Substituted [10]Cycloparaphenylenes : Synthesis and their Supramolecular Behavior

Abstract

Cycloparaphenylenes (CPPs), the shortest section of armchair carbon nanotubes, are a class of organic compounds with exceptional structural characteristics and potential applications across various scientific and technological domains. Their potential application in carbon-based functional materials derives from the radially oriented π system and the inherent strain of these nanohoops. The former not only confers unusual optoelectronic properties of CPPs, but also makes them excellent hosts for fullerenes. In this thesis, a new strategy for the synthesis of a substituted [10]CPP derivative was developed. The [2+2+2] cycloaddition reaction was used as key step to introduce substituents in this synthesis to obtain a diethyl phthalane-containing [10]CPP in seven steps and with 8% overall yield. This efficient synthesis allowed additional studies on the behavior of these nanohoop in supramolecular assemblies. The diethyl phthalane-containing CPP was used together with di- and tetra-tert-butyl ester-substituted [10]CPP to investigate the substitution effect in supramolecular fullerene (C60 and C70) architectures. Experimental analysis, supported by theoretical investigations, revealed that in complexes of the ellipsoidal C70 the attractive substituent-fullerene interactions are enhanced with respect to C60. Furthermore, a systematic study of the substituent-substituent interactions in such supramolecular motifs was conducted with di-tert-butyl ester-substituted [10]CPP and a series of methano-fullerenes. These Bingel adducts of fullerene C60 were functionalized with different linear or branched alkyl esters and the interaction between these and the tert-butyl ester substituted CPP was evaluated. While all alkyl ester derivatives showed a stabilizing effect – based on a double mutant cycle – these effects were enhanced with longer chain length, while the steric demand plays a significant role in the branched alkyl derivatives. As an exception, the adamantyl substitution on the fullerene shows an increased stabilizing effect being rationalized with the increased London dispersion ability.