T-shaped D?π?A?(π?A)2 chromophores with two auxiliary electron acceptors

Article abstract of DOI:10.1016/j.dyepig.2018.10.077

A series of tripodal push-pull chromophores based on central indan-1,3-dione scaffold has been designed and synthesized by Knoevenagel condensation and Pd-catalyzed Suzuki-Miyaura cross-coupling reaction. Target molecules possess D?π?A?(π?A)₂ e

Full text of DOI:10.1016/j.dyepig.2018.10.077

Accepted Manuscript
T-shaped D−π−A−(π−A) chromophores with two auxiliary electron acceptors
2
Parmeshwar Solanke, Oldřich Pytela, Filip Bureš, Milan Klikar
PII:
S0143-7208(18)31988-0
https://doi.org/10.1016/j.dyepig.2018.10.077
DYPI 7143
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 7 September 2018
Revised Date: 31 October 2018
Accepted Date: 31 October 2018
Please cite this article as: Solanke P, Pytela Oldř, Bureš F, Klikar M, T-shaped D−π−A−(π−A)
2
chromophores with two auxiliary electron acceptors, Dyes and Pigments (2018), doi: https://
doi.org/10.1016/j.dyepig.2018.10.077.
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1
ACCEPTED MANUSCRIPT
T-shaped D−π−A−(π−A) Chromophores with
2
Two Auxiliary Electron Acceptors
a
a
a
a
Parmeshwar Solanke, Oldřich Pytela, Filip Bureš, and Milan Klikar*
a
Institute of Organic Chemistry and Technology, Faculty of Chemical Technology,
University of Pardubice, Studentská 573, Pardubice, 532 10, Czech Republic. Email:
Milan Klikar - milan.klikar@upce.cz (Web: http://bures.upce.cz/klikar.html)
TOC
Abstract
A series of tripodal push-pull chromophores based on central indan-1,3-dione scaffold
has been designed and synthesized by Knoevenagel condensation and Pd-catalyzed
Suzuki-Miyaura cross-coupling reaction. Target molecules possess D−π−A−(π−A)2
extraordinary T-shaped structural arrangement. The electron donor attached at C2
position as well as the peripheral acceptor branches at C4 and C7 positions of the
parent indan-1,3-dione have been systematically modified to achieve property tuning.
Fundamental thermal and optoelectronic properties have been investigated by
differential scanning calorimetry, electrochemistry, UV/Vis absorption spectroscopy,

2
ACCEPTED MANUSCRIPT
and DFT calculations. Based on the experimental and theoretical data, we herewith
discuss thorough structure–property relationships.
Keywords: indan-1,3-dione; T-shaped; donor/acceptor; intramolecular charge-
transfer; push-pull chromophore.
Introduction
During the last 30−40 years, a great progress in developing new push-pull
systems has been performed. Push-pull chromophores have become very popular and
important substances used across many areas of materials chemistry. Nowadays, they
represent well-developed and burgeoning area especially targeting organic electronics
[
1-2]
and optoelectronics.
Wide applications of push-pull molecules can be attributed to
[
3]
their unique features such as their well-defined and tunable structural arrangement.
The optoelectronic properties such as color, high (hyper)polarizabilities, intensive
absorption, emission, and electrochemical behavior are predominantly controlled by
the extent of the intramolecular charge-transfer (ICT), which is dictated by a mutual
[
4-7]
communication between the particular donor (D) and acceptor (A) via a π-linker.
Hence, push-pull chromophores have been utilized as active materials in nonliear
[8-10]
[11-13]
[14-
optics,
bulk heterojunction (BHJs)
or dye sensitized solar cells (DSSCs),
1
6]
[17]
organic light-emitting diodes (OLEDs),
organic field-effect transistors
[
18-20]
[21-22]
[23-25]
(OFETs),
two-photon absorbers (2PAs),
3D optical data storage,
etc.
With respect to its commercial availability, low cost, extended π-system, and
strong electron accepting character, indan-1,3-dione and its derivatives are widely
[
26]
used as terminal withdrawing moieties in push-pull chromophores.
Incorporation of
indan-1,3-dione fragment into the chromophore backbone can be accomplished very

3
ACCEPTED MANUSCRIPT
[
27-34]
conveniently via Knoevenagel condensation under mild reaction conditions.
These features predestinate push-pull systems with indan-1,3-dione acceptors to be
[
35-46]
[47]
[48-49]
applied in nonlinear optics,
DSSCs,
BHJSCs,
organic photovoltaic cells
[
50-51]
[52]
[53-54]
(OPVCs),
OLEDs,
as vesicle-, gel-, and glass-forming molecules
or
[
55-57]
chromoionophores for anion sensing and recognition.
Indan-1,3-dione-terminated
push-pull molecules may adopt linear (D-π-A) or various extraordinary arrangements
[
58]
resembling letters of the alphabet.
Recently we focused our research efforts
towards new class of T-shaped molecules that utilizes indan-1,3-dione as a central
[
59-60]
acceptor and π-conjugated backbone.
Thus, the indan-1,3-dione was modified
not only at C2 position but also at positions C4 and C7 of the fused benzene ring to
[61]
afford tripodal D–π–A–(π–D) molecules applicable in BHJSCs.
More recently, we
2
have investigated a series of linear, quadrupolar, and T-shaped chromophores with
[
62]
varied number of peripheral electron donors.
In order to further elucidate the structure-property relationships in indan-1,3-
dione based push-pull molecules and in contrast to previously published T-shaped
[
62]
molecules having (D–π–A–(π–D)2,
we report herein nonsymmetrical T-shaped
chromophores 1−2 with novel D–π–A–(π–A) structural arrangement (Figure 1).
2
Whereas the branch at C2 remained donor-substituted, two peripheral branches at C4
and C7 bear auxiliary acceptors. Both series differ in the peripheral acceptors A (CN
vs NO ; 1 vs. 2), the donor D (DMA vs. PIT; a/b vs. c/d), and the number of double
2
bonds within the C2 donor branch (n = 0 or 1; a/c vs. b/d). Previously reported linear
D−π−A chromophores 3a−d without peripheral C4/C7 substituents have also been
[26]
included in the study to facilitate elucidation of the structure-property relationships.

4
ACCEPTED MANUSCRIPT
Figure 1: Structural arrangements of tripodal T-shaped and linear indan-1,3-dione
chromophores 1−3. DMA = 4-(N,N-dimethylamino)phenyl; PIT = 5-(piperidin-1-
yl)thiophen-2-yl.
Results and Discussion
Synthesis
T-shaped chromophores 1 and 2 were prepared by Pd-catalyzed Suzuki-
Miyaura cross-coupling reactions (Scheme 1) between boronic acids 5 and 6 and
particular 4,7-diiodoindan-1,3-dione derivatives 4a−d under standard reaction
conditions in satisfactory yields (52−76 %). Linear chromophores 3a-b were
synthesized via Al O -catalyzed Knoevenagel condensation starting from commercial
2
3
available indan-1,3-dione 7 and benzaldehyde 8 or cinnamaldehyde 9 with the yields
about 80 %. The preparations and full characterization of remaining linear molecules
3
c−d as well as indan-1,3-dione intermediates 4a−d were described in our recent
[
26,59-60]
reports.

5
ACCEPTED MANUSCRIPT
HO
HO
NC
CN
CN
B
5
O
O
D
1a: D = DMA, n = 0, 65 %
1b: D = DMA, n = 1, 58 %
1c: D = PIT, n = 0, 63 %
1d: D = PIT, n = 1, 55 %
(
a)
I
I
n
O
O
HO
HO
O N
2
NO2
n
B
NO2
D
6
4
4
4
4
a: D = DMA, n = 0
b: D = DMA, n = 1
c: D = PIT, n = 0
d: D = PIT, n = 1
O
O
2
2
2
2
a: D = DMA, n = 0, 75 %
b: D = DMA, n = 1, 76 %
c: D = PIT, n = 0, 52 %
d: D = PIT, n = 1, 70 %
(a)
n
D
O
N
8
(b)
O
O
3
3
a: n = 0, 78 %
b: n = 1, 80 %
O
O
O
N
n
7
9
N
(b)
Scheme 1: Synthetic pathway towards linear and T-shaped indan-1,3-dione based
chromophores 1−3. (a) THF/H O 4:1, PdCl (PPh ) , Na CO ; (b) CH Cl , Al O
3
2
2
3 2
2
3
2
2
2
(activity II−III).
Thermal properties
Thermal characteristics of target chromophores 1-3 were measured by
differential scanning calorimetry. The DSC curves were determined with a scanning
rate of 3 °C/min within the range 25–400 °C. The measured melting points (T ) as
m
well as the decomposition temperatures (T ) are summarized in Table 1.
d
Representative DSC curves are shown in Figure 2, for all DSC curves see the SI.

6
ACCEPTED MANUSCRIPT
T-shaped molecules 1 with peripheral cyano acceptors showed melting (Figure
2
) immediately followed by exothermal and very vigorous decomposition (1b, 1c) or
the melting process is directly accompanied by degradation (1a, 1d). Thermal
behavior of the nitro derivatives 2a−d is dominated by direct decomposition without
previous melting. Linear D−π−A analogues 3b−3d with extended π-system underwent
sharp melting process accompanied by gradual degradation. On the contrary, linear
molecules 3a/3c proved to be stable in the liquid phase for additional 70 °C after their
melting.
Figure 2: Representative DSC curves for chromophores 1a−d with peripheral cyano
acceptors within the range of 200−400 °C (melting and decomposition peaks are
visualized).
In general, all studied compounds are highly thermally robust, especially
T-shaped ones with the temperature of decomposition ranging from 240 to 330 °C.
Linear chromophores 3a−b bearing DMA donor provided higher T and T values,
m
d
compared to PIT analogues 3c−d. From the DSC data is also obvious that embedding

7
ACCEPTED MANUSCRIPT
the double bond (n = 0 or 1) led to increased T and T values for all molecules under
m
d
the study. In contrast to linear series 3, the highest T values in T-shaped series 1−2
d
have been detected for molecules 1c/2c (T = 327/330 °C) with appended PIT donor.
d
Cyano (1) as well as nitro derivatives (2) afforded comparable temperatures of
decomposition. Thus, the type of the peripheral acceptor group influences thermal
stability of T-shaped indan-1,3-diones only negligibly.
Table 1: Thermal, electrochemical, and absorption properties of chromophores 1−3.
A
Tm
Td
Ep(ox1) Ep(red1)
∆E
EHOMO ELUMO
λmax
εmax
Comp.
a
b
c
c
c
d
d
e
3
-1
-1 e
[
°C] [°C]
[V]
[V]
[eV]
[eV]
[eV]
[nm/eV] [10 M cm ]
1
a
-
295
1.04
0.86
0.83
0.61
1.07
0.88
0.84
0.61
1.05
0.84
0.80
0.57
–1.11
–0.90
–1.16
–0.90
–1.02
–0.88
–1.11
–0.89
–1.20
–0.95
–1.23
–0.94
2.15
1.76
1.99
1.51
2.09
1.76
1.95
1.50
2.25
1.79
2.03
1.51
–5.43
–5.25
–5.22
–5.00
–5.46
–5.27
–5.23
–5.00
–5.44
–5.23
–5.19
-4.96
–3.28
–3.49
–3.23
–3.49
–3.37
–3.51
–3.28
–3.50
–3.19
–3.44
–3.16
–3.45
501/2.48
566/2.19
532/2.33
630/1.97
504/2.46
569/2.18
534/2.32
634/1.96
483/2.57
535/2.32
516/2.40
605/2.05
46.9
43.4
80.0
68.3
62.9
41.3
81.6
83.5
45.3
42.9
90.6
71.4
1b
292
324
-
295
327
284
299
243
330
272
274
257
246
213
1
c
1d
2a
-
2b
-
2
c
-
2d
-
3a
203
253
182
208
3b
3
c
3d
a
T = melting point (the point of intersection of a baseline and a tangent of thermal
m
b
effect = onset). T = thermal decomposition (pyrolysis in N atmosphere).
d
2
c
Ep(ox1) and Ep(red1) are peak potentials of the first oxidation and reduction (irreversible
processes), respectively, as measured by CV; all potentials are given vs. SSCE,
d
[63]
∆
(
E = Ep(ox1) – Ep(red1). –E
= Ep(ox1/red1) + 4.35 (in DMF vs. SCE)
+ 0.036
HOMO/LUMO
[
64]
e
difference between SCE (0.241 vs. SHE) and SSCE (0.205 vs. SHE)) . Measured
in CH Cl .
2
2

8
ACCEPTED MANUSCRIPT
Electrochemistry
The electrochemical behavior of target chromophores 1−3 were investigated by
cyclic voltammetry in DMF containing 0.1 M Bu NBF in a three electrode cell by
4
4
cyclic voltammetry (CV). The working electrode was glassy carbon disk (1 mm in
diameter). As the reference and auxiliary electrodes were used leakless Ag/AgCl
electrode (SSCE) containing filling electrolyte (3.4 M KCl) and titanium rod with a
thick coating of platinum, respectively. All peak potentials are given vs. SSCE. The
acquired data are summarized in Table 1; representative CV diagrams of compounds
1
d, 2d, and 3d are given in the SI.
The observed first oxidations and reductions were determined as irreversible
processes (quasi-reversible for some molecules) generally followed by subsequent
oxidations and reductions. Therefore, the potentials of the first oxidation and reduction
were obtained only as peak potentials Ep(ox1/red1) which were found within the range of
0
.57 to 1.07 and −1.23 to −0.88 V, respectively. The first oxidation and reduction are
typical one-electron processes; their potentials are obviously a function of the
chromophore structure. Whereas the first oxidation takes place predominantly at the
amino donor group, the first reduction most likely involves the central indan-1,3-dione
as well as the C4 and C7 peripheral acceptors. The peak potentials of the first
oxidation and reduction were further recalculated to the energies of the HOMO and the
LUMO (Table 1) and these values were visualized in the energy level diagram (Figure
3
). Despite the fact that the electrochemically derived peak potentials do not
correspond in absolute values with the HOMO/LUMO levels (half-wave potentials not
available), these values can be used for describing the trends within the given series of
molecules.

9
ACCEPTED MANUSCRIPT
Figure 3: Energy level diagram of electrochemical (black) and DFT calculated (red)
HOMO/LUMO energies of chromophores 1−3.
A comparison of the electrochemical data allows to deduce the following
general trends and relationships:
•
The HOMO levels reflect solely the used donor D (DMA vs. PIT) as well as
the length of the C2-appended π-linker (n = 0 or 1) and is almost not
influenced by the presence of peripheral acceptors A. For analogous
chromophores (e.g. 1b/2b/3b) are the HOMO energies very close
(
−5.25/−5.27/−5.23 eV). The EHOMO values gradually increase within the order:
a (DMA) → b (DMA + =) → c (PIT) → d (PIT + =); see Table 1 and Figure 3
= stands for an additional double bond).
(
•
The LUMO level is affected by the peripheral acceptors A and less by the
donor and the length of the π-linker. As expected, the LUMO values decrease

1
0
ACCEPTED MANUSCRIPT
within the order: 3 → 1 → 2 (e.g. −3.16/−3.23/−3.28 eV for 3c/1c/2c). This
reflects none auxiliary acceptors (3) and higher electron withdrawing ability of
[
3]
the nitro (2) over the CN (3) group. π-Linker enlargement generally
deepened the measured ELUMO values (compare a vs. b or c vs. d series of
molecules). In overall, the LUMO levels alternate within the order: ↑a ↓b ↑c
↓d; see Table 1 and Figure 3.
•
The HOMO-LUMO gap (∆E) is predominantly influenced by the length of
π-backbone as well as the type of the used donor. The spatial arrangement of
chromophore (linear vs. T-shaped) affects the electrochemical gap rather less
substantially. Considering the particular chromophore parts, the HOMO-
LUMO gap decreases within the order: 3 (none auxiliary acceptor) → 1 (−CN)
→
2 (−NO ), e.g. 2.25/2.15/2.09 eV for 3a/1a/2a; a (DMA) → c (PIT) → b
2
(DMA + =) → d (PIT + =), e.g. 2.15/1.99/1.76/1.51 eV for 1a/1c/1b/1d; see
Table 1, Figure 3.
In summary, the HOMO/LUMO levels are affected by the type and the length
of donor branch attached at C2-position. Utilization of polarizable PIT donor and
extension of C2-backbone via additional ethylene spacer lead to significant reduction
of ∆E. On the contrary, introducing auxiliary peripheral acceptors at C4 and C7
improves the overall withdrawing ability only negligibly. As expected, the nitro group
proved to be slightly more powerful acceptor than cyano. Hence, the lowest
electrochemical HOMO-LUMO gap was determined for T-shaped indan-1,3-dione
chromophore 2d (∆E = 1.50 eV) possessing PIT donor attached at the extended π-
linker and two peripheral 4-nitrophenyl withdrawing units.

1
1
ACCEPTED MANUSCRIPT
Electronic absorption spectra
Chromophores 1−3 represent highly colored substances with the color ranging
from dark red to blue; their linear optical properties were investigated by UV-Vis
absorption spectroscopy. Fluorescence behavior was not observed and, therefore,
emission spectra were not measured. The measured longest-wavelength absorption
maxima λmax and molar extinction coefficients εmax are summarized in Table 1. The
λmax values range from 483 to 634 nm with the εmax found within the range of
3
-1
-1
4
1.3−90.6 × 10 M ·cm . Representative absorption spectra of chromophores 1a−d
with peripheral cyano acceptors as well as a series of compounds 1a, 2a, and 3a with
C2-attached DMA donor branch are shown in Figure 4. For complete listing see the
SI. The absorption spectra of chromophores 1−3 exhibited one apparent CT-band, its
position correlates tightly with the electrochemical gaps as shown in the SI (Figure
S35).
From the measured data we can deduce the following trends:
•
Positions of the CT-bands are influenced by the type of the peripheral
withdrawing unit only negligibly. The difference (∆λmax) between cyano
(1a−d) and nitro (2a−d) analogues is only 2−4 nm; see Table 1 or Figure 4b.
•
•
The absence of auxiliary peripheral acceptors blue-shifts the CT-bands by
about 15−35 nm; compare series 3 vs. 1−2 in Figure 4b.
The presence of polarizable PIT donor in series c−d clearly red-shifts the
CT-bands compared to DMA donor in series a−b. This red-shift is
considerably pronounced for molecules with embedded double bond; b vs. d in
Figure 4a.
•
Chromophores in series c−d bearing PIT donor showed considerably higher
molar extinction coefficients (Figure 4a).

1
2
ACCEPTED MANUSCRIPT
•
Embedding an additional double bond into the π-linker causes distinct
bathochromic shift of about 50−65/90−100 nm for chromophores with attached
DMA/PIT donors; compare compounds 1b/1d vs. 1a/1c in Figure 4a.
The optical properties of chromophores 1−3 are predominantly dictated by (in
descending order): the type of C2 donor used, the extent of π-linker, and the
structural/spatial arrangement (linear vs. T-shaped; presence of the auxiliary
acceptors). Hence, the most bathochromically shifted CT-band (634 nm) has been
observed for T-shaped push-pull chromophore 2d that possesses two auxiliary
peripheral nitro acceptors, extended π-linker, and polarizable PIT donor. This
correspond to electrochemical outcomes.
Figure 4: a) Representative UV/Vis absorption spectra of chromophores 1a–d bearing
peripheral cyano acceptors; b) representative absorption spectra of chromophores 1a,
2
a, and 3a with attached DMA donor at C2-position (measured in CH Cl at c ≈ 2 ×
2 2
–
5
1
0 M).

1
3
ACCEPTED MANUSCRIPT
Theoretical DFT calculations
Spatial and electronic properties of linear and T-shaped chromophores 1−3
(R)
[65]
were investigated using Gaussian 16 software package at the DFT level. Initial
geometries of molecules 1−3 were optimized by DFT B3LYP/6-311+G(2d,p) method.
Energies of the HOMO and the LUMO, their differences ∆E and ground state dipole
moments
acetonitrile (AN), and DMF. The first hyperpolarizabilities
B3LYP/6-311+G(2d,p) level in CH Cl at 1907 nm. All calculated data are
µ
were calculated at DFT B3LYP/6-311+G(2d,p) level in vacuum,
β
were computed at DFT
2
2
summarized in Table 2.
The calculated HOMO/LUMO energies in both solvents proved to be identical
due to very similar parameters of both solvents in the PCM solvation model (εAN
5.7; εDMF = 37.2). The HOMO/LUMO energies in vacuum are listed in Table S1. The
=
3
relationships between the HOMO/LUMO energies calculated for vacuum and polar
solvent are depicted in Figures S36−S37. The plotted points are in these graphs
divided by a line featuring unit slope and zero intercept, which clearly distinguishes
(de)stabilization induced by the solvent. Figure S36 shows that, in contrast to linear
molecules 3, the HOMOs of T-shaped chromophores 1−2 are stabilized by polar
solvent (an apparent collinearity with the line). The LUMOs are stabilized only for
cyano derivatives 1, which ELUMO is collinear and localized above the line (Figure
S37). Linear chromophores 3 and T-shaped nitro derivatives 2 showed ELUMO
localized below the line, either collinear or as a cluster of points.
The calculated HOMO and LUMO energies range from −5.77 to −5.34
and −3.22 to −2.56 eV and showed dependence on the structural arrangement of the
particular chromophore. The HOMO energies correlate very tightly with the

1
4
ACCEPTED MANUSCRIPT
experimental data obtained by the electrochemical measurements as shown in Figure
S38. On the contrary, the withdrawing ability of peripheral nitro acceptors in T-shaped
molecules 2 is computationally overestimated. Hence, the calculated LUMO levels for
nitro derivatives 2a−d are the lowest, almost identical (−3.16 to −3.22 eV), and not
reflecting the alternating trend as seen by electrochemistry for the remaining
chromophores 1a−d and 3a−d (Figure 3). This phenomenon is clearly depicted in
Figure S39 showing the LUMO energies of T-shaped nitro derivatives 2 distinctly
separated from the others. This overestimation also influences the calculated gaps of
T-shaped nitro derivatives 2, which are obviously narrowed compared to linear 3 as
well as T-shaped 1 (Figure 3). The calculated HOMO/LUMO energies and their
differences are affected by the same structural modifications and keep the same trends
as seen by electrochemical measurements. The length of the π-linker attached at C2
position proved the most crucial factor, whereas type of the donor (DMA vs. PIT) and
the auxiliary acceptor affected the calculated properties less obviously. A similar set of
calculated EHOMO/LUMO and ∆E values for T-shaped 1 and linear 3 (Table 2) also points
to a poor involvement of auxiliary acceptors in the ICT.
The frontier molecular orbital’s localizations in representative chromophores
1
b, 2b, and 3b are shown in Figure 5; for complete listing see the SI. As a general
feature, the HOMO-1 is localized on the DMA and PIT donor, respectively, whereas
the LUMO+1 is spread over the central withdrawing indan-1,3-dione moiety. The
HOMO is localized on the C2 donor-substituted branch jointly with the LUMO and a
partial separation. In T-shaped molecules 1–2, the LUMO may further occupy the
indan-1,3-dione fused ring as well as the peripheral phenylene rings.

1
5
ACCEPTED MANUSCRIPT
Figure 5: The HOMO (red) an LUMO (blue) localizations in representative
chromophores 1b, 2b, and 3b.
Whereas linear chromophores 3a−b with DMA donor possess Cs group of
symmetry, the remaining target molecules are non-symmetrical. There is an apparent
trend in ground state dipole moments
moments obey the trend seen for the HOMO energies (Figure S40). The
lowest/highest values were calculated for chromophores in series a/d possessing
elementary DMA/extended PIT donor, whereas the b/c pairs provided comparable
µ for molecules 1−3 (Table 2). The dipole
µ

1
6
ACCEPTED MANUSCRIPT
µ
values. Linear chromophores 3 afforded generally lower dipole moments compared
to T-shaped analogous 1−2 (e.g. 16.9 → 18.7 → 19.2 D for 3d/1d/2d).
Table 2: DFT calculated properties of chromophores 1−3.
-30
EHOMO ELUMO ∆E
µ
β × 10
Comp.
a
a
a
a
b
[eV]
[eV]
[eV] [D]
[esu]
155
401
95
1
a
−5.76 −2.83 2.93 10.3
−5.54 −3.00 2.54 13.9
−5.56 −2.68 2.88 13.8
−5.37 −2.89 2.48 18.7
−5.77 −3.19 2.58 10.6
−5.56 −3.22 2.34 14.3
−5.58 −3.16 2.42 14.1
−5.39 −3.17 2.22 19.2
−5.73 −2.72 3.01 8.5
−5.52 −2.92 2.60 11.9
−5.54 −2.56 2.98 12.1
−5.34 −2.81 2.53 16.9
1b
1
c
1d
234
195
486
154
355
108
312
57
2
a
2b
2
c
2d
3
a
3b
3
c
3d
158
a
b
Calculated at the DFT B3LYP/6-311+G(2d,p) level in DMF/AN. Calculated at the
DFT B3LYP/6-311+G(2d,p) level in CH Cl at 1907 nm (−2ω;ω,ω).
2
2
-30
The calculated first hyperpolarizabilities β range from 57 to 486 × 10 esu for
linear as well as T-shaped compounds 1 3, respectively (Table 2). In general, clear
values with the π-linker elongation/planarization was observed
−
trend in increasing
β
-30
(
e.g. 155/401 × 10 esu for 1a/1b). The type of C2 donor plays also a crucial role.
The larger first hyperpolarizabilities were computed for chromophores bearing DMA
-30
donor compared to the corresponding PIT derivative (e.g. 155/95 × 10 esu for

1
7
ACCEPTED MANUSCRIPT
1
a/1c). Concerning the spatial arrangement, the
β values increase within the order:
linear 3 → T-shaped 1 (cyano) → T-shaped 2 (nitro). Based on the aforementioned
-30
trends, the largest first hyperpolarizability
β = 486 × 10 esu was calculated for
T-shaped chromophore 2b possessing extended DMA donor branch and peripheral
auxiliary nitro acceptors.
Conclusion
As a continuation and further extension of our previous studies on linear D-π-
A, quadrupolar (D-π) -A, and tripodal (D-π) -A push-pull chromophores built on
2
3
[
59-62]
central electron-withdrawing indan-1,3-dione moiety,
we have reported herein
the new strategy to design molecules with D-π-A-(π-A) structural arrangement. In
2
overall, eight new push-pull chromophores 1a−d and 2a−d with tripodal T-shaped
arrangement have been prepared together with four linear analogues 3a−d. N,N-
Dimethylanilino and 2-(piperidin-1-yl)thiophen with systematically enlarged π-linker
via embedded double bond have been utilized as electron donors attached to the
central indan-1,3-dione at C2 position via Knoevenagel condensation. Peripheral 4-
cyanophenyl and 4-nitrophenyl acceptors were introduced at C4/C7 via subsequent
Pd-catalyzed twofold Suzuki-Miyaura cross-coupling reaction.
Thermal properties studied by DSC revealed thermal robustness of all
T-shaped molecules with T between 213 and 330 °C. The extent of the ICT has been
d
evaluated by electrochemical measurements and UV/Vis absorption spectra and
completed by DFT calculations. From the gathered data we can conclude that the
fundamental property tuning in chromophores 1–3 can be achieved by alternating the
type of electron donor appended at C2 (DMA vs. PIT) and the π-backbone length. The

1
8
ACCEPTED MANUSCRIPT
presence of auxiliary acceptors at C4/C7 positions has diminished effect and can rather
be used for final fine-tuning.
As mentioned earlier, indan-1,3-dione push-pull molecules found tremendous
applications across nonlinear optics, organic-based solar and photovoltaic cells or as
sensors for ion recognition. In view of the current interest in organic push-pull
molecules with various arrangement and tunable properties, the present study is
intended to serve as an useful guide for the advanced design of functional indan-1,3-
dione derivatives.
Experimental section
General
All target T-shaped chromophores 1a–d and 2a–d are new compounds. Linear
[26]
compounds 3c–d with PIT donor were firstly prepared in our recent study. The
[66]
13
linear chromophore 3a is well known. Full structural characterization such as C-
[67]
NMR or HR-MS analyses are not available for remaining linear molecule 3b.
Details concerning material, apparatus, and methods are provided in the SI. Synthesis
and full spectral characterization of previously known target chromophores 3a−b is
given in the SI.
General Method for Suzuki-Miyaura Cross-couplig Reaction (i)
4
,7-Diiodoindan-1,3-dione 4a, 4b, 4c or 4d (265, 278, 288, 300 mg; 0.5 mmol) and
-cyanophenylboronic acid 5 (162 mg, 1.1 mmol) or 4-nitrophenylboronic acid (187
4
mg, 1.1 mmol) were dissolved in the mixture of THF/H O (20 mL, 4:1). Argon was
2
bubbled through the solution for 15 min whereupon [PdCl (PPh ) ] (18 mg, 0.025
2
3 2
mmol) and Na CO (159 mg, 1.5 mmol) were added and the reaction mixture was
2
3
stirred at 60 °C for 3 h. The reaction was diluted with H O (50 mL) and extracted with
2

1
9
ACCEPTED MANUSCRIPT
CH Cl (2 × 50 mL). The combined organic extracts were dried (Na SO ), the solvents
2
2
2
4
were evaporated in vacuo, and the crude product was purified by column
chromatography.
General Method for Al O -Catalyzed Knoevenagel Condensation (ii)
2
3
Indan-1,3-dione 7 (1.46 g, 10.0 mmol) and 4-(N,N-dimethylamino)benzaldehyde 8
1.57 g, 10.5 mmol) or 4-(N,N-dimethylamino)cinnamaldehyde 9 (1.84 g, 10.5 mmol)
were dissolved in CH Cl (20 mL), Al O (5.1 g, 50.0 mmol, activity II-III) was added
(
2
2
2
3
and the reaction mixture was stirred at 25 °C for 3 h. Al O was filtered off, the
2
3
solvent was evaporated in vacuo, and the crude product was purified by column
chromatography.
Chromophore 1a. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
a and boronic acid 5 following the general procedure (i). The title compound was
1
afforded as a red solid (156 mg, 65 %). R = 0.25 (SiO ; CH Cl /hexane, 3:1). H-
f
2
2
2
NMR (400 MHz, CDCl , 25 °C):
δ = 3.13 (s, 6H, CH ), 6.68 (d, J = 8.8 Hz, 2H, CH ),
3 ar
3
7
.55−7.60 (m, 2H, CH ), 7.64−7.68 (m, 5H, CH+CH ), 7.76−7.79 (m, 4H, CH ), 8.40
ar ar ar
1
3
ppm (d, J = 8.4 Hz, 2H, CHar). C-NMR (125 MHz, CDCl , 25 °C):
δ
= 40.37,
3
1
1
1
4
1
11.73, 112.14, 112.20, 119.11, 119.18, 121.92, 122.11, 130.46, 130.49, 131.86,
31.92, 135.54, 136.13, 136.70, 138.30, 138.38, 138.79, 142.45, 142.92, 148.74,
+
54.56, 188.58, 190.40 ppm. HR-MALDI-MS (DHB): calcd for C H N O (M+H)
3
2
22
3
2
80.17065; found 480.17067. IR (HATR):
ν = 2913, 2224, 1664, 1557, 1515, 1377,
–
1
324, 1177, 1114, 814, 525 cm .
Chromophore 1b. The title compound was prepared from 4,7-diiodoindan-1,3-dione
b and boronic acid 5 following the general procedure (i). The title compound was
afforded as a brown-black solid (158 mg, 58 %). R = 0.20 (SiO ; CH Cl /hexane, 3:1).
4
f
2
2
2

2
0
ACCEPTED MANUSCRIPT
1
H-NMR (400 MHz, CDCl , 25 °C):
δ = 3.08 (s, 6H, CH ), 6.67 (d, J = 8.8 Hz, 2H,
3
3
CH ), 7.28 (d, J = 15.2 Hz, 1H, CH), 7.53−7.61 (m, 5H, CH+CH ), 7.63−7.66 (m,
ar
ar
4
H, CH ), 7.75−7.80 (m, 4H, CH ), 8.14 ppm (dd, J = 15.2 Hz, J = 12.4 Hz, 1H,
ar ar 1 2
1
3
CH). C-NMR (125 MHz, CDCl , 25 °C):
δ
= 40.40, 112.10, 112.27, 112.31, 119.10,
3
1
19.40, 123.06, 123.74, 130.40, 130.46, 131.89, 131.94, 132.17, 135.80, 136.01,
1
37.40, 138.29, 138.49, 138.64, 142.27, 142.61, 148.07, 153.06, 155.83, 189.41,
+
1
89.95 ppm. HR-MALDI-MS (DHB): calcd for C H N O (M+H) 506.18630;
3
4
24
3
2
found 506.18573. IR (HATR):
ν = 2921, 2225, 1669, 1556, 1380, 1325, 1174, 813,
–
1
5
47 cm .
Chromophore 1c. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
c and boronic acid 5 following the general procedure (i). The title compound was
1
afforded as a red-brown solid (165 mg, 63 %). R = 0.20 (SiO ; CH Cl ). H-NMR
f
2
2
2
(
400 MHz, CDCl , 25 °C): δ = 1.72 (bs, 6H, CH ), 3.53−3.54 (m, 4H, NCH ), 6.26 (d,
3 2 2
J = 4.0 Hz, 1H, CH ), 7.47−7.60 (m, 4H, CH+CH +CH ), 7.67 (bs, 4H, CH ),
th
th
ar
ar
1
3
7
5
1
1
5
1
.74−7.75 ppm (m, 4H, CH ). C-NMR (125 MHz, CDCl , 25 °C):
δ
= 23.67, 25.51,
ar
3
1.66, 108.34, 111.68, 111.79, 119.22, 119.33, 122.99, 130.53, 131.65, 131.83,
34.78, 135.28, 136.78, 136.99, 137.27, 137.99, 142.81, 143.05, 150.42, 173.70,
+
89.06, 190.05 ppm. HR-MALDI-MS (DHB): calcd for C H N O S (M+H)
3
3
24
3
2
26.15837; found 526.15867. IR (HATR):
ν = 2937, 2222, 1644, 1569, 1518, 1475,
–
1
408, 1375, 1239, 1173, 1125, 1075, 1001, 823, 771, 558 cm .
Chromophore 1d. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
d and boronic acid 5 following the general procedure (i). The title compound was
1
afforded as a black solid (151 mg, 55 %). R = 0.20 (SiO ; CH Cl ). H-NMR (500
f
2
2
2
MHz, CDCl , 25 °C):
δ = 1.61 (bs, 2H, CH ), 1.69−1.73 (m, 4H, CH ), 3.41−3.43 (m,
2 2
3
4
H, NCH ), 6.10 (d, J = 4.5 Hz, 1H, CH ), 7.22 (d, J = 4.5 Hz, 1H, CH ), 7.33 (d, J =
2 th th

2
1
ACCEPTED MANUSCRIPT
1
4.0 Hz, 1H, CH), 7.41 (d, J = 12.5 Hz, 1H, CH), 7.50−7.51 (m, 2H, CH ), 7.60 (d, J
ar
1
3
=
13.5 Hz, 1H, CH), 7.65−7.66 (m, 4H, CH ), 7.74−7.78 ppm (m, 4H, CH ). C-
ar ar
NMR (125 MHz, CDCl , 25 °C):
δ = 23.70, 25.27, 51.72, 106.90, 111.98, 117.12,
3
1
1
19.22, 119.75, 126.11, 130.49, 131.76, 131.81, 135.12, 135.41, 137.26, 137.56,
37.82, 138.53, 140.82, 142.66, 143.04, 146.94, 147.86, 168.28, 189.69, 190.10 ppm.
+
HR-MALDI-MS (DHB): calcd for C H N O S (M+H) 552.17402; found
3
5
26
3
2
5
52.17458. IR (HATR): ν = 2928, 2224, 1648, 1554, 1518, 1414, 1330, 1213, 1158,
–
1
1
109, 1051, 987, 821 cm .
Chromophore 2a. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
a and boronic acid 6 following the general procedure (i). The title compound was
1
afforded as a red solid (195 mg, 75 %). R = 0.60 (SiO ; CH Cl /hexane, 3:1). H-
f
2
2
2
NMR (400 MHz, CDCl , 25 °C):
δ
= 3.13 (s, 6H, CH ), 6.68 (d, J = 9.2 Hz, 2H, CH ),
3
3
ar
7
.59−7.64 (m, 2H, CH ), 7.70−7.74 (m, 5H, CH+CH ), 8.33−8.41 ppm (m, 6H, CH ).
ar
ar
ar
1
3
C-NMR (125 MHz, CDCl , 25 °C):
δ = 40.37, 111.75, 121.82, 122.13, 123.34,
3
1
1
23.41, 130.66, 130.71, 135.48, 136.01, 136.81, 138.03, 138.13, 138.84, 138.93,
44.37, 144.88, 147.86, 147.92, 148.88, 154.61, 188.49, 190.31 ppm. HR-MALDI-MS
+
(
DHB): calcd for C H N O (M+H) 520.15032; found 520.15055. IR (HATR):
ν
=
3
0
22
3
6
–
1
2
917, 1665, 1507, 1317, 1174, 1108, 1002, 828, 747, 694, 523 cm .
Chromophore 2b. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
b and boronic acid 6 following the general procedure (i). The title compound was
1
afforded as a black solid (207 mg, 76 %). R = 0.30 (SiO ; CH Cl /hexane, 2:1). H-
f
2
2
2
NMR (400 MHz, CDCl , 25 °C):
δ = 3.08 (s, 6H, CH ), 6.67 (d, J = 8.8 Hz, 2H, CH ),
3 ar
3
7
.30 (d, J = 14.8 Hz, 1H, CH), 7.54−7.58 (m, 3H, CH+CH ), 7.61−7.65 (m, 2H,
ar
CH ), 7.71 (dd, J = 8.4 Hz, J = 2.8 Hz, 4H, CH ), 8.15 (dd, J = 15.2 Hz, J = 12.4
ar
1
2
ar
1
2
1
3
Hz, 1H, CH), 8.33−8.39 ppm (m, 4H, CH ). C-NMR (125 MHz, CDCl , 25 °C):
δ =
ar
3

2
2
ACCEPTED MANUSCRIPT
4
1
1
5
1
0.56, 112.36, 119.54, 123.04, 123.38, 123.44, 130.61, 130.68, 132.19, 135.77,
35.95, 137.50, 138.05, 138.24, 138.73, 144.17, 144.53, 147.93, 148.16, 152.88,
+
55.87, 189.33, 189.86 ppm. HR-MALDI-MS (DHB): calcd for C H N O (M+H)
3
2
24
3
6
46.16596; found 546.16667. IR (HATR):
ν = 2920, 1665, 1552, 1507, 1343, 1323,
–
1
171, 994, 817, 749, 696, 598 cm .
Chromophore 2c. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
c and boronic acid 6 following the general procedure (i). The title compound was
1
afforded as a red solid (159 mg, 52 %). R = 0.30 (SiO ; CH Cl /hexane, 3:1). H-
f
2
2
2
NMR (500 MHz, CDCl , 25 °C):
δ = 1.73 (bs, 6H, CH ), 3.55 (bs, 4H, NCH ), 6.27
2 2
3
(
d, J = 4.5 Hz, 1H, CH ), 7.52−7.62 (m, 4H, CH+CH +CH ), 7.73 (bs, 4H, CH ),
th th ar ar
1
3
8
5
1
.32−8.33 ppm (m, 4H, CH ). C-NMR (125 MHz, CDCl , 25 °C): δ = 23.71, 25.56,
ar 3
1.71, 108.47, 123.09, 123.20, 123.36, 130.76, 130.84, 134.75, 135.20, 136.93,
37.02, 137.10, 137.21, 138.15, 144.83, 145.07, 147.74, 150.61, 173.89, 190.03 ppm.
+
HR-MALDI-MS (DHB): calcd for C H N O S (M+H) 566.13803; found
3
1
24
3
6
5
66.13867. IR (HATR): ν = 2931, 1651, 1569, 1510, 1332, 1240, 1181, 1130, 1072,
–
1
1
003, 830, 747 cm .
Chromophore 2d. The title compound was prepared from 4,7-diiodoindan-1,3-dione
4
d and boronic acid 6 following the general procedure (i). The title compound was
1
afforded as a black solid (206 mg, 70 %). R = 0.25 (SiO ; CH Cl /hexane, 3:1). H-
f
2
2
2
NMR (400 MHz, CDCl , 25 °C):
δ = 1.57−1.70 (m, 6H, CH ), 3.42 (bs, 4H, NCH ),
2 2
3
6
1
7
2
1
.10 (d, J = 4.0 Hz, 1H, CH ), 7.23 (d, J = 4.5 Hz, 1H, CH ), 7.34 (d, J = 14.0 Hz,
th th
H, CH), 7.43 (d, J = 12.4 Hz, 1H, CH), 7.54 (bs, 2H, CH ), 7.59−7.66 (m, 1H, CH),
ar
13
.71 (d, J = 7.6 Hz, 4H, CH ), 8.33 ppm (bs, 4H, CH ). C-NMR (125 MHz, CDCl ,
ar
ar
3
5 °C):
δ = 23.68, 25.26, 51.73, 107.01, 117.11, 119.55, 123.24, 123.30, 126.14,
30.69, 135.02, 135.26, 137.26, 137.37, 137.53, 138.62, 141.03, 144.62, 144.99,

2
3
ACCEPTED MANUSCRIPT
1
47.01, 147.77, 147.97, 168.44, 189.61, 190.01 ppm. HR-MALDI-MS (DHB): calcd
+
for C H N O S (M) 591.14586; found 591.14612. IR (HATR):
ν = 2925, 1643,
3
3
25
3
6
–
1
1
555, 1514, 1413, 1334, 1212, 1156, 1105, 1050, 984, 821 cm .
Supporting information (SI) available: Experimental procedures and
characterization of compounds, DSC analyses, electrochemical data, UV-Vis
1
13
absorption spectra, DFT calculations, correlations, H and C NMR spectra, and HR-
MALDI-MS spectra.
Acknowledgements
This research was supported by the Technology Agency of the Czech Republic
(TE01020022, Flexprint).
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Highlights
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•
•
Threefold acceptor/donor substitution of central indan-1,3-dione to gain extraordinary
T-shaped push-pull chromophores.
Fundamental thermal and optoelectronic properties studied by differential scanning
calorimetry, electrochemistry, UV/Vis absorption spectroscopy, and DFT calculations.
Thorough structure–property relationships/intramolecular charge-transfer assessment
and correlation of the experimental and theoretical data.