Synthesis, optical and electrochemical properties of luminescent copolymers containing N-hexyl-3,8-iminodibenzyl chromophores

Novel copolymers carrying N-hexyl-3,8-iminodibenzyl chromophores have been synthesized by polycondenzation of N-hexyl-3,8-diformylminodibenzyl with 1,4-xylylene-bis(diethylphosphonate) via the Horner reaction (P1) or with 1,4-phenylenediacetonitrile via the Knoevenagel reaction (P2). The reduced viscosities of P1 and P2 are 1.17 and 0.43 dl/g, respectively. The P2 with electron-withdrawing CN groups can be dissolved in common organic solvents such as chloroform, THF, and toluene. Absorption, fluorescence, and cyclic voltammetric methods were employed to investigate their optical and electrochemical properties. The PL wavelength maxima of P1 and P2 are 494 (blue–green) and 542 nm (yellow–green), respectively. The oxidation potential of model N-hexyliminodibenzyl (1.33 V) is much smaller than that of conventional 9-hexylcarbazole (1.73 V), indicating iminodibenzyl is an effective chromophore in raising HOMO level. Comparing with P1 (HOMO: 4.96 eV, LUMO: 2.41 eV), incorporation of CN groups in P2 readily lowers the energy levels of HOMO (5.15 eV) and LUMO (2.84 eV). The energy barrier between aluminum cathode (Φ=4.3 eV) and P2 is narrowed significantly so that improved charge injection can be attained.