A family of rigid rod-like phenylethynylene oligomers and the homologue polymer were characterized by X-ray diffraction, DSC, UV-Vis and fluorescence spectroscopy. The pentamer as well as the heptamer exhibit liquid crystal properties characterized by a strong birefringence as observed by polarized microscopy, by DSC and by the X-ray diffraction pattern, where a lamellar ordered phase with layer spacing of 2.6 nm was determined by Bragg's equation. The optical absorption and emission spectra in CHCl3 showed that the conjugation increases with the oligomer length and the limit value is reached for the polymer, although a close saturation of the ?-? conjugation is almost obtained for the heptamer. In a preliminary study, diodes were fabricated by spin coating thin films of pentamer and polymer on ITO electrodes and by subsequent vacuum deposition of aluminum cathodes. The (ITO/film/Al) devices showed intrinsic electroluminescent properties with low threshold voltage around 4 V and yielding close to 10-6. These results are interesting in view of a further study of the optoelectronic properties of the whole family of oligomers.
Dodecanoxy Phenylethynylene Oligomers For Light Emitting Diodes
E Giorgetti;
2004
Abstract
A family of rigid rod-like phenylethynylene oligomers and the homologue polymer were characterized by X-ray diffraction, DSC, UV-Vis and fluorescence spectroscopy. The pentamer as well as the heptamer exhibit liquid crystal properties characterized by a strong birefringence as observed by polarized microscopy, by DSC and by the X-ray diffraction pattern, where a lamellar ordered phase with layer spacing of 2.6 nm was determined by Bragg's equation. The optical absorption and emission spectra in CHCl3 showed that the conjugation increases with the oligomer length and the limit value is reached for the polymer, although a close saturation of the ?-? conjugation is almost obtained for the heptamer. In a preliminary study, diodes were fabricated by spin coating thin films of pentamer and polymer on ITO electrodes and by subsequent vacuum deposition of aluminum cathodes. The (ITO/film/Al) devices showed intrinsic electroluminescent properties with low threshold voltage around 4 V and yielding close to 10-6. These results are interesting in view of a further study of the optoelectronic properties of the whole family of oligomers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
