Synthesis and Photoluminescence Studies of Siloles with Arylene Ethynylene Strands

Changhua Ding; Govindarajulu Babu; Akihiro Orita; Takayoshi Hirate; Junzo Otera

doi:10.1055/s-2007-986641

LETTER

Synthesis and Photoluminescence Studies of Siloles with Arylene Ethynylene Strands

Changhua Ding, Govindarajulu Babu, Akihiro Orita*, Takayoshi Hirate, Junzo Otera*
Department of Applied Chemistry, Okayama University of Science, Ridai-cho, Okayama 7000005, Japan
Fax: +81(86)256 4292; e-Mail: orita@high.ous.ac.jp; e-Mail: otera@high.ous.ac.jp;

Abstract

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Abstract

Siloles attached to phenylene ethynylene strands were prepared successfully by Sonogashira coupling of 2,5-dibromosilole with ethyne-terminated phenylene ethynylenes. Elongation of the arylene ethynylene chain involving up to at least three aromatic rings leads to high quantum yields in solution.

Key words

alkynes - sulfones - aldehydes - eliminations - siloles

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Referenzen

References and Notes

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UV-Vis and photofluorescence were recorded with JASCO V-560 and JASCO FP-6500 instruments at r.t., respectively. Absolute quantum yields of photofluorescence were recorded by an integration sphere system (Hamamatsu photonics C9920-02).

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Representative Experimental Procedure:
(i) Preparation of 3e: To a THF solution (40 mL) of phenyl 4-(trimethylsilylethynyl)phenylmethyl sulfone (1.57 g, 4.8 mmol) was added LiHMDS (4.8 mL, 1.0 M THF solution, 4.8 mmol) at -78 °C, and the mixture was stirred for 0.5 h. To this solution was added a THF solution (5 mL) of 2,5-diethyl-4-(4-methoxyphenylethynyl)benzaldehyde (1.16 g, 4.0 mmol), and the mixture was stirred for 1 h. After ClP(O)(OEt)₂ (0.694 mL, 4.8 mmol) had been added, the mixture was stirred at r.t. for 2 h. After LiHMDS (20.0 mL, 1.0 M THF solution, 20.0 mmol) had been added at -78 °C, the reaction mixture was stirred at -78 °C for 1 h and then at 30 °C for 17 h. After usual workup with EtOAc and aq NH₄Cl, the organic layer was dried over MgSO₄ and filtered. The solvents were evaporated, and the residue was chromatographed (CH₂Cl₂-hexane, 3:7) to give 3e (1.73 g, 94%) as a colorless solid. ¹H NMR (500 MHz, CDCl₃): δ = 0.26 (s, 9 H), 1.29 (t, J = 7.6 Hz, 6 H), 2.81-2.86 (m, 4 H), 3.82 (s, 3 H), 6.87 (d, J = 8.8 Hz, 2 H), 7.36 (s, 2 H), 7.45 (s, 4 H), 7.46 (s, 1 H), 7.48 (s, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = -0.12, 14.6, 14.7, 27.1, 27.2, 55.1, 86.9, 90.3, 93.5, 94.3, 96.2, 104.7, 114.0, 115.5, 121.7, 122.8, 123.1, 123.6, 131.2, 131.3, 131.5, 131.8, 132.9, 143.1, 143.3, 159.6. Other TMS-protected phenylene ethynylenes 3c and 3d were prepared similarly from the corresponding sulfones and aldehydes by one-shot double elimination process.^6l,m
(ii) Preparation of 4e: A 100-mL flask was charged with 3e (1.73 g, 3.76 mmol), K₂CO₃ (2.6 g, 18.8 mmol), THF (20 mL) and MeOH (20 mL). The mixture was stirred at r.t. for 2 h. After usual workup with EtOAc and aq NH₄Cl, the organic layer was dried over MgSO₄ and filtered. The solvents were evaporated, and the residue was chromatographed (CH₂Cl₂-hexane, 3:7) to give 4e (1.35g, 93%) as a colorless solid. ¹H NMR (500 MHz, CDCl₃): δ = 1.27-1.31 (m, 6 H), 2.80-2.86 (m, 4 H), 3.16 (s, 1 H), 3.77 (s, 3 H), 6.84 (d, J = 8.6 Hz, 2 H), 7.36 (s, 2 H), 7.45 (s, 5 H), 7.47 (s, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 14.6, 14.7, 27.1, 30.2, 55.2, 78.9, 83.3, 86.8, 90.3, 93.3, 94.4, 114.0, 115.4, 121.6, 121.7, 123.1, 123.9, 131.3, 131.4, 131.5, 132.0, 132.9, 143.2, 143.4, 159.6.
(iii) Preparation of 10a: A solution of lithium naph-thalenide was prepared by stirring a mixture of naphthalene (1.17 g, 9.16 mmol) and lithium (63.6 mg, 9.16 mmol) in THF (8 mL) at r.t. for 3 h. To the above lithium naph-thalenide solution, diethylbis(phenylethynyl)silane (0.66 g, 2.29 mmol) in THF (8 mL) was added over 15 min, and the mixture was stirred at r.t. for 15 min. ZnCl₂ (1.56 g, 11.4 mmol) in THF (12 mL) was added at -20 °C, and the mixture was stirred for 20 min. After N-bromosuccinimide (1.01 g, 5.72 mmol) had been added at -78 °C, the flask was shielded from light by covering with foil and stirred at -78 °C for 1 h. After usual workup with Et₂O and aq NH₄Cl, the organic layer was washed with half-saturated Na₂S₂O₃ solution, dried over MgSO₄ and filtered. The solvents were evapor-ated, and the crude dibromosilole 7 was used for the next step without further purification. To a solution of ZnCl₂ (0.625 g, 4.58 mmol) in THF (8 mL) and Et₃N (1.85 g, 18.3 mmol) were added dibromosilole 7 in THF (4 mL) and 4e (1.779 g, 4.58 mmol) in THF (4 mL). After Pd(Ph₃P)₄ (0.264 g, 0.22 mmol) had been added, the mixture was stirred at 65 °C for 13 h. After evaporation of the solvents, the residue was chromatographed (EtOAc-hexane, 1:9) to give 10a (2.82 g, 58%) as a yellow solid. ¹H NMR (500 MHz, CDCl₃)): δ = 1.13-1.31 (m, 22 H), 2.84 (m, 8 H), 3.84 (s, 6 H), 6.90 (d, J = 8.5 Hz, 4 H), 7.19-7.24 (m, 14 H), 7.36 (s, 4 H), 7.42 (d, J = 8.0 Hz, 4 H), 7.48 (d, J = 9.0 Hz, 4 H). ¹³C NMR (125 MHz, CDCl₃): δ = 2.6, 7.1, 14.6, 14.7, 27.1, 55.2, 86.8, 90.2, 92.7, 93.8, 94.2, 99.6, 114.0, 115.4, 121.8, 122.2, 122.7, 122.9, 124.2, 127.2, 127.5, 129.3, 131.2, 131.4 (2), 132.9, 137.5, 143.1, 143.3, 159.6, 162.7. ESI-MS: m/z [M + H] calcd for C₇₈H₆₇O₂Si: 1063.49; found: 1063.1.