Design, Synthesis, Characterization and Redox Properties of Planar and Non-planar Macrocycles Derived from Thiophene Subunits

Abstract

Oligomers and macrocycles of thiophene have attracted significant attention for their structural, electronic, and redox properties. Synthesis of macrocyclic thiophenes is a challenging task due to the competitive and facile formation of their oligomeric counterparts. Invariably, macrocyclic thiophenes demand a multi-step protocol to be synthesized in moderate yields. Simplifying the synthetic strategies to stitch multiple units of thiophenes into size and shape-specific cyclic structures is an arduous task. In this seminar, attempts to cyclize functionalized bithiophene and terthiophene will be discussed in detail. Success of this synthetic protocol depends on the nature of end product. Analysis of reactions by mass spectrometry revealed the formation of planar conjugated macrocycles along with unstable radical species and partially conjugated macrocycles. Formation of semi conjugated products was found to be dependent on the nature of oxidizing agents employed in the reaction medium. These macrocycles were found to lose their planar structure upon incorporating benzene units in the cyclic framework. It was observed that disubstituting benzene with thiophene in ortho positions provided further scope to oxidative coupling reactions. Products identified from such reactions revealed the formation of macrocyclic framework with a combination of condensation reaction and oxidative coupling between the thiophene units. Irrespective of being planar or otherwise, these conjugated macrocycles displayed two-electron ring oxidation to yield the respective dicationic species. Details of synthetic strategies, analysis of products by analytical techniques and relevant computational studies of the thesis will be highlighted in this seminar.