Design and synthesis of push-pull chromophores based on diketopyrrolopyrrole

Abstract

Diketopyrrolopyrrole (DPP) pigment was first developed and synthesized by Farnum et al. featuring two phenyl units. This 8-π electron fused ring known as pentalene, displayed remarkable insolubility in typical organic solvents and bright red colouration. Later, Iqbal and co-workers improved the synthetic process using succinic method. Subsequently, a wide range of DPP derivatives, displaying colours from red to blue, have been designed which include DPP pigments flanked by phenyl, pyridyl, thienyl, furayl, and seleneyl groups. These substituents can influence the planarity of the DPP pigment, its energy levels, and the distance between π-π stacked molecules. DPP pigments contain two amine and carbonyl units in their structure (Figure 1), capable to form strong hydrogen bonds, which leads to less solubility in common organic solvents. However, alkylation can disrupt these hydrogen bonds, significantly and improves the solubility. To synthesize DPP-based small organic molecules (SOMs)/polymers, reactions such as Stille, Suzuki coupling, electrochemical polymerization, and Buchwald coupling were used. Strong electron deficiency, outstanding planarity of the DPP unit, a broad π-conjugation system, and exceptional aggregation qualities are the favourable features of DPP-based small organic molecules (SOMs).