Fluorene-based conjugated poly(arylene ethynylene)s containing heteroaromatic bicycles: preparation and electro-optical properties
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A series of high molecular weight fluorene-based soluble poly(arylene ethynylene)s (PAEs) have been prepared and characterized. The polymers consist of 2,5-bis(3-tetradecylthiophen-2-yl)-3a,6a-dihydrothieno[3,2-b]thiophene, 2,5-bis(3-tetradecylthiophen-2-yl)-3a,6a-dihydrothiazolo[5,4-d]thiazole, or 4,7-bis(3-tetradecylthiophen-2-yl)benzo[c] [1, 2, 5] thiadiazole unit with an electron donor 9,9-bis(2-ethylhexyl)-9H-fluorene unit connected via electron accepting ethynylene linkage. The molecular weights (M w) of the polymers were found to be in the range of 103600–179000 g/mol with polydispersity index (PDI) of 3.9–5.0. Optical and redox properties have been investigated by UV–visible, fluorescence spectroscopy, and cyclic voltammetry (CV) measurements. Combination of experimental and density functional theory (DFT) calculations indicated that the benzothiadiazole unit incorporated polymer has lowest band gap with most stable lowest unoccupied molecular orbital (LUMO) energy level. Polymer light emitting diode properties have been investigated for the polymer having highest molecular weight with device configuration ITO/PEDOT:PSS/Polymer/LiF/Al. Well-behaved diode characteristics with EL maxima at 600 nm were observed.
KeywordsHigh Occupied Molecular Orbital Lower Unoccupied Molecular Orbital Lower Unoccupied Molecular Orbital Energy Benzothiadiazole Lower Unoccupied Molecular Orbital Energy Level
The authors thank M. N. Kamalasanan and R. Srivastava from NPL, New Delhi for their help in PLED device fabrication and characterization. The authors would also like to thank Professor Seungmoon Pyo, Konkuk University, Seoul, Republic of Korea and Professor Soonmin Jang, Sejong University, Seoul, Republic of Korea for their help in DFT calculations.
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