Synthesis and luminescence properties of fluorene-based copolymers containing an anthracene derivative

Abstract

We report poly{9,9’-bis-(4-octoloxy-phenyl)-fluorene-2,7-diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}s (PFAnts), containing fluorene and anthracene via Suzuki coupling. The feed ratios of Ant were 1, 5, 10, 30, and 50 mol % of the total amount of monomer. The synthesized polymers were characterized by $^1H-NMR$, $^{13}C-NMR$, elemental analysis and MALDI-TOF mass spectroscopy. The number-average molecular weights ($M_n$) of the synthesized polymers were ranged from 5,100 to 12,000 (PDI = 1.63 ~ 2.99). These polymers were thermally stable and soluble in common organic solvents such as chloroform, chlorobenzene and toluene, etc. The PL spectra of these polymers were shifted to longer wavelength with increase of portion of an anthracene derivative and they emitted various colors from sky blue to orange. Both HOMO and LUMO energy levels of PFAnts were getting lower than PBOPF as an anthracene portion increases due to the better electron accepting ability of the anthracene moiety than the fluorene moiety. The band gaps of polymers tend to get smaller because of energy transfer and aggregations. The thermal properties of these polymers were measured by TGA and DSC, and electrochemical properties were studied by cyclic voltammetry. We could control HOMO and LUMO energy levels conduced toward enhanced hole and electron charge balance. OLED devices with the configuration of ITO/PEDOT(40 nm)/polymer(60 nm)/Ca(10 nm)/Al(100 nm) were fabricated. They emitted the colors from sky blue to orange as expected in PL spectra. PFAnt05 exhibits the green light that is relatively close to the standard green for HDTV, and PFAnt30 and PFAnt50 have wide fwhm which is promising for WOLED application. PFAnt01 showed the highest maximum brightness of $1187 cd/m^2$ at 8 V, maximum current efficiency of 0.50 cd/A, and the maximum external quantum efficiency (EQE) of 0.23 %. Remarkably, the maximum current efficiency of PFAnt01 was increased twice as much of that of PBOPF.