Fused ambipolar aza-isoindigos with NIR absorption†
Abstract
Due to their advantages of being low-cost and light weight, and having mechanical flexibility, great attention has been focused on π-conjugated organic semiconductors. Many high-performing materials have been developed in the past decade. However, constructing electron-deficient ladder-type conjugated systems is far more challenging than constructing electron-rich systems. We have successfully synthesized a series of larger and extended novel electron-deficient aza-isoindigos (AIID-12, FAIID-12, and AIID-14) with up to 14 rings. Terminal fluorine atoms and the fusion of an additional naphthalene ring are also introduced to compare the properties of the resulting compounds to those of phenyl aza-isoindigos. Compared with isoindigo, the absorption spectra of AIID-12, FAIID-12, and AIID-14 extend into the NIR region at 900 nm due to their extended conjugation systems. These fused aza-isoindigo conjugated systems exhibit excellent solubility, highly planar backbones, substantial crystallinity, tunable conjugation lengths, and optoelectrical properties. The more extensive conjugated system with higher highest occupied molecular orbital (HOMO) and unchanged lowest unoccupied molecular orbital (LUMO) energy levels shows a narrow band gap and near-infrared absorption. Thus, the enhanced electron affinities (EAs) can facilitate the realization of electron-transport properties. As a result, OTFT devices based on AIID-14 exhibit a hole mobility of 0.076 cm2 V−1 s−1 and electron mobility of 0.003 cm2 V−1 s−1. Our results demonstrate the great potential of these aza-isoindigo systems for small-molecule semiconductor use.
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