Design, Synthesis, And Characterization Of Novel Copolymers Based On Spiro[Fluorene-9,9'-xanthene]

Polyfluorene(PF) derivatives have attracted much attention as promising materials in organic electronic devices such as light-emitting diodes(LEDs),photovoltaic ceils,and field-effect transistors(FETs) for their high quantum yields,excellent solubility and film-formation ability.However,it is difficult for PF to obtain pure and stable blue light emission due to the presence of undesirable green emission upon exposure to heat or during device operation. Two explanations have been given for the green emission:one was the formation of interchain excimers,and the other was the keto defect.The introduction of spiro structures is thought as one of the most promising solutions to the problem.However,because of the lack of convenient and efficient synthetic routes,much effort has been devoted to exploring spirobifluorene derivatives instead of other spiro compounds.Starting from the design of molecular structure,a series of novel soluble alternating conjugated copolymers,comprised of spiro[fluorene-9,9'-xanthene]and aromatic moieties, were proposed for the first time to develop new functional materials in this paper.A short, efficient one-pot synthetic route has been developed for the preparation of spiro[fluorene-9, 9'-xanthene],and Three types of novel copolymers containing benzene(PFP),biphenylene (PFDP),and thiophene(PFT) units based on spiro[fluorene-9,9'-xanthene]were synthesized. The structures and properties of the conjugated copolymers were characterized by ¹HNMR, ¹³CNMR,FT-IR,gel permeation chromatography(GPC),thermal gravimetric analysis (TGA),differential scanning calorimetry(DSC),UV-visible(UV-vis)absorption spectroscopy, and photoluminescence(PL) spectroscopy.TGA and DSC analysis revealed that the copolymers possessed good thermal stability, and the temperature at 5%weight loss of PFDP and PFT both were 422℃,the values of Tg were enhanced due to the presence of rigid,bulky spiroxanthene pendent group at C-9 position of the fluorene unit.UV-vis and PL analysis revealed that the copolymers containing benzene and biphenylene emitted blue light,the PL peaks of the two copolymers presented at 409 nm and 406nm in THF,respectively.As a consequence of the incorporation of low energy thiophene moiety,the absorption and emission spectras both exhibited a red shift.So replacing the flexible hexyl chains on the repeating fluorene units with rigid spiroxanthene pendent groups did not cause perturbation of the main chain's conjugation.