Evaluation of the β Value of the Phenylene Ethynylene Unit by Probing the Exchange Interaction between Two Nitronyl Nitroxides

Abstract

A series of nitronyl nitroxide radicals having different lengths of phenylene ethynylene molecular wire were synthesized to investigate the decay constant of p-phenylene ethynylene. By the measurement and simulation of the ESR spectra of the biradicals, it was found that the exchange interaction decreased with a decay constant (β) of 0.39 Å–1 as the length of the molecule increased. This result indicates that the spin–spin exchange interaction between neutral radicals has a decay constant similar to that of the molecular conductance. This value of the decay constant indicates that a hopping mechanism does not take place in the measurement of the exchange interaction between neutral radicals even when the molecular wire has enough length to show hopping conduction of electrons