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Synthesis 2013; 45(21): 3044-3051
DOI: 10.1055/s-0033-1339664
paper
© Georg Thieme Verlag Stuttgart · New York

T-Shaped Push–Pull Chromophores: First Modification of the Indan-1,3-dione-Fused Benzene Ring by Cross-Coupling Reactions

Parmeshwar Solanke
a   Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic   Fax: +420(46)6037068   Email: filip.bures@upce.cz
,
Filip Bureš*
a   Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic   Fax: +420(46)6037068   Email: filip.bures@upce.cz
,
Olřich Pytela
a   Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic   Fax: +420(46)6037068   Email: filip.bures@upce.cz
,
Jiří Kulhánek
a   Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic   Fax: +420(46)6037068   Email: filip.bures@upce.cz
,
Zdeňka Padělková
b   Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic
› Author Affiliations
Further Information

Publication History

Received: 04 July 2013

Accepted after revision: 01 August 2013

Publication Date:
29 August 2013 (online)

 
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Abstract

A series of eight novel T-shaped chromophores with indan-1,3-dione central acceptor moiety and peripheral N,N-dimethylamino and thiophene donors were synthesized. 4,7-Diiodoindan-1,3-dione was prepared in a straightforward manner from phthalanhydride. Its modification with donors was accomplished by Knoevenagel, Suzuki–Miyaura, and Sonogashira reactions. Target push–pull chromophores were further investigated by X-ray analysis, UV/Vis spectra, and theoretical calculations.


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Key words

chromophores - cross-coupling - conjugation - UV/Vis spectroscopy - theoretical calculations

Extended and functionalized organic aromatics can be considered as modern, tunable, and active substances for materials chemistry.[1] The presence of delocalized clouds of π-electrons determines their unique properties such as reactivity towards electrophiles, color, spectral properties, π–π interactions, crystallinity, polarizability, chemical, and thermal stability as well as their typical smell.

An attachment of an electron donor (D) and an electron acceptor (A) to a π-conjugated molecule renders them an even more interesting class of compounds, the so-called push–pull chromophores. In these molecules, D–A interaction through the π-systems causes molecule polarization and D-π-A system constitute a dipole. This direct interaction or intramolecular charge-transfer (ICT), which can be expressed by limiting resonance structures (aromatic vs quinoid arrangement), is primarily responsible for the linear as well as nonlinear optical (NLO) properties of organic D-π-A chromophores.[1] Organic push–pull molecules attract considerable attention due to their prospective and manifold applications in organic-light emitting diodes (OLEDs), organic-photovoltaic cells (OPVCs), dye-sensitizing solar cells (DSSCs), organic field effect transistors (OFETs), optical memories, etc.[2] We have recently developed a variety of (hetero)organic push–pull chromophores featuring various donors, acceptors, π-systems, and arrangements (linear, Y-shaped, X-shaped, etc.).[3] Hence, as a part of our ongoing research on NLO-active chromophores (NLOphores), we report herein a new series of indan-1,3-dione-derived push–pull systems 1–8 (Figure [1]). Indan-1,3-dione is a well known diketone, which has widely been used as terminal acceptor moiety in D-π-A chromophores.[4] The main reasons of its popularity and wide use can be attributed to i) the presence of reactive methylene and thus resulting possible modification via Knoevenagel condensation and ii) the relatively strong electron-withdrawing character, which can be further enhanced by replacement of one or both oxo groups by dicyanovinyl moieties.[5] Indan-1,3-dione-derived push–pull chromophores recently found applications as active organic layers in DSSC, OLED, and OPVC devices,[6] [7] [8] molecular glasses with NLO properties,[9] chromoionophores for anion sensing and recognition,[10] as well as in biological sciences.[11]

Zoom Image
Figure 1 Linear versus T-shaped arrangement of indan-1,3-dione-derived push–pull chromophores

In contrast to common linear indan-1,3-dione based charge-transfer chromophores known to date,4–12 the new series of compounds 1–8 possess T-shaped (D-π)3–A arrangement with indan-1,3-dione central acceptor, one N,N-dimethylamino-substituted π-linker at C2, and two peripheral donors at C4 and C7. Whereas the substituents at C2 can conveniently be introduced via Knoevenagel condensation, indan-1,3-diones disubstituted at C4 and C7 are scarce. Only methyl- and methoxy-substituted indan-1,3-diones are known to date.[11a] [13] To the best of our knowledge, no synthetic attempts were made to modify indan-1,3-dione acceptor moiety on the fused benzene ring. Hence, we report herein our synthetic strategy to target push–pull chromophores 1–8, their full spectral characterization, and further evaluation of the ICT by X-ray analysis, UV/Vis spectra, and calculations.

The obvious retrosynthetic strategy leading to chromophores 1–8 involves preparation of dihaloindan-1,3-dione and its subsequent Knoevenagel and cross-coupling reactions with appropriately donor-substituted π-linkers. Several mono- or polyhalogenated indan-1,3-dione derivatives are known,[14] but none of them has halogens appended to the C4 and C7. Considering the fact that indan-1,3-diones can conveniently be synthesized from phthalanhydrides,[11a] it was desirable to start from this readily available and inexpensive starting material. However, phthalanhydride iodinations reported to date gave generally poor regioselectivities or polyiodinated products.[15] Hence, we have attempted the iodination using modified Leznoff’s protocol originally developed for the iodination of phthalimide.[16] In contrast to 4,5-regioselectivity on phthalimide, a similar reaction on phthalanhydride afforded smoothly the desired product 9 with iodo substituents at C3 and C6 (Scheme [1]). Thus, the iodination of phthalanhydride using I2 in 25% oleum showed the same regioselectivity as its recently published bromination[17] and afforded 3,6-diiodophthalanhydride 9 in 46% yield. The conversion of 9 to 4,7-diioiodoindan-1,3-dione 10 was accomplished by reaction with ethyl acetoacetate and subsequent decarboxylation[11a] in 50% yield. The regioselective outcome of the aforementioned iodination, molecular structures, and spatial arrangements of 9 and 10 were also confirmed by X-ray analysis as can be seen from the ORTEP views in Figure [2]. Al2O3-catalyzed Knoevenagel condensation of 10 with 4-(N,N-dimethylamino)-substituted benzaldehyde and cinnam­-aldehyde afforded indan-1,3-dione derivatives 11 and 12 in good yield of 80 and 77%, respectively.

Zoom Image
Scheme 1 Synthesis of target T-shaped chromophores 1–8
Zoom Image
Figure 2 Crystal structures of compounds 9 (R = 0.03), 10 (R = 0.02) and 1 (R = 0.08); vibrational ellipsoids of the ORTEP plots are shown at the 50% probability level (150 K), molecules of solvents (CH2Cl2) were omitted for clarity.[18]

4,7-Diiodoindan-1,3-dione derivatives 11 and 12 were further treated with 4-(N,N-dimethylamino)phenylboronic acid pinacol ester,[19] 4-ethynyl-N,N-dimethylaniline, thiophen-2-ylboronic acid, and 2-ethynylthiophene[20] in terms of two-fold Suzuki–Miyaura and Sonogashira cross-coupling reactions to afford target T-shaped chromophores 1–8 in the indicated yields (Scheme [1]).

Monocrystals suitable for X-ray analysis of compounds 1, 9, and 10 were prepared by slow diffusion of hexane into their CH2Cl2 solutions. Whereas the crystal structures of compounds 9 and 10 confirm the regioselective outcome of phthalanhydride iodination, the X-ray analysis of target chromophore 1 can be used to determine the extent of the ICT (Figure [2]). The indandione moiety with appended 4-(N,N-dimethylamino)benzylidene substituent can be considered as a fully planar π-system. However, both N,N-dimethylanilino rings (DMA) at C4 and C7 are twisted out of the main chromophore plain with average torsion angles 43° and 46°. For direct DMA to benzene connections, torsion angles of 25–35° were usually observed.[3d] [e] Strong out of plain deviations of the DMA rings in 1 are most likely caused by a repulsion of the indan-1,3-dione oxygen atoms and DMA ortho hydrogens. Therefore, both DMA rings are twisted and slightly bent. A polarization of NLOphore 1 can also be assessed by evaluating the quinoid character δr of appended DMA rings.[3b] Whereas both lateral DMA ring possess δr equal to 0.031 and 0.033, the lower DMA ring has δr = 0.041 (for benzene, δr = 0; in fully quinoid structure such as benzoquinone, δr = 0.1). The difference clearly reflects the planar versus out of plane arrangements of both types of connections. Hence, the lower DMA ring contributes to the ICT more significantly.

All target compounds 1–8 are highly colored solids. Their optical properties were studied by UV/Vis absorption spectroscopy as shown in Figure [3, ]Table [1], and the Supporting Information. The spectra were measured in dichloromethane at a concentration of 1 × 10–5 M and are dominated by intensive CT-peaks appearing within the range of 486–570 nm (2.55–2.18 eV) with molar absorption coefficients ε = 31.9–87.9 × 103 M·cm–1.

Table 1 Measured and Calculated (MOPAC2012) Properties of Chromophores 1–8

Product

λmax

ε

Mp

E HOMO

E LUMO

ΔE

μ

β

γ

[nm (eV)]a

(mol–1dm3cm–1]a

(°C)

(eV)b

(eV)b

(eV)b

(D)c

(10–29 esu)d

(10–29 esu)e

1

486 (2.55)

53600

 280–283

–7.89

–0.70

–7.19

3.79

  1.70

   295

2

530 (2.34)

50100

 265–267

–7.90

–1.01

–6.89

4.46

  4.11

   527

3

503 (2.46)

87900

>400

–7.81

–0.94

–6.87

4.86

  1.63

   867

4

546 (2.27)

31900

>400

–7.83

–1.12

–6.71

5.30

  3.92

  1110

5

495 (2.51)

70500

 253–255

–8.27

–1.06

–7.21

3.98

173.9

205071

6

554 (2.23)

43100

 241–243

–8.16

–1.24

–6.92

4.96

278.5

341715

7

510 (2.43)

55400

 222–224

–8.40

–1.41

–6.99

3.86

293.9

778606

8

570 (2.18)

41700

 185–187

–8.17

–1.45

–6.72

4.99

443.5

842837

a Position (λmax) and molar absorption coefficient (ε) of the longest-wavelength absorption maxima (measured in CH2Cl2, c = 1 × 10–5 M).

b Calculated energies of HOMO and LUMO and their differences ΔE (gap).

c Calculated ground state permanent dipole moment μ.

d Calculated first hyperpolarizability β.

e Calculated second hyperpolarizability γ.

Zoom Image
Figure 3 UV/Vis absorption spectra of chromophores 1–8 measured in dichloromethane (c = 1 × 10–5 M)

The positions of the longest-wavelength absorption maxima (λmax) are obviously dependent on the π-system length, terminal acceptor used (DMA vs thienyl) and chromophore overall planarity. The influence of the π-system length and planarity can be demonstrated on chromophores 1–4 in which the π-spacer was systematically extended by olefinic and acetylenic subunits. This extension shifted the λmax by 60 nm. Chromophore 4, which possesses the longest π-system with one additional double bond (cinnamaldehyde moiety at C2) and two acetylenic subunit separating lateral DMA donors, showed the most bathochromically shifted CT-band at 564 nm. On the contrary, chromophore 1 without additional olefinic and acetylenic units showed significant out of plain twist (see the X-ray data discussion above), which caused hypsochromic shift of the CT band to 486 nm. A similar trend can be seen in the chromophore series 5–8 with thienyl lateral donors. However, a comparison of both series allowed evaluation of donating nature of both moieties. A comparison of λmax values across the structural analogues 1/5, 2/6, 3/7 and 4/8 revealed bathochromic shift with Δλmax 9, 24, 7, and 24 nm for thienyl-substituted chromophores 5–8. These changes are remarkably pronounced for chromophores 6 and 8 with the cinnamaldehyde moiety at C2. Chromophore 8 with indan-1,3-dione acceptor core functionalized by one 4-(N,N-dimethylamino)cinnamaldehyde moiety combined with two lateral thienyl donors linked through ethynyl spacers showed the most bathochromically shifted CT band up to 570 nm.

A comparison of the longest-wavelength absorption maxima of target compounds 1–8 (λmax = 486–570 nm) with diiodo-substituted molecules 11 of (λmax = 502 nm; SI) and 12 (λmax = 562 nm; SI) clearly demonstrates, that the lower DMA rings appended to C2 contribute more significantly to the ICT. This is in agreement with the aforementioned conclusions deduced from the X-ray data. Hence, the lateral donors appended at C4 and C7 can be denoted as auxiliary.

Electronic properties such as HOMO and LUMO energies, ground state permanent dipole moment μ and first and second hyperpolarizabilities β and γ were calculated and visualized for the most stable conformers using PM3 (ArgusLab),[21] PM7 (MOPAC2012),[22] and OPchem.[23] The acquired data are summarized in Table [1]. Visualizations of the HOMO and LUMO for representative chromophores 1, 4, 6 and 8 are shown in Figure [4] (for complete listing, see the Supporting Information).

Zoom Image
Figure 4 Optimized geometries and HOMO (red) and LUMO (blue) localizations in representative chromophores 1, 4, 6, and 8

As expected, the HOMO is generally localized on the donor moieties while the LUMO is spread over the indan-1,3-dione and C2-appended part of the π-system. The optimized geometries of 1 and 4 (Figure [1]) confirmed the difference in anchoring the lateral DMA groups through sigma or triple bonds (compare with Figure [2]). The latter connection caused planarization of the entire π-system. In contrast to DMA, directly appended thiophene rings were less twisted from indan-1,3-dione plain (average torsion angles 22–28°). However, planarization of the π-system through an additional ethynylene unit as in 7 and 8 resulted in extension of the LUMO over the indan-1,3-dione-fused benzene ring.

The calculated HOMO/LUMO energies and their respective differences ΔE reflect the same trends as seen by the absorption spectroscopy. Thus, the π-system extension and molecule planarization led to lowered HOMO-LUMO gap. The lowest ΔΕ values and highest dipole moments were calculated for planar molecules 4 (ΔΕ = –6.71 eV; μ = 5.30 D) and 8 (ΔΕ = –6.72 eV; μ = 4.99 D) featuring the largest π-system.

The calculated first and second hyperpolarizabilities β and γ were affected by similar structural features as the aforementioned properties. The values in Table [1] clearly demonstrates that, within the particular series 1–4 and 5–8, both hyperpolarizabilities increase with the π-system extension and planarization. For instance, a simple replacement of 4-(N,N-dimethylamino)benzaldehyde moiety in 1 with its cinnamaldehyde derivative as in 2 resulted in doubling of their hyperpolarizabities β (1.7 vs 4.11 × 10–29 esu) and γ (295 vs 527 × 10–29 esu). However, the most dramatic changes were caused by replacing the lateral DMA donor groups with thiophene rings. Such relatively small structural modification resulted in a hundred-fold increase of the calculated first hyperpolarizabilities β! The second hyperpolarizabilites γ increased even in three orders of magnitude. Although the auxiliary electron-donating ability and high polarizability of thiophene ring are well known,[24] [25] such dramatic increase is remarkable. Hence, T-shaped push–pull chromophores 1–8, which can be prepared from readily available phthalic anhydride in a four step synthesis, proved to be very promising candidates for further elaboration and application as active layers in optoelectronic devices.

Reagents and solvents were reagent-grade and were purchased from Penta, Aldrich, and Acros and used as received. Column chromatography was carried out with silica gel 60 (particle size 0.040–0.063 mm, 230–400 mesh; Merck) and commercially available solvents. TLC was conducted on aluminum sheets coated with silica gel 60 F254 obtained from Merck, with visualization by UV lamp (254 or 360 nm). Melting points were measured on a Büchi B-540 melting point apparatus in open capillaries and are uncorrected. 1H and 13C NMR spectra were recorded in CDCl3 at 400 MHz and 100 MHz, respectively, with a Bruker Avance 400 instruments at 25 °C. Chemical shifts are reported in ppm relative to the signal of Me4Si. The residual solvent signal in the 1H and 13C NMR spectra was used as an internal reference (CDCl3: 7.25 and 77.23 ppm). Coupling constants (J) are given in Hz. Standard abbreviations are used for indicating signal multiplicities. Quaternary carbons of compound 11 were not observed due to its sparing solubility in deuterated solvents. EI-MS spectra were measured on a GC/MS configuration comprised of an Agilent Technologies – 6890N gas chromatograph (HP-5MS column, length 30 m, I.D. 0.25 mm, film 0.25 μm) equipped with a 5973 Network MS detector (EI 70 eV, mass range 33−550 Da). 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 50–1500) with the following setting of tuning parameters: resolution 100,000 at m/z = 400, laser energy 17 mJ, number of laser shots 5, respectively. The survey crystal positioning system (survey CPS) was set for the random choice of shot position by automatic crystal recognition. The isolation width Δm/z 4, normalized collision energy 25%, activation Q value 0.250, activation time 30 ms and helium as the collision gas were used for CID experiments in LTQ linear ion trap. The used matrix was 2,5-dihydroxybenzoic acid (DHB). Mass spectra were averaged over the whole MS record (30 s) for all measured samples. IR spectra were recorded as neat using HATR adapter on a PerkinElmer FTIR Spectrum BX spectrometer. UV/Vis spectra were recorded on a HP LE2201 spectrophotometer in CH2Cl2 (c = 1 × 10–5 M). Elemental analyses were performed on an EA 1108 Fisons instrument.


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3,6-Diiodophthalanhydride (9)

Into a solution of phthalic anhydride (14.80 g, 100.0 mmol) in fuming H2SO4 (60 mL, 25%) was added I2 (50.8 g, 200.0 mmol) and the reaction mixture was stirred at 70 °C for 24 h. The mixture was poured over crushed ice (400 g), the precipitate was collected by filtration and washed with H2O (2 × 100 mL), 2% aq Na2CO3 (1 × 100 mL), sat. aq Na2S2O3 (1 × 100 mL), and H2O (1 × 100 mL) and dried on air. The crude product was extracted with CH2Cl2 (3 × 200 mL), the combined organic extracts were dried (Na2SO4), and evaporated to afford the title compound 9 as an off-white solid (18.4 g, 46%); mp 229–233 °C; Rf  = 0.7 (CH2Cl2–hexane, 2:1).

IR (HATR): 3627, 2998, 1716, 1501, 1393, 1213, 1186, 1135, 905, 836, 743 cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.91 (s, 2 H, 2 × CH).

13C NMR (100 MHz, CDCl3): δ = 91.3, 134.3, 147.45, 159.7.

MS (EI, 70 eV): m/z (%) = 400 (100, [M]+), 356 (45), 229 (49), 201 (54), 127 (11), 74 (44).


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4,7-Diiodoindan-1,3-dione (10)

Into a solution of 3,6-diiodophthalanhydride 9 (4.0 g, 10.0 mmol) in Ac2O (10 mL) and Et3N (5.5 mL) was added ethyl acetoacetate (1.52 mL, 12.0 mmol) and the reaction mixture was stirred at 25 °C for 24 h. Crushed ice (20 g) and 35% aq HCl (10 mL) were added with stirring and the precipitate was collected by filtration. The resulting solid was treated with hot (70–80 °C) 10% aq HCl (900 mL) to assure complete decarboxylation. The title compound 10 was obtained as a light-yellow solid (2.0 g, 50%); mp 180–183 °C; Rf  = 0.4 (CH2Cl2–hexane, 2:1).

IR (HATR): 3647, 3006, 1732, 1502, 1184, 1134, 1087, 909, 764 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.33 (s, 2 H, CH2), 7.88 (s, 2 H, 2 × CH).

13C NMR (100 MHz, CDCl3): δ = 44.8, 89.0, 143.8, 147.7, 193.7.

MS (EI, 70 eV): m/z (%) = 398 (100, [M]+), 370 (10), 342 (8), 229 (20), 215 (14), 201 (23), 74 (19).

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C9H5I2O2: 398.8373; found: 398.8371.


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Knoevenagel Condensation Reactions of 1,3-Dione 10; General Procedure

4,7-Diiodoindan-1,3-dione (10; 3.98 g, 10.0 mmol) and 4-(N,N-dimethylamino)benzaldehyde (1.57 g, 10.5 mmol) or 4-(N,N-dimethylamino)cinnamaldehyde (1.84 g, 10.5 mmol) were dissolved in CH2Cl2 (20 mL). Al2O3 (5.1 g, 50.0 mmol, activity II–III) was added and the reaction mixture was stirred at 25 °C for 3 h. Al2O3 was filtered off, the solvent was evaporated in vacuo, and the crude product was purified by column chromatography (SiO2; CH2Cl2–hexane, 1:1).


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2-[4-(N,N-Dimethylamino)benzylidene]-4,7-diiodoindan-1,3-dione (11)

The title compound was prepared from 4-(N,N-dimethylamino)benzaldehyde following the general procedure (4.2 g, 80%); orange solid; mp 228–230 °C; Rf  = 0.5 (CH2Cl2–hexane, 2:1).

IR (HATR): 3627, 3009, 1716, 1494, 1386, 1184, 1135, 1087, 907, 789 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.17 [s, 6 H, N(CH3)2], 6.74 (d, J = 9.6 Hz, 2 H, 2 × CH), 7.73–7.78 (m, 2 H, 2 × CH), 7.82 (s, 1 H, CH=), 8.54 (br s, 1 H, CH), 8.57 (br s, 1H, CH).

13C NMR (100 MHz, CDCl3): δ = 40.4, 88.3, 88.4, 111.8, 122.3, 139.0, 146.0, 146.5, 149.7 (signals of six Cq are missing).

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C18H14I2NO2: 529.9108; found: 529.9106.

UV/Vis (CH2Cl2): λmax (log ε) = 502 (4.80), 279 (4.04), 229 nm (4.33).


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2-{(2E)-3-[4-(N,N-Dimethylamino)phenyl]prop-2-en-1-ylidene}-4,7-diiodoindan-1,3-dione (12)

The title compound was prepared from 4-(N,N-dimethylamino)cinnamaldehyde following the general procedure (4.3 g, 77%); dark metallic solid; mp 277–281 °C; Rf  = 0.5 (CH2Cl2–hexane, 2:1).

IR (HATR): 3625, 2918, 1732, 1506, 1384, 1210, 1185, 1136, 1087, 907, 812, 624 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.12 [s, 6 H, N(CH3)2], 6.67 (d, J = 8.8 Hz, 2 H, 2 × CH), 7.38 (d, J = 14.8 Hz, 1 H, CH=), 7.61 (d, J = 8.8 Hz, 2 H, 2 × CH), 7.68 (d, J = 12.0 Hz, 1 H, CH=), 7.74 (s, 1 H, CH), 7.75 (s, 1 H, CH), 8.31 (dd, J 1 = 14.8 Hz, J 2 = 12.0 Hz, 1 H, CH=).

13C NMR (100 MHz, CDCl3): δ = 40.4, 88.1, 88.5, 112.1, 119.7, 121.9, 123.8, 132.3, 142.0, 146.2, 146.3, 149.0, 153.3, 156.2, 157.7, 187.8, 190.0.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C20H16I2NO2: 555.9265; found: 555.9257.

UV/Vis (CH2Cl2): λmax (log ε) = 562 (4.80), 338 (4.03), 232 nm (4.36).


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Suzuki–Miyaura Reactions of 11 and 12; General Procedure

Diiodo derivatives 11 (265 mg, 0.5 mmol) or 12 (278 mg, 0.5 mmol) and 4-(N,N-dimethylamino)phenylboronic acid pinacol ester (272 mg, 1.1 mmol) or thiophen-2-ylboronic acid (141 mg, 1.1 mmol) were dissolved in a mixture of THF–H2O (20 mL, 4:1). Argon was bubbled through the solution for 15 min whereupon [PdCl2(PPh3)2] (18 mg, 0.025 mmol) and Na2CO3 (159 mg, 1.5 mmol) were added and the reaction mixture was stirred at 60 °C for 3 h. The reaction mixture was diluted with H2O (50 mL) and extracted with CH2Cl2 (2 × 50 mL). The combined organic extracts were dried (Na2SO4), the solvents were evaporated in vacuo, and the crude product was purified by column chromatography (SiO2; indicated solvent system).


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2-[4-(N,N-Dimethylamino)benzylidene]-4,7-bis[4-(N,N-dimethylamino)phenyl]indan-1,3-dione (1)

The title compound was prepared from 11 and 4-(N,N-dimethylamino)phenylboronic acid pinacol ester following the general procedure (211 mg, 82%); orange solid; mp 280–283 °C; Rf  = 0.1 (CH2Cl2–hexane, 2:1).

IR (HATR): 3115, 2920, 1658, 1548, 1516, 1340, 1170, 1108, 1018, 812, 624 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.03 [s, 6 H, N(CH3)2], 3.05 [s, 6 H, N(CH3)2], 3.08 [s, 6 H, N(CH3)2], 6.65 (d, J = 8.8 Hz, 2 H, 2 × CH), 6.83 (d, J = 8.8 Hz, 4 H, 4 × CH), 7.49–7.59 (m, 6 H, 6 × CH), 7.69 (s, 1 H, CH=), 8.45 (s, 1 H, CH), 8.47 (s, 1 H, CH).

13C NMR (100 MHz, CDCl3): δ = 40.2, 40.6, 40.7, 111.4, 111.8, 122.4, 124.3, 125.8, 126.1, 130.7, 135.9, 136.4, 136.7, 138.0, 138.5, 139.2, 146.5, 150.3, 150.5, 153.7, 189.5, 191.1.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C34H34N3O2: 516.2646; found: 516.2642.

UV/Vis (CH2Cl2): λmax (log ε) = 256 (4.46), 307 (4.38), 486 nm (4.73).

Anal. Calcd for C34H33N3O2: C, 79.19; H, 6.45; N, 8.15. Found: C, 79.12; H, 6.49; N, 8.20.


#

2-{(2E)-3-[4-(N,N-Dimethylamino)phenyl]prop-2-en-1-ylidene}-4,7-bis[4-(N,N-dimethylamino)phenyl]indan-1,3-dione (2)

The title compound was prepared from 12 and 4-(N,N-dimethylamino)phenylboronic acid pinacol ester following the general procedure (163 mg, 60%); dark metallic solid; mp 265–267 °C; Rf  = 0.1 (CH2Cl2–hexane, 2:1).

IR (HATR): 3318, 2904, 1642, 1537, 1419, 1313, 1156, 1101, 1019, 810 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.03 [s, 12 H, 2 × N(CH3)2], 3.05 [s, 6 H, N(CH3)2], 6.62 (d, J = 8.4 Hz, 2 H, 2 × CH), 6.83 (t, J = 9.2 Hz, 4 H, 4 × CH), 7.18 (d, J = 14.8 Hz, 1 H, CH=), 7.45–7.59 (m, 9 H, 6 × CH + 2 × CH + CH=), 8.24 (dd, J 1 = 14.8 Hz, J 2 = 12.4 Hz, 1 H, CH=).

13C NMR (100 MHz, CDCl3): δ = 40.3, 40.6, 40.7, 111.8, 111.9, 120.0, 124.1, 125.5, 125.6, 125.8, 130.7, 130.7, 131.2, 136.1, 136.6, 137.1, 138.5, 139.2, 139.4, 145.5, 150.4, 150.5, 152.3, 152.6, 190.3, 190.8.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C36H36N3O2: 542.2802; found: 542.2791.

UV/Vis (CH2Cl2): λmax (log ε) = 253 (4.52), 320 (4.47), 530 nm (4.70).

Anal. Calcd for C36H35N3O2: C, 79.82; H, 6.51; N, 7.76. Found: C, 79.59; H, 6.47; N, 7.68.


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2-[4-(N,N-Dimethylamino)benzylidene]-4,7-bis(thiophen-2-yl)indan-1,3-dione (5)

The title compound was prepared from 11 and thiophen-2-ylboronic acid following the general procedure (66 mg, 30%); dark red solid; mp 253–255 °C; Rf  = 0.2 (CH2Cl2–hexane, 1:1).

IR (HATR): 3295, 2905, 1653, 1532, 1382, 1320, 1247, 1158, 1105, 1034, 989, 699 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.11 [s, 6 H, N(CH3)2], 6.68 (d, J = 9.2 Hz, 2 H, 2 × CH), 7.15–7.19 (m, 2 Hthiophene), 7.46 (t, J = 5.0 Hz, 2 Hthiophene), 7.56 (d, J = 4.0 Hz, 1 Hthiophene), 7.67 (d, J = 4.0 Hz, 1 Hthiophene), 7.67–7.74 (m, 3 H, 2 × CH + CH=), 8.46 (s, 1 H, CH), 8.48 (s, 1 H, CH).

13C NMR (100 MHz, CDCl3): δ = 40.3, 111.6, 122.3, 123.0, 127.0, 127.2, 127.5, 127.6, 129.3, 129.7, 132.2, 132.3, 136.1, 136.6, 137.0, 138.5, 138.8, 139.0, 139.1, 147.9, 154.2, 188.7, 190.4.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C26H20NO2S2: 442.0930; found: 442.0930.

UV/Vis (CH2Cl2): λmax (log ε) = 242 (4.46), 286 (4.40), 364 (3.88), 495 nm (4.85).

Anal. Calcd for C26H19NO2S2: C, 70.72; H, 4.34; N, 3.17. Found: C, 70.59; H, 4.29; N, 3.13.


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2-{(2E)-3-[4-(N,N-Dimethylamino)phenyl]prop-2-en-1-ylidene}-4,7-bis(thiophen-2-yl)indan-1,3-dione (6)

The title compound was prepared from 12 and thiophen-2-ylboronic acid following the general procedure (175 mg, 75%); dark brown solid; mp 241–243 °C; Rf  = 0.2 (CH2Cl2–hexane, 1:1).

IR (HATR): 3610, 2929, 1741, 1542, 1369, 1180, 964, 676 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.05 [s, 6 H, N(CH3)2], 6.63 (d, J = 9.0 Hz, 2 H, 2 × CH), 7.15–7.20 (m, 2 Hthiophene), 7.24 (d, J = 15.0 Hz, 1 H, CH=), 7.45–7.48 (m, 2 Hthiophene), 7.54–7.58 (m, 4 H, 2 × CH + thiophene + CH=), 7.66–7.74 (m, 3 H, thiophene + CH + CH), 8.22 (dd, J 1 = 15.0 Hz, J 2 = 12.3 Hz, 1 H, CH=).

13C NMR (100 MHz, CDCl3): δ = 40.3, 112.0, 119.8, 124.0, 124.2, 127.1, 127.3, 127.5, 127.6, 129.3, 129.7, 131.7, 132.1, 132.5, 136.3, 136.9, 137.2, 138.7, 138.8, 138.9, 147.0, 152.7, 154.3, 189.5, 190.1.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C28H22NO2S2: 468.1086; found: 468.1088.

UV/Vis (CH2Cl2): λmax (log ε) = 245 (4.45), 295 (4.36), 554 nm (4.63).

Anal. Calcd for C28H21NO2S2: C, 71.92; H, 4.53; N, 3.00. Found: C, 72.22; H, 4.48; N, 3.04.


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Sonogashira Reactions of 11 and 12; General Procedure

Diiodo derivatives 11 (265 mg, 0.5 mmol) or 12 (278 mg, 0.5 mmol) and 4-ethynyl-N,N-dimethylaniline (160 mg, 1.1 mmol) or 2-ethynylthiophene (119 mg, 1.1 mmol) were dissolved in a mixture of THF–Et3N (20 mL, 4:1). Argon was bubbled through the solution for 15 min whereupon [PdCl2(PPh3)2] (18 mg, 0.025 mmol) and CuI (10 mg, 0.05 mmol) were added and the reaction mixture was stirred at 60 °C for 3 h. The reaction mixture was diluted with H2O (50 mL) and extracted with CH2Cl2 (2 × 50 mL). The combined organic extracts were dried (Na2SO4), the solvents were evaporated in vacuo, and the crude product was purified by column chromatography (SiO2; indicated solvent system).


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2-[4-(N,N-Dimethylamino)benzylidene]-4,7-bis{[4-(N,N-dimethylamino)phenyl]ethynyl}indan-1,3-dione (3)

The title compound was prepared from 11 and 4-ethynyl-N,N-dimethylaniline following the general procedure (132 mg, 47%); dark metallic solid; mp >400 °C; Rf  = 0.2 (CH2Cl2–hexane, 2:1).

IR (HATR): 3346, 2884, 1697, 1540, 1362, 1338, 1310, 1159, 1101, 1030, 642 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.01 [s, 6 H, N(CH3)2], 3.02 [s, 6 H, N(CH3)2], 3.13 [s, 6 H, N(CH3)2], 6.66–6.75 (m, 6 H, 6 × CH), 7.58–7.65 (m, 6 H, 6 × CH), 7.78 (s, 1 H, CH=), 8.57 (s, 1 H, CH), 8.59 (s, 1 H, CH).

13C NMR (100 MHz, CDCl3): δ = 40.3, 40.3, 40.4, 86.1, 86.2, 99.1, 99.5, 109.8, 110.0, 111.6, 111.9, 112.1, 118.9, 119.0, 122.5, 123.5, 131.5, 133.8, 136.6, 137.5, 138.3, 139.0, 141.1, 147.2, 150.7, 150.8, 154.0, 188.3, 190.1.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C38H34N3O2: 564.2646; found: 564.2636.

UV/Vis (CH2Cl2): λmax (log ε) = 273 (4.52), 358 (4.62), 503 nm (4.94).

Anal. Calcd for C38H33N3O2: C, 80.97; H, 5.90; N, 7.45. Found: C, 80.78; H, 5.98; N, 7.47.


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2-{(2E)-3-[4-(N,N-Dimethylamino)phenyl]prop-2-en-1-ylidene}-4,7-bis{[4-(N,N-dimethylamino)phenyl]ethynyl}indan-1,3-dione (4)

The title compound was prepared from 12 and 4-ethynyl-N,N-dimethylaniline following the general procedure (221 mg, 75%); dark metallic solid; mp >400 °C; Rf  = 0.2 (CH2Cl2–hexane, 2:1).

IR (HATR): 3732, 2924, 1716, 1522, 1362, 1338, 1227, 1156, 1055, 943, 812, 641 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.00 [s, 6 H, N(CH3)2], 3.01 [s, 6 H, N(CH3)2], 3.06 [s, 6 H, N(CH3)2], 6.65–6.67 (m, 6 H, 6 × CH), 7.26 (d, J = 15.0 Hz, 1 H, CH=), 7.57–7.64 (m, 9 H, 6 × CH + 2 × CH + CH=), 8.33 (dd, J 1 = 15.0 Hz, J 2 = 12.2 Hz, 1 H, CH=).

13C NMR (100 MHz, CDCl3): δ = 40.3, 40.4, 40.5, 86.0, 86.1, 99.3, 99.6, 109.7, 109.8, 111.9, 112.0, 118.8, 119.1, 120.0, 124.1, 124.8, 131.5, 133.7, 136.8, 137.4, 139.7, 140.9, 146.2, 150.7, 150.8, 152.5, 153.4, 189.2, 189.6.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C40H36N3O2: 590.2802; found: 590.2797.

UV/Vis (CH2Cl2): λmax (log ε) = 279 (4.40), 361 (4.40), 546 nm (4.50).

Anal. Calcd for C40H35N3O2: C, 81.47; H, 5.98; N, 7.13. Found: C, 82.05; H, 5.87; N, 7.09.


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2-[4-(N,N-Dimethylamino)benzylidene]-4,7-bis[(thiophen-2-yl)ethynyl]indan-1,3-dione (7)

The title compound was prepared from 11 and 2-ethynylthiophene following the general procedure (78 mg, 32%); dark metallic solid; mp 222–224 °C; Rf  = 0.1 (CH2Cl2–hexane, 1:1).

IR (HATR): 3724, 2915, 1660, 1514, 1392, 1180, 1138, 968, 693 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.14 [s, 6 H, N(CH3)2], 6.73 (d, J = 9.2 Hz, 2 H, 2 × CH), 7.05–7.08 (m, 2 Hthiophene), 7.39 (d, J = 5.2 Hz, 2 Hthiophene), 7.47 (d, J = 4.0 Hz, 1 Hthiophene), 7.49 (d, J = 4.0 Hz, 1 Hthiophene), 7.67–7.73 (m, 2 H, 2 × CH), 7.80 (s, 1 H, CH=), 8.55 (s, 1 H, CH), 8.57 (s, 1 H, CH).

13C NMR (100 MHz, CDCl3): δ = 40.3, 90.7, 90.9, 90.9, 91.0, 111.7, 118.4, 118.5, 122.4, 122.7, 123.0, 123.1, 127.5, 127.6, 128.8, 129.0, 133.5, 133.6, 136.6, 137.5, 138.6, 139.4, 141.5, 148.1, 154.3, 187.8, 189.6.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C30H20NO2S2: 490.0930; found: 490.0925.

UV/Vis (CH2Cl2): λmax (log ε) = 292 (4.41), 320 (4.42), 405 (4.35), 510 nm (4.74).

Anal. Calcd for C30H19NO2S2: C, 73.60; H, 3.91; N, 2.86. Found: C, 73.59; H, 3.89; N, 2.79.


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2-{(2E)-3-[4-(N,N-Dimethylamino)phenyl]prop-2-en-1-ylidene}-4,7-bis[(thiophen-2-yl)ethynyl]indan-1,3-dione (8)

The title compound was prepared from 12 and 2-ethynylthiophene following the general procedure (139 mg, 54%); dark metallic solid; mp 185–187 °C; Rf  = 0.1 (CH2Cl2–hexane, 1:1).

IR (HATR): 3630, 3006, 1688, 1510, 1182, 1136, 1087, 911, 813, 642 cm–1.

1H NMR (400 MHz, CDCl3): δ = 3.06 [s, 6 H, N(CH3)2], 6.65 (d, J = 9.0 Hz, 2 H, 2 × CH), 7.04–7.08 (m, 2 Hthiophene), 7.28 (d, J = 15.0 Hz, 1 H, CH=), 7.37–7.40 (m, 2 Hthiophene), 7.46 (d, J = 4.0 Hz, 1 Hthiophene), 7.50 (d, J = 4.0 Hz, 1 Hthiophene), 7.58 (d, J = 9.0 Hz, 2 H, 2 × CH), 7.64 (d, J = 12.2 Hz, 1 H, CH=), 7.68 (s, 1 H, CH), 7.69 (s, 1 H, CH), 8.30 (dd, J 1 = 15.0 Hz, J 2 = 12.2 Hz, 1 H, CH=).

13C NMR (100 MHz, CDCl3): δ = 40.3, 90.7, 90.8, 90.9, 91.0, 112.0, 118.3, 118.6, 119.8, 123.0, 123.9, 127.5, 127.6, 128.9, 129.0, 131.8, 133.5, 133.6, 136.8, 137.4, 140.1, 141.3, 147.2, 152.8, 154.6, 188.6, 189.0.

HR-MALDI-MS (DHB): m/z [M + H]+ calcd for C32H22NO2S2: 516.1086; found: 516.1084.

UV/Vis (CH2Cl2): λmax (log ε) = 246 (4.38), 334 (4.50), 420 (4.21), 570 nm (4.62).

Anal. Calcd for C32H21NO2S2: C, 74.54; H, 4.11; N, 2.72. Found: C, 74.35; H, 4.20; N, 2.71.


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Acknowledgment

This research was supported by the Czech Science Foundation (P106/12/0392).

Supporting Information

    for this article is available online at http://www.thieme-connect.com.accesdistant.sorbonne-universite.fr/ejournals/toc/synthesis.
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Zoom Image
Figure 1 Linear versus T-shaped arrangement of indan-1,3-dione-derived push–pull chromophores
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Scheme 1 Synthesis of target T-shaped chromophores 1–8
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Figure 2 Crystal structures of compounds 9 (R = 0.03), 10 (R = 0.02) and 1 (R = 0.08); vibrational ellipsoids of the ORTEP plots are shown at the 50% probability level (150 K), molecules of solvents (CH2Cl2) were omitted for clarity.[18]
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Figure 3 UV/Vis absorption spectra of chromophores 1–8 measured in dichloromethane (c = 1 × 10–5 M)
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Figure 4 Optimized geometries and HOMO (red) and LUMO (blue) localizations in representative chromophores 1, 4, 6, and 8