Optical and Electroluminescent Properties of Novel Poly(aryl ether)s with Isolated Carbazole and p-Quaterphenyl Fluorophores

We report the optical and electroluminescent properties of four novel poly(aryl ether)s (P1-P4) consisting of alternate isolated hole-transporting [carbazole or 3,6-bis(styryl)carbazole] and electron-transporting [dicyano-p-quaterphenyl or bis(trifluoromethyl)-p-quaterphenyl] fluorophores. The photoluminescence (PL) spectra of the four polymeric films show maximum peaks around 407-413 nm for PI, P2 and 442-447 nm for P3, P4. The PL spectra of P1-P4 are dependent on the composition of the two isolated fluorophores. According to the observation of relative quantum yield in poor solvent (cyclohexane), P2 containing more bulky trifluoromethyl groups in p-quaterphenyl segments prevented aggregate quenching processes more than P1. Compared with P1 and P2 with carbazole segments, P3 and P4 with 3,6-bis(styryl)carbazole segments exhibited less interchain interaction and a low threshold electric field in a single-layer device. The p-quaterphenyl and carbazole [or 3,6-bis(styryl)carbazole] segments were regarded as electron-transporting and hole-transporting units, respectively, in the single-layer light-emitting diodes (Al/P1-P4/ITO). In the double-layer device (ITO/MEH-PPV/P2/Al), the maximum luminance was doubled, and the threshold electric fields diminished because P2 functioned as an electron-transporting and hole-blocking layer. Furthermore, the voltage-tunable multicolor emission from orange to green was observed.