| Life-time and luminescent efficiency are two key parameters for organic light emitting devices (OLEDs). It has been proved that the stability can be improved by substitution of hydrogen with fluorine atoms on the luminescent chromophores. Meanwhile, high luminescent efficiency can be obtained by control the formation of intermolecular aggregates. In this dissertation, we adopted a strategy, introducing a branched core in conjugation with peripheral fluorination, to realize some stable blue light-emitter with high luminescent efficiency. Three model compounds of fluorinated oligo(phenylenevinylene) molecules, trans-2,3,4,5,6-pentafluorostilbene (trans-PFS), frans-1,3,5-tri-(2,3,4,5,6-pentafluoro-styryl)benzene (trans-TPFSB) and 2,5,2',5'-Tetra(2,3,4,5,6-pentafluoro-styryl)-biphenyl (TPFSBP), were synthesized and purified. The aggregation behaviors in solutions and films, the film formation characteristics respect to these model compounds were investigated and their luminescent properties were elucidated.trans-PFS is a fundamental model of oligo(phenylenevinylene). The blueshift in the absorbance spectrum show the adjacent molecules are easy to form H-aggregates where the exciton splitting will result in luminescence quenching. Raman spectrum and XRD patterns show the spin-coated thin films are highly ordered with the molecules erecting on the substrate and this molecule orientation can be improved by substrate modification. This result is significant to the research solution processing of highly ordered thin film from conjugated organic semiconductor.trans-TPFSB is a typical model of trifurcate oligo(phenylenevinylene). The branch-like shape and the peripheral fluorine bring special mode of thin film formation. The absorbance and photo-luminescence spectra show that trans-TPFSB molecules are prone to aggregation; even in the concentration of 10-4 mol/L, the molecules aggregate predominantly and present the excitonic feature of both H and J-aggregates. However, the absorption feature observed for solid films can be ascribed to monomolecule, which means weak intermolecular interactions in the solid films. Meanwhile, the solid is a kind molecular glass with the melting point above 100℃and does not recrystallize in high temperature up to 70-centigrade degree. These properties contribute to high photo-luminescent efficiency by removal of aggregation inducing luminescence quenching. Atomic force microscopy (AFM) was utilized to study the morphology of the vacuum deposited films in different thickness. It was found that the vacuum deposition film of trans-TPFSB obeyed an island growth mode. In the nanoscale film, trans-TPFSB couldn't cover the entire surface so it is unsuitable for OLED fabrication. However, the surface exhibits a hierarchical micro-and nanostructure which bring the water-repellent property demonstrated by water contact angle measurement. This result is significant to the fabrication of water-resistant opto/electronic devices.The biphenyl core in a TPFSBP molecule bonds two fluorinated trimeric phenylenevinylene chains in a criss-cross shape, which avoids the face-to-face interaction between the two nearby chains. The photoluminescent properties of TPFSBP were investigated in comparison with a reference molecule, trans-2,5-bis(2,3,4,5,6-pentafluoro-styryl)bromobenzene (trans- BPFSB). It was found that the emission maximum of trans-BPFSB in THF solution and film was at 413nm and 489nm,respectively, while the correspondent maximum for TPFSBP was at 427 and 451 nm. These data showed that the biphenyl core effectively prevents the formation of aggregates, which lead to luminescence quenching and bathoshift of fluorescence. The spectroscopy feature of TPFSBP film shows that TPFSBP is a promising blue emitter.All these results are of fundamental significance to the long-life blue OLED with high luminescence efficiency. |
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