Design and Synthesis of N-Phenylcarbazole-Substituted Diketopyrrolopyrrole-Based Monomers and Dimers: A Comparative Study

Abstract

In an effort to see the effect of conjugation length and substitution at different positions of N-phenylcarbazole, herein we have designed and synthesized symmetrical and unsymmetrical acetylene bridged N-phenylcarbazole-based diketopyrrolopyrroles (DPPs 5–9) by the Pd-catalyzed Sonogashira cross-coupling and Stille coupling reactions. A comparative study of isomeric N-phenylcarbazole (meta- and para-isomers) attached to the DPP is performed. The N-phenylcarbazole-based DPP monomers (5–7, 10 and 11) exhibit absorption in the visible region, whereas the corresponding dimers (8 and 9) show broad absorption towards the near-infrared (NIR) region with lowering of the HOMO–LUMO gap. The para-N-phenylcarbazole-based DPPs (8, 10, and 11) show red shifted absorption compared to their meta-substituted analogues (9, 5, and 6). The emission spectra reveal that DPP monomers (5–7) are fluorescent in nature, whereas quenching of fluorescence was observed in DPP dimers (8 and 9). The thermogravimetric analysis shows higher thermal stability for meta-N-phenylcarbazole-based DPPs as compared to their para-based analogues. Monomers of carbazole-based DPPs are thermally more stable than their dimers. The electrochemical study reveals multiple oxidation waves related to donor moieties (such as thiophene and carbazole) and one reduction wave corresponding to the DPP unit. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim