How Long Can A C-C σ-Single Bond Be?

In a specifically designed molecular structure, two sp2-hybridized carbon atoms align their unhybridized 2pz orbitals in the same orientation to form an extremely long C2pz-C2pz σ-single bond that goes beyond 3 Å in length. This new type of C-C σ-bond (coined as a fringe bond) can be made more than 1 Å longer than the current experimental world record (∼1.8 Å) and 300 kJ/mol weaker than the ordinary C-C σ-bond (∼330 kJ/mol). If such molecular monomers are polymerized into infinite chains, the extended long C-C saturated σ-bonding framework manifests band gaps similar to those of some conventional iconic organic-conducting polymers based on conjugated networks of unsaturated bonds.