Green syntheses of stable and efficient organic dyes for organic hybrid light-emitting diodes

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-06, Vol.9 (23), p.7274-7283
• Main Authors: Huang, Yunping, Cohen, Theodore A, Sommerville, Parker J. W, Luscombe, Christine K
• Format: Article
• Language: English
• Subjects: Butadiene; Converters; Destabilization; Dyes; Energy levels; Light emitting diodes; Phosphors; Photoluminescence; Photooxidation; Polystyrene resins; Rare earth elements; Stability; Styrenes; Thiadiazoles; Waveguides
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d1tc01567b

Organic hybrid light-emitting diodes (hybrid-LEDs) employ organic dyes as light converters on top of commercial blue inorganic LEDs, replacing incumbent inorganic phosphor light converters synthesized from rare-earth and/or toxic metallic elements to optimize device environmental sustainability. Here, we present two naturally derived organic dyes for hybrid-LEDs, highlighting stability and efficiency enhancement based on a novel "acceptor-acceptor" molecular design. This "acceptor-acceptor" skeleton comprises theobromine and thiadiazole, two electron-withdrawing groups that lower energy levels and suppress photooxidation. This differentiates these dyes from the widely adopted "donor-acceptor" skeleton, where photooxidation is facilitated by the presence of electron-donating units. Simultaneously, sidechains on organic dyes used to enhance solution processability, crucial for film transparency, introduce an additional photooxidation pathway. With this "acceptor-acceptor" skeleton, the destabilization from sidechains was offset by the stability enhancement from the electronic effects in the backbone. When blended within an industrial polymer, poly(styrene-butadiene-styrene) (SBS), their enhanced solubility enables the formation of highly transparent films, crucial for reducing scattering loss in LEDs. Furthermore, resultant dye-SBS films achieved photoluminescence quantum yields (PLQYs) of around 90% under ambient conditions. Taking advantage of their transparency and solution processability, we fabricated a waveguide with this theobromine-dye-SBS composite, which was subsequentially assembled into an edge-lit LED device of no glare and enhanced aesthetics. Transmuting a natural product in chocolate into phosphors for light-emitting diodes.