Cite this: RSC Advances, 2013, 3, 9381 Spirally configured cis-stilbene/fluorene hybrids as ambipolar, fluorescent materials for organic light emitting diode applications3 Received 5th April 2013, Accepted 25th April 2013 DOI: 10.1039/c3ra41642a www.rsc.org/advances Chien-Tien Chen,* a Wei-Shan Chao, b Hao-Wei Liu, a Yi Wei, a Jwo-Huei Jou* c and Sudhir Kumar c A new class of cis-stilbene/fluorene spiro hybrid systems with paired diphenylamino donor and cyano, N-phenylbenzimidazole, dimesitylboranyl, or b,b-diphenylethenyl acceptor units was synthesized as ambipolar materials for organic light-emitting diode applications. When coupled with hole transporting 4,49-bis(1-naphthylphenylamino)-1,19-biphenyl (a-NPB) and electron transporting 2,29,299-(1,3,5-benzene- triyl)-tris(1-phenyl-1-H-benzimidazole) layers, they served as one of the best bluish green and pure green emitting layers with excellent external quantum efficiencies of 3.9–5.2%, electroluminescent brightness of 2202–3069 cd m 22 , luminance efficiencies of 11.0–15.8 cd A 21 , and power efficiencies of 5.7–6.6 lm W 21 at 20 mA cm 22 , which were about 2–3 times better than those based on standard a-NPB/tris(8- hydroxyquinoline)aluminum bilayer devices. 1. Introduction Organic light-emitting diodes (OLEDs) have attracted con- siderable attention for potential applications in next genera- tion flat panel displays and solid-state lighting sources. 1 Molecular designs of linearly donor–(p-spacer)–acceptor con- jugated templates were often adopted in nonlinear optics, 2 OLED, 3 dye-sensitized solar cell, 4 and organic photovoltaic cell 5 advancement. In the aspect of materials designs for OLEDs, integrating electron-transporting (ET) and hole-trans- porting (HT) components into molecular scaffolds may effectively improve OLED device performance in view of enhanced balance in charge transports of both carriers. 3 In terms of p-spacer selection, oligo-fluorene, -aryl 6 and -styryl templates were often preferred. When combined with diaryla- mine donors (D), the acceptor (A) segments benzimidazole, 1,3,4-oxadiazole, 1,2,4-triazole, and quinoxaline were often adopted. So far the D–(p-spacer)–A conjugated templates based on these scenarios 7–10 have been explored with significant success including several attempts towards single-layered devices. 11 As part of our on-going researches on the uses of dibenzosuber- ene (DBE) and iminostilbene (IMS) templates as chirochromic optical switches 12 and OLED applications, we have pioneered on the development of spirally configured, N-anthryl-dipheny- lamines and 9,9-diphenyl-fluorenes bearing doubly ortho- linked quinoxaline units derived from these two templates (Scheme 1). They served as highly efficient ambipolar materials with tunable, panchromatic emission colors. 13 We have subsequently developed spirally configured, cis- stilbene/fluorene hybrids (STIF) with diarylamino capping groups at both C3 and C7 positions (D = A = NAr 2 in Scheme 2). They served as highly efficient hole-transporting type, sky blue emitting OLED materials. 14 We therefore sought to extend the utility of STIF template towards ambipolar optoelectronic materials by appending diphenylamino donor and various different acceptor groups at C3 and C7 positions, respectively. a Department of Chemistry, National Tsing Hua University, #101, Sec 2, Kuang-Fu Rd., Hsinchu, Taiwan b Department of Chemistry, National Taiwan Normal University, #88, See.4, Ding-jou Road, Taipei 11677, Taiwan c Department of Materials Science and Engineering, National Tsing Hua University, #101, Sec 2, Kuang-Fu Rd., Hsinchu, Taiwan E-mail: ctchen@mx.nthu.edu.tw; jjou@mx.nthu.edu.tw 3 Electronic supplementary information (ESI) available: Experimental procedures, characterization and NMR spectra for all compounds. CCDC 876488–876491, 880009–880010. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3ra41642a Scheme 1 Quinoxaline-fused IMS and DBE ambipolar materials. RSC Advances PAPER This journal is ß The Royal Society of Chemistry 2013 RSC Adv., 2013, 3, 9381–9390 | 9381