Formation and Characterization of the π-Radical Cation and Dication of π-Extended Tetrathiafulvalene Materials

The π-radical cation as well as the dication species of a series of quinonoid π - extended TTF have been generated by means of time-resolved and steady-state radiation chemical techniques. The spectral characteristics of the π-radical cation revealed fingerprint absorptions, which are predominantly in the red region of the spectrum (570−690 nm). The maxima vary markedly upon altering (i) the substitution pattern of the TTF rings (i.e., H, S−CH 3 and S−CH 2 −CH 2 −S) and (ii) the different backbone structures (i.e., anthracene, tetracene, and pentacene). In accordance with the electrochemical studies, which give rise to a single two-electron oxidation step forming directly the π - extended TTF dication, the π-radical cation intermediate is short-lived and decays on a time scale of several tens of milliseconds. Clean second-order decay dynamics, indicative for a disproportionation reaction of the π-radical cation into the corresponding dications, govern the instability of the π-radical cation. By contrast the dication species is stable without showing a significant degradation over minutes. All the generated dications show transitions that are significantly shifted to the blue (455−490 nm) relative to the π-radical cation intermediates and are dominated by the polyacenic unit.