Arene Trifluoromethylation: An Effective Strategy to Obtain Air-Stable n-Type Organic Semiconductors with Tunable Optoelectronic and Electron Transfer Properties

Modulation of organic semiconductor band gap, electron affinities (EA), ionization potentials (IP), and reorganization energies (λ) associated with charge transfer is critical for its applications. We report here that trifluoromethylation not only increases both IP and EA significantly as expected but also narrows the HOMO-LUMO band gaps and increases considerably the air-stability of arene-based n-type organic semiconductors. The increased air-stability results from relatively high EA energies and a change in oxidation mechanism. Calculated EAs and IPs show that trifluoromethylated arenes are excellent candidates for n-type semiconductor materials; though a moderate increase of inner-sphere reorganization energy (λi) associated with charge transfer is the penalty for the improved performance of the trifluoromethylated compounds. However, since λi decreases as the π conjugation increases, a rational design to produce air-stable n-type semiconductor materials with reasonably small λi is simply to prepare trifluoromethylated arenes with extended π conjugation. Furthermore, we found that structural isomerization can fine-tune the optoelectronic and electronic transfer properties of the corresponding aromatics.