D-A-D Compounds Combining Dithienopyrrole Donors and Acceptors of Increasing Electron-Withdrawing Capability: Synthesis, Spectroscopy, Electropolymerization, and Electrochromism.

Five compounds consisting of the same donor unit (dithieno[3,2-:2',3'-]pyrrole, ), the same π-linker (2,5-thienylene), and different acceptors of increasing electron-withdrawing ability (1,3,4-thiadiazole (), benzo[][1,2,5]thiadiazole (), 2,5-dihydropyrrolo[3,4-]pyrrole-1,4-dione (), 1,2,4,5-tetrazine (), and benzo[][3,8]phenanthroline-1,3,6,8(2,7)-tetraone ()) were synthesized. , , and turned out to be interesting luminophores emitting either yellow ( or near-infrared ( and ) radiation in dichloromethane solutions. The emission bands were increasingly bathochromically shifted with increasing solvent polarity. Electrochemically determined electron affinities (|EA|s) were found to be strongly dependent on the nature of the acceptor changing from 2.86 to 3.84 eV for and , respectively, while the ionization potential (IP) values varied only weakly. Experimental findings were strongly supported by theoretical calculations, which correctly predicted the observed solvent dependence of the emission spectra. Similarly, the calculated IP and EA values were in excellent agreement with the experiment. , , , and could be electropolymerized to yield polymers of very narrow electrochemical band gap and characterized by redox states differing in color coordinates and lightness. and showed promising electrochromic behavior, not only providing a rich color palette in the visible but also exhibiting near-infrared (NIR) electrochromism.