Theoretical investigation of the β value of the phenylene and phenylene ethynylene units by evaluating exchange interaction between organic radicals

The nature of π-conjugated wire is characterized by the decay constant β of electron tunneling. To evaluate the decay constant, intramolecular magnetic exchange interaction was calculated by density functional theory for organic biradicals: nitronyl nitroxide and verdazyl were chosen for the radical substituent and oligophenylene and oligo(phenylene ethynylene) were chosen for the wire. For phenylene and phenylene ethynylene units, β was calculated to be 0.42 Å−1 and 0.24 Å−1, respectively, and the β value was independent of radical species. The obtained β values are in good agreement with the experimental value of the molecular tunneling conductance.