Quasi-reversible electrochromic behavior of alkyl viologens dispersed mono-molecularly in double-stranded DNA chains

We study the electrochromic response of N,N-diheptyl-4,.4'-bipyridinium dibromide (heptyl viologen, HV) incorporated mono-molecularly into DNA minor grooves. DNA in which Na+ cations have been substituted by 1-dodecyl-3-methylimidazolium (C(12)MIDNA) was prepared and cast as a thin film on an ITO glass electrode. HV was then introduced into the DNA film by soaking. HV was introduced (ca. 20%) to the DNA base-pairs after soaking for 60 min. The resulting HV introduced DNA film was used to prepare electrochromic cells. The cell showed reversible colour change of monomeric HV, depending on the applied potential. For this HV introduced DNA cell, N,N,N',N'-tetramethyl-p-phenylenediamine was introduced as an active material at the counter electrode to realise a reversible colour change at +/- 0.7 V.