Structure And Properties Of Fluorene-based Organic Functional Materials

Organic electronics appears with the development of electrical industry,and it relates to the research about organic conductors,superconductors,organic semiconductors and organic insulators.At the present time organic electronics focus on the research area of organic semiconductors,and the applications to related materials and devices have been developed rapidly.Major areas of organic semiconductors study include organic film transistors,organic electroluminescence displays,organic solar battery,organic lasers,organic sensors and organic memorizers. At present,studies on organic electronics are still in developing,and which related to electronic structure of materials,electronic transfer,energy transfer and diversion mechanism of photo-electricity are still in the exploring stage and have no acknowledged and logical theoretical model.Thiophene compounds used as filed effect channel materials have high mobility, but stability of these materials is not perfect.Polyfluorene derivatives possess good thermal stability and atoms in C9 of fluorene can be substituted easily.Therefore, preparation and characterization of a series of compounds with fluorene-thiophene groups are the goal of my dissertation,which may have high mobility and good thermal stability.At first,2,5-bis(9-hydroxyfluoren-9-yl)-[2,2']thiophene(BHFT), 2,5-bis(9-hydroxyfluoren-9-yl)-[2,2']bithiophene(BHFBT)and 2,5-bis(9-hydroxyfl uoren-9-yl)-[2,2':5',2"]trithiophene(BHFTT)were synthesized via classic Grignard Reagent Reaction and characterized by nuclear magnetic resonance,mass spectrum and elemental analysis.By using solvent evaporation,crystals of BHFBT and BHFTT were grown.The compound BFTQ was prepared through heating in the solid state, however the yield is very low and the crystal was not got.The compounds 2,5-bis(9-fluoren-9-yl)-thiophene(BFT),9-9'bisfiuorene(9-9'BF)and 9-6 bisfluorene (9-6BF)were prepared through Stille Reaction and it is difficult to purify because of many by-products.Crystals were gained by column chromatography and re-crystallization. The crystal structures were determined by single crystal X-ray diffraction method. From crystal structures of BHFBT and BHFTT we can see that the two C-OH bonds directed to the same side to each other for BHFBT but directed to opposite sides for BHFTT.The fluorenyl groups and thiophene rings constitute a "wheel and axle". There are strong intermolecular interactions in compounds.From crystal structures of 9-9'BF and 9-6BF we can see that there are strong interactions among the molecules.The UV-Vis absorption spectra and fluorescent spectra were also measured.The results show that both absorption and fluorescent bands of BHFBT and BHFTT are red-shifted compared with BHFT showing a better electronic conjugation which improves the molecular rigidity in ground and excited states.Band gaps of compounds were obtained according to the experience formula of Eg=1240/λ,which has a similar trend to the results gained from program Gaussian03.The crystal structures and optical characters indicated that compounds BHFBT and BHFTT may be semiconductors with fine performance.The absorption peak of 9-6BF is slightly red-shifted in the solution.There is a weak shoulder of 9-6BF emission bands while 9-9'BF has only two sharp peaks.The emission peaks of compounds 9-9'BF and 9-6BF with comparably strong photoluminescence are in the range of blue light,so they are expected as blue emitters.