Statistical Copolymers for Blue-Light-Emitting Diodes

Abstract

Fluorene-based statistical copolymers with m- and p-divinylbenzene were synthesized by the Heck reaction to fabricate blue-light-emitting diodes (LEDs). Photoluminescence (PL) spectra of the copolymers showed the maximum at 475 nm regardless of the concentration ratios between m- and p-divinylbenzene to reveal the complete energy transfer from the chromophore with the meta unit to the fluorophore of the para unit while 100% of the meta unit exhibited the emission maximum at 430 nm. The highest PL intensity was obtained with the ratio of 7/3 between the meta and para units. However, the time-resolved picosecond fluorescence study on the polymer solution revealed that the intramolecular energy transfer alone in the copolymers was incomplete to suppress the emission at 430 nm. The electroluminescence (EL) center of the copolymers was the same as that of the PL to show the maximum at 475 nm. The highest quantum efficiency of a single-layered LED fabricated with the light emissive copolymer with 30% of the para unit was observed to be 0.04%, which would be improved by optimization of the device characteristics.

Enhanced light output in bilayer light-emitting diodes with film thickness variations

“…Co., and PDHFPPV, the emitting polymeric material, was synthesized according to the reported synthesis scheme [14]. The EL devices with PVK/ PDHFPPV bilayer were prepared according to the following method.…”

Effect of meta-linkages on the photoluminescence and electroluminescence properties of light-emitting polyfluorene alternating copolymers

“…The film was then annealed in air for 24 h, as done for the measurement of the photoluminescence spectra. Over this period, and beyond, a peak at 1740 cm 21 emerges which can be attributed to the n(CLO) stretching frequency of a fluorenone group (Fig. 6).…”

“…19 Clearly, the introduction of meta linkages will influence both the electron delocalisation and the degree of order of fluorene-based and other light-emitting polymers. This has been investigated previously for poly(9,9-dihexylfluorenealt-1,3-phenylenevinylene), [20][21][22][23][24][25] poly(m-phenylenevinylene)-alt-(p-phenylenevinylene) [26][27][28][29][30][31][32] and fluorene-pyridine copolymers. 33 Theoretical studies on meta linked phenylene polymers suggest that these groups interrupt the conjugation by introducing kinks into the chain which lead to a helical conformation.…”

Synthesis, characterization, and optoelectronic properties of two new polyfluorenes/poly(p‐phenylenevinylene)s copolymers

“…Yield: 93%; m.p., 44. [20][21][22] The polymerization as shown in Scheme 1 was carried out under nitrogen atmosphere employing the Heck reaction. A mixture of compound 2 (1.46 mmol, 0.666 g), compound 6a (1.46 mmol, 0.564 g), palladium(II) dichloride (0.0472 mg), and 0.248 g of tri-o-tolylphosphine was added to 12 mL of DMF via a syringe.…”