Synthesis and optical properties of two series of soluble acridine-containing copolyimides

Two series of copolyimides were designed and synthesized by one-step polycondensation of two diamines, 3,6-diaminoacridine (Acridine) and 4,4′-(9H-fluoren-9-ylidene)bisphenylamine (FBPA), with a dianhydride 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), respectively. The copolyimides were named as AFFx (Acridine-FBPA-6FDA polyimide) and AFBx (Acridine-FBPA-BTDA polyimide), respectively, where x (x = 0, 1, 3, 5 10, 15 and 20) represents the mole percentage of acridine among the sum of two diamines. Characterization of the polymers was conducted by using FT-IR, EA, GPC, TGA, DSC, UV-vis and FL techniques. The Mw and MWD of AFFx are in the range of 2.29-5.09 × 10⁴ and 1.93-2.72, respectively, as determined using GPC. AFFx could be dissolved in some low boiling point solvents such as THF, CH₂Cl₂, CHCl₃, etc. Thin AFFx films could be prepared by spin coating its CHCl₃ or THF solution onto glass. The temperature of 10% weight loss (T₁₀) for the copolyimides was above 540 °C. The emission maximum of AFFx in solution at the excitation wavelength of 480 nm was near 545 nm. And that of AFBx solution at the excitation wavelength of 390 nm was near 525 nm. UV-vis and FL spectra of the copolyimides indicated that the main chromophores in the copolyimides were acridine moieties and the excitation energy transfer from fluorene moieties to acridine moieties could take place. The copolyimides maybe a potential thermostable light-emitting material for organic light-emitting diodes.