PNNL

Abstract

Modulation of organic semiconductor band gap, electron affinities (EA), ionization potentials (IP), and reorganization energies (?) 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 airstability 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 (?i) associated with charge transfer is the penalty for the improved performance of the trifluoromethylated compounds. However, since ?i decreases as the p conjugation increases, a rational design to produce air-stable n-type semiconductor materials with reasonably small ?i is simply to prepare trifluoromethylated arenes with extended p conjugation. Furthermore, we found that structural isomerization can finetune the optoelectronic and electronic transfer properties of the corresponding aromatics.