C 3-Symmetric star shaped donor-acceptor truxenes: Synthesis and photophysical, electrochemical and computational studies

Article abstract of DOI:10.1039/c7nj03934d

This manuscript reports the design and synthesis of C₃-symmetric star shaped donor and acceptor substituted truxenes 6, 7, 10 and 11 using Pd-catalyzed Sonogashira cross-coupling and [2+2] cycloaddition-retroelectrocyclization reactions. Their photophysical, electrochemical and computational studies were explored, which indicate strong donor-acceptor interactions and effective tuning of the HOMO-LUMO gap. The computational studies reveal that the TCNE and TCNQ substituted truxenes 10 and 11 exhibit lower HOMO-LUMO gaps compared to truxenes 6 and 7. The reaction pathway of [2+2] cycloaddition-retroelectrocyclization was studied using computational calculations, which reveal that the donor substituted truxene 7 is favourable for cycloaddition-retroelectrocyclization reactions, whereas acceptor substituted truxene 6 is not favourable.

Full text of DOI:10.1039/c7nj03934d

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C ꢀSymmetric Star Shaped DonorꢀAcceptor Truxenes: Synthesis,
3
Photophysical, Electrochemical and Computational Studies
Rekha sharma, Ramesh Maragani, Rajneesh Misra*
Abstract:
This manuscript reports the design and synthesis of C
3
ꢀsymmetric star shaped donor and
acceptor substituted truxenes 6, 7, 10 and 11 using Pdꢀcatalyzed Sonogashira crossꢀcoupling
and [2+2] Cycloadditionꢀretroelectrocyclization reactions. Their photophysical,
electrochemical and computational studies were explored, which exhibits strong donorꢀ
acceptor interaction and effective tuning of the HOMO–LUMO gap. The computational
studies reveal that the TCNE and TCNQ substituted truxenes 10 and 11 exhibit lower
HOMO–LUMO gap compared to truxene 6 and 7. The reaction pathway of [2+2]
cycloadditionꢀretroelectrocyclization was studied by computational calculations, which
reveals that, the donor substituted truxene 7 is favourable whereas acceptor substituted
truxene 6 is not favourable for cycloaddition-retroelectrocyclization reactions.
Introduction:
The development of novel π‐ conjugated donor–acceptor (D–A) molecular systems have
drawn immense attention of the scientific community due to their potential applications in
multiꢀphoton absorption, organic light emitting diodes (OLEDs) and organic field effect
1,2
transistors (OFETs), organic photovoltaics (OPVs). The electronic and photonic properties
of the π‐ conjugated D–A molecular systems can be tuned by altering the HOMO‐ LUMO
3
gap. The HOMO‐ LUMO gap in D–π–A molecular systems can be tuned either by altering
4,5
the strength of D/A units or by varying the πꢀbridge.
The D–A systems incorporating the cyanoꢀbased acceptors such as tetracyanoethylene
(TCNE) and 7,7,8,8ꢀtetracyanoquinodimethane (TCNQ) are potential candidates for dyeꢀ
1

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6
–8
sensitized solar cells (DSSCs), organic photovoltaics and nonꢀlinear optics. Diederich and
others have reported the synthesis and properties of various TCNE and TCNQ substituted
9a–c
derivatives using [2+2] cycloaddition–retroelectrocyclization reaction.
Michinobu et al.
have explored the TCNE and TCNQ substituted polymers which are promising materials for
9
d,e
photovoltaic applications.
Shoji et al. have reported donor–acceptor based TCNE and
9
f,g
TCNQ molecules as a redox active ICT chromophores.
Butenschoen et al. have
9h
synthesized a variety of 1,1´ꢀdisubstituted ferrocenyl TCBD derivatives. Our group is
interested in the design and synthesis of novel D–A molecular systems for optoelectronic
10
applications.
The starꢀshaped truxene is a rigid building block for constructing extended πꢀconjugated
molecular systems due to its easy functionalization, excellent solubility, high thermal and
1
1–13
chemical stability.
molecules based on the truxene core for optoelectronic applications.
that truxene based donor–acceptor systems have potential applications in organic lightꢀ
Jian Pei et al. have explored various star shaped πꢀconjugated
1
2,14
Literature reveals
15–17
emitting diodes (OLED), organic solar cells (OSC) and organic fluorescent probes.
Recently, we have explored the reaction pathway and tuning of HOMOꢀLUMO gap of TCNE
2
1
functionalized bisthiazole based donorꢀacceptor systems. We were further interested to
study the [2+2] cycloadditionꢀretroelectrocyclization reaction pathway and tuning of HOMOꢀ
LUMO energy gap of triphenylamine (donor), naphthalimide (acceptor) substituted truxene
and their TCNE and TCNQ derivatives. The triphenylamine and naphthalimide substituted
truxenes were synthesized by the Pdꢀcatalyzed Sonogashira crossꢀcoupling reaction and their
photophysical, electrochemical and computational studies were performed. The
triphenylamine (donor) substituted truxene 7 was further subjected to the [2+2]
cycloaddition–retroelectrocyclization reaction with tetracyanoethylene (TCNE) and 7,7,8,8ꢀ
2

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tetracyanoquinodimethane (TCNQ), which resulted in truxenes 10 and 11. On the other hand
the naphthalimide (acceptor) substituted truxene 6 does not undergo the cycloaddition
retroelectrocyclization reaction due to the lower HOMO and higher LUMO energy level of
1
8
TCNE.
Results and discussion:
The donor (TPA) and acceptor (NDI) substituted substituted truxenes 6, 7, 10 and 11 were
synthesized by the Pdꢀcatalyzed Sonogashira crossꢀcoupling reaction and [2+2]
cycloaddition-retroelectrocyclization reactions (Scheme 2). The truxene 1 was synthesized by
19
1
ꢀindanone in the presence of acetic acid and hydrochloric acid. Truxene exhibits poor
solubility due to its flat disc like conformation. Therefore, in order to improve the solubility
six hexyl groups were attached to the Cꢀ5, Cꢀ10, and Cꢀ15 positions of the truxene moiety by
alkylation reaction using bromoꢀhexane, which resulted readily soluble hexahexylated
19
3 2
truxene 2 (Scheme 1). The iodination reaction of truxene 2 in the presence of HIO and I
20
resulted in triꢀiodo truxene 3 in 80% yield (Scheme 1).
Scheme 1: Synthesis of triꢀiodotruxene 3.
3

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The intermediates 4ꢀethynylꢀN,Nꢀdiphenylaniline (5), 4ꢀethynylꢀ1,8ꢀnaphthalimide (4) were
21
synthesized by reported procedure. To overcome the solubility problem nꢀbutyl group was
attached at the Nꢀposition of 4ꢀethynylꢀ1,8ꢀnaphthalimide. The reaction of triꢀiodo truxene 3
with 4ꢀethynylꢀ1,8ꢀnaphthalimide 4, 4ꢀethynylꢀN,Nꢀdiphenylaniline 5 under the catalytic
system Pd(dba) /AsPh resulted truxene 6 and 7 in 70% and 75% yield respectively (Scheme
2
3
2
). The triphenylamine substituted truxene 7 was further subjected to the [2+2]
o
cycloadditionꢀretroelectrocyclization reactions with TCNE and TCNQ at 100 C for 16 h,
which resulted truxene 10 and 11 in 71%, and 65% yield respectively. The reaction of
naphthalimide substituted truxene 6 with TCNE and TCNQ did not lead to the product
formation (Scheme 2). The truxenes 6, 7, 10 and 11 showed good solubility in common
1
13
organic solvents and were well characterized by H NMR, C NMR, and HRMS techniques.
O
N
O
NC
NC
CN
CN
8
No reaction
No reaction
DCE, 100 °C,reflux
O
N
O
C6H13
C6H13
NC CN
C6H13
I
4
O
C6H13
C6H13
Pd(dba)2/AsPh3
Toluene/TEA
80 °C
N
C6H13
C6H13
NC CN
9
C6H13
O
6
O
N
(70%)
N
DCE, 100 °C,reflux
NC
NC
N
NC
I
O
CN
CN
C6H13
C6H13
NC
C6H13
I
Pd(dba)2/AsPh3
Toluene/TEA
3
NC
NC
NC
CN
CN
CN
C6H13
C6H13
8
0 °C
N
C6H13
C6H13
8
N
DCE, 100 °C,reflux
CN
CN
C6H13
C6H13
NC
NC
N
C6H13
C6H13
5
C6H13
N
10
(71%)
NC CN
N
NC
CN
N
NC
NC
N
NC CN
C6H13
CN
CN
9
7
(75%)
NC
DCE, 100 °C,reflux
C6H13
CN
C6H13
C6H13
C6H13
CN
CN
NC
NC
N
11
(65%)
Scheme 2: Synthesis of donor/acceptor substituted truxenes 6, 7, 10 and 11.
4

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The triphenylamine substituted truxene 7 undergoes cycloaddition reaction with TCNE as
shown by negative Gibbs free energy ꢀ0.14 kcal/mol calculated by computational studies,
shown in Figure 1. In case of naphthalimide substituted truxene 6 the cycloaddition reaction
2
2
was unsuccessful as shown by positive Gibbs free energy (0.59 kcal/mol). This confirms
that donor substituted truxenes are favourable for cycloaddition reaction, whereas truxenes
substituted by electron withdrawing groups are not favourable (Figure 1).
Figure 1. The Gibbs free energy differences of the truxenes 6 and 7 by using 6ꢀ311+ g(d,p)/
B3LYP at 100 °C in 1,2ꢀdichloroethane solvent.
In triphenylamine substituted truxene (7) the HOMO energy level (ꢀ4.99 eV) is closer to the
LUMO level of TCNE (ꢀ4.56 eV) as compared to HOMO energy level of truxene 6 (ꢀ5.68
eV) (Figure 2). Therefore overlapping of HOMO orbital of truxene 7 and LUMO orbital of
TCNE is feasible in cycloaddition reaction whereas the overlapping of orbitals between
23
TCNE and truxene 6 is not favourable.
5

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Figure 2. The HOMO and LUMO molecular orbitals of truxene 7, TCNE and truxene 6 by
+
using 6ꢀ311 g(d,p)/B3LYP at 100 °C in 1,2ꢀdichloroethane solvent.
The thermal stability of the donor and acceptor substituted truxenes 6, 7, 10 and 11 were
−
1
explored using thermogravimetric analysis (TGA) at a heating rate of 10 °C min under
nitrogen atmosphere (Figure 3). The decomposition temperature for 10% weight loss in
truxenes 6–11 were above 370 °C. The naphthalimide substituted truxene 6 showed better
thermal stability, as the 10% weight loss is at higher temperature (426 °C) as compared to
other truxenes (Table 1). The overall thermal stability of truxenes follow the order 6 > 7 > 11
>
10.
Figure 3. TGA plots of truxenes 6, 7, 10 and 11
6

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Photophysical properties:
The UVꢀvis absorption spectra of the truxenes 6, 7, 10 and 11 were recorded in
dichloromethane at room temperature (Figure 4), and the data are listed in Table 1. The
truxenes exhibit absorption band between 273–320 nm corresponding to πꢀπ* transition. The
absorption spectra of truxene 6 and 7 exhibit charge transfer (CT) band at 418 nm and 383
nm respectively. In truxene 10, the incorporation of TCNE unit results in red shifted strong
charge transfer band at 433 nm whereas TCNQ acceptor unit result in multiꢀCT bands in
24
truxene 11. This indicates strong donor–acceptor interaction in truxene 10 and 11 with
TCNE and TCNQ linkers. The presence of strong CT transition results in intense colour
solution of truxenes 6–11 in dichloromethane (Figure 5).
Figure 4: (a) Normalized electronic absorption spectra of truxene 6, 7, 10 and 11 and (b)
ꢀ5
fluorescence spectra of truxenes 6 and 7 (1.0×10 M concentration) in dichloromethane.
The trend observed in the HOMO–LUMO gap values exhibit the order 7>6>10>11. This
reveals that the HOMO–LUMO gap values were considerably lowered in the TCNQ linked
truxene 11 followed by the TCNE substituted truxene 10 and naphthalimide substituted
truxene 6. Hence, HOMO‐ LUMO gap in these truxene derivatives are function of the
acceptor strength. The fluorescence emission wavelengths for truxenes 6 and 7 were observed
7

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at 611 nm and 430 nm respectively (Table 1). The TCNE and TCNQ linked truxenes 10 and
2
5,26
11 are nonꢀemissive in nature.
−5
Figure 5: Truxenes 6, 7, 10 and 11 at 1 × 10 M concentration in dichloromethane in day
light.
Table 1. Photophysical and electrochemical data of truxenes 6, 7, 10 and 11
b
c
d
°C
Compound Photophysical Emission
Φ
f
Electroꢀchemical data
T
d
a
a
data
λ
max[nm]
Theoretical
HOMOꢀ
LUMO
λ
max, [nm]
E
ox(V)
Ered(V)
5
–1
–1
(
ε×10 [mol cm ])
gap (eV)
Ferrocene
6
ꢀ
ꢀ
ꢀ
0.00
ꢀ
320(1.1), 418
611
0.42 1.31
0.54 0.37
ꢀ1.47
ꢀ1.44
2.98
3.31
426
424
7
300(1.2), 383
430
0
.96
1
1
0
1
273(1.5), 433
290(1.8), 380,
ꢀ
ꢀ
ꢀ
ꢀ
1.30
1.25
ꢀ1.49
ꢀ1.46
2.34
1.92
370
388
4
40, 655
a
b
Measured in DCM at T = 25 °C, λmax (nm): absorption maximum. ε, extinction coefficient. Determined by using quinine sulphate as a
standard (Φ = 0.54). Recorded by cyclic voltammetry using 1.0 × 10 M solutions of 6–11 containing 0.1 M solution of Bu NPF in
4 6
DCM at 100 mV s scan rate, vs. FcH/FcH . Decomposition temperature at 10% weight loss, determined by TGA.
st
c
−3
−1
+ d
Electrochemical propetries:
The electrochemical behaviour of the truxenes 6, 7, 10 and 11 were investigated by the cyclic
voltammetric analysis in dry dichloromethane solution at room temperature (25 °C) using
6
tetrabutylammoniumhexafluorophosphate (TBAPF ) as a supporting electrolyte. The
electrochemical data are listed in Table 1. The cyclic voltammograms of the truxenes 6, 7, 10
8

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and 11 are shown in the ESI section. All potentials are corrected to be referenced against
+
27
FcH/FcH , as required by IUPAC. The cylic voltammogram of the truxenes 6, 10 and 11
show one irreversible oxidation wave in the range of 1.25–1.31 V (Figure S1). The
triphenylamine substituted truxene 7 shows one reversible oxidation peak and one
quasireversible peak. The first oxidation potentials of truxene 7 is at E1/2 = 0.37 V, and the
second oxidation potential at
E1/2 = 0.96 V, suggesting a successive formation of the
monocation and then dication radical, which is attributed to the removal of electrons from the
28
triphenylamine moiety.
The truxenes 6, 7, 10 and 11 exhibit one reversible reduction wave in the range of ꢀ1.44 to ꢀ
.49 V. The acceptor substituted truxenes 6, 10, and 11 exhibit harder oxidation and
1
reduction as compared to donor substituted truxene 7. This reflects strong donorꢀacceptor
interaction in truxene 6, 10 and 11.
TimeꢀDependent Density Functional (TDꢀDFT) Studies:
To understand the photophysical and electrochemical properties of donorꢀacceptor substituted
truxenes 6, 7, 10 and 11 the density functional theory (DFT) and time dependent density
functional (TDꢀDFT) calculations were performed. The structures 6, 7, 10 and 11 were
2
9
optimized using Gaussian 09 program at the B3LYP/6ꢀ31G** level. The TDꢀDFT
calculations were carried out in the 1,2ꢀdichloroethane (DCE) using the polarized continuum
model (CPCM) of Gaussian 09 software. The 6ꢀ31G**/CAMꢀB3LYP basis set was used for
29
all the calculations.
The TDꢀDFT predicted vertical excitation energies of truxene 6 and 7 are shown in Figure 6
truxene 10 and 11 can be found in ESI Figure S2) along with experimental UVꢀvis spectra
(
and data are listed in Table 2. The truxene 6 shows absorption bands calculated at CAMꢀ
B3LYP level at 284 nm and 389 nm. The experimental values for these transitions are 320
9

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nm and 418 nm respectively. The truxene 7 shows calculated band at 272 nm and 355 nm
which corresponds to experimental bands at 300 nm and 383 nm (Figure 6). The
incorporation of TCNE (truxene 10) results major intense transitions at 383 nm and TCNQ
(truxene 11) results bands at 370 nm and 570 nm, which belongs to intramolecular charge
transfer (ICT), this is in accordance with the experimental values (Figure S2). These bands
are supported by the frontier molecular orbitals, which show that intramolecular charge
transfer (ICT) takes place from triphenylamine (donor) to TCNE or TCNQ (acceptor) as
shown in Figure S4.
Figure 6. The comparison of experimental and calculated (TDꢀDFT at CAMꢀB3LYP level)
absorption spectrum of truxene 6, 7 in 1,2ꢀdichloroethane solution.
Figure 7. The major transitions in truxene 6
1
0

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Figure 8. The DFT optimized structures of the truxenes 6, 7, 10 and 11 with Gaussian 09 at
the B3LYP/6ꢀ31G** level of theory.
Table 2. Computed vertical transition energies and their Oscillator strengths (f) and major
contributions for the truxenes 6, 7, 10 and 11
Truxenes
TDꢀDFT/ CAMꢀB3LYP (DCE)
a
λ
max
f
Major contribution (%)
6
284 nm
89 nm
272 nm
55 nm
0.0087
2.29
HOMO−1→LUMO+1(12%)
HOMO−2→LUMO+1(26%)
HOMO−2→LUMO+9 (15%)
HOMO−2→LUMO (21%)
HOMO−4→LUMO+2 (12%)
HOMO−1→LUMO (27%)
HOMO−5→LUMO (11%)
3
7
0.352
3
3.369
1
0
383 nm
370 nm
0.6231
0.2677
0.7923
11
520 nm
a
f is Oscillator strengths
The optimized structures of truxene 6 and 7 exhibit planar conformation with respect to
truxene core. The incorporation of the TCNE and TCNQ groups results in loss of planarity in
truxene 10 and 11. The dihedral angle between the triphenylamine groups and truxene core is
76.1°, 89.6°, 74.9° in truxene 10, and 74.0°, 74.8°, 74.8° in truxene 11 (Figure 8).
1
1

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Figure 9 shows the electron density distribution of the HOMO and LUMO of the truxenes 6,
, 10 and 11. In truxene 6 the HOMO is delocalized on the truxene core and LUMO is on the
7
naphthalimide unit, this separation of HOMO and LUMO results in strong charge transfer
and low energy gap (2.98 eV). The truxene 7 shows that, the HOMO is delocalized over the
triphenylamine groups, whereas the LUMO is delocalized on the tuxene core. In case of
TCNE and TCNQ substituted truxene 10 and 11 the HOMO is delocalized over the
triphenylamine group and LUMO is on TCNE and TCNQ acceptor unit respectively. Thus,
the electron density transfers from triphenylamine groups (HOMO) to TCNE (LUMO) and
TCNQ groups in truxene 10 and 11. The HOMOꢀLUMO gap is lowest in truxene 11 as
compared to other truxenes due to the incorporation of TCNQ as a strong acceptor.
Figure 9. The energy level diagram of the frontier molecular orbitals of the truxenes 6, 7, 10
and 11 calculated using B3LYP/6ꢀ31G(d,p) level of DFT theory.
1
2

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Conclusions
In summary, we have described the synthesis of star shaped donorꢀacceptor substituted
truxenes 6, 7, 10 and 11. Their photophysical, electrochemical properties, thermal stability
and HOMOꢀLUMO gap can be tuned by varying the strength of donor and acceptor groups.
The optical properties of the truxenes 6, 7, 10 and 11 were explained from the TDꢀDFT
calculations. The computational calculation show significant lowering of the HOMO‐
LUMO gap by the incorporation of TCNE and TCNQ groups in truxene 7. The truxene 10
and 11 are nonꢀemissive in nature which further supports strong donor–acceptor interaction.
The thermal stability can be improved by the incorporation of planar naphthalimide unit on
truxene core. The [2+2] cycloaddition retroelectrocyclization reaction pathway was studied
by computational calculations. These studies show that, the donor substituted truxenes are
favorable for the cycloaddition reaction whereas truxene substituted by acceptor groups are
not favourable for [2+2] cycloaddition-retroelectrocyclization reactions. The results obtained
here, provide a new avenue for the design and synthesis of organic molecules with low
HOMO‐ LUMO gap and enhanced thermal stability for various optoelectronic applications.
The study on photovoltaic properties of truxenes 6, 7, 10 and 11 are currently in progress in
our laboratory.
Experimental section
General experimental. All reagents were obtained from commercial sources, and used as
1
13
received unless otherwise stated. H NMR (400 MHz) and C NMR (100 MHz) spectra were
1
recorded on a Bruker Avance (III) 400 MHz instrument by using CDCl
3
as solvent. H NMR
chemical shifts are reported in parts per million (ppm) relative to the solvent residual peak
CDCl , 7.26 ppm). Multiplicities are given as s (singlet), d (doublet), t (triplet), q (quartet),
and m (multiplet), and the coupling constants, J, are given in Hz. C NMR chemical shifts
are reported relative to the solvent residual peak (CDCl , 77.36 ppm). Thermogravimetric
(
3
1
3
3
1
3

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analyses were performed on the Mettler Toledo Thermal Analysis system. UV−visible
absorption spectra were recorded on a Caryꢀ100 Bio UV−visible spectrophotometer. Cyclic
voltamograms (CVs) were recorded on a CHI620D electrochemical analyser using glassy
carbon as the working electrode, Pt wire as the counter electrode, and the saturated calomel
−
1
electrode (SCE) as the reference electrode. The scan rate was 100 mV s . A solution of
tetrabutylammonium hexafluorophosphate (TBAPF ) in CH Cl (0.1 M) was employed as the
supporting electrolyte. DCM was freshly distilled from CaH prior to use. All potentials were
6
2
2
2
experimentally referenced against the saturated calomel electrode couple but were then
+
manipulated to be referenced against FcH/FcH as recommended by IUPAC. Under our
+
conditions, the FcH/FcH couple exhibited E° = 0.38 V versus SCE. HRMS was recorded on
BrukerꢀDaltonics micrOTOFꢀQ II mass spectrometer.
Synthesis and Characterization
21
The reactants 4 and 5 were synthesized according to known methods.
Procedure for the preparation of truxenes 6 and 7.
A solution of triꢀiodotruxene 3 (250 mg, 0.20 mmol) and the corresponding alkyne (4.5
equivalent) in toluene–triethylamine 5 : 1 (60 mL) was deareated for 30 min with argon
2 3
bubbling and then Pd(dba) (40 mg, 0.07 mmol) and AsPh (170 mg, 0.55 mmol) were added.
The solution was deareated for a further 5 min. The mixture was heated at 80 ºC for 48 h. The
solvent was removed; the remaining residue was suspended in water (50 mL) and extracted
with DCM (3 x 20 mL). The combined organic layers were dried (MgSO
in vacuum. The resulting crude product was purified by column chromatography on silica gel
eluting with CH Cl /hexane (10%). The desired compounds obtained from the column was
4
) and concentrated
2
2
1
4

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recrystallized from DCM/methanol to give compound 6 and 7 in 70% and 75% yield
respectively.
Procedure for the preparation of truxenes 10 and 11.
A solution of alkyne derivative (40 mg) and TCNE/TCNQ (5 equivalent) in 1,2ꢀ
o
dichloroethane was refluxed for 24 h at 100 C. After completion of the reaction, the reaction
mixture was concentrated under reduced pressure. The crude compound was purified by
column chromatography on silica eluting with CH
2 2
Cl /hexane (10%) and crystallized
multiple times with DCM/methanol to afford truxene 10 and 11 in 71% and 65% yield.
ꢀ1
Truxene 6: yellow solid (yield: 70%), M. P. above 280 °C. IR data (KBr, cm )ꢀ 754, 815,
1
8
8
8
54, 1083, 1381, 1661, 1701, 2159. H NMR (400 MHz, CDCl
3
): δ (ppm) 8.86 (d, 3H, J =
.18 Hz,ꢀnaphthalimide core protons), 8.69 (d, 3H, J = 7.36 Hz,ꢀnaphthalimide core protons),
.61 (d, 3H, J = 7.77 Hz,ꢀnaphthalimide core protons), 8.46 (d, 3H, J = 8.45 Hz, ꢀ
naphthalimide core protons), 8.05 (d, 3H, J = 7.77 Hzꢀtruxene core protons), 7.90 (t, 3H,ꢀ
naphthalimide core protons), 7.76ꢀ7.82 (m, 6H, truxene core protons), 4.21 (t, 6H, Nꢀbutul
chain protons), 2.94ꢀ3.01 (m, 6H, truxene hexyl chain protons), 2.14ꢀ2.25 (m, 6H, truxene
hexyl chain protons), 1.70ꢀ1.80 (m, 6H, Nꢀbutyl chain protons), 1.41ꢀ1.51 (m, 6H, Nꢀbutul
chain protons), 0.80ꢀ1.05 (m, 45H, truxene hexyl chain and methyl protons of butyl chain),
1
3
0
1
1
2
1
3
.47ꢀ0.68 (m, 30H, truxene hexyl chain protons) C NMR (100 MHz, CDCl ): δ = 164.0,
63.8, 153.9, 146.6, 141.1, 138.0, 132.4, 131.6, 130.8, 130.5, 130.4, 128.2, 127.7, 127.4,
25.5, 124.7, 123.1, 122.1, 120.3, 99.9, 87.0, 56.07, 40.0, 37.0, 31.5, 30.2, 29.7, 29.4, 24.0,
+
2.2, 20.4, 13.9, 13.8. HRMS (ESI) m/z, calcd for M (C117
129 3 6
H N O ): 1671.9981; found:
671.9994.
ꢀ1
Truxene 7: brown solid (yield: 75%), M.P. 130 °C, IR data (KBr, cm )ꢀ 617, 648, 695,
1
2
160. H NMR (400 MHz, CDCl ): δ (ppm) 8.31 (d, 3H, J = 8.91 Hz, truxene core protons),
3
7.52ꢀ7.61 (m, 6H, truxene core protons), 7.44 (d, 6H, J = 7.80 Hz, triphenyl amine core
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protons), 7.24ꢀ7.32 (m, 12H, triphenyl amine core protons), 7.01ꢀ7.06 (m, 24H, triphenyl
amine core protons), 2.85ꢀ2.91 (m, 6H, hexyl chain protons), 2.00ꢀ2.15 (m, 6H, hexyl chain
protons), 0.77ꢀ0.91 (m, 36H, hexyl chain protons), 0.39ꢀ0.66 (m, 30H, hexyl chain protons).
13
C NMR (100 MHz, CDCl ): δ = 153.6, 147.9, 147.2, 145.7, 140.0, 138.0, 132.5, 129.4,
3
1
2
29.7, 125.0, 124.4, 123.5, 122.3, 121.2, 116.2, 99.0, 89.4, 55.7, 36.9, 31.5, 29.6, 29.4, 23.9,
+
2.2, 13.8. HRMS (ESI) m/z, calcd for M (C123
H
129
N
3
): 1649.0214; found: 1649.0620.
ꢀ1
Truxene 10: Reddish brown solid (yield: 71%), M. P. above 280 °C. IR data (KBr, cm )ꢀ
1
8
03, 748, 1185, 1337, 1466, 1443, 2158, 2221. H NMR (400 MHz, CDCl
3
): δ (ppm) 8.44 (d,
3H, J = 8.01 Hz, TPA core protons), 8.17 (s, 3H, truxene core protons), 7.77 (d, 6H, J = 9.01
Hz, truxene core protons),7.37ꢀ7.50 (m, 13H, Triphenyl amine core protons), 7.20ꢀ7.32 (m,
0H, Triphenyl amine core protons), 6.99 (d, 6H, J = 10.01 Hz, Triphenyl amine core
protons), 2.79ꢀ2.91 (m, 6H, hexyl chain protons), 2.11ꢀ2.24 (m, 6H, hexyl chain protons),
2
1
3
0
.74ꢀ0.98 (m, 36H, hexyl chain protons), 0.35ꢀ0.60 (m, 30H, hexyl chain protons). C NMR
(
100 MHz, CDCl ): δ = 168.6, 163.8, 154.6, 153.9, 150.0, 145.3, 144.4, 137.5, 132.0, 130.5,
3
1
5
2
30.1, 128.3, 126.9, 126.8, 125.5, 124.0, 121.7, 118.0, 113.6, 112.6, 112.4, 111.4, 86.3, 78.0,
+
6.8, 36.7, 31.4, 29.1, 24.0, 22.1, 13.8. HRMS (ESI) m/z, calcd for M (C141
129
H N15):
032.0555; found: 2032.1007.
ꢀ1
Truxene 11: Black solid (yield: 65%), M. P. above 280 °C. IR data (KBr, cm )ꢀ 695, 755,
1
8
15, 1177, 1575, 2209. H NMR (400 MHz, CDCl ): δ (ppm) 8.37 (d, 3H, J = 9.23 Hz, TPA
3
core protons), 7.90 (s, 3H, truxene core protons), 7.65 (d, 3H, J = 9.80 Hz, truxene core
protons), 7.58 (d, 3H, J = 9.80 Hz, triphenyl amine core protons), 7.29ꢀ7.38 (m, 15H,
triphenyl amine core protons), 7.19ꢀ7.25 (m, 12H, triphenyl amine core protons), 7.13ꢀ7.19
(m, 15H, triphenyl amine core protons), 7.04 (d, 3H, J = 10.38 Hz, triphenyl amine core
protons), 6.97 (d, 6H, J = 9.23 Hz, triphenyl amine core protons), 2.74ꢀ2.86 (m, 6H, hexyl
chain protons), 1.99ꢀ2.10 (m, 6H, hexyl chain protons), 0.72ꢀ0.91 (m, 36H, hexyl chain
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protons), 0.32ꢀ0.56 (m, 30H, hexyl chain protons).
13
3
C NMR (100 MHz, CDCl ): δ = 171.4, 154.5, 153.7, 151.6, 150.5, 149.5, 145.2, 140.6,
1
1
37.5, 135.2, 134.0, 133.4, 133.0, 132.7, 129.9, 128.5, 127.1, 126.5, 126.0, 125.4, 123.7,
19.1, 114.0, 113.8, 113.3, 112.3, 86.6, 74.8, 56.5, 53.4, 36.5, 31.2, 28.9, 23.9, 22.0, 13.8.
+
HRMS (ESI) m/z, calcd for M (C H N ): 2261.1521; found: 2261.2406.
1
59 141 15
Supporting Information
1
13
The H NMR, C NMR spectra, mass spectroscopy data, cyclic voltammograms, UVꢀvis
graphs, and DFT calculations of truxenes 6, 7, 10 and 11 are provided.
Corresponding Author
*Eꢀmail: rajneeshmisra@iiti.ac.in.
Tel.: +91 7312438754; fax: +91 7312361482.
Acknowledgements
We acknowledge support by INSA (Project No. SP/YSP/139/2017/2293), Department of
Science and Technology (Project No. EMR/2014/001257), and Council of Scientific and
Industrial Research (Project No. 01/(2795)/14/EMRꢀII), New Delhi for the financial support.
We also thank the Sophisticated Instrumentation Centre (SIC), Indian Institute of Technology
(IIT) Indore.
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