Tailoring pyrene excimer luminescence via controlled sulfur oxidation

Abstract

To facilitate the formation of efficient fluorescent pyrene excimers in solids, sulfide-, sulfoxide-, and sulfone-substituted pyrenes (Py–S, Py–SO, and Py–SOO) showing different oxidation degrees were designed and synthesized. All molecules possess side groups oriented perpendicular to the pyrene plane, which promote the formation of an antiparallelly stacked π–π pyrene dimer and the resulting excimer. Analysis of the photophysical properties measured in solutions, crystals, and films reveals that the resulting excimer species for these three molecules have similar emission wavelengths. However, the excimer of Py–SOO demonstrates the highest photoluminescence quantum efficiency due to molecular rigidity of its crystal and evaporated film. Non-doped organic light-emitting diodes were fabricated using these materials as emitters, and Py–SOO exhibits the best electroluminescence performance with a stable excimer emission, an external quantum efficiency of 2.53%, and a maximum luminance of 21 428 cd m⁻². These findings show that the introduction of a sulfone group can improve the luminescence efficiency of the pyrene-based excimers and present a valuable guideline for designing high-performance solid-state pyrene excimers.