Near Infrared Fluorescent and Phosphorescent Organic Light-Emitting Devices
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Near Infrared Fluorescent and Phosphorescent Organic Light-Emitting Devices Yixing Yang,1 Richard T. Farley,2 Timothy T. Steckler,2 Jonathan Sommer,2 Sang-Hyun Eom,1 Kenneth R. Graham,2 John R. Reynolds,2 Kirk S. Schanze,2 and Jiangeng Xue1 1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA 2 Department of Chemistry, Center for Macromolecular Science and Engineering, University of Florida, Gainesville, Florida 32611, USA ABSTRACT Organic light-emitting devices (OLEDs) emitting near-infrared (NIR) light have many potential applications, yet the efficiency of these devices remains very low, typically ~0.1% or less. Here we report efficiency NIR OLEDs based on two fluorescent donor-acceptor-donor oligomers and a phosphorescent Pt-containing organometallic complex. External quantum efficiencies in the range of 0.5-3.8% with emission peak ranging from 700 to 890 nm have been achieved. INTRODUCTION There has been a growing interest in the development of near-infrared (NIR) organic light-emitting devices (OLEDs) due to their potential applications in security and defense, biomedical devices, and telecommunications [1-3]. Existing NIR OLEDs are primarily based on lanthanide complexes [1,4-5], but they generally have very low external quantum efficiencies (EQE~0.1%) because of the inherent low efficiency of emission from these complexes. Only recently were high efficiency NIR OLEDs reported, in which peak emission at λ ≈ 770 nm and a maximum EQE up to 8.5% were achieved using a phosphorescent Pt-porphyrin complex [6]. Nonetheless, alternative materials and devices that exhibit longer wavelength (λ > 800 nm) emissions with high efficiencies are still needed. π-conjugated donor-acceptor-donor (DAD) oligomers and polymers have been extensively investigated for their tunable optoelectronic properties [7]. In these DAD molecules, it is possible to tune their energy gap by using appropriate structures of the donor and acceptor units, which control the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. By covalently combining strong donors with strong acceptors, a set of DAD oligomers and polymers with narrow HOMO-LUMO gaps have been achieved [8-9]. These oligomers have especially long wavelength absorption and efficient photoluminescence (PL), making them excellent candidates as NIR light emitting species in OLEDs. Alternatively, a family of complexes of metalloporphyrins has shown intense absorption and emission in the red-to-NIR region. High efficiencies can be achieved when they are used as the phosphorescent emitters in OLEDs [6]. By extending the conjugation of the porphyrin core, the emission can be further shifted to longer wavelengths. Here, we report NIR OLEDs based on two DAD conjugated oligomers, 4,8-bis(2,3-dihydrothieno-[3,4-b][1,4]dioxin-5-yl)benzo[1,2-c;4,5-c´]bis[1,2,5]thiadiazole
(BEDOT-BBT) and 4,9-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-6,7-dimethyl-[1,2,5] thiadiaz
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