Alternating Donor–Acceptor Thienoacenes Featuring Up to 23 Linearly Fused Rings

A group of ladder-type imide-functionalized thienoacenes including <b>[9]ITAa</b>, <b>[9]ITAb</b>, <b>[16]ITA</b>, and <b>[23]ITA</b>, featuring 9, 16, and 23 linearly fused rings, respectively, were readily synthesized through stitching thienannulation of polyalkyne precursors composed of alternating naphthalene diimide (NDI) and <i>m</i>-phenylenediyne units. A single crystal of <b>[16]ITA</b>, with a molecular length of 33.8 Å, was obtained, representing the longest reported single crystal of a linear thienoacene. The optical and electronic properties of these soluble alternating donor-acceptor (D-A) type thienoacenes with varying fused lengths were elucidated using UV-vis-NIR spectroscopy, cyclic voltammetry, and machine learning-enhanced quantum chemical and density functional theory calculations, revealing their low energy gap characteristics. This work shows that the stitching thienannulation strategy, when applied with rationally designed precursors, can precisely synthesize fully π-conjugated molecules with previously unachievable topologies.