Synthesis of carbazole derivatives with high quantum yield and high glass transition temperature Xiqi Zhang a , Zhenguo Chi a,b, * , Zhiyong Yang a , Meina Chen a , Bingjia Xu a , Lin Zhou a , Chengcheng Wang a , Yi Zhang a,b , Siwei Liu a,b , Jiarui Xu a,b, * a PCFM Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China b DSAPM Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China article info Article history: Received 24 April 2009 Received in revised form 16 June 2009 Accepted 17 June 2009 Available online 16 July 2009 PACS: 78.55.Kz Keywords: Carbazole derivatives High glass transition temperature High quantum yield abstract A series of fluorescent compounds derived from carbazole were synthesized via the Wittig–Horner reac- tion. The compounds had high glass transition temperatures (T g ), in the region of 172–232 °C, and high decomposition temperatures (T d ), ranging from 456 to 491 °C. The derivatives showed very high fluores- cence efficiency in solution, with fluorescence quantum yields in the range of 0.88–1.00. The substituent effects on fluorescence emission differed between solution and solid state. In dichloromethane solutions, the substituents had only a minimal effect on the maximum emission wavelength of the compounds with the same bridge. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction During the past few years, the synthesis and application of car- bazole derivatives has been of great interest to chemists and mate- rials scientists, due to their well-known semiconducting properties and excellent thermal properties [1–8]. Adachi et al. [9,10] reported that 4,4 0 -bis[(N-carbazole)styryl]biphenyl (BSB-Cz) exhibited 100% fluorescence efficiency and a very low amplified spontaneous emis- sion threshold. However, the glass transition temperature (T g ) of BSB-Cz is only ca. 113 °C, which is not yet adequate for application purposes. It is well-known that a fluorescence compound possess- ing both high fluorescence efficiency and high T g is essential for a high-performance device. In this report, we describe the synthesis and characterization of five new carbazole derivatives, which pos- sess both a high T g and high fluorescence efficiency. 2. Experimental 2.1. Materials and methods All reagents and chemicals purchased from Alfa Aesar were used as received. Analytical grade DMF was purified by distillation under an inert nitrogen atmosphere. Tetrahydrofuran (THF) was distilled from sodium/benzophenone. Ultra-pure water was used in the experiments. All other solvents were purchased as analytical grade from Guangzhou Dongzheng Company and used without further purification. 4-(9H-carbazol-9-yl)benzaldehyde (CBA) was prepared according to literature procedure [11]. 1 H NMR was mea- sured on a Mercury-Plus 300 spectrometer with chemical shifts re- ported as ppm (in CDCl 3 , TMS as internal standard). Mass spectra were measured with Thermo spectrometers (MAT95XP-HRMS and DSQ-MS). Elemental analysis was done with an Elementar Var- io EL Elemental Analyzer. Fluorescence spectra were determined with a Shimadzu RF-5301PC spectrometer and the slit width was 3 nm for both excitation and emission. The fluorescence quantum yields (/ FL ) were measured by the standard optically diluted meth- od [12] in degassed CH 2 Cl 2 solutions (ca. 10 À5 M) using 9,10- diphenylanthracene (/ FL = 0.90, in CH 2 Cl 2 ) as a reference standard [13,14]. Differential scanning calorimetry (DSC) curves were ob- tained with a TA thermal analyzer (Q10) at a heating rate of 10 °C/min under a N 2 atmosphere. Thermogravimetric analyses (TGA) were performed with a TA thermal analyzer (A50) under a N 2 atmosphere with a heating rate of 20 °C/min. 2.2. Synthesis of 4-(3,6-dibromo-9H-carbazol-9-yl)benzaldehyde (BCBA) To a stirred CBA (5.7 g, 21 mmol) in anhydrous DMF (100 mL) in ice water bath, NBS (11 g, 62 mmol) was added to avoid light under 0925-3467/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2009.06.009 * Corresponding authors. Address: PCFM Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China. E-mail addresses: chizhg@mail.sysu.edu.cn (Z. Chi), xjr@mail.sysu.edu.cn (J. Xu). Optical Materials 32 (2009) 94–98 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat