Poly(9,9-dihexylfluorene) derivatives containing electron-transporting aromatic triazole segments: Synthesis,optical and electrochemical properties

摘要

We prepared three new poly(9,9-dihexylfluorene) derivatives (P1-P3) containing kinked aromatic triazole (triphenyl-1,2,4-triazole derivative) via Suzuki coupling polymerization.These copolymers were soluble in common organic solvents and showed high decomposition temperatures (T_d = 416-454 deg C).The optical and electrochemical properties of P1-P3 were compared with poly(9,9-dihexylfiuorene) (PFO) and P4 and P5 in which the linkages of the aromatic triazole were different.After introducing the triazole units,absorption spectra showed blue shift (388 nm -> 372 nm) due to reduced conjugation,but PL spectra remained almost unchanged (417-418 nm).The linkages of triazole with fluorene segments in P1- P5 were different: (1) fluorene segments linked with triazole through a kinked angle (P1 and P2),(2) triazole as a branch unit (P3) and as terminal groups (P4),(3) fluorene segments linked with triazole in a linear way (P5).As estimated from semi-empirical MNDO calculation,two twisted conformations (ca.90 deg each) exist between triazole core and fluorene groups.These kinked conformation and twisted structure increased the PL efficiency (PHI_(PL) = 0.60-0.73,PHI_(PL) = 0.58 for PFO) and partially inhibited annealing-induced excimer formation.From cyclic voltammetric results,P1-P3 exhibited better electron affinity (LUMO: -2.75 to -2.82 eV) than PFO (LUMO: -2.52 eV).