Synthesis, characterization and device application of a novel blue-emitting copolymer incorporating fluorene and benzothiazole backbone units

Abstract

Utilizing benzothiazole (BTz) combined with fluorene as backbone units, we designed and synthesized a novel blue-emitting copolymer poly[(9,9-dioctyl-9H-fluorene)-alt-(2-heptylbenzo[d]thiazole)] (PF-BTz). PF-BTz shows excellent thermal stability with the 5% weight-loss decomposition temperature above 410 °C. According to the molecular geometry analyzed by density functional theory (DFT) calculations, PF-BTz should possess clearly twisted backbone and weak molecule coplanarity. The photophysical properties of PF-BTz were discussed, and particularly the photoluminescence (PL) spectra of PF-BTz in solution and film both display the blue emission with peaks wavelength of 420 nm and 429 nm, respectively. Then the polymer light-emitting diodes (PLEDs) was fabricated by using PF-BTz as emitting layer, and the PF-BTz-based device also shows the blue emission with CIEx,y of (0.23, 0.25) and a maximal luminous efficiency (LEmax) of 0.25 cd/A. The results indicate that the PF-BTz copolymer incorporating fluorene and benzothiazole backbone units would be a promising blue emitter for high-performance PLEDs.