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Synlett 2006(17): 2841-2845  
DOI: 10.1055/s-2006-950266
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis and Optical Properties of Starburst Carbazoles Based on 9-Phenylcarbazole Core

Guo-Liang Fenga, Shun-Jun Ji*a, Wen-Yong Laib, Wei Huang*b,c,d
a Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering, Suzhou (Soochow) University, Hengyi Road, Suzhou Industrial Park, Suzhou 215123, P. R. of China
Fax: +86(512)65880089; e-Mail: shunjun@suda.edu.cn;
b Institute of Advanced Materials (IAM), Fudan University, 220 Handan Road, Shanghai 200433, P. R. of China
c Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, 66 XinMoFan Road, Nanjing 210003, P. R. of China
d Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Republic of Singapore
Fax: +86(25)83492349; e-Mail: wei-huang@njupt.edu.cn;
Further Information

Publication History

Received 25 May 2006
Publication Date:
09 October 2006 (online)

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Abstract

New well-defined starburst carbazole derivatives, which contain N-phenylcarbazole as the central core joining 9-hexylcarbazole or 9-phenylcarbazole as arms, are presented. All these compounds were obtained via Suzuki cross-coupling in moderate yields. Their structures were confirmed by 1H NMR, MALDI-TOF mass spectrometry and elementary analysis. Moreover, the fluorescence spectra showed that these compounds exhibited good blue fluorescence with the maximum wavelengths ranging from 410 nm to 430 nm.

Key words

carbazole - starburst - boronic acids - Suzuki cross-coupling - fluorescence

8

Synthesis of Compounds 9 and 11; Typical Procedure
To a solution of the corresponding 3-bromocarbazole derivatives 6 or 7 (10 mmol) in anhyd THF (50 mL) was slowly added n-BuLi (2.5 M in hexane, 4.8 mL, 12.0 mmol) at -78 °C. At this temperature, the reaction mixture was stirred for 1 h before adding triisopropyl borate (3.5 mL, 15.0 mmol). The mixture was allowed to warm to r.t. for
15 h. It was quenched with HCl (2.0 M, 40 mL) and poured into a large amount of water. After extraction with Et2O (3 × 20 mL), the organic portions were washed with brine before drying over anhyd MgSO4 and the solvent was evaporated to afford the crude carbazoleboronic acids. The crude product was purified by column chromatography on a silica gel column, eluting with PE and EtOAc (2:1) to afford carbazoleboronic acids, which were then dried in vacuo at 35 °C.
Compound 9: 1H NMR (400 MHz, CDCl3): δ = 8.54 (s, 1 H), 8.34-8.38 (m, 2 H), 8.12 (d, J = 8.0 Hz, 1 H), 7.78-7.82 (m, 3 H), 7.60 (s, 1 H), 7.25-7.48 (m, 6 H), 4.34-4.39 (m, 4 H), 1.90-1.98 (m, 4 H), 1.20-1.46 (m, 12 H), 0.88-0.90 (m, 6 H).
Compound 11: 1H NMR (400 MHz, CDCl3): δ = 8.60 (s, 1 H), 8.36-8.40 (m, 2 H), 8.07-8.14 (m, 2 H), 7.80-7.86 (m, 2 H), 7.58-7.70 (m, 4 H), 7.28-7.50 (m, 12 H).

9

Synthesis of Starburst Compounds 12-15; General Procedure
To a degassed (N2) solution of 9-(4-bromophenyl)-3,6-dibromocarbazole (1; 1.0 g, 2.1 mmol) and Pd(PPh3)4 catalyst (0.5 g, 0.44 mmol, 7 mol% per C-Br bond) in toluene (30 mL), a solution of carbazoleboronic acid (9.45 mmol) in toluene (20 mL) and a 2 M aq K2CO3 solution (13 mL) were added via syringe. The reaction mixture was stirred at 80 °C for 48 h. After cooling, the product was extracted with CH2Cl2, washed with water and dried over MgSO4. The solvent was evaporated to afford the crude mixture. After column chromatography on silica gel, eluting with PE and CH2Cl2 (5:1), pure compounds 12-15 were obtained. All the compounds were fully characterized. The analytical and spectral data for these compounds follow:
Compound 12: 1H NMR (400 MHz, CDCl3): δ = 8.58 (s, 2 H), 8.46 (d, J = 7.6 Hz, 3 H), 8.21 (d, J = 7.6 Hz, 3 H), 8.01 (d, J = 7.4 Hz, 2 H), 7.78-7.88 (m, 6 H), 7.65 (d, J = 7.4 Hz, 2 H), 7.43-7.56 (m, 7 H), 7.25-7.30 (m, 6 H), 4.32-4.39 (m, 6 H), 1.89-1.92 (m, 6 H), 1.28-1.37 (m, 18 H), 0.87-0.91 (m, 9 H). Anal. Calcd for C72H70N4: C, 87.23; H, 7.12; N, 5.65. Found: C, 87.30; H, 7.27; N, 5.60. MS (MALDI-TOF): m/z [M+] calcd for C72H70N4: 991; found: 991.
Compound 13: 1H NMR (400 MHz, CDCl3): δ = 8.60 (s, 2 H), 8.52 (d, J = 7.6 Hz, 3 H), 8.26 (d, J = 7.6 Hz, 3 H), 8.02 (d, J = 7.4 Hz, 2 H), 7.76-7.86 (m, 6 H), 7.63-7.68 (m, 12 H), 7.44-7.57 (m, 12 H), 7.25-7.36 (m, 6 H). Anal. Calcd for C72H46N4: C, 89.41; H, 4.79; N, 5.79. Found: C, 89.23; H, 4.82; N, 5.43. MS (MALDI-TOF): m/z [M+] calcd for C72H46N4: 967; found: 967.
Compound 14: 1H NMR (400 MHz, CDCl3): δ = 8.63 (s, 2 H), 8.54-8.57 (m, 6 H), 8.45 (s, 3 H), 8.17-8.20 (m, 3 H), 8.04 (d, J = 7.4 Hz, 2 H), 7.79-7.90 (m, 10 H), 7.67 (d, J = 7.4 Hz, 2 H), 7.25-7.49 (m, 15 H), 7.20-7.23 (m, 6 H), 4.3-4.4 (m, 12 H), 1.82-1.97 (m, 12 H), 1.25-1.56 (m, 36 H), 0.84-0.92 (m, 18 H). Anal. Calcd for C126H127N7: C, 87.00; H, 7.36; N, 5.64. Found: C, 87.15; H, 7.13; N, 5.80. MS (MALDI-TOF): m/z [M+] calcd for C126H127N7: 1739; found: 1739.
Compound 15: 1H NMR (400 MHz, CDCl3): δ = 8.64 (s, 2 H), 8.58-8.62 (m, 6 H), 8.50 (s, 3 H), 8.22-8.23 (m, 3 H), 8.05 (d, J = 7.4 Hz, 2 H), 7.78-7.88 (m, 12 H), 7.39-7.67 (m, 42 H), 7.24-7.26 (m, 9 H). Anal. Calcd for C126H79N7: C, 89.49; H, 4.71; N, 5.80. Found: C, 89.32; H, 4.49; N, 5.94. MS (MALDI-TOF): m/z [M+] calcd for C126H79N7: 1691; found: 1691.