Heterocyclic quinones as core units for redox switches: UV–vis/NIR, FTIR spectroelectrochemistry and DFT calculations on the vibrational and electronic structure of the radical anions

Spectroscopic and quantum chemical studies on benzodithiophene quinone (2) and benzodifuran quinone (3) and their radical anions are reported. Investigations by UV–vis and FTIR spectroelectrochemistry were undertaken. The electrochemical and spectroscopic properties of the neutral and charged heterocyclic systems are compared with those of anthraquinone (4). On reduction to the radical anions the ν(CO) stretching frequency of 2 diminishes from 1660 to 1502 cm−1 and of 3 from 1684 to 1536 cm−1. Molecular orbital calculations at the density functional (DF) level were carried out. In their electrochemical and optical properties, 2 and 3 are alike functionalized 1,4-benzoquinones. The design of an electrochemical cell for FTIR spectroelectrochemistry with exceptional mechanical stability for experiments under strictly anaerobic conditions is presented.