Synthesis and electrochemical properties of intramolecular multi-electron transfer probe compounds

Abstract

The absorption spectra of diquinone pentacene-5,7,12,14-tetrone (PDQ), have been studied and it was found that the long wavelength absorption of the neutral quinone and of the semiquinone anion radicals were different. For example, λ max(PDQ) = 375 nm, λ max(PDQ −) = 1350 nm, λ max(PDQ 2−) = 850 nm. PDQ can be used as an electron acceptor which can accept up to four electrons. Investigations of absorption spectra readily determines how many electrons have been transferred. We have now synthesized a series of compounds containing PDQ as acceptor and carbazole as donor, linked by a chain of variable length. The intramolecular multi-electron transfer ‘probe’ compounds prepared can be reduced chemically or electrochemically to give the corresponding anion radicals. The reduction potentials for these compounds were estimated by cyclic voltammetry at a mid point between the anodic and cathodic peak potentials. The reduction of the quinones to the semiquinone anion radicals was carried out using 0·1 M tetrabutylammonium tetrafluoroborate in CH 3CN under a N 2 atmosphere.