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. Investi gations by UV-vis and FTIR spectroelectrochemistry were undertaken. The ele ctrochemical and spectroscopic properties of the neutral and charged hetero cyclic systems are compared with those of anthraquinone (4). On reduction t o the radical anions the nu(C=O) stretching frequency of 2 diminishes from 1660 to 1502 cm-(1) and of 3 from 1684 to 1536 cm(-1). Molecular orbital ca lculations 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 spectroelec trochemistry with exceptional mechanical stability for experiments under st rictly anaerobic conditions is presented. (C) 2000 Elsevier Science S.A. Al l rights reserved.