From Langmuir-Blodgett Films to Electroluminescent Devices with an Amphiphilic Phenyl-Ethynylene Oligomer
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. In the present work we report on the physical properties of Langmuir-Blodgett films of phenyl ethynylene oligomers (oPYn). These oligomers, bearing a single side chain per phenyl ring as an alkyl-hydroxylic ester group, are enough amphiphilic to give stable Langmuir films. It allows producing multilayer films by transfer from the water surface to different hydrophilic substrates such as glass, ITO or silicon. We demonstrate that the LB deposition technique applied to amphiphilic oligo-phenyethynylenes can be successfully developed to the preparation of light emitting devices. EXPERIMENTAL The pentamer and heptamer, hereafter named oPY5 and oPY7 respectively, were synthesized according to a protecting general route already used for the oligophenyle ethynyle derivatives 10. The detailed chemical routes will be published elsewhere19. (oPY5): recrystallized in MeOH, Mp 91-94°C; 1H NMR (200 MHz, CDCl3): δ(ppm) 8.24(s, 1H, -PhH), 8.18(s, 4H, -PhH), 8.04(dt, 2H, -PhH), 7.76(dt, 2H, -PhH), 7.67(s, 6H, -PhH), 7.45(t, 2H, -PhH), 4.38(m, 10H, -COOCH2-), 3.63(m, 10H, -CH2OH) 1.80 (m, 10H, -CH2-β-COO), 1.54(m, 10H, -CH2-β-OH), 1.31(m, 70H, -CH2-); Anal. Calcd (%) for C98H132O15: C, 75.93; H, 8.58; O, 15.48. Found: C, 75.31; H, 8.55; O, 15.12. (oPY7): recrystallized in MeOH, Mp 104-107ºC; 1H NMR (200 MHz, CDCl3): δ(ppm) 8.24(s, 1H, -PhH), 8.18(s, 6H, -PhH), 8.04(dt, 2H, -PhH), 7.76(dt, 2H, -PhH), 7.68(s, 10H, -PhH), 7.46(t, 2H, -PhH), 4.38(m, 14H, -COOCH2-), 3.63(m, 14H, -CH2 OH), 1.80(m, 14H, -CH2-β-COO), 1.54(m, 14H, -CH2-β-OH), 1.31(m, 98H, -CH2. Anal. Calcd (%) for C138H184O21: C, 76.06; H, 8.51; O, 15.41. Found: C, 75.73; H, 8.58; O, 15.18. Langmuir film data were collected with a KSV LB5000® system using a symmetrical compression Teflon® trough and hydrophobic barriers in a clean dust free environment. The Wilhelmy plate method (platinium) was used for surface pressure measurements, the monolayer and preassembled bilayer were compressed with a typical speed of 0.1 to 0.3 nm2/ (molecule.min). Isotherms were reproducible from run to run and showed no noticeable hysteresis. LB films were obtained by transfer on glass slides, ITO or hydrophilic silicon wafers (100) at surface pressures ranging from 15-16 mNm-1. Transfers started from below the surface, with a typical emersion speed of 1-5 mm/min. The grazing incidence X-ray studies of LB films were performed on a X'PERT-MPD device from Philips. All measurements have been recorded immediately after the LB transfer. Data were analyzed by using GIXA (V2.1) software from Phillips Electronics Instruments. The AFM measurements were carried out with a Nanoscope III Dimension 3100 microscope from Digital Instruments operating at ambient atmosphere. The images were recorded at room temperature using the tapping mode. Electroluminescent diodes were prepared as described previously 17 on a patterned ITO (15 Ω/¨) coated glass. Multilayers of oPY7 LB-films were directly deposited on top of the ITO coated glass. Films were subsequently dried 12 h in a 10-7 mb-vacuum. 1 nm-LiF and 5
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