Synthesis and investigation of 7,7’ disubstituted Isoindigo for organic electronic applications
Résumé
The development of novel electron-deficient acceptor building blocks plays a vital role in conjugated materials for electronic applications. Incorporation of lactam moieties on conjugated backbones is one of the most important design concepts of acceptor units. Isoindigo (iI) is a lactam core fused with phenyl group, it is an excellent electron-accepting building block and recently it has become very popular in semiconductors for OPV applications. Isoindigo can be functionalized on different position. The electronic effects of substitution pattern (5,5’ vs. 6,6’) and substituent nature have been reported. The study showed that substitution patterns played significant roles on the photo-physical properties of molecular iI compounds. The 6,6’ substituted derivatives had more extended conjugation than the 5,5’ substituted derivatives because of the large contribution of electronic transition dipole moment in the axis aligned with the 6, 6’ carbons. However, little attention has been paid to the substitution at 4,4’ positions and 7,7’ positions, Figure 1.
Figure 1: Structure of Isoindigo derivatives
In this work, we report on the effect of the substituent at the 4,4’ and 7,7’-positions of the iI-core. Hence, we have developed a new method for the synthesis of various bromo-isatin and bromo oxindole derivatives. Extending the conjugation at the 7-position via Suzuki or Stille cross-coupling reaction yields to useful functionalized-isatin, as synthon for further transformation. Direct condensation of 7-bromoisatin and 7-bromo-oxindole in acetic acid afforded 7,7′-dibromo-iI. However, the large steric hindrance induced by the bromine atom at