Electronic properties modulation of tetraoxidothieno[3,2-b]thiophene-based quinoidal compounds by terminal fluorination†
The electronic properties of quinoidal compounds can be modulated both by their central quinoidal cores and by their end groups. However, there have only been a few studies of the effects of end-groups on the electronic properties of quinoidal compounds, due to synthetic challenges. In this study, we have prepared four quinoidal compounds, IDOTT, 2FIDOTT, 4FIDOTT, and 6FIDOTT, with different numbers of fluorine (F) atoms on the terminal isatin units, and the effects of terminal fluorination on their optical properties, energy levels, molecular packing (as single crystals and thin-films), and electron transport properties have been evaluated. The incorporation of F atoms decreased the HOMO/LUMO levels and blue-shifted the absorption spectra. All four quinoidal compounds showed n-type transport behavior in organic thin-film transistor (OTFT) devices, but their electron mobilities strongly depended on the number of F atoms. Among these compounds, 4FIDOTT exhibited the highest electron mobility (0.16 cm2 V−1 s−1), due to its two-dimensional electron transport, highly ordered thin-film, and appropriate morphology.