The Synthesis and Optical Properties of Fluorescent Quinoxalines and of Electrospun Fibers Containing Fluorescent Quinoxaline

Abstract

Heterocyclic fluorophores are useful materials in the search for new biologically active compounds and diagnostic methods. We have been interested in the chemistry of nitrogen-containing heterocyclic molecules for many years. Quinoxaline is a representative fluorophore. We have reported on several quinoxalines in recent years. Quinoxaline can easily change its absorption and emission wavelength by oxidation with the proton base in the nitrogen of the quinoxaline ring. In this study, we designed and synthesized several 2,3-distyrylquinoxaline and thieno[3,4-b]quinoxaline derivatives, Each with different electron-donating capabilities. The designed quinoxalines were substituted for the dodecyloxy groups on the benzene ring and stillbene groups were attached by knoevenagel reaction or Hornor-Wadsworth-Emmons (HWE) reaction on the 2,3-positions of the pyrazine ring. They amplified the electron donating capability of the quinoxaline structure. Thus, the weak base property of nitrogen in the heterocyclic ring was increased, especially in a protonic condition. The property in an acidic condition was revealed by fluorescence quenching. However, fluorescent spectral change was observed, especially when the N,N-dimethylamino group was attached to the stillbene group. These properties were also observed in electrospun fibers containing those synthesized compounds. Electrospun fibers contained quinoxaline colorants are expected to have various applications in chemosensors.