[4]Rhombene: Solution‐Phase Synthesis and Application in Distributed Feedback Lasers With Emission Beyond 830 nm.

Graphene‐like molecules with multiple zigzag edges are emerging as promising gain materials for organic lasers. Their emission wavelengths can vary widely, ranging from visible to near‐infrared (NIR), as the molecular size increases. Specifically, rhombus‐shaped molecular graphenes with two pairs of parallel zigzag edges, known as [n]rhombenes, are excellent candidates for NIR lasers due to their small energy gaps. However, synthesizing large‐size rhombenes with emission beyond 800 nm in solution remains a significant challenge. In this study, we present a straightforward synthesis of an aryl‐substituted [4]rhombene derivative, [4]RB‐Ar, using a method that combines intramolecular radical‐radical coupling with Bi(OTf)3‐mediated cyclization of vinyl ethers. The structure of [4]RB‐Ar was confirmed through X‐ray crystallographic analysis. Bond length analysis and theoretical calculations indicate that aromatic sextets are predominantly localized along the molecule's long axis. Significantly, [4]RB‐Ar demonstrates narrow amplified spontaneous emission at around 834 nm when dispersed in polystyrene thin films. Moreover, solution‐processed distributed feedback lasers employing [4]RB‐Ar as the active gain material display tunable narrow emissions in the range of 830 to 844 nm. [ABSTRACT FROM AUTHOR]