Connecting π-Chromophores by σ-P−P Bonds:  New Type of Assemblies Exhibiting σ−π-Conjugation

To study the ability of σ-P−P skeleton to mediate interaction between π-chromophores, 1,1‘-biphospholes bearing phenyl or thienyl substituents at the 2,2‘ and 5,5‘-position have been prepared and studied. These air-stable derivatives are readily available via a “one-pot” synthesis starting from diynes. Theoretical studies and UV−vis data clearly establish that the two π-systems interact via the σ-P−P bridge. This through-bond interaction results in a lowering of the optical HOMO−LUMO gap of the assemblies. The nucleophilic σ3-P centers of these 1,1‘-biphospholes allow chemical modifications of the σ-bridge. These modifications offer further tuning of the optical properties of the assembly. Electrooxidation of the thienyl-substituted 1,1‘-biphosphole results in electroactive materials characterized by low optical band gap and reversible p-doping.