Mixed valence radical anions of 4,4″-dinitro-p-terphenyl and its aza derivatives as models for electronic communication in conducting polymers

Abstract

Cyclic voltammetry, UV/Vis/NIR spectroscopy, EPR spectroscopy and theoretical calculations were used to study the mixed valence radical anions of 4,4″-dinitro-p-therphenyl (2), of 3,6-bis(4-nitrophenyl)-1,2-diazine (3) and of 2,5-bis(4-nitrophenyl)-1,4-diazine (4) as models to understand the effect of the structural changes on the conductivity of poly-p-phenylene polymers. All the results show an increase of the electronic communication between nitro groups in the order 2 < 3 < 4. Substitution of CH units by nitrogen atoms in the central aromatic ring lowers the reduction potential of the bridge, increasing the electronic coupling through the triaryl bridge and the rate of intramolecular electron transfer in the same order. Additionally, calculations show that the 1,2-diazine ring of 3, and specially the 1,4-diazine ring of 4, allow a higher planarity of the molecule by decreasing the steric strain between rings, which also increases the conjugation through the bridge. The results suggest that incorporating pyrazine (1,4-diazine) and pyridazine (1,2-diazine) units in poly-p-phenylene polymers should enhance the electronic properties of these conducting polymers.