main structure of
truxene while contains two sets of methylene carbon atoms
(Figure 1). One set of methylene carbon atoms is in 6-, 14-, and
22-positions, and the other is in 8-, 16-, and 24-positions. These
two sets of methylene carbon atoms can be substituted
independently, providing more diverse combinations of
substituents. However, the previous synthetic procedures, in
which precursors undergo trimerization to form triindolo-truxene
alkylated in 8-, 16-, and 24-positions, can hardly produce
triindolo-truxene alkylated in 6-, 14-, and 22-positions. In
addition, the effects of substituents and substitution patterns on
triindolo-truxene have never been investigated.
Introduction
Herein, we report new design and synthesis of eight triindolo-
truxene derivatives (Figure 2), and the systematic investigation
of their structure-property relationships. These eight triindolo-
truxene derivatives were developed by introducing different
substituents into three aromatic carbon atoms (2-, 10-, and 18-
positons) and/or six methylene carbon atoms (6-, 14-, 22-, or 8-,
16-, 24-positions), including butyl, carbonyl, cyano, and
malononitrile groups. The photophysical and electrochemical
Carbon-rich π-conjugated materials play key roles in organic
electronics, such as organic field-effect transistors,[1-4] organic
solar cells,[5-10] and organic light-emitting diodes.[11-15] To achieve
high-performance organic devices, it is essential to develop new
building blocks and to understand their structure−property
relationships. In the past decades, several high-performance
building
blocks
have
been
developed
such
as
perylenediimide,[16-18] diketopyrrolopyrrole,[7,19-20] isoindigo,[21-23]
and BDOPV.[24-26] To alter their electronic properties, varies
substituents, such as alkyl groups, fluorine atoms, and cyano
groups, have been introduced to their molecular backbones.[24,27]
[a]
J.-B. Chen, Dr. C. Zhou, R.-Q. Lu, Dr. X.-C. Wang, H. Qu, Dr. M.
Saha, H.-L. Liu, Prof. H. Zhang, Prof. X.-Y. Cao
State Key Laboratory of Physical Chemistry of Solid Surfaces
Key Laboratory of Chemical Biology of Fujian Province
Collaborative Innovation Center of Chemistry for Energy Materials
(iChEM)
College of Chemistry and Chemical Engineering, Xiamen University
Xiamen 361005 (P. R. China).
Email: xcao@xmu.edu.cn
Figure 1. Molecular structures of truxene and triindolo-truxene.
Supporting information for this article is given via a link at the end of
the document.
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Figure 2. Molecular structures of triindolo-truxene derivatives 2a–2d and 3a–3d.
measurements suggested that incorporating electron-deficient
groups into triindolo-truxene can dramatically lower its energy
levels and narrow its energy gap. In addition, the substitutions of
electron-deficient groups at 6-, 14-, and 22-methylene carbon
atoms led to different properties of triindolo-truxene compared
with their analogues substituted at 8-, 16-, and 24-methylene
carbon atoms. These influences of substituents and substitution
patterns on the optical and electrochemical properties of
triindolo-truxene derivatives were rationalized by density
functional theory (DFT) and time-dependent DFT (TD-DFT)
calculations. Moreover, their photoluminescence quantum yields
and lifetimes can also be modulated by substituents and
substitution patterns. We also investigated the molecular
packing of these triindolo-truxene derivatives in single crystals
through single crystal X-ray diffraction, as well as their
triton B. Compound 2c was obtained by cyanation of compound
8 in the total yield of 54%
1
aggregation in solutions via concentration-dependent H NMR.
Our work provides efficient methods to construct triindolo-
truxene and to manipulate its properties, which may facilitate its
applications, for instance, in organic electronics and
supramolecular chemistry.
Results and Discussion
Synthesis of triindolo-truxene derivatives
Scheme 1. Synthetic approaches toward 2a–2d.
The synthetic approaches toward 2a–2d and 3a–3d are outlined
in Scheme 1 and Scheme 2, respectively. Compound 6 was
synthesized according to the similar method reported by Pei
from 2-bromofluorene (see Supporting Information).[46]
Trimerization of compound 6 using POCl3 as solvent gave 2a in
88% yield. The oxidation of 2a at 6-, 14-, and 22-methylene
carbon atoms by oxygen in the presence of triton B and pyridine
afforded 2b in 65% yield. Compound 2b was further treated by
malononitrile to give 2d in 47% yield. Bromination of 2a at 2-,
10-, and 18-atoms produced compound 7. Then compound 7
was oxidized into compound 8 by oxygen in the presence of
Friedel-Crafts acylation of 5,5,10,10,15,15-hexabutyltruxene
afforded 11 in 83% yield. Compound 11 underwent Pd-catalyzed
three-fold intramolecular couplings to give 3b in 59% yield.
Compound 3d was obtained in 65% yield by treating 3b with
malononitrile. Reduction of 3b using triethylsilane afforded 3a in
88% yield. Compound 3a was treated by bromide to give 12 in
88% yield. Oxidation of 12 using oxygen delivered 13 in 62%
yield. The subsequent cyanation of 13 by copper(I) cyanide gave
3c in 94% yield. Notably, we have successfully developed a new
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strategy to produced 6-, 14-, and 22-positions alkylated triindolo-
starting from 2a. The synthesis of 3a–3d was initiated from
5,5,10,10,15,15-hexabutyltruxene. The truxene 3a, which is a
full complement of the previous synthetic route to produced 8-,
16-, and 24-positions alkylated triindolo-truxene 2a.
positions (Figure 1). Electron-deficient substituents at different
types of methylene carbon atoms result in different absorption of
corresponding triindolo-truxene derivatives (Figure S1). For
example, compound 2b has carbonyl groups in 6-, 14-, 22-
positions and butyl groups in 8-, 16-, and 24-positions, whereas
3b has butyl groups in 6-, 14-, 22-positions and carbonyl groups
in 8-, 16-, and 24-positions (Figure 2). These different
substitution patterns lead to much different absorption of 2b and
3b. Compound 2b shows three absorption peaks at 284 nm, 348
nm, and 368 nm, whereas 3b exhibits four absorption peaks at
263 nm, 307 nm, 361 nm, and 410 nm. To elucidate this
difference, TD-DFT calculations were performed at the
B3LYP/6-31G+(d) level of theory, and their natural transition
orbitals[47-50] (NTOs) corresponding to S0→S1 are shown in
Figure S3–S10. The hole-NTOs of 2b–2d are localized on the
truxene core while the electron-NTOs are delocalized over the
whole molecule. Such distribution of NTOs indicates that the
intramolecular charge transfer is from the fluorene arms (Figure
S60) to the truxene core.[51] On the contrary, the hole-NTOs of
3b–3d are localized on the fluorene arms while the electron-
NTOs are delocalized over the whole molecule, suggesting that
the intramolecular charge transfer is from the
Scheme 2. Synthetic approaches toward 3a–3d.
Photophysical properties
The absorption spectra of eight derivatives in dichloromethane
are illustrated in Figure 3, and the corresponding data are
summarized in Table 1. As shown in Figure 3a and 3b,
incorporating increasingly electron-deficient substituents into
triindolo-truxene resulted in gradual red shifts of absorption
onsets and absorption maxima in both series of 2a–2d and 3a–
3d. The colors of the solutions changed from pale yellow (2a or
3a) to red (2d or 3d) (Figure 4). The absorption maximum of 2a
is at 338 nm, whereas the absorption maxima of 2b–2d with
increasingly electron-deficient substituents were red-shifted from
348 nm of 2b to 412 nm of 2d. In addition, the absorption onsets
of 2a–2d were also red-shifted from 355 nm of 2a to 610 nm of
2d. The influences of substituents on absorption of 3a–3d are
similar to those of 2a–2d (Table 1).
Figure 3. UV-vis absorption spectra of (a) 2a–2d and (b) 3a–3d. Normalized
fluorescence spectra of (c) 2a–2d and (d) 3a–3d. All spectra were
characterized in CH2Cl2 (1 × 10-5 M).
Moreover, substitution patterns also affect the photophysical
properties of triindolo-truxene derivatives. A triindolo-truxene
molecule contains two types of methylene carbons atoms. One
type is in 6-, 14-, 22-positions, and the other is in 8-, 16-, 24-
Figure 4. Photos of triindolo-truxene derivatives in CH2Cl2 (1 × 10-5 M) under
sunlight (top), and under 365 nm UV light (bottom).
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Table 1. Summary of photophysical and electrochemical characterization of 2a–2d and 3a–3d.
[a]
red1[b]
ox1[b]
[c]
[c]
cv[d]
opt[e]
Compound

onset, max
,
max
ΦPL
[a]
(ns)
Eonset
[V]
Eonset
[V]
ELUMO
[eV]
EHOMO
[eV]
Eg
Eg
abs.[a] [nm]
em.[a] [nm]
(%)
[eV]
[eV]
[g]
2a
2b
2c
2d
3a
3b
3c
3d
355, 338
500, 348
492, 366
610, 412
355, 340
492, 410
490, 413
607, 498
351, 367[f]
506, 527[f]
492[f], 520
602
32.27
3.85
1.84
−
1.17
1.66
1.69
1.67
1.27
1.68
1.73
1.72
−2.08[h]
−3.48
−3.59
−4.03
−2.18[h]
−3.22
−3.43
−3.77
−5.57
−6.06
−6.09
−6.07
−5.67
−6.08
–6.13
−6.12
−
3.49
2.48
2.52
2.03
3.49
2.52
2.53
2.04
2.34
−0.92
−0.81
−0.37
2.58
2.50
2.04
−
1.52
1.85
0.13
0.82
[g]
362, 379[f]
512
26.37
21.44
29.17
0.38
10.65
13.57
16.35
0.76
−
−1.18
−0.97
−0.63
2.86
2.70
2.35
511
601
[a] Measured in CH2Cl2 at room temperature. [b] Measured in CH2Cl2 with tetra-n-butylammonium hexafluorophosphate as electrolyte. [c] Determined
cv
against the external standard for Fc/Fc+. [d] Eg = ELUMO − EHOMO. [e] Calculated from the onsets of the UV-vis absorption. [f] Shoulder peaks. [g] Not
opt
detected owing to that the reduction potential are out of the electrochemical window of CH2Cl2. [h] ELUMO = EHOMO + Eg
.
truxene core to the fluorene arms. Thus, by changing the
positions of substituents, we successfully developed different
intramolecular donor-acceptor systems.
progressively lower their HOMO and LUMO levels. The first
oxidation potential onsets of 2a–2d were shifted from 1.17 V of
2a to 1.69 V of 2c. Thus, the HOMO levels of 2a–2d are aligned
from –5.57 eV to –6.09 eV. The first reduction potential onsets of
2a–2d were shifted gradually from lower than –2 V of 2a to –
0.37 V of 2d. Accordingly, the LUMO levels of 2a–2d are aligned
from –2.08 eV of 2a (calculated from EHOMO + Egopt) to –4.03 eV
of 2d. For 3a–3d, the changes of HOMO/LUMO levels are
similar to those of 2a–2d. This efficient strategy to tune energy
levels of triindolo-truxene can be used to design triindolo-
truxene-based materials with different charge transport polarities
(i.e. n-, p-channel or ambipolar transport). For instance, 2d
exhibits the LUMO level as low as –4.03 eV. Such low LUMO
level is beneficial for electron injection, hence making 2d a
promising candidate for n-channel semiconductors.[52-54]
In addition, the HOMO–LUMO band gaps of these derivatives
were narrowed by introducing increasingly electron-deficient
substituents. The band gaps are aligned from 3.49 eV of 2a to
2.04 eV of 2d, and from 3.49 eV of 3a to 2.35 eV of 3d. The
shrinkage of band gaps is consistent with the red-shift of
absorption. To further reveal the changes of HOMO/LUMO
levels, DFT calculations were carried out at the B3LYP/6-
311g(d,p) level of theory (Figure 6). The theoretical LUMO levels
are aligned from –1.02 eV of 2a to –3.76 eV of 2d with
increasing electron deficiency of the substituents, while the
We also investigated the influences of substituents on the
fluorescence of eight derivatives (Figure 3c and 3d). Increasing
the electron deficiency of substituents led to progressively red-
shifted emissions. The luminescent colors upon UV irradiation at
365 nm changed from pale yellow (2a or 3a) to red (2d or 3d).
the emission maxima of 2a–2d are significantly red-shifted from
351 nm of 2a, which does not contain any electron-deficient
substituents, to 602 nm of 2d, which has the strongest electron-
deficient substituents. Compounds 3a–3d show similar tendency
of fluorescence changes compared with that of 2a–2d. The
photoluminescence quantum yields and lifetimes of eight
triindolo-truxene derivatives were measured in dichloromethane
(Table 1). Compound 2a shows a photoluminescence quantum
yield of 32.27%, while 2b–2d exhibit much lower quantum yields
aligned from 3.85% to 0.13% with the increasingly electron-
deficient substitutions. Compounds 3a, 3b, and 3c show
quantum yields of 26.37%, 21.44%, and 29.17%, respectively.
The strongly electron-deficient 3d exhibits a quantum yield of
0.38%. The lifetimes of 2a–2d are aligned from 2.34 ns to 0.82
ns, while the lifetimes of 3a–3d are in a range of 16.35 ns to
0.76 ns. These results indicate that different substituents and
substitution patterns can modulate the photophysical properties
of triindolo-truxene derivatives.
Electrochemical properties
To investigate the electrochemical properties of eight triindolo-
truxene derivatives, cyclic voltammetry (CV) studies were
employed in dichloromethane using a glassy carbon electrode
as
a
working
electrode,
tetra-n-butylammonium
hexafluorophosphate as electrolyte, and Fc/Fc+ as an external
standard. The cyclic voltammograms are shown in Figure 5, and
the corresponding data are summarized in Table 1. Increasing
the electron deficiency of triindolo-truxene derivatives can
Figure 5. Cyclic voltammograms of (a) 2a–2d and (b) 3a–3d in CH2Cl2.
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Figure 6. Degenerated molecular orbitals and energy levels calculated at the B3LYP/6-311G(d,p) level of theory. Butyl chains were replaced by methyl groups to
simplify the calculations.
HOMO levels are aligned from –5.51 eV of 2a to –6.71 eV of 2c.
This result is in accordance with the tendency from experiments.
The substitution patterns of electron-deficient groups also
dramatically affect the LUMO levels of these derivatives. For
example, compound 2b, whose carbonyl groups are in the 6-,
14-, and 22-positions, possesses a lower LUMO level than that
of 3b, whose carbonyl groups are in the 8-, 16-, and 24-positions.
Similar phenomena were also observed in other derivatives,
which would be a consequence of different electronic structures.
The LUMO of 2b is localized in the truxene core, while the
LUMO of 3b most situates in its fluorene arms. This result
reveals that different electronic structures were produced by
introducing substituents into different types of methylene carbon
atoms.[55-56]
Molecular assembly
To reveal the effects of substituents and substitution patterns on
molecular packing of triindolo-truxene derivatives, single crystals
of these derivatives were obtained by phase-transfer or vapour-
diffusion methods, and analysed by single crystal X-ray
diffraction. The structures and molecular packing of 2c, 3a, 3c,
and 3d are shown in Figure 7. Compound 2c displays an
approximately planar molecular backbone. Its Ca…O distances
Figure 7. Crystal structures and packing of (a) 2c, (b) 3a, (c) 3c, and (d) 3d.
The red-, purple-, grey-, and white-coloured atoms represent O, N, C, and H,
respectively. All of the hydrogen atoms in molecular packing figures were
omitted for clarity. The red dash lines indicate distances.
are about 3.0 Å, which indicate that three intramolecular
hydrogen bonds are formed because these Ca…O distances are
shorter than those of the combined van der Waals radius (3.3
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Å).[57-58] These intramolecular hydrogen bonds are beneficial to
the planarity of molecular backbone and then to its
intermolecular packing. Four molecules of 2c form a stacked
tetramer along the c axis with strong π-π interaction (π-π
distance was ca. 3.4 Å). Their intermolecular π-π overlaps most
focus on the center of molecule. These tetramers are organized
in a layer-by-layer fashion with a 7.3 Å of interlayer distance. On
the contrary, 3a, 3c, and 3d are difficult to stack along the cores
of molecules owing to the large steric hindrance of butyl chains
at 6-, 14-, and 22-positions. Compounds 3a and 3c arrange at
edge-to-face modes, and both adopted herringbone stacking
mode.[24] Compound 3d displays a layered packing mode with a
π-π distance of 3.6 Å.
General remarks
All of chemicals and solvents from commercial sources were utilized as
received without further purification unless otherwise mentioned. 1H and
13C NMR spectra were recorded on a Bruker Avance II 400MHz, Avance
III 500 MHz, or Avance III 600 MHz NMR spectrometer. High-resolution
mass spectra (HRMS) were recorded on Bruker En Apex Ultra 7.0T
FTMS mass spectrometer or Bruker Impact II mass spectrometer.
Absorption spectra were recorded on SHIMADZU UV-2550 spectrometer.
Fluorescence measurements were recorded on HITACHI F-7000
fluorescence spectrophotometer. Photoluminescence quantum yields
and lifetimes were recorded on Edinburgh FLS980 fluorescence
spectrometer. Cyclic voltammetry (CV) was performed on a CHI660E
electrochemical workstation in anhydrous dichloromethane containing n-
Bu4NPF6 (0.1 M) as supporting electrolyte. All potentials were recorded
versus Ag/AgCl (saturated) as a reference electrode. The scan rate was
100 mV·s-1. Single crystal X-ray diffraction data were collected on Rigaku
SuperNova X-Ray single crystal diffractometer using Cu Kα (λ= 1.54184
Å) micro-focus X-ray sources.
To investigate the aggregation of eight triindolo-truxene
derivatives in solutions, concentration-dependent 1H NMR
experiments of eight triindolo-truxene derivatives were
1
performed in benzene-d6. Compound 2a showed a broaden H
NMR spectrum at 298 K, which became sharper at elevated
temperature (e.g. 333 K). At 333 K, the aromatic proton Ha of 2a
was remarkably upfield shifted by 193 ppb when the
concentration was increased from 0.1378 mM to 4.411 mM
(Figure S17), suggesting an aggregation process. The self-
association constant of 2a was determined to be 316 M-1 by an
isodesmic aggregation model (Figure S18) at 333 K.[59]
Compounds 2b and 2c also showed clear aggregation with self-
association constants of 15 M-1 and 57 M-1 at 298 K, respectively
(Figure S19–S22). In contrast, 2d and 3a–3d did not exhibit
obvious changes of chemical shifts in aromatic region under
various concentrations at 298 K (Figure S23–S27), probably due
to that the bulky groups in 6-, 14-, and 22-positions of triindolo-
truxene prohibit the molecular aggregation. These results
confirm that substituents and substitution patterns can effectively
alter molecular assembly of triindolo-truxene derivatives.
Exemplified synthesis
Synthesis of 3b. Compound 11 (0.20 g, 0.146 mmol), KOAc (0.12 g,
1.17 mmol), tetrabutylammonium bromide (0.24 g, 0.73 mmol), Pd(OAc)2
(0.013 g, 0.058 mmol), and anhydrous N,N-dimethylformamide (3 mL)
were added in a Schlenk tube. After removing oxygen by three freeze-
pump-thaw cycles, the reaction was heated at 153 °C for 36 h. The
solution was cooled and poured into ice water. The precipitate was
filtered, and dissolved using dichloromethane. The organic phase was
washed with water and brine, and dried over anhydrous sodium sulphate.
The crude product was purified by column chromatography over silica gel
using a mix solvent of petroleum ether and dichloromethane (1:1, v/v) as
mobile phase to afford 3b as a yellow solid (0.084 g, 59%). 1H NMR (500
MHz, CDCl3, 298 K) δ (ppm) = 8.56 (s, 3H), 7.83 (s, 3H), 7.73 (t, J = 7.0
Hz, 6H), 7.61 (t, J = 8.0 Hz, 3H), 7.36 (t, J = 7.0 Hz, 3H), 2.97–2.94 (m,
6H), 2.30–2.26 (m, 6H), 0.99–0.92 (m, 12H), 0.68–0.67 (m, 6H), 0.56–
0.54 (m, 6H), 0.49 (t, J = 7.3 Hz, 18H). 13C NMR (126 MHz, CDCl3, 298
K) δ (ppm) = 193.83, 155.09, 148.46, 145.64, 144.72, 143.60, 138.10,
135.12, 134.90, 133.25, 129.07, 124.38, 119.90, 118.37, 116.31, 55.93,
36.61, 26.68, 22.80, 13.79. APCI-HRMS (m/z): [M+H]+ calcd. for
C72H73O3, 985.5554; found, 985.5553.
Conclusions
In summary, we have designed and synthesized eight triindolo-
truxene derivatives with different combinations of butyl, carbonyl,
cyano, or malononitrile substituents at six methylene carbon
atoms (6-, 14-, 22-, or 8-, 16-, 24-positions) and/or three
aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-
truxene. Their photophysical and electrochemical properties, as
well as molecular packing in single crystals and aggregation in
solutions can be finely tuned by different substituents and
substitution patterns. The HOMO/LUMO levels of these triindolo-
truxene derivatives are aligned from –5.57 eV/–2.08 eV to –6.13
eV/–4.03 eV, and their optical band gaps are ranged from 3.49
eV to 2.03 eV. We provide here not only the strategies of
functionalizations on triindolo-truxene but also the systematic
investigations on their structure-property relationships. The facile
modifications, the tunable energy levels, and the controllable
molecular packing of triindolo-truxene derivatives make them
promising building blocks for organic electronics and also for
constructions of more complicated architectures, such as
covalent/metal organic frameworks,[60-61] molecular cages,[62] and
supramolecular complexes.[63]
Synthesis of 3a. Compound 3b (5.2 g, 5.3 mmol) was dissolved in
anhydrous dichloromethane (38 mL). Under a nitrogen atmosphere,
Et3SiH (12.3 g, 106 mmol) was added, and the solution was stirred for 10
min. Then BF3•OEt2 (15.0 g, 106 mmol) was slowly added. The solution
was warmed to room temperature and stirred at room temperature for 24
h until becoming colourless. The reaction was quenched by saturated
sodium carbonate solution. The organic layer was washed with water and
brine, and dried over anhydrous sodium sulphate. The crude product was
purified by column chromatography over silica gel with petroleum ether
as mobile phase to afford 3a as a white solid (4.4 g, 88%). 1H NMR (500
MHz, CDCl3, 298 K) δ (ppm) = 8.86 (s, 3H), 7.99 (d, J = 7.5 Hz, 3H), 7.68
(s, 3H), 7.62 (d, J = 7.0 Hz, 3H), 7.49 (t, J = 7.5 Hz, 3H), 7.35 (t, J = 7.0
Hz, 3H), 4.06 (s, 6H), 3.19–3.15 (m, 6H), 2.30–2.26 (m, 6H), 0.98–0.91
(m, 12H), 0.70–0.63 (m, 12H), 0.44–0.47 (m, 18H). 13C NMR (126 MHz,
CDCl3, 298 K) δ (ppm) = 153.74, 144.88, 143.57, 142.45, 142.08, 140.13,
139.30, 138.54, 126.82, 126.38, 125.20, 119.32, 118.90, 115.83, 55.29,
36.96, 36.86, 26.76, 22.97, 13.90. APCI-HRMS (m/z): [M+H]+ calcd. for
C72H79, 943.6176; found, 943.6200.
Acknowledgements
We are thankful to Jian Pei, Lei Fang, Wei Zhang, and Yan Xia
for their grateful suggestions and help. This work is supported by
the 973 Program (No. 2015CB856505), the NSFC (Nos.
Experimental Section
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10.1002/chem.201804457
Chemistry - A European Journal
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21722304, 91427304, 21573181, and 91227111), the Top-Notch
Young Talents Program of China, and the Fundamental
Research Funds for the Central Universities of China (No.
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Keywords: triindolo-truxene• π-conjugated• substitution effects•
intramolecular charge transfer
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10.1002/chem.201804457
Chemistry - A European Journal
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Entry for the Table of Contents
FULL PAPER
Eight triindolo-truxene derivatives with
different substituents and substitution
patterns were developed. Their
photophysical and electrochemical
properties, as well as molecular
Jun-Bo Chen, Cen Zhou, Ru-Qiang Lu,
Xin-Chang Wang, Hang Qu, Mithu Saha,
Hao-Liang Liu, Hui Zhang and Xiao-Yu
Cao*
Page No. – Page No.
assembly were facilely manipulated by
substituents and substitution patterns
.
Novel Triindolo-Truxene Derivatives:
Design, Synthesis, and Fine-Tuning
of Electronic Properties and
Molecular Assembly through
Molecular Engineering
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