Redox‐Activated Near Infrared/Shortwave Infrared Emissive Chromophores: Synthesis of Triphenylamine‐Appended Pyrazinacenes

Organic dyes showing absorbance and fluorescence in the near infrared and short-wave infrared regions are attractive for a variety of applications. Redox-coupled reversible switching of absorbance or fluorescence implies enhanced functionality of such dyes, especially where large changes in photophysical properties across the redox process can be realized. Here, the synthesis of two new pyrazinacenes containing four and five fused pyrazine units, appended with electron-donor triphenylamine groups, and redox-coupled switching of their photophysical properties is reported. In their reduced state, the compounds show absorbance and fluorescence in the visible region. Reversible shifts in absorbance and fluorescence from the visible to the near infrared or even short-wave infrared regions are observed upon chemical and electrochemical oxidations. Such large redox-coupled shifts in photophysical properties are unprecedented for a redox process that affects only a single, six-membered ring in which both reduced and oxidized states consist of neutral, closed-shell species. The compounds show high fluorescence quantum yields in their reduced states, and oxidized species show fluorescence quantum yields that compare well with existing near infrared and short-wave infrared active fluorescent dyes.