Solid-state red-emissive (cyano)vinylene heteroaromatics via Pd-catalysed C-H homocoupling

• Published in: Organic & biomolecular chemistry 2023-05, Vol.21 (19), p.4123-4129
• Main Authors: Nipate, Atul B, Rajeswara Rao, M
• Format: Article
• Language: English
• Subjects: Fluorescence; Solid state; Steric hindrance; Substrates
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/d3ob00560g

Thiophene-based π-conjugated systems are important materials for organic electronics; thus, their synthesis is of topical interest. We report fluorescent thiophene/furan-based vinylene and cyanovinylene systems Pd-catalysed homocoupling [Pd(OAc) , pivalic acid, KOAc, DMAc, 140 °C]. The methodology is versatile and allows the development of a variety of π-conjugated systems without the need for pre-functionalized building units. The reaction tolerates electron-rich, electron-deficient and large π-conjugated substrates. The developed compounds absorb in the visible region (400-515 nm) and emit green to orange fluorescence in the solution state (510-600 nm). Most importantly, the compounds exhibit strong aggregation-induced emission (AIE) in the NIR region ( = 650 nm), with quantum yields reaching up to 10%. Steric hindrance imparted by vinylene/cyanovinylene units is responsible for the strong solid-state luminescence. DFT-optimized structures reveal an apparent twist of 20-40° in the molecular backbone of the compounds, supporting the AIE behaviour of the compounds.