title: Synthesis of 1,2-Bis(2-aryl-1H-indol-3-yl)ethynes via 5-exo-Digonal Double Cyclization Reactions of 1,4-Bis(2-isocyanophenyl)buta-1,3-diyne with Aryl Grignard Reagents.
abstract: New π-conjugated 1,2-bis(2-aryl-1H-indol-3-yl)ethynes 1a-j having various substituents on the two aryl groups were efficiently synthesized via unusual 5-exo-digonal double isocyanide-acetylene cyclization reactions of 1,4-bis(2-isocyanophenyl)buta-1,3-diyne 3 and aryl Grignard reagents (R-MgBr, R = C6H5(1a), 4-H3CC6H4(1b), 2-H3CC6H4(1c), 3-MeOC6H4(1d), 3-(CH3)2NC6H4(1e), 4-F3CC6H4(1f), 4-FC6H4(1g), 3-FC6H4(1h), 4-PhOC6H4(1i), and 2-Naph (1j)) in 19-85% yields. The UV-vis spectra were rationalized in detail using time-dependent DFT and single point calculations. The fluorescence emission peaks for 1a-j were observed at around 450 nm. Especially for 1f and 1j, those spectra displayed broad emission bands and relatively large Stokes shifts (3977-4503 cm-1), indicating the contribution of an intramolecular charge transfer. The absolute quantum yields (0.50-0.62) of 1a-j were higher than those of parent 8 (0.19) and 2-phenyl-1H-indole (0.11). The electrochemical features for 1a-j were investigated by cyclic voltammetry. The frontier molecular orbital levels for 1a-j were estimated based on the combination of oxidation potentials, UV-vis, and DFT calculated data. The structural property of 1,2-bis(2-phenyl-1H-indol-3-yl)ethyne 1a was characterized by several spectroscopic methods and finally determined by X-ray analysis of a single crystal of 1a recrystallized from ethyl acetate. The structural features of 1a-j were also supported by DFT calculations.
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
authors.forename: Rino
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authors.lastname: Ishikawa
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
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authors.lastname: Iwasawa
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
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authors.lastname: Takiyama
authors.affiliation: Department of Chemistry, Faculty of Science, Okayama University of Science , 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan.
authors.forename: Tomokazu
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authors.lastname: Yamauchi
authors.affiliation: Department of Chemistry, Faculty of Science, Okayama University of Science , 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan.
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authors.lastname: Iwanaga
authors.affiliation: Department of Chemistry, Faculty of Science, Okayama University of Science , 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan.
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authors.lastname: Takezaki
authors.affiliation: International Institute for Carbon-Neutral Energy Research (I2CNER), Molecular Photoconversion Devices Division, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Motonori
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authors.lastname: Watanabe
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
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authors.lastname: Teramoto
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
authors.forename: Toshiaki
authors.identifier: 0000-0002-3447-7435
authors.initials: T
authors.lastname: Shimasaki
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology , 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Shibata