Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.

Tetraaryl[5]cumulenes react with low-valent nickel complexes at the second double bond to produce novel [4]radialene derivatives that are head-to-head dimers of [5]cumulenes. The head-to-head dimers are also synthesized by a stepwise route. On the other hand, the nickel-catalyzed dimerization of [5]cumulenes with bulky substituents produces other types of extended [4]radialenes and [5]radialenones depending on the bulkiness of the terminal alkyl substituents. Thus, tetrakis-t-butyl[5]cumulene and 1,4-bis(2,2,6,6-tetramethylcyclohexylidene)[3]cumulene react at the central double bond to give the corresponding [4]radialene and [5]radialenone, whereas 1,4-bis(2,2,5,5-tetramethylcyclopentylidene)[3]cumulene and its benzo-annelated derivative react at the second double bond in a head-to-tail manner to afford the corresponding extended [4]radialenes. Tetrakis-t-butyl[5]radialenone was converted into [5]radialene by using a methylation–dehydration procedure. The extended [4]- and [5]radialenes and [5]radialenones have been fully characterized by spectroscopic analyses, X-ray crystallography, and/or independent chemical synthesis. The properties of these novel exocyclic π-electron systems have been investigated in detail. The aryl-substituted [4]radialenes exhibit facile bond rotation with low energy barriers. The [5]radialene and [5]radialenone form the corresponding cations easily by the addition of an acidic proton. The selectivity of the nickel-catalyzed dimerization of [5]cumulenes is discussed on the basis of theoretical calculations.

A series of di-, tri-, and tetraferrocenylarenes were synthesized by using the nickel- and palladium-catalyzed cross coupling reactions of ferrocenylzinc chloride with the corresponding di-, tri-, and tetrahalogenoarenes. Redox properties of these ferrocenylarenes were studied by cyclic voltammetry in order to examine the intramolecular interaction between the ferrocenyl substituents.

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