Synthesis and electroluminescent properties of π-conjugated copolymer based on 10-hexylphenothiazine and aromatic 1,2,4-triazole

A new polymer, poly((10-hexyl-3,7-phenothiazine)-alt-(4-(4-butyl-phenyl)-3,5-diphenyl-4H-[1,2,4]triazole)-3,5-diyl) (PT-TAZ), has been synthesized. In order to improve electron injection/transporting ability, we introduce electronegative 1,2,4-triazole group in the backbone. We also synthesized poly(10-hexylphenothiazine-3,7-diyl) (PT) to compare the physical properties with PT-TAZ. The photoluminescence (PL) maximum wavelength, the band gap energy, and the HOMO energy level of PT-TAZ film were 509 nm, 2.67 eV, and −5.06 eV, respectively, which are very comparable to those of PT. The maximum efficiency and brightness of the electroluminescent (EL) device based on PT-TAZ were 0.247 cd/A and 771 cd/m2, respectively, which were significantly higher than those of the device based on the polymer without 1,2,4-triazole (TAZ) as a repeat unit (PT) (1.05 × 10−4 cd/A and 4.4 cd/m2). This is because TAZ unit improves the electron transporting ability in the emissive layer. The turn-on voltage of brightness of the device based on PT-TAZ was 5.0 V, which was slightly higher than that of the based on PT (4.5 V). This is because the ionization potential of PT-TAZ is very similar to that of PT.