Fluorene-based conjugated poly(azomethine)s: Synthesis, photophysical properties, and theoretical electronic structures

摘要

Soluble conjugated poly(azomethine)s, PFI and PFCI, were synthesized from 2,7-diformyl-9,9'-dioetylfluorene (DFOF) with diamines. The replacement of the fluorene (PFI) by carbazole (PFCI) reduces the ionization potential but enhances the band gap (E-g) due to the kink disorder introduced by the 3,6-carbazole. The optical absorption or photoluminescence of the synthesized PFI or PFCI is sensitive to good/poor solvent ratio, acid environment, or metal ions. The variation of the planarity on the polymer backbone and intermolecular charge transfer explain the above spectral tuning by chemical species. The theoretical results based on the density functional theory (DFT) suggest that the PFI and PFCI show a non-coplanar conformation due to steric repulsion force between the adjacent hydrogen atoms. It could be resolved by replacing the fluorene or carbazole ring by thiophene (PFTI) or 3,4-ethylenedioxythiophene (PFEI). The coplanar geometry and possible intramolecular charge transfer lead to the E-g of 2.17 and 2.03 eV for the PFTI and PFEI, respectively. The smaller effective mass of the PFTI or PFEI also indicates that both polymers could be p-type semiconductors for organic electronics.