Exploratory Synthesis and Luminescence Study of the First π-Conjugated Tin-Based Alternating Copolymers for Blue Light-Emitting Diodes at the Very Low Operating Voltage

Abstract

Tin-based alternating copolymers with a uniform π-conjugated segment were synthesized using the Heck reaction between distyrylstannane monomer and various difunctionalized monomers. The UV-vis absorption maximum peaks of the resulting polymers in chloroform solution and in thin films appeared in the wavelength range of 347-394 nm. Upon photoexcitation with light of wavelength 350 nm, their photoluminescence spectra exhibited an emissive maximum peak around 470-502 nm, corresponding to blue light emission. Multilayered light-emitting diodes with ITO/PEDOT (50 nm)/polymer (80 nm)/Ca (50 nm)/Al (200 nm) composition were fabricated. These LED devices exhibited an emissive maximum peak in the range of 464-472 nm. All of the materials exhibited a very low turn-on voltage of less than 4 V. From cyclic voltammetric studies and optical data, the LUMO level is estimated to be 3.20 eV for SnPhFPV and 2.90 eV for SnPhPVK, and the ionization potentials (HOMO level) were estimated to be 5.90 eV for SnPhFPV and 5.60 eV for SnPhPVK. This lowered LUMO level, in comparison to those of poly(p-phenylene) derivatives (such as PPP, ladderlike PPP, and PAF), reduces the energy barrier to electron injection, resulting in a lowering of the operating voltage in the polymeric LED. Compared to devices based on the tin-based polymers alone, devices based on blends between the tin-based polymers and PVK showed improved efficiency of power and luminescence by at least 2-4 times and 3-6 times, respectively. Also for these polymer:PVK blends, the electroluminescence efficiency enhances up to the range of 0.1-0.3 lm/W, and the purity of the emitted blue color improves. These results may be attributed to the intramolecular confinement by diluting the EL polymers with PVK. One of the devices based on a blend system between a tin-based polymer and PVK has a brightness of 2047 cd/m 2 at 11 V with a power efficiency of 0.3 cd/A. † This paper is dedicated to Prof. Won-Jei Cho on the occasion of his retirement.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

“…Materials with ester, ,− amide, ,,− imide, carbonate, or urethane − linkages are usually made by the condensation of a chromophore with a linker group. Polymers with alkane, , stannane, or sil(ox)ane ,,− linking groups, however, are generally made by the Wittig, Heck, or Horner routes. For a review on the synthesis and uses of polymers with alternating organosilicon and conjugated units, see ref .…”

Optically active composite nanoparticles with chemical bonds between core and shell

“…Conjugated polymers including substituted polyacetylenes,1–9 polythiophenes,10–12 polyanilines,13–16 polypyrroles,17–19 poly( p ‐phenylene)s,20–23 and polyfluorenes24–29 have recently attracted much attention mainly because of their interesting electrical and optical properties and their potential applications in electronic and photonic applications as well 30–32. Among these polymers, those capable of adopting helical structure (e.g., substituted polyacetylenes) are of great importance as they might perform intriguing properties such as molecular recognition ability and catalytic ability for asymmetric synthesis,1 and could be developed as data storage and display materials 33, 34.…”

Synthesis and Characterization of Poly(N-propargylsulfamides)

“…High-quality polyacetylene film which exhibits high electrical conductivity upon doping became available with the advent of the Shirakawa method . Since then, conjugated polymers including substituted polyacetylene, polythiophene, polyaniline, polypyrrole, poly- p -phenylene, and polyfluorene have received a great deal of attention mainly because of their excellent electronic and optical properties and, in turn, their potential in electronic and photonic applications . Studies on σ-conjugated materials like polysilanes have also been performed .…”