Design,synthesis And Properties Of Nonplanar Aromatic Hydrocarbon Molecules Containing Helicene Structure

Polycyclic aromatic hydrocarbons（PAHs）have unique optoelectronic properties and are widely used in many fields such as organic light-emitting diodes,field effect transistors,fluorescent sensors,and photodetectors.Among them,the construction and application of nanographene fragments containing helicene unit have attracted much attention because the combination of chirality and graphene will undoubtedly create new functional materials.Based on the preliminary work in our lab,a series of non-planar graphene fragments with different scale and size have been constructed by using twisttetracene as the precursor,and the basic photophysical properties and potential applications were examined.The thesis is mainly divided into three parts:First,the five-membered ring embedded[n]helicene（n=5,6）derivatives 6b and 8 have been designed and synthesized,where their structures are determined NMR spectroscopy,mass spectrometry,and X-ray single crystal diffraction analyses.The single crystal analyses show that 6b and 8 contain（P₆,P₅）and（M₆,M₅）two configurations.U-vis absorption and fluorescence spectra suggest that 6b and 8 exhibit obvious red-shift compared with the precursors 5 and 7.DFT calculations show that the racemization energy barriers of 6b and 8are 40.95 kcal/mol and 40.25 kcal/mol,respectively.Subsequently,chiral separation of 6b and8 was carried out using chiral high-pressure preparative chromatography,and a pair of enantiomers of 6b was obtained.Circular dichroism（CD）and circularly polarized luminescence（CPL）tests indicate that the spectra are mirror-symmetrical,and the asymmetric luminescence factor g_lum is 8×10^-4.Intermediate 3 presents weak blue fluorescence in solution but strong green light in the solid state.Therefore,we speculate that this molecule might have an AIE response.For comparison,10,one of isomer of 3 was prepared according to the reported method.In the THF/H₂O system,the fluorescence intensity increase gradually upon addition of water,implying that AIE occurs.The electroluminescent performance of the as-prepared OLED devices using 3 and 10 as emitters will be examined in due course.Secondly,curved PAHs have unique electronic properties and usually unveil the structure and performance in organic devices.On the basis of the previous work,the seven-membered ring embedded[5]helicene 11 and 12 have been constructed.Among them,the seven-membered ring is derived from the Pd₂（dba）₃ catalyzed cyclization reaction.Single crystal X-ray diffraction analysis shows the existence of the seven-membered ring.A five-membered ring embedded[5]helicene 12 was formed through the Scholl reaction.All the novel molcules were characterized through NMR spectroscopy and mass spectrometry.Other photophysical properties are being tested.Finally,two novel phenanthro/pyrene-fused furan derivatives 17 and 21 have been designed and synthesized.Both of them emit strong blue fluorescence in dichloromethane and in the solid state.The electroluminescent devices with structures of ITO/PEDOT:PSS（40 nm）/TAPC（15 nm or 10 nm）/17 or 21（x nm）/Tm Py Pb（45 nm or 40 nm）/Li F（1 nm）/Al（100 nm）were fabricated and the results suggest that single molecule 17 or 21 can radiate white light.The CIE coordinate of device-17 and device-21 are（0.31,0.30）and（0.31,0.29）,being close to the data of the standard white light（0.33,0.33）.