Tuning the Solid State Luminescence of Benzofuran‐Cyanostilbenes by Functionalization with Electron Donors or Acceptors

Abstract

Three series of linear extended benzofuran derivatives associating cyanovinyl unit and electron withdrawing systems such as paracyanophenyl (series 1) or pentafluorophenyl (series 2) moeities or the electron donor 3,4‐dimethoxyphenyl (series 3) moiety have been prepared. The donor character of the benzofuran part is carried out either without modifying the conjugation by adding the electron donor methoxy groups to the 5 and 6 positions of the benzofuran (compounds BF2 and BF3) or by increasing the extension of the conjugation with the naphthofuran unit (BF4), and by the insertion of a furan ring between the benzofuran and the cyanovinylene bond (BF5). While all compounds show very low emission in solution, microcrystalline powders of almost all compounds show strong emission under excitation at 350 ‐ 400 nm with emission colors ranging from blue ‐ green to red. It is shown that this variation of the emission colors is essentially due to the type of stacking of the molecules in the solids for series 1 and 2. For series 3, it is above all the extension of the conjugation of the compounds which causes the red shift.