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Organic Light Emitting Diode Material Process and Devices Part 3

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Tham khảo tài liệu 'organic light emitting diode material process and devices part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Synthesis and Photophysical Properties of Pyrene-Based Multiply Conjugated Shaped Light-Emitting Architectures Toward Efficient Organic-Light-Emitting Diodes 41 computed structures AM1 analysis of 49 Py 5 and 50 Py 17 revealed that the calculated dihedral angle between the core and the first branch is 65-66o for Py 5 and 71-73 for Py 17 with the angle between the first and the second branch in Py 17 around 84-89 Thus the rigid and strongly twisted 3D structure allows a precise spatial arrangement in which each unit is a chromophore. Furthermore the results on photophysical properties and molecular structure design make these dendrimers model compounds or attractive candidates for use as fluorescence labels or optoelectronics applications. 47 Py 2 48 Py 3 49 Py 5 50 Py 17 Fig. 8. Polypyrene light emitting dendrimers 47-50 . In recent years one-dimensional self-assembly of functional materials has received considerable interest in the fabrication of nanoscale optoelectronic devices Lehn 1995 . Research reports Hill et al. 2004 Kastler et al. 2004 Balakrishnan et al. 2006 suggest that the aromatic organic molecules and large macromolecules are prone to one-dimensional self-assembly through strong K-K interactions. For example the self-assembly of stiff polyphenylene dendrimers with pentafluorophenyl units has reported by Mullen group Bauer et al. 2007 in which the driving force for nanofiber formation is attribute to the increase in intermolecular K-K stacking and van der Waals interactions among dendrons by pentafluorophenyl units. On the other hand for the acetylene-linked dendrimers their stretched and planar structures may enable facial K-K stacking resulting in efficient intermolecular electronic coupling. More recently Lu and co-workers Zhao et al. 2008 reported two new solution-processable fluorinated acetylene-linked light emitting dendrimers 51a TP1 and 51b TP2 Figure 9 composed of a pyrene core and carbazole fluorene dendrons. The strong electron-withdrawing