1,4-Dihydropyrrolo[3,2-b]pyrrole and Dipyrrolonaphthyridinedione – Novel Building Blocks for Optoelectronics
Abstract: Recently we have discovered and optimized the first practical synthesis of non-fused pyrrole[3,2-b]pyrroles via domino reaction of aldehydes, primary amines, and butane-2,3-dione.1 Six bonds are formed in heretofore unknown tandem process, which gives rise to substituted pyrrole[3,2-b]pyrroles – the ‘missing link’ on the map of aromatic heterocycles. Unparalleled simplicity and versatility of this one-pot reaction, non-chromatographic purification and superb optical properties (including strong violet, blue or green fluorescence both in solution as well as in the solid state), brought these molecules from virtual non-existence to the intensively investigated area functional π-systems. The parent 1,4-dihydro-pyrrolo[3,2-b]pyrroles served as building block to construct various π-expanded analogs including nitrogen-embedded buckybowl with inverse Stone–Thrower–Wales topology2,3 and diindolo[2,3-b:2‘,3‘–f]pyrrolo[3,2-b]pyrroles. These compounds constitute the most electron-rich ladder-type heteroacenes known to date – EHOMO was located at ca. −4.6 eV. Recently, we have proved that the dipyrrolonaphthyridinedione (DPND) core constitutes an excellent scaffold for the design of strongly fluorescent dyes or quadrupolar-type materials with large two-photon absorption (TPA) cross-sections (up to 5,180 GM).37 These properties result from an unusual arrangement of donor (pyrrole ring) and acceptor (carbonyl group) moieties within the DPND core.