Synthesis and Optical Properties of a Novel Oligobipyridine
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Synthesis and Optical Properties of a Novel Oligobipyridine Y. J. Fua, T.K.S. Wonga, H.X. Zhanga, G. M. Wangb, X. Hub, Z.S. Gaoc, M.H. Jiangc a. Division of Microelectronics, School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore 639798 b. Division of Materials Technology, School of Material Engineering, Nanyang Technological University, Singapore 639798 c. State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. CHINA ABSTRACT In this paper, 5,5’ –bis [ 4’– methyl- ( 2,2’– bipyridin– 4- yl)- ethyl ]- 2,2’– bipyridine (BMBPYBPY), a partially conjugated derivative of oligobipyridine, has been synthesized and found to show strong photoluminescence (PL). Compared with the pyridine-based conjugated polymers, the shortened conjugation length shifts the emission color from green to violet-blue. The effects of morphology on its PL properties have been studied. From its as-precipitated powder state, an emission peak at 418 nm can be observed. However the emission spectra from its diffused states such as doped in KBr, or dissolved in CHCl3, as well as from its amorphous film state fabricated by vacuum evaporation are more complex. Also carried out are preliminary electroluminescent studies. Single layer devices ITO/BMBPYBPY/Al do not emit although current can be observed prominently. Double layer devices ITO/TPD/ BMBPYBPY/Al show emissions both from TPD and BMBPYBPY. INTRODUCTION Luminescent materials used in the field of organic light-emitting device (OLED) are quite different in their molecular structures, but they have some common features in electronic structures, i.e., conjugated structures in different degree. The conjugation has two roles. The first is their ability to act as antennae to absorb light in order to be excited or transfer the energy to the emitting center. The second is to act as a conductor to transport charge carriers. Conjugated polymer based OLEDs have been a topic of great interest since the report of electroluminescence (EL) in poly (phenylene vinylene) (PPV) [1]. A large variety of conjugated polymers, copolymers, and their derivatives exhibit EL properties [1-3], including PPVs, poly (phenylphenylene vinylene), polyphenylenes, polyfluorenes, polythiophenes, polyquinolines. But the long π-conjugation in conjugated polymer materials causes two difficulties. One is the difficulty in obtaining blue emitting materials and the other is in obtaining high fluorescence quantum yield, which limits the EL efficiency of the OLED. Polypyridines (PPy) [4,5], poly(pyridyl vinylenes) (PPyV) [6-8], polybipyridine (PBPy) [9] have been reported to be promising light emitting materials with good processing and electron affinity properties, but they can only emit in the green to red range. Here we report the synthesis and luminescent properties of pyridine-based partially conjugated oligomers, and propose the possibility to obtain blue emission materials by designing new partially conjugated oligomers or polymers.
C8.31.1
EXPERIMENTAL Synthesis of mater
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