Synthesis and characterization of fully p-conjugated oligothiophene-based macrocycles

Abstract

The aim of this thesis was the development of a new concept that enables the efficient synthesis of fully conjugated macrocyclic oligothiophenes. Cyclo[n]thiophenes represent a particularly interesting new class in the field of shape-persistent macrocycles. Their core comprises solely conjugated thiophenes; thus, these macrocycles describe systems in which an infinite p-conjugated chain of an ideal polymer is perfectly combined with the advantages of a structural well-defined oligomer. The initial synthetic strategy relies on the macrocyclization of diethynylated oligothiophenes to the corresponding oligothiophene-diacetylene macrocycles by oxidative coupling reaction. First, the effective synthesis of the homologue series of linear conjugated oligothiophenes is described. The macrocyclization of diethynylated oligothiophenes and detailed aspects of the reactions are discussed. Two complete homologues series of conjugated oligothiophene-diacetylenes macrocycles including terthiophene and quinquethiophene units are presented. The main goal of the thesis was to develop a new effective method to synthesize fully conjugated cyclothiophenes. Towards this end, the metal template approach was developed. This approach is based on the thermodynamically controlled reaction of appropriate diethynylated oligothiophenes with transition metal affording stable dimeric oligothiophene-platinacycles in excellent yields. By the help of an oxidant induced reductive elimination from the dimeric platinacycles is induced resulting in elimination of two Pt-corners and subsequent C-C bond formation. Under preservation of the cyclic structure, mainly the corresponding dimeric oligothiophene-diacetylene macrocycle is formed in very good yields. Finally, the reaction of oligothiophene-diacetylene macrocycles with sodium sulfide afforded the synthesis and characterization of the targeted homologues series of fully conjugated cyclo[n]thiophenes (n = 8, 12, 16, 18).