Next Article in Journal
4-Methyl-7-((2-((5-methyl-1,3,4-thiadiazol-2-yl)thio)ethyl)thio)-coumarin
Previous Article in Journal
5-Chloro-6-oxo-6H-xantheno[4,3-d]thiazole-2-carbonitrile
 
 
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Short Note

2-((4-(2-Ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile

N. D. Zelinsky Institute of Organic Chemistry Russian Academy of Sciences, 47 Leninsky Prospekt, Moscow 119991, Russia
*
Author to whom correspondence should be addressed.
Molbank 2022, 2022(4), M1490; https://doi.org/10.3390/M1490
Received: 7 October 2022 / Revised: 8 November 2022 / Accepted: 9 November 2022 / Published: 11 November 2022
(This article belongs to the Section Organic Synthesis)

Abstract

:
New small acceptor–donor (A–D) molecules have been recently investigated as a component of organic solar cells. In this research, 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile was prepared from 4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole in a two-step process via Vilsmeier–Haack formylation and Knoevenagel reaction with malononitrile. The structures of newly synthesized compounds were established by means of elemental analysis, high-resolution mass spectrometry, 1H, 13C NMR, IR and UV–Vis spectroscopy, as well as mass spectrometry.

Graphical Abstract

1. Introduction

The development of the components of organic photovoltaic devices (solar cells (OSCs) and light-emitting diodes (OLEDs)) has led to a significant increase in the structural complexities of organic compounds so that their physicochemical and special properties correspond to the necessary data [1,2]. Over the past decades, the small molecules used in these photovoltaic devices have evolved from the simplest ones with the structure D-A, D-π-A, D-A-D or A-D-A to more complex ones containing several different donor and acceptor moieties in various combinations (for example, D-A1-π-A2, A-π-D-π-A, etc.) [3]. The complication of the structure of organic compounds has led to difficulties in their synthesis, high costs of starting compounds, and, ultimately, the understanding that these compounds cannot be used in final devices [4]. This is all the more surprising because one of the advantages of using organic substances has always been their cheapness [5,6]. Recently, small molecules of the acceptor–donor type (A–D) have become more actively studied to create single-component organic solar cells with a homojunction (HOSC) based on small donor–acceptor molecules [7,8]. As a rule, triphenylamine [7,8] or phenothiazine [9] groups were studied as a donor component, while dicyanovinyl moiety was most often used as an acceptor [7,8,9]. Herein, we report the synthesis of 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile as a new small molecule and study its photophysical properties.

2. Results and Discussion

The target 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1 was synthesized in two steps. The treatment of N-(2-ethylhexyl) 1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole 2 with the Vilsmeier–Haack reagent prepared in situ from POCl3 and DMF at 85 °C for 24 h resulted in the formation of 7-carbaldehyde derivative 3 (Scheme 1) as for other N-substituted 1,2,3,3a,4,8b-hexahydrocyclopenta[b]indoles [10,11]. The resulting aldehyde 3, in turn, was introduced in the Knoevenagel condensation reaction with malononitrile by refluxing the reaction mixture in toluene for 4 h. The total yield of 1 for the two steps was 55%.
The structures of 4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole-7-carbaldehyde 3 and 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1 were confirmed by means of elemental analysis, high-resolution mass spectrometry, 1H, 13C NMR, IR and UV–Vis spectroscopy, as well as mass spectrometry. Based on the 13C NMR data, compounds 1 and 3 were found to exist as mixtures of two diastereomers due to the stereocenter in the 2-ethylhexyl group (see Materials and Methods and Supplementary Materials).
We measured the optical absorption spectra for compound 1 in DMSO and compared it with the spectra of compounds containing the dicyanomethylene group [12], a similar donor framework and a rhodanine acceptor fragment (Figure 1) [13]. It was found that chromophore 1 intensely absorbs visible light, with a maximum intensity at a wavelength of 430 nm (ε = 97,028 M−1⋅cm−1). For this chromophore, an emission spectrum was also recorded; the emission band turned out to be a mirror absorption band, and its maximum was 510 nm (Stokes shift = 2038 cm–1).
Compared to the most studied analogue, 2-(4-(dimethylamino)-benzylidene)-malononitrile 4, chromophore 1 has a longer wavelength absorption maximum with a slightly higher extinction coefficient and, at the same time, a shorter wavelength emission band and, consequently, a smaller Stokes shift. This can be explained by the greater rigidity of the amino group and the absence of rotational degrees of freedom of this fragment in compound 1, in comparison with analogue 4. If we compare compound 1 with compounds containing a similar donor framework and a rhodanine acceptor fragment (5,6), compound 1 exhibits a shift, in the absorption band, to the blue region due to the lower electron-withdrawing ability of the dicyanomethylidene fragment, and the Stokes shift is slightly smaller but, at the same time, it is comparable (Table 1).

3. Materials and Methods

4-(2-Ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole 2 was prepared according to the published method [14]. The solvents and reagents were purchased from commercial sources and used as received. Elemental analysis was performed on a 2400 Elemental Analyzer (Perkin Elmer Inc., Waltham, MA, USA). 1H and 13C NMR spectra were taken with a Bruker AM-300 machine (Bruker AXS Handheld Inc., Kennewick, WA, USA) (at frequencies of 300 and 75 MHz) in CDCl3 solution, with TMS as the standard. J values are given in Hz. MS spectrum (EI, 70 eV) was obtained with a Finnigan MAT INCOS 50 instrument (Hazlet, NJ, USA). IR spectrum was measured with a Bruker “Alpha-T” instrument in KBr pellet. High-resolution MS spectrum was measured on a Bruker micrOTOF II instrument (Bruker Daltonik Gmbh, Bremen, Germany) using electrospray ionization (ESI). Solution UV–visible absorption spectra were recorded using an Agilent Cary 60 UV–Vis spectrophotometer (Agilent Technologies, Inc. Headquarters, Santa Clara, CA, USA) in standard 10 mm photometric quartz cells in HPLC-grade DMSO at a concentration of 5 × 10−6 M. Luminescence spectra were recorded using an Agilent Cary Eclipse (Agilent Technologies, Inc. Headquarters, Santa Clara, CA, USA) in HPLC-grade DMSO at a concentration of 10−6 M.
Synthesis of 4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole-7-carbaldehyde 3 (Supplementary Materials).
POCl3 (2.53 mL, 27.42 mmol) was introduced dropwise into dry DMF (15 mL) at 5 °C, and the reaction mixture was stirred at room temperature for 30 min. Then, a solution of 4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole 2 (630 mg, 2.32 mmol) in dichloroethane (15 mL) (preliminarily distilled over P2O5) was added, and the reaction mixture was kept for 24 h at 85 °C in an argon atmosphere, and then cooled, poured into cold water (50 mL) and extracted with chloroform (3 × 35 mL). The combined organic extracts were washed with brine, dried over MgSO4 and evaporated. The residue was purified by column chromatography on silica gel (Silica gel Merck 60, eluent hexane/ethyl acetate, 10:1, v/v). Yield 414 mg (60%), pale-yellow oil. Rf = 0.26 (Hexane:ethyl acetate, 10:1, v/v). 1H NMR (300 MHz, CDCl3): 9.54 (s, 1H), 7.54–7.41 (m, 2H), 6.21 (d, J = 8.6, 1H), 4.36–4.24 (m, 1H), 3.78–3.63 (m, 1H), 3.24–3.12 (m, 1H), 3.08–2.96 (m, 1H), 2.08–1.57 (m, 9H), 0.97–0.78 (m, 6H). 13C NMR (75 MHz, CDCl3, signals of the second diastereomer are given in brackets): 189.4, 157.6, 134.8, 134.1, 126.0, 124.4, 103.4, 69.3 (68.9), 49.0 (48.8), 44.7, 37.7 (37.6), 35.3, 32.6 (32.4), 31.1 (30.9), 28.9 (28.8), 24.4, 24.3 (24.1), 23.2, 14.1, 10.9 (10.8). HRMS-ESI (m/z): calcd for (C20H29NO) 300.2321, found m/z 300.2322. MS (EI, 70 eV), m/z (I, %): 299 (27), 200 (100), 172 (4), 158 (12), 143 (4), 130 (8), 57 (3), 41 (8), 29 (9), 18 (25). IR, ν, cm−1: 2957, 2929, 2860, 2729, 1672, 1602, 1511, 1455, 1327, 1229, 1163, 1100, 801, 734. UV–Vis spectrum, λmax: 358 nm (ε = 18,323 M-1cm−1). Anal. calcd for C20H29NO (300.2321): C, 80.22; H, 9.76; N, 4.68. Found: C, 80.24; H, 9.73; N, 4.72%.
Synthesis of 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1 (Supplementary Materials).
A mixture of aldehyde 3 (142 mg, 0.48 mmol), malononitrile (47 mg, 0.712 mmol), NH4OAc (55 mg, 0.712 mmol) and AcOH (1 mL) in toluene (40 mL) was refluxed with molecular sieves 4 Å (3 g) for 4 h. The reaction mixture was diluted with water (50 mL) and extracted with ethyl acetate (3 × 30 mL). The combined organic extracts were washed with a 1% sodium carbonate solution (3 × 50 mL), dried over MgSO4 and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel (Silica gel Merck 60, eluent dichloromethane/methanol, 10:1, v/v). Yield 92 mg, (55 %), dark-red oil. Rf = 0.53 (CHCl3). 1H NMR (300 MHz, CDCl3): 7.67 (1H, s), 7.43 (d, J = 8.6, 1H), 7.29 (s, 1H), 6.22 (d, J = 8.6, 1H), 4.42–4.31 (m, 1H), 3.78–3.66 (m, 1H), 3.27–3.16 (m, 1H), 3.12–3.01 (m, 1H), 2.06–1.60 (m, 6H), 1.43–1.18 (m, 9H), 0.94–0.79 (m, 6H). 13C NMR (75 MHz, CDCl3, signals of the second diastereomer are given in brackets): 157.7, 157.39, 157.36, 136.8, 135.1, 126.1, 120.2, 116.8, 115.8, 104.4, 69.4 (69.0), 48.6 (48.4), 44.5, 37.7 (37.5), 35.4, 32.1 (32.3), 31.0 (30.8), 28.9 (28.8), 24.3, 24.13 (24.07), 23.1, 14.1, 10.8 (10.7). HRMS-ESI (m/z): calcd for (C23H29N3) 348.2434, found m/z 348.2434. MS (EI, 70eV), m/z (I, %): 347 (17), 248 (100), 232 (11), 220 (15), 206 (67), 192 (8), 182 (11), 165 (7), 152 (10), 140 (12), 127 (4), 115 (3), 57 (8), 41 (17), 29 (17). IR, ν, cm−1: 2957, 2925, 2857, 2389, 2214, 1727, 1616, 1499, 1328, 1178, 1104, 805, 604. UV–Vis spectrum, λmax: 462 nm (ε = 97,028 M−1cm−1). Emission spectrum, λmax: 510 nm. Anal. calcd for C23H29N3: C, 79.50; H, 8.41; N, 12.09. Found: C, 79.54; H, 8.37; N, 12.11%.

Supplementary Materials

The following are available online: copies of 1H, 13C NMR, IR, UV-Vis, LR and HR mass spectra for compounds 1 and 3, as well as luminescence spectrum for compound 1.

Author Contributions

Conceptualization, E.A.K.; methodology, O.A.R.; software, E.A.K.; validation, O.A.R.; formal analysis, investigation, N.S.G. and K.P.T.; resources, O.A.R.; data curation, N.S.G.; writing—original draft preparation, N.S.G.; writing—review and editing, E.A.K.; visualization, N.S.G.; supervision, O.A.R.; project administration, O.A.R.; funding acquisition, O.A.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zampetti, A.; Minotto, A.; Cacialli, F. Near-Infrared (NIR) Organic Light-Emitting Diodes (OLEDs): Challenges and Opportunities. Adv. Funct. Mater. 2019, 29, 1807623. [Google Scholar] [CrossRef]
  2. Lee, C.-P.; Li, C.-T.; Ho, K.-C. Use of organic materials in dye-sensitized solar cells. Mater. Today 2017, 20, 267–283. [Google Scholar] [CrossRef]
  3. Knyazeva, E.A.; Rakitin, O.A. Influence of structural factors on the photovoltaic properties of dye-sensitized solar cells. Russ. Chem. Rev. 2016, 85, 1146–1183. [Google Scholar] [CrossRef]
  4. Zhang, Y.; Song, J.; Qu, J.; Qian, P.-C.; Wong, W.-Y. Recent progress of electronic materials based on 2,1,3-benzothiadiazole and its derivatives: Synthesis and their application in organic light-emitting diodes. Sci. China Chem. 2021, 64, 341–357. [Google Scholar] [CrossRef]
  5. van der Staaij, F.M.; van Keulen, I.M.; von Hauff, E. Organic Photovoltaics: Where Are We Headed? Sol. RRL 2021, 5, 2100167. [Google Scholar] [CrossRef]
  6. Carella, A.; Borbone, F.; Centore, R. Research Progress on Photosensitizers for DSSC. Front. Chem. 2018, 6, 481. [Google Scholar] [CrossRef] [PubMed]
  7. Nakayama, K.; Okura, T.; Okuda, Y.; Matsui, J.; Masuhara, A.; Yoshida, T.; White, M.S.; Yumusak, C.; Stadler, P.; Scharber, M.; et al. Single-Component Organic Solar Cells Based on Intramolecular Charge Transfer Photoabsorption. Materials 2021, 14, 1200. [Google Scholar] [CrossRef] [PubMed]
  8. Terenti, N.; Giurgi, G.-I.; Crişan, A.P.; Anghel, C.; Bogdan, A.; Pop, A.; Stroia, I.; Terec, A.; Szolga, L.; Grosu, I.; et al. Structure–properties of small donor–acceptor molecules for homojunction single-material organic solar cells. J. Mater. Chem. C 2022, 10, 5716–5726. [Google Scholar] [CrossRef]
  9. Slodek, A.; Zych, D.; Kotowicz, S.; Szafraniec-Gorol, G.; Zimosz, S.; Schab-Balcerzak, E.; Siwy, M.; Grzelak, J.; Maćkowski, S. “Small in size but mighty in force”—The first principle study of the impact of A/D units in A/D-phenyl-π-phenothiazine-π-dicyanovinyl systems on photophysical and optoelectronic properties. Dye. Pigment. 2021, 189, 109248. [Google Scholar] [CrossRef]
  10. Matsui, M.; Fujita, T.; Kubota, Y.; Funabiki, K.; Jin, J.; Yoshida, T.; Miura, H. Substituent effects in a double rhodanine indoline dye on performance of zinc oxide dye-sensitized solar cell. Dye. Pigment. 2010, 86, 143–148. [Google Scholar] [CrossRef]
  11. Matsui, M.; Shiota, T.; Kubota, Y.; Funabiki, K.; Jin, J.; Yoshida, T.; Higashijima, S.; Miura, H. N-(2-Alkoxyphenyl)-substituted double rhodanine indoline dyes for zinc oxide dye-sensitized solar cell. Tetrahedron 2012, 68, 4286–4291. [Google Scholar] [CrossRef]
  12. Gupta, V.K.; Singh, R.A. An investigation on single crystal growth, structural, thermal and optical properties of a series of organic D–π–A push–pull materials. RSC Adv. 2015, 5, 38591–38600. [Google Scholar] [CrossRef]
  13. Tanaka, T.; Watanabe, K.; Nomoto, T.; Okano, M.; Shintou, T.; Miyazaki, T.; Nishimura, Y.; Shimada, Y. Evaluation Probe for Central Nervous System Permeability, Evaluation Method for Central Nervous System Permeability, and Screening Method Using an Evaluation Probe for Central Nervous System Permeability. U.S. Patent 10,227,337, 12 March 2019. [Google Scholar]
  14. Tanaka, E.; Mikhailov, M.S.; Gudim, N.S.; Knyazeva, E.A.; Mikhalchenko, L.V.; Robertson, N.; Rakitin, O.A. Structural features of indoline donors in D–A-π-A type organic sensitizers for dye-sensitized solar cells. Mol. Syst. Des. Engl. 2021, 6, 730–738. [Google Scholar] [CrossRef]
Scheme 1. Synthesis of 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1.
Scheme 1. Synthesis of 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1.
Molbank 2022 m1490 sch001
Figure 1. Chromophores with a structure close to that of compound 1.
Figure 1. Chromophores with a structure close to that of compound 1.
Molbank 2022 m1490 g001
Table 1. Photophysical parameters obtained for 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1 and similar chromophores 46: absorption maximum wavelength λabs, maximum molar extinction coefficient ε, emission maximum wavelength λem and Stokes shift ∆ν.
Table 1. Photophysical parameters obtained for 2-((4-(2-ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile 1 and similar chromophores 46: absorption maximum wavelength λabs, maximum molar extinction coefficient ε, emission maximum wavelength λem and Stokes shift ∆ν.
Compoundλabs
nm
εmax
mol × 1−1 × cm−1
λem
nm
Stokes Shift ∆ν cm−1
146297,0285102038
444781,0085574418
55195922376
65175902393
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Gudim, N.S.; Knyazeva, E.A.; Trainov, K.P.; Rakitin, O.A. 2-((4-(2-Ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile. Molbank 2022, 2022, M1490. https://doi.org/10.3390/M1490

AMA Style

Gudim NS, Knyazeva EA, Trainov KP, Rakitin OA. 2-((4-(2-Ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile. Molbank. 2022; 2022(4):M1490. https://doi.org/10.3390/M1490

Chicago/Turabian Style

Gudim, Nikita S., Ekaterina A. Knyazeva, Konstantin P. Trainov, and Oleg A. Rakitin. 2022. "2-((4-(2-Ethylhexyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)methylene)malononitrile" Molbank 2022, no. 4: M1490. https://doi.org/10.3390/M1490

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop