BNB-Modified Perylene, Terrylene, and Quaterrylene Diimides: Introduction of the π-Accepting and Aggregation-Suppressing Diborinic Imide Group in Rylene Dyes

Rylene diimides are among the most intensively researched classes of functional organic dyes. They are characterized by outstanding photoabsorption and -emission properties in combination with excellent photostability and thermal stability. Due to strong intermolecular π-π interactions, the larger, peri-extended rylene diimides, in particular, require the complex attachment of solubilizing substituents to enable their handling and processing in the solution phase. Herein, we introduce the diborinic imide functional group as a substitute for the commonly used dicarboximide moiety at the peri-termini of rylenes, thus leading to a new class of well-soluble rylene dyes with excellent optoelectronic properties. We synthesized borinic diimides of perylene (PDBI 5), terrylene (TDBI 7), and quaterrylene (QDBI 9) starting from a BNB-modified phenalenyl (1). These compounds show progressively bathochromically shifted absorption and emission characteristics with increasing system size, with fluorescence quantum yields up to ΦF = 0.92 for 5, and extended NIR (near-infrared) emission for 9. Single-crystal X-ray diffraction (XRD) studies reveal modified molecular packing in the solid state, pointing to a reduced tendency to aggregation. The new compounds undergo two reversible successive reductions, which were monitored by UV-vis-NIR spectroelectrochemistry. We performed the chemical reduction of 5 to obtain the potassium salts of the mono- and the dianion, K[5] and K2[5], respectively. Both the dianion and, in contrast to common rylene diimide dyes, also the monoanion show fluorescence emission, which extends into the NIR region. Quantum chemical ACID and 2D-NICSZZ calculations reveal a transition from mainly local aromaticity to global aromaticity upon reduction.