ThDione: A Powerful Electron-Withdrawing Moiety for Push–Pull Molecules

Article abstract of DOI:10.1002/cplu.202000395

A series of new push–pull chromophores based on a combined cyclopenta[c]thiophene-4,6-dione (ThDione) acceptor, N,N-dimethylaniline, N-piperidinylthiophene or ferrocene donors, and ethylene or buta-1,3-dienylene π-linkers has been designed and synthesized. Utilizing one or two ThDione acceptors afforded linear or branched push–pull molecules. Experimental and theoretical study of their fundamental properties revealed thermal robustness up to 260 °C, a electrochemical/optical HOMO–LUMO gap that is tunable within the range of 1.47–2.19/1.99–2.39 eV, and thorough elucidation of structure–property relationships. Compared to currently available portfolio of heterocyclic electron-withdrawing units, ThDione proved to be a powerful and versatile acceptor unit. It imparts significant intramolecular charge transfer and polarizes the π-system, which results in enhanced (non)linear optical response.

Full text of DOI:10.1002/cplu.202000395

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ThDione: A Powerful Electron-Withdrawing Moiety for
Push–Pull Molecules
Eva Novotná,[a] Iwan V. Kityk,[b] Oldřich Pytela,[a] Filip Bureš,*[a] Miroslav Ludwig,[a]
Milan Klikar,*[a] Katarzyna Ozga,[b] and Jaroslaw Jedryka[b]
Dedicated to Iwan V. Kityk
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A series of new push–pull chromophores based on a combined
cyclopenta[c]thiophene-4,6-dione (ThDione) acceptor, N,N-
dimethylaniline, N-piperidinylthiophene or ferrocene donors,
and ethylene or buta-1,3-dienylene π-linkers has been designed
and synthesized. Utilizing one or two ThDione acceptors
afforded linear or branched push–pull molecules. Experimental
and theoretical study of their fundamental properties revealed
HOMO–LUMO gap that is tunable within the range of 1.47–
2.19/1.99–2.39 eV, and thorough elucidation of structure–prop-
erty relationships. Compared to currently available portfolio of
heterocyclic electron-withdrawing units, ThDione proved to be
a powerful and versatile acceptor unit. It imparts significant
intramolecular charge transfer and polarizes the π-system,
which results in enhanced (non)linear optical response.
°
thermal robustness up to 260 C, a electrochemical/optical
Introduction
powerful yet simple acceptor with 1,3-dicarbonyl arrangement
and fused benzene ring, which allows further delocalization. We
have recently demonstrated its first structural modification on
the fused benzene ring affording novel T-shaped push-pull
chromophores.[30–32] Malonic acid and its derivatives, namely
cyanoacetic acid, malononitrile, dialkyl malonate, Meldrum's or
(thio)barbituric acid, are another class of popular acceptors with
related 1,3-dicarbonyl arrangement.[33] Fundamental optoelec-
tronic properties of push-pull chromophores are considerably
affected by the intramolecular charge-transfer (ICT) between
the particular donor and acceptor mediated via a π-system.
Hence, polarizability of the used π-system is also an important
aspect which has to be taken into account. Whereas six-
membered (hetero)aromatic compounds are considered as
electron deficient, five-membered rings are generally electron
rich. However, we have demonstrated that proper decoration of
five-membered heteroaromatic compounds such as imidazole,
thiazole or thiophene with electron withdrawing substituents
may reverse their electronic behavior and dicyanoimidazole,
dicyanothiazole, dicyanothiophene or dinitrothiophene may be
used as electron withdrawing moieties of push-pull
chromophores.[34–39] Thiophene is inherent, highly polarizable,
and electron rich heteroaromatics referred to as auxiliary
donor.[38,40] Its electronic properties are often further modified
by sulfur oxidation,[41] or fusing with another (hetero)aromatic
compound, e.g. thienothiophene,[42] isothianaphtene[43] or
benzothiadiazoles.[44–46]
Organic π-systems with D-π-A/push-pull arrangement belong
to prominent organic chromophores with extraordinary opto-
electronic properties and wide applications.[1–4] During the last
decades, a plethora of donor-π-acceptor molecules has been
synthesized and utilized across material chemistry fields such as
dyes, colorants, active layers of organic devices, emitters,
nonlinear optical (NLO) media, switches etc.[5–27] A push-pull
molecule can easily be designed by a combination of available
electron releasing/withdrawing substituents interconnected by
various π-systems. To this date, a large number of donor/
acceptor groups has been developed and well-examined.[28]
Beside elementary D/A substituents with mesomeric effect such
as alkoxy, diakylamino, cyano or nitro, more complex and
advanced D/A units based on heterocyclic systems or multi-
heteroatom sequences have also been designed.[29] 1,3-
Dicarbonyl compounds represent very popular group of
electron withdrawing moieties, mostly due to their instant
availability and active methylene moiety, which allows their
easy incorporation into the chromophore backbone via Knoeve-
nagel condensation. Indan-1,3-dione is a typical example of
[a] E. Novotná, Prof. O. Pytela, Prof. F. Bureš, Prof. M. Ludwig, Dr. M. Klikar
Institute of Organic Chemistry and Technology
University of Pardubice
Faculty of Chemical Technology
Studentská 573, Pardubice, 53210 (Czech Republic)
E-mail: filip.bures@upce.cz
Considering the aforementioned structural aspects, we have
recently designed and prepared cyclopenta[c]thiophene-4,6-
dione (ThDione, Figure 1).[42,47,48] It combines polarizable electron
rich thiophene and 1,3-dicarbonyl arrangement similar to that
in indan-1,3-dione or malonic acid derivatives, while presence
of CH2 moiety allows its facile introduction via Knoevenagel
condensation. According to the very recent comparison of the
most popular electron withdrawing moieties, ThDione proved
milan.klikar@upce.cz
[b] Prof. I. V. Kityk, Prof. K. Ozga, Dr. J. Jedryka
Chair of Control Engineering
Electrical Engineering and Optoelectronics,
Czestochowa University of Technology
Al. Armii Krajowej 17, Czestochowa, 42-200 (Poland)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cplu.202000395
This article is part of a Special Collection on “Chemistry in the Czech Re-
public”.
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between both D and A parts. We present herein a thorough
structure-property relationship study based on evaluation of
thermal, (opto)electronic, and DFT data.
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Results and Discussion
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Synthesis
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The synthesis of all target chromophores is based on simple
Knoevenagel condensation between an aldehyde and ThDione.
DMA aldehydes 4a–b and ferrocenecarboxaldehyde 6a are
commercial available. The preparations of PIT aldehydes 5a–d
and ThDione were described earlier.[33,47] As depicted in
Scheme 1, aldehyde 6c was prepared by twofold direct
formylation of ferrocene 7.[49] Well-established protocol employ-
ing tributyl (1,3-dioxolan-2-ylmethyl)phosphonium bromide has
been utilized for Wittig olefination (Method A).[50] Starting from
6a, extended aldehyde 6b was obtained in high 92% yield.
Similar twofold olefination of 6c yielded a 1:2 mixture of
aldehydes 6d and 6e (overall 92% yield), which was success-
fully separated by a column chromatography on alumina.
With all desired aldehydes in hand, the final Knoevenagel
condensation employing ThDione was carried out (Scheme 2,
Method B). Piperidine was used as suitable catalyst which
assured sufficient reactivity of ThDione with all types of
aldehydes. Despite similar in principle, the separation and
purification of the Knoevenagel products were the most
challenging. Target molecules, especially chromophores 2c–d
and 3c–e with elongated and planarized π-linkers, are sparingly
soluble in common solvents used for chromatography. More-
over, some chromophores underwent partial hydrolysis during
chromatography affording starting aldehyde and ThDione.
Intense degradation occurred for Fc chromophore 3b which
could be isolated in diminished 3% yield. All chromophores
were further crystallized and, therefore, the isolated yields are
generally low, which mostly reflects their difficult purification.
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Figure 1. Relation between popular 1,3-dicarbonyl electron acceptors.
to be powerful acceptor comparable to tricyanovinyl or
thiobarbituric acid.[42]
However, since today no systematic study of its connection
to various electron donors has been carried out. Figure 2 shows
structure of novel D-π-A and A-π-D-π-A systems with ThDione
acceptor and three representative electron donors that include
widely used N,N-dimethylaniline (DMA), very powerful 2-
(piperidin-1-yl)thiophene (PIT),[33] and organometallic ferrocene
(Fc). Olefinic π-system has been selected to allow efficient ICT
Thermal analysis
Figure 2. General structures of target molecules 1–3.
Thermal behavior of all target molecules 1–3 (except 3b) was
examined by different scanning calorimetry (DSC). Figure 3
Scheme 1. Synthesis of ferrocene aldehydes 6b–e: i) 1. Tributyl (1,3-
°
dioxolan-2-ylmethyl)phosphonium bromide, NaH, THF, 25 C, 12 h; 2. HCl,
°
°
°
THF, 25 C, 1 h (Method A). ii) 1. n-BuLi, hexane, TMEDA, 25 C; 2. DMF, 0 C,
Figure 3. Representative DSC curves of compounds 2a–d (PIT chromo-
°
2 h; 3. HCl.
phores) determined with a scanning rate of 3 C/min under N2 atmosphere.
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°
Scheme 2. Synthesis of target chromophores 1–3 (Method B): iii) ThDione, piperidine, CH2Cl2 or CH3CN, 25 C, 16 h.
shows thermograms of representative compounds 2a–d while
Table 1 lists all measured melting points (Tm) and temperatures
of thermal decompositions (Td). All DCS records are provided in
the Supporting Information. The measured melting points and
temperature of decomposition range from 172–250 and 195–
Figure 3). Decomposition of branched ferrocene derivatives 3c–
e is also represented by two exothermic steps; the first one is
broad and less pronounced, the second one is sharp and
vigorous.
Based on the performed DSC analysis the following out-
comes can be deduced:
π-Linker elongation reduces thermal robustness in DMA and
PIT series (see Figure 3, 2a/c vs. 2b/d, ΔTd =40–50 C). In
general, thermal robustness may be improved by introducing
rigid (hetero)aromatic or organometallic moieties, simple
connectors such as olefinic or acetylenic bridge bring rather
°
260 C, respectively. Linear 1a–b, 2a–b, and 3a melted sharply
and their liquid phase proved unstable with immediate
decomposition during following heating process (Td exceeded
*
°
°
Tm by about 5–25 C). On the contrary, branched 2c–d
decomposed directly without previous melting. Their degrada-
tion generally took place in two consecutive steps (e.g.
Table 1. Summary of thermal, electrochemical, and optical properties of chromophores 1–3.
A
~
[V][d]
Comp.
Tm
Td
Ep(ox1)
Ep(red1)
E
EHOMO
ELUMO
λmax
[nm/eV][f]
ɛmaxA ×103[M-1·cm-1][f]
[V][d]
[V][d]
[eV][e]
[eV][e]
[a]
[b]
°
°
[ C]
[ C]
1a
1b
2a
2b
2c
2d
3a
237
250
225
190
/
260
255
240
200
245
195
195
0.98
0.76
0.73
0.48
0.94
0.72
0.66
À 1.21
À 0.98
À 1.27
À 0.99
À 0.88
À 0.82
À 1.20
2.19
1.74
2.00
1.47
1.82
1.54
1.86
À 5.37
À 5.15
À 5.12
À 4.87
À 5.33
À 5.11
À 5.05
À 3.18
À 3.41
À 3.12
À 3.40
À 3.51
À 3.57
À 3.19
494/2.51
551/2.25
529/2.34
622/1.99
577/2.15
591/2.10
367/3.38
583/2.13[g]
416/2.98
602/2.06[g]
333/3.72
518/2.39[g]
378/3.28
570/2.18[g]
349/3.55
533/2.33 [g]
60
47
96
72
47
/
46
172
11
3[g]
18
[c]
[c]
3b
3c
3d
3e
0.63
0.83
0.72
0.79
À 0.96
À 1.03
À 0.93
À 0.92
1.59
1.86
1.65
1.71
À 5.02
À 5.22
À 5.11
À 5.18
À 3.43
À 3.36
À 3.46
À 3.47
7[g]
42
/
/
/
195
200
210
7[g]
75
14[g]
46
10[g]
[a] Tm =melting point (the point of intersection of a baseline and a tangent of thermal effect=onset). [b] Td =thermal decomposition (pyrolysis in N2
atmosphere). [c] Not measured. [d] Ep(ox1) and Ep(red1) are peak potentials of the first oxidation and reduction (irreversible processes), respectively, as measured
by CV at scan rate 100 mVsÀ 1; all potentials are given vs. SSCE; ΔE=Ep(ox1) À Ep(red1). [e] À EHOMO/LUMO =Ep(ox1/red1) +4.35 (in DMF vs. SCE)[51] +0.036 [difference
between SCE (0.241 vs. SHE) and SSCE (0.205 vs. SHE)].[52] [f] Measured in CH2Cl2 at concentration 10À 5 M. [g] Absorption maxima corresponding to HE and LE
bands.
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thermal instability. However, introducing olefinic linker has
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less negative effect on thermal robustness as compared to
other acetylenic chromophores.[34,41–42]
*
*
*
Compared to 1 and 2, the ferrocene compounds 3 possess
slightly reduced thermal stability as judged by their lower Td
values. Nevertheless, presence of the ferrocene moiety
suppresses negative effect of the olefinic linker and 3a–e
°
showed almost identical Td values (195–210 C).
Td values are comparable between analogical pairs of
compounds with D-π-A and A-π-D-π-A structural arrange-
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°
ment (2a/2b/3a vs. 2c/2d/3c, ΔTd �5 C). Hence, the
branching of chromophore structure does not influence its
thermal robustness.
Thermal stability is mainly dictated by the type of donor with
the order: Fc<PIT<DMA. The highest thermal stability was
°
recorded for DMA chromophore 1a (Td =260 C).
Figure 4. Energy level diagram of electrochemical (black) and DFT calculated
(red) values for chromophores 1–3.
Electrochemistry
Electrochemical investigation of chromophores 1–3 were
carried out in DMF containing 0.1 M Bu4NBF4 in a three
electrode cell by cyclic voltammetry (CV). The acquired data are
summarized in Table 1, all CV diagrams are shown in Fig. S7
and S8 (see the Supporting Information).
generally given by the π-system extension, the effect of the
branching and the number of ThDione acceptors is dimin-
ished.
*
The ΔE of unsymmetrical Fc derivative 3e lies between those
The first oxidations and reductions are irreversible processes
followed by additional oxidations and reductions. Quasi-rever-
sible reductions were detected only for linear chromophores
1a, 2a, and 3a. The first reductions were determined as one-
electron and the first oxidations as one or multiple-electron
processes (especially for DMA and Fc series). It is well-know that
the ferrocene first oxidation involves iron(II) redox center as
fully reversible process.[36] However, Fc derivatives 3a–e under-
went irreversible first oxidation, which points to a significant
DÀ A interaction of ferrocene donor with ThDione acceptor.
Both potentials of the first oxidation/reduction are certainly a
function of particular chromophore structure. The recorded
peak potentials Ep(ox1/red1) were recalculated to EHOMO/LUMO values
and these are visualized in the energy level diagram in Figure 4.
Based on the electrochemical measurements, the following
relationships can be deduced:
measured for 3c and 3d.
In 1–2, the HOMO–LUMO gap is clearly controlled by the
*
type of donor, π-linker length, and the number of acceptor
units. However elongation of the π-system has the most
pronounced effect on reducing ΔE (e.g. 1a vs. 1b, ΔE=2.19
vs.1.74 eV). Linear and branched chromophores exhibited
similar ΔE values (e.g. 2b vs. 2d, ΔE=1.47 vs.1.54 eV), which
implies that structural branching deepened both the HOMO
and LUMO, but their difference remained almost unaltered.
*
Chromophore 2b with PIT donor and elongated π-system
showed the narrowest HOMO–LUMO gap of 1.47 eV.
Linear optical properties
All target chromophores 1–3 are intensely colored solids; their
color ranges from yellow to dark blue (Figure S9 in the
Supporting Information). Due to the strong ICT, no emission has
been detected. The absorption spectra were recorded in three
solvents with different polarity (toluene, CH2Cl2, and DMF). The
longest absorption maxima (λmax) and their corresponding
molar extinction coefficients (ɛmax) are summarized in Table 1
and S1. The absorption spectra in CH2Cl2 are shown in Figure 5,
all spectra are depicted in Figures S10–S12.
All linear D-π-A chromophores 1a–b, 2a–b, and 3a–b
exhibited one distinct CT-absorption peak corresponding to a
strong DÀ A interaction. On the contrary, branched A-π-D-π-A
chromophores 2c–d and 3c–e possess one dominant CT-band
with an additional shoulder shifted either hypsochromically (PIT
series) or bathochromically (Fc series). This splitting of the
absorption bands is due to a coupling between branches and
reflects quadrupolar arrangement of target chromophores 2c–d
*
LUMO: Chromophores with the same π-linker showed almost
constant LUMO level (e.g. 1b/2b/3b, ELUMO =À 3.41/ À 3.40/
À 3.43 eV). Thus, it is obvious that LUMO must be localized on
ThDione electron withdrawing moiety. The LUMO level is
mostly affected by elongation and branching of the π-
system.
*
HOMO: Chromophores within particular series possess differ-
ent EHOMO values, which indicates the HOMO localization at
the DMA, PIT or Fc donor. The HOMO level is further
controlled by the π-system length and branching. Embed-
ding ethenylene unit increases the EHOMO by 0.03–0.25 eV,
whereas it becomes deepened when going from D-π-A to A-
π-D-π-A arrangement (e.g. 2a vs. 2c, À 5.12 vs. À 5.33 eV).
*
Compared to DMA and PIT molecules, the structural mod-
ifications affect the HOMO/LUMO levels in Fc derivatives 3a–
e less significantly (Figure 4). The HOMO-LUMO gap is
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Figure 5. UV-Vis absorption spectra of target chromophores in CH2Cl2 (10À 5 M).
and 3c–e.[53] Moreover, the ferrocene is considered as a donor
with dual ICT from the cyclopentadienyl (Cp) and Fe moieties.[36]
Whereas the Cp!ThDione interaction is observed as high
energy (HE) band, the Fe!ThDione interaction is shifted to low
energy (LE) and appears as a weak peak. Both HE and LE peaks
are clearly observed in solvents with low polarity, e.g. toluene
and CH2Cl2. In polar aprotic DMF, both peaks are merged
together and appear as a structured bands with one or more
shoulders. The absorption maxima of 3a–e in DMF range
between 450–520 nm and are localized between the high and
low energy bands found in toluene/CH2Cl2. A correlation of
electrochemical and optical gaps (1240/λmax) is very tight for
chromophores 1a–b and 2a–d with standard mesomeric DMA
and PIT donors. The ferrocene derivatives 3a–e were clearly
identified as outliers (Figure S13 in the Supporting Information).
This observation corroborates aforementioned electrochemical
behavior of 3a–e and points to a specific solute-solvent
interaction in DMF.
demonstrates their donating ability (PIT>Fc>DMA). The
most red-shifted absorption maxima was measured for linear
chromophore 2b (λmax =622 nm), which feature PIT donor
and extended π-system. On the contrary, the most hypso-
chromically shifted CT-band was observed for DMA chromo-
phore 1a (λmax =494 nm).
When comparing the absorption maxima measured in differ-
ent solvents (Table S1), a slight bathochromic shift occurs
when going from nonpolar toluene to polar DMF. The
positive solvatochromism indicates more polar excited state.
*
Nonlinear optical properties
The fundamental nonlinear optical responses of chromophores
1–3 were preliminarily investigated by laser stimulated second-
and third-harmonic generation (SHG and THG) of the light. The
experimental set-up and details are provide in the Supporting
Information. The SHG and THG measurements were carried out
with powder samples and a 1064 nm Nd:YAG laser source beam
employing reflected light geometry.
Figure 6 shows the dependency between the SHG and the
fundamental energy density. The data is referenced to Ba
(BO2)2δ: 5%Nd (BBOδ) crystal. The maximal energy density was
about 100 JmÀ 2; the higher densities caused sample degrada-
tion (especially for 2b). At first sight, there are remarkable
differences between the particular NLOphores.
Most of the samples showed relatively weak SHG response
slightly above the noise level. For Fc-chromophores 3, the SHG
signal increases to a certain level and then rapidly decreases to
the noise level, which is associated with their photo-degrada-
tion. However, chromophores 1b and 2c provided a clear green
SHG signal at 532 nm with the intensity about 15% lower as
compared to the reference crystal. Both chromophores possess
strong DMA or PIT donors and extended or branched π-system,
respectively.
Considering the linear optical properties, we can deduce
the following relationships:
*
Elongation of the π-system by ethenylene spacer induces a
significant bathochromic shift of 20–90 nm.
When going from linear D-π-A to quadrupolar A-π-D-π-A
*
systems, the molar extinction coefficient either decrease (e.g.
PIT derivatives 2b vs. 2d, Δɛmax =À 24×103 MÀ 1 cmÀ 1) or
increase (e.g. Fc derivatives 3c vs. 3a, Δɛmax =37×
103 MÀ 1 cmÀ 1).
*
CT-band positioning of linear and branched analogues obey
the Frankel exciton model.
The longest-wavelength absorption peak in 1 and 2 with
*
amino-based donors undergo significant hypsochromic shift
upon protonation (see the Figure S14). The original band
may be regenerated upon neutralization with trimeth-
ylamine, which confirm its CT nature.
*
Asymmetric Fc derivative 3e possesses the CT-band localized
between the absorption maxima of symmetric analogues 3c
and 3d.
A comparison of the absorption maxima for analogous
THG responses vs. fundamental laser energy for the
particular chromophores are given in Figure 7. To prevent
sample degradation, the maximal energy was reduced to
*
chromophores with different donors (e.g. 1b, 2b, 3b)
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molecular orbitals, their differences ΔE and ground state dipole
1
2
3
4
5
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moments μ were calculated at DFT B3LYP/6-311+ +G(3d,f,2p)
level in DMF. The first hyperpolarizabilities β were computed at
DFT B3LYP/6-311+ +G(3d,f,2p) level in vacuum at 1064 nm.
Theoretical electronic absorption spectra were calculated at TD-
DFT (nstates=8) B3LYP/6-311+ +G(3d,f,2p) level in vacuum
and corresponding λmax values were deduced. All calculated
data are summarized in Table 2.
The calculated HOMO and LUMO energies range from
À 6.20 to À 5.37 and À 3.30 to À 2.66 eV and are clearly depend-
ent on the structural arrangement of the particular chromo-
phore as can be seen from the energy level diagram in Figure 4.
As deduced from the experimental and calculated data, both
obtained LUMO levels correlate tightly (Figure S16). Compared
to experimental values, the calculated HOMO levels for Fc
derivatives 3 are negatively shifted. The difference is probably
due to a specific interactions of 3 measured in DMF (see above).
However, the theoretical HOMO levels obey the same trends as
those measured by cyclic voltammetry. A correlation of both
quantities as well as the HOMO-LUMO gaps splits into two
sections (1+2 vs. 3) with high correlation coefficients (Figur-
es S17-18). These tight correlations indicate that theoretical
calculations are capable to describe similar structure-property
relationships as seen by the electrochemical measurements.
Namely, elongation of the π-linker via double bond(s) reduces
the energy gap in the most pronounced way. The calculated
data also shows that the HOMO-LUMO gap is affected by the
chromophore branching. The lowest gaps were calculated for
PIT chromophores 2.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Figure 6. SHG vs. fundamental energy density for 1–3.
The HOMO/LUMO localizations were calculated at DFT
B3LYP/6-311+G(2d,f,p) level using DFT-optimized geometries
Figure 7. THG vs. fundamental energy density for 1–3.
Table 2. DFT-calculated properties of chromophores 1–3.
[c]
Comp. EHOMO
ELUMO
ΔE[a] μ [a]
λmax
[nm/eV]
β×10À 30
GoS[e]
[eV][a]
[eV][a]
[eV]
[D]
[esu][b]
1a
1b
2a
2b
2c
2d
3a
À 5.75 À 2.82 2.93
8.9
418/2.97
462/2.68
431/2.88
475/2.61
501/2.48
544/2.28
380/3.26
642/
206
761
146
691
445
3540
18
Cs
Cs
non
non
non
non
non
70 JmÀ 2. In general, DMA and PIT chromophores 1 and 2
showed the best performance. In contrast to SHG measure-
ments, chromophore 2c possesses weak third-order NLO
activity. Despite its non-centrosymmetric quadrupolar molec-
ular arrangement (see below), it may adopt a centrosymmetric
supramolecular layout with a diminished response. All remain-
ing chromophores in the series 2 showed a clear THG signal.
However, simple DMA- and ThDione-terminated chromophores
1a and 1b proved to be the most efficient third-order
NLOphores, especially at lower energy densities. The THG
response of ferrocene chromophores 3 was about 50% lower as
compared to 1 and 2.
À 5.54 À 3.00 2.54 12.5
À 5.56 À 2.66 2.90 12.4
À 5.37 À 2.89 2.48 17.3
À 5.84 À 3.18 2.66
À 5.57 À 3.30 2.27
À 5.92 À 2.88 3.04
7.7
9.7
2.3
1.93[d]
3b
3c
3d
3e
À 5.82 À 3.07 2.75
À 6.20 À 3.12 3.08
À 6.06 À 3.23 2.83
À 6.10 À 3.20 2.90
4.8
2.2
1.4
3.0
400/3.10
630/
404
4
non
C2
1.97[d]
453/2.74
732/
1.69[d]
447/2.77
36
C2
678/
1.83[d]
461/2.69
346
non
705/
Theoretical calculations
1.76[d]
[a] Calculated at the DFT B3LYP/6-311+ +G(3d,f,2p) level in DMF. [b]
Calculated at the DFT B3LYP/6-311+ +G(3d,f,2p) level in vacuum at
1064 nm (À 2ω;ω,ω). [c] Calculated at the TD-SCF (nstates=8) B3LYP/6-311
+ +G(3d,f,2p) level in vacuum. [d] Absorption maxima corresponding to
HE and LE bands. [e] Group of symmetry.
Spatial and electronic properties of target chromophores were
investigated using Gaussian® 16 W software[54] package at the
DFT level. Initial geometries of molecules 1–3 were optimized
by DFT B3LYP/6-311+G(2d,f,p) method. Energies of the frontier
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and visualized in OPchem.[55] The frontier molecular orbitals in
representative chromophores 1b, 2b, and 3b are shown in
Figure 8; for complete listing see the Supporting Information. In
linear chromophores with mesomeric donors (DMA and PIT),
the HOMO-1 is spread over the ThDione C1-C3 atoms and the
adjacent π-linker, similarly to the LUMO+1. This reflects
combination of electron-rich thiophene with electron-withdraw-
ing cyclopentandione moieties of ThDione. The HOMO/LUMO
are generally localized over the central π-system involving both
donors and acceptors. Branched molecules 2c and 2d possess
the HOMO-1/LUMO+1 spread over one branch, while HOMO/
LUMO is localized centrally. In Fc derivatives 3a–b, the HOMO-1
is centralized on the Fe atom. The LUMO+1 is spread over
either the ferrocene or ThDione moieties. The branched
chromophores 3c–e possess the frontier molecular orbitals
centrally localized involving ferrocene and adjacent π-system of
both branches.
The linear DMA and PIT chromophores 1a–b and 2a–b
showed higher dipolar character resulting in the larger ground
state dipole moments (μ=9–17 D). Quadrupolar molecules 2c–
d and ferrocene derivatives possess diminished dipole moments
of 1–10 D. The calculated second-order polarizabilities β obey
quite similar trends. Whereas Fc derivatives 3 possess modest
NLO coefficients, DMA and PIT derivatives 1–2 showed higher
NLO activity. Overestimated β value for PIT derivative 2d should
be considered as outlier. The π-linker elongation (e.g. 2a/2b!
146/691×10À 30 esu) and branching (e.g. 2a/2c!146/445×
10À 30 esu) generally enhances the calculated NLO response. On
the contrary, molecular symmetrization via structural branching
significantly suppresses the β polarizabilities; for instance see
the non-symmetric and C2-symmetric 3b and 3d with β equal
to 404 and 36×10À 30 esu, respectively. The largest NLO
coefficients β were calculated for DMA and PIT chromophores
1b (761×10À 30 esu) and 2b (691×10À 30 esu) with enlarged π-
systems. This is in a very good agreement to the aforemen-
tioned experimental values.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
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53
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55
56
57
Figure 9. TD-DFT calculated (black) and experimentally obtained (violet) UV-
Vis spectra of chromophore 3a in CH2Cl2. Both spectra were overlapped and
normalized to have maximal absorbance (A) of 1.
0.6 eV) and Fc 3 (when considering both HE and LE bands).
However, both theoretical and experimental UV-Vis spectra
possess the same bands and shoulders. The calculated longest-
wavelength absorption maxima are affected by the same
structural features as discussed for the experimental ones
measured in dichloromethane. According to the analysis of the
particular oscillators, the CT-band of chromophores 1–2 consists
of the HOMO!LUMO transition. The high energy shoulders of
branched PITs 2c–d correspond to the HOMO!LUMO+1
transition. As expected, the LE bands of 3 are originated from
the HOMO!LUMO transition with weaker oscillator strength,
while the HE bands are generated by the subsequent transitions
(from HOMO-2 to LUMO+2) and possess larger oscillator
strength.
Figure 9 shows
a representative electronic absorption
spectra of chromophore 3a overlapped with the experimental
one; for complete listing see the Supporting Information. The
calculated λmaxDFT values are listed in Table 2. As can be deduced Conclusion
from Figures 9 and S22–24, TD-DFT spectra are either blue- or
red-shifted for DMA 1 and PIT series 2 (Δλmax �50–150 nm/0.2–
Inspired by very successful and widely used indan-1,3-dione,
ThDione combines highly polarizable thiophene ring fused with
cyclopentan-1,3-dione bearing active methylene group. It
represents an electron-withdrawing moiety, which features
facile preparation and allows easy introduction via Knoevenagel
condensation. Its systematic employment as electron acceptor
was investigated on a series of D-π-A and A-π-D-π-A molecules
with three widely used electron donors. All prepared chromo-
phores showed thermal robustness sufficiently high to be
considered as materials suitable for organic electronics. We
have demonstrated extensive property tuning in terms of
varying their fundamental parameters such as HOMO-LUMO
gap and optical properties. Both parameters are tunable within
a wide range by introducing one or two ThDione acceptors,
chromophore branching, replacing the appended electron
donor, and varying the interconnecting π-system. These
Figure 8. The HOMO (red) an LUMO (blue) localizations in representative
chromophores 1b, 2b, and 3b.
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chemistry software. The set-up used for NLO measurements is given
in the Supporting Information.
structural features have influenced also their nonlinear optical
properties that were preliminarily screened by SHG and THG. All
experimental data are corroborated by DFT calculations. We
believe that this contribution will serve as useful guide for
organic and material chemists looking for new and powerful
heterocyclic acceptor moiety.
1
2
3
4
5
6
7
8
9
General Method B (Knoevenagel condensation)
The Knoevenagel condensation was carried out according to
modified procedure.[56] ThDione (100 mg, 0.66 mmol) and corre-
sponding aldehyde (0.44/0.26 mmol for mono/twofold condensa-
tion) were dissolved in CH2Cl2 (30 mL; for 1a, 2b–c, and 3a–e) or
CH3CN (30 mL; for 1b, 2a, and 2d) and piperidine (5 drops) was
Experimental Section
°
added. The reaction mixture was stirred at 25 C for 18 hours. The
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
solvent was evaporated in vacuo and the crude product was
purified by column chromatography and crystallized from CH2Cl2/
hexane mixture (2:1).
General methods
All target chromophores 1–3 are new compounds. The preparation
and characterization of ferrocene aldehydes 6b–e are given in the
Supporting Information. All commercial chemicals, reagents and
solvents were purchased from suppliers such as Sigma Aldrich, TCI,
Acros, Penta at reagent grade and were used as obtained. The dry
THF was always freshly distilled from Na/K alloy and benzophenone
under an inert atmosphere of argon. The preparations of ferrocene
aldehydes 6b–e were carried out in flame-dried flasks under argon.
Column chromatography was carried out with silica gel or alumina
and commercially available solvents. Thin-layer chromatography
(TLC) was conducted on aluminum sheets coated with SiO2 or Al2O3
(60 F254), obtained from Merck, with visualization by a UV lamp (254
or 360 nm). Melting points of 6b–e were determined by using
Büchi B-540 instrument in open capillaries. Thermal properties of all
target chromophores were measured by differential scanning
Chromophore (1a)
The title compound was prepared from DMA aldehyde 4a (66 mg)
following the general method B. Chromophore 1a was obtained as
1
a pink solid (31 mg, 25%). Rf =0.8 (SiO2; CH2Cl2/EtOAc 3:1). H-NMR
°
(500 MHz, CDCl3, 25 C): δ=3.14 (s, 6H, N(CH3)2), 6.72 (d, 2H, J=
9.0 Hz, Ph), 7.74 (s, 1H, CH), 7.84 (d, 1H, J=2.2 Hz, ThDione), 7.85 (d,
1H, J=2.2 Hz, ThDione), 8.49 ppm (d, 2H, J=9.0 Hz, Ph). 13C-NMR
°
(125 MHz, CDCl3, 25 C): δ=40.3, 111.6, 122.1, 124.1, 124.2, 131.1,
138.5, 146.0, 147.6, 149.3, 154.3, 183.6, 185.0 ppm. FT-IR (HATR): ν=
3068, 2918, 1702, 1648, 1524, 1468, 1357, 1232, 1142, 1060, 1004,
818 cmÀ 1. HR-FT-MALDI-MS (DHB) m/z calcd. for C16H14NO2S+ ([M+
H]+): 284.07398; found 284.07336 (Δ=2.18 ppm).
calorimetry with
a Mettler-Toledo STARe System DSC 2/700
equipped with FRS 6 ceramic sensor and cooling system HUBER
TC100-MT RC 23. The measurements were carried out in open
aluminous crucibles under N2 inert atmosphere. DSC curves were
Chromophore (1b)
°
determined with a scanning rate of 3 C/min within the range 25–
The title compound was prepared from DMA aldehyde 4b (77 mg)
following the general method B. Chromophore 1b was obtained as
°
400 C. Melting point and temperature of decomposition were
determined as intersection of baseline and tangent of peak (onset
a dark purple solid (89 mg, 65%). Rf =0.8 (SiO2; CH2Cl2/EtOAc 3:1).
point). H and 13C NMR spectra were recorded at 400 and 100 MHz,
1
1
°
H-NMR (500 MHz, CDCl3, 25 C): δ=3.08 (s, 6H, N(CH3)2), 6.68 (d, 2H,
respectively, with a Bruker AVANCE 400/500 instrument or 500 and
J=9.0 Hz, Ph), 7.28 (d, 1H, J=15.0 Hz, CH), 7.58 (d, 2H, J=9.0 Hz,
Ph), 7.61 (d, 1H, J=12.0 Hz, CH), 7.84 (d, 1H, J=2.2 Hz, ThDione),
125 MHz, respectively, with Bruker AscendTM 500 at 25 C. Chemical
°
shifts are reported in ppm relative to the signal of Me4Si. The
7.85 (d, 1H, J=2.2 Hz, ThDione)„ 8.24 ppm (dd, 1H, J1 = 15.0 Hz, J2
1
residual solvent signal in the H and 13C NMR spectra was used as
13
°
= 12.0 Hz Ph). C-NMR (125 MHz, CDCl3, 25 C): δ=40.4, 111.6,
an internal reference (CDCl3 7.25 and 77.23 ppm). Apparent
resonance multiplicities are described as s (singlet), d (doublet), dd
(doublet of doublet), t (triplet) and m (multiplet); the coupling
constants of multiplets (3J or 4J) are given in Hz. High resolution
MALDI MS spectra were measured on a MALDI mass spectrometer
LTQ Orbitrap XL (Thermo Fisher Scientific, Bremen, Germany)
equipped with nitrogen UV laser (337 nm, 60 Hz). The LTQ Orbitrap
instrument was operated in positive-ion mode over a normal mass
range (m/z 50–2000) with resolution 100 000 at m/z=400. The
survey crystal positioning system (survey CPS) was set for the
random choice of shot position by automatic crystal recognition.
2,5-Dihydroxybenzoic acid (DHB) was used as a matrix. Mass spectra
were averaged over the whole MS record for all measured samples.
The absorption spectra were measured on a Hewlett-Packard 8453
spectrophotometer in toluene, CH2Cl2, and DMF at c �1×10À 5 M.
The IR spectra were measured on a FT-IR Nicolet iS50 spectrometer
with a diamond ATR adapter. The electrochemical behavior of
target chromophores were investigated by cyclic voltammetry in
DMF containing 0.1 M Bu4NPF6 in a three electrode cell by cyclic
voltammetry (CV). The working electrode was glassy carbon disk
(1 mm in diameter). Leak-less Ag/AgCl electrode (SSCE) containing
filling electrolyte (3.4 M KCl) and titanium rod with a thick coating
of platinum were used as the reference and auxiliary electrodes. All
peak potentials are given vs. SSCE. Voltammetric measurements
were performed by using an integrated potentiostat system ER466
(eDAQ Europe, Warszawa, Poland) operated with EChem Electro-
119.4, 123.9, 124.2, 124.4, 131.8, 132.4, 146.6, 147.6, 148.5, 152.8,
154.4, 184.1, 184.6 ppm. FT-IR (HATR): ν=2905, 1645, 1521, 1463,
1360, 1308, 1273, 1221, 1113, 990, 758 cmÀ 1. HR-FT-MALDI-MS
(DHB) m/z calcd. for C18H16NO2S+ ([M+H]+): 310.08963; found
310.08874 (Δ=2.87 ppm).
Chromophore (2a)
The title compound was prepared from PIT aldehyde 5a (86 mg)
following the general method B. Chromophore 2a was obtained as
a gold-brown solid (48 mg, 33%). Rf =0.6 (SiO2; CH2Cl2/EtOAc 3:1).
1
°
H-NMR (400 MHz, CDCl3, 25 C): δ=1.72–1.75 (m, 6H, 3×CH2), 3.56–
3.58 (m, 4H, 2×CH2), 6.27 (d, 1H, J=4.8 Hz, Th), 7.54 (d, 1H, J=2 Hz,
Th), 7.63 (d, 1H, J=2.4 Hz, ThDione), 7.68 (d, 1H, J=2.4 Hz,
ThDione), 7.71 ppm (s, 1H, CH). C-NMR (125 MHz, CDCl3, 25 C): δ=
13
°
23.8, 25.5, 51.6, 108.0, 122.1, 122.6, 123.1, 136.9, 138.0, 146.5, 147.1,
149.8, 173.4, 184.4, 185.0 ppm. FT-IR (HATR): ν=2934, 2855, 1683,
1626, 1462, 1361, 1240, 1153, 1075, 1004, 748 cmÀ 1. HR-FT-MALDI-
MS (DHB) m/z calcd. for C17H16NO2S2 ([M+H]+): 330.06170; found
+
330.06121 (Δ=1.48 ppm).
Chromophore (2b)
The title compound was prepared from PIT aldehyde 5b (98 mg)
following the general method B. Chromophore 2b was obtained as
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a dark green-blue solid (70 mg, 45%). Rf =0.7 (SiO2; EtOAc). 1H-NMR
crystallized and then purified via column chromatography on
alumina (Al2O3; CH2Cl2/hexane 2:1). Chromophore 3b was obtained
1
2
3
4
5
6
7
8
9
°
(500 MHz, CDCl3, 25 C): δ=1.68–1.73 (m, 6H, 3×CH2), 3.40–3.42 (m,
4H, 2×CH2), 6,08 (d, 1H, J=4.5 Hz, Th), 7.20 (d, 1H, J=4.5 Hz, Th),
as a dark green solid (5 mg, 3%). Rf =0.5 (Al2O3; CH2Cl2/hexane 2:1).
1
°
7.33 (d, 1H, J=14.0 Hz, CH), 7.50 (d, 1H, J=12.5 Hz, CH), 7.72–
H-NMR (500 MHz, CDCl3, 25 C): δ=4.19 (s, 5H, Cp), 4.63–4.64 (m,
13
°
7.78 ppm (m, 3H, CH+ThDione). C-NMR (125 MHz, CDCl3, 25 C):
2H, Cp), 4.68–4.69 (m, 2H, Cp), 7.31 (d, 1H, J=15.0 Hz, CH), 7.51 (d,
δ=23.8, 25.3, 51.6, 106.3, 117.3, 122.9, 123.3, 126.3, 129,7, 139.6,
146.6, 146.7, 147.6, 147.7, 167.4, 184.5, 185.1 ppm. FT-IR (HATR): ν=
3088, 2922, 2849, 2111, 1680, 1632, 1565, 1520, 1409, 1337, 1206,
1H, J=12.0 Hz, CH), 7.88–7.98 ppm (m, 3H, CH+ThDione).13C-NMR
°
(125 MHz, CDCl3, 25 C): δ=70.0, 70.6, 73.1, 80.3, 121.7, 124.6, 124.8,
132.5, 146.5, 147.0, 147.6, 155.9, 184.0, 184.4 ppm. FT-IR (HATR): ν=
3095, 2921, 1710, 1665, 1561, 1476, 1447, 1325, 1143, 992,
762 cmÀ 1. HR-FT-MALDI-MS (DHB) m/z calcd. for C20H14FeO2S+
([M]+): 374.00584; found 374.00625 (Δ=1.10 ppm).
1059, 979, 744 cmÀ 1
. HR-FT-MALDI-MS (DHB) m/z calcd. for
+
C19H18NO2S2
0.59 ppm).
([M+H]+): 356.07735; found 356.07714 (Δ=
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Chromophore (2c)
Chromophore (3c)
The title compound was prepared from PIT aldehyde 5c (59 mg)
following the general method B. Chromophore 2c was obtained as
The title compound was prepared from Fc aldehyde 6c (63 mg)
following the general method B. Chromophore 3c was obtained as
a dark purple solid (47 mg, 37%). Rf =0.6 (SiO2; CH2Cl2/EtOAc 3:1).
a dark purple solid (89 mg, 67%). Rf =0.3 (SiO2, CH2Cl2/EtOAc 5:1).
1
1
°
°
H-NMR (500 MHz, CDCl3, 25 C): δ=1.78–1.89 (m, 6H, 3×CH2), 3.69–
H-NMR (500 MHz, CDCl3, 25 C): δ=4.78 (s, 4H, Cp), 5.43 (s, 4H, Cp),
3.71 (m, 4H, 2×CH2), 7.65 (s, 1H, Th), 7.82 (d, 1H, J=2.0 Hz,
ThDione), 7.86 (d, 1H, J=2.2 Hz, ThDione), 7.87 (s, 1H, CH), 7.92 (d,
7.32 (s, 2H, CH), 7.67 ppm (s, 4H, ThDione). 13C-NMR (125 MHz,
°
CDCl3, 25 C): δ=76.5, 78.6, 124.6, 124.7, 126.8, 134.0, 145.5, 146.5,
1H, J=2.0 Hz, ThDione), 7.95 (d, 1H, J=2.2 Hz, ThDione), 8.92 ppm
147.2, 182.1, 182.8 ppm. FT-IR (HATR): ν=3064, 1715, 1672, 1595,
13
1569, 1526, 1480, 1359, 1209, 1173, 1006, 832, 767, 485 cmÀ 1. HR-
°
(s, 1H, CH). C-NMR (125 MHz, CDCl3, 25 C): δ=23.8, 25.9, 56.8,
+
118.7, 123.3, 124.3, 124.5, 125.1, 125.3, 129.0, 131.5, 136.4, 139.2,
145.8, 146.4, 146.9, 147.4, 150.2, 178.7, 182.9, 183.6, 183.8,
183.9 ppm. FT-IR (HATR): ν=3100, 2919, 1707, 1658, 1550, 1453,
1369, 1276, 1212, 1152, 1063, 945, 755 cmÀ 1. HR-FT-MALDI-MS
FT-MALDI-MS (DHB) m/z calcd. for C26H14FeO4S2 ([M]+): 509.96774;
found 509.96881 (Δ=2.10 ppm).
(DHB) m/z calcd. for C25H18NO4S3 ([M+H]+): 492.03925; found
+
Chromophore (3d)
492.03951 (Δ=0.53 ppm).
The title compound was prepared from Fc aldehyde 6d (77 mg)
following the general method B. Chromophore 3d was obtained as
a dark green-purple solid (69 mg, 47%). Rf =0.4 (SiO2, CH2Cl2/EtOAc
Chromophore (2d)
1
°
5:1). H-NMR (400 MHz, CDCl3, 25 C): δ=4.58 (s, 4H, Fc), 4.62 (s, 4H,
The title compound was prepared from PIT aldehyde 5d (72 mg)
following the general method B. 2d is sparingly soluble in common
organic solvents which limits its purification via column chromatog-
raphy or crystallization. Chromophore 2d was obtained as a dark
purple solid (45 mg, 32%). Rf =0.6 (SiO2; CH2Cl2/EtOAc 3:1).
Although 2d provides dark colored solutions, it is sparingly soluble
Fc), 6.76 (d, 2H, J=15.0 Hz, CH). 7.30 (d, 2H, J=12.0 Hz, CH), 7.49
(dd, 2H, J1 =15.0 Hz, J2 =12.0 Hz, CH), 7.62–7.68 ppm (m, 4H,
13
°
ThDione). C-NMR (125 MHz, CDCl3, 25 C): δ=71.3, 74.1, 82.8,
123.6, 124.3, 124.4, 133.0, 146.3, 146.5, 147.3, 149.9, 183.3,
183.5 ppm. FT-IR (HATR): ν=3073, 1704, 1661, 1559, 1475, 1445,
1325, 1145, 980, 768, 486 cmÀ 1. HR-FT-MALDI-MS (DHB) m/z calcd.
1
+
in common solvents for NMR analysis. H NMR spectra showed a
for C30H18FeO4S2
1.81 ppm).
([M]+): 561.99904; found 562.00006 (Δ=
mixture of 2d and residual highly soluble impurities roll up from
baseline. Hence, the purity of 2d cannot be verified via NMR
analysis but only by using TLC. Despite this fact, the structure of 2d
was confirmed by HR-MS analysis. FT-IR (HATR): ν=3078, 2928,
Chromophore (3e)
1705, 1659, 1555, 1451, 1399, 1141, 1060, 987, 827, 760 cmÀ 1. HR-
The title compound was prepared from Fc aldehyde 6e (70 mg)
following the general method B. Chromophore 3e was obtained as
+
FT-MALDI-MS (DHB) m/z calcd. for C29H22NO4S3
544.07055; found 544.07286 (Δ=4.25 ppm).
([M+H]+):
a dark green solid (46 mg, 33%). Rf =0.5 (SiO2, CH2Cl2/EtOAc 5:1).
1
°
H-NMR (400 MHz, CDCl3, 25 C): δ=4.57–4.58 (m, 2H, Cp), 4.68–4.69
(m, 2H, Cp, 4.77–4.78 (m, 2H, Cp), 5.40 À 5.41 (m, 2H, Fc), 6.64 (d,
1H, J=15.0 Hz, CH), 7.13 (d, 1H, J=12.5 Hz, CH), 7.29 (s, 1H, CH),
7.45 (dd, 1H, J1 =15.0 Hz, J2 = 12.5 Hz, CH), 7.64 (d, 2H, J=2.2 Hz,
ThDione), 7.84 ppm (d, 2H, J=2.3 Hz, ThDione). 13C-NMR (125 MHz,
Chromophore (3a)
The title compound was prepared from Fc aldehyde 6a (94 mg)
following the general method B. Chromophore 3a was obtained as
a purple solid (60 mg, 39%). Rf =0.9 (SiO2; CH2Cl2/EtOAc 3:1). H-
1
°
CDCl3, 25 C): δ=71.2, 74.1, 76.5, 76.9, 78.9, 83.7, 122.6, 124.7, 124.8,
°
NMR (500 MHz, CDCl3, 25 C): δ=4.22 (s, 5H, Cp), 4.85–4.86 (m, 2H,
124.9, 125.3, 133.1, 133.5, 145.5, 146.0, 146.5, 146.6, 147.1, 147.3,
149.5, 182.4, 183.1, 183.2, 183.3 ppm. FT-IR (HATR): ν=3087, 1708,
1671, 1589, 1479, 1451, 1360, 1147, 991, 827, 759, 459 cmÀ 1. HR-FT-
Cp), 5.37–5.38 (m, 2H, Cp), 7.84 (s, 1H, CH), 7.89 (d, 1H, J=2.0 Hz,
ThDione), 7.91 ppm (d, 1H, J=2.0 Hz, ThDione).13C-NMR (125 MHz,
CDCl3, 25 C): δ=71.1, 75.7, 75.8, 76.4, 124.6, 124.9, 132.1, 145.9,
MALDI-MS (DHB) m/z calcd. for C28H16FeO4S2 ([M]+): 535.98339;
+
°
147.6, 151.3, 183.0, 183.7 ppm. FT-IR (HATR): ν=3109, 1715, 1665,
1590, 1526, 1478, 1355, 1207, 1000, 828, 765, 475 cmÀ 1. HR-FT-
MALDI-MS (DHB) m/z calcd. for C18H12FeO2S+ ([M]+): 347.99019;
found 347.99065 (Δ=1.32 ppm).
found 535.98439 (Δ=1.87 ppm).
Acknowledgements
Chromophore (3b)
This research was supported by the Ministry of Education, Youth
and Sports of the Czech Republic (LTAIN19101).
The title compound was prepared from Fc aldehyde 6b (106 mg)
following the general method B. The crude product was firstly
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Full Papers
doi.org/10.1002/cplu.202000395
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Keywords: diones
·
donor–acceptor
systems
·
electrochemistry · (non)linear optics · thiophenes
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Manuscript received: May 21, 2020
Revised manuscript received: July 8, 2020
Accepted manuscript online: July 9, 2020
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