Near-infrared absorbing tetracyanobutadiene-bridged diketopyrrolopyrroles

Abstract

In order to investigate the effects of end capping donors and secondary acceptors on the photonic and electrochemical properties of diketopyrrolopyrrole (DPP), the tetracyanobutadiene (TCBD) bridged D-A1-A2-π-D type DPPs V-VII have been designed and synthesized by a [2+2] cycloaddition-retroelectrocyclization reaction. Optical, thermal, electrochemical and computational studies are performed and compared with their para N-phenyl carbazole-based analogue DPP-VIII. The TCBD bridged DPPs V-VIII exhibit electronic absorption in the visible to near infrared (NIR) region with low HOMO-LUMO gap values compared to their acetylene bridged precursors DPPs I-IV. The DPPs V-VIII exhibit excellent thermal stability. Electrochemical studies reveal additional reduction waves in DPPs V-VIII corresponding to two successive reductions of the TCBD moiety. The introduction of electron-withdrawing TCBD to acetylene-bridged DPPs extends the absorption and lowers the HOMO-LUMO gap which is supported by computational calculations. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.