Breaking the Stability Barrier of Large Acenes

The synthesis and stabilization of large acenes have long been impeded by their inherent instability, which has limited their potential in electronic and magnetic applications. In this study, we present a breakthrough in the solution-phase synthesis of unprecedentedly stable long acenes, specifically [11]acenes and [13]acenes. This achievement was realized through a para-quinodimethane (p-QDM)-based design strategy combined with bulky trialkylsilylethynyl substitution, a method that surpasses all previously reported approaches for stabilizing large acenes. Comprehensive structural and spectroscopic characterization, including X-ray crystallography, UV–vis-NIR spectroscopy, electrochemical analysis, and EPR spectroscopy, confirmed the successful synthesis of these acenes. The results revealed that these large acenes exhibit significant open-shell biradical character in their ground states, accompanied by small singlet-to-triplet energy gaps. Their unique electronic and magnetic properties were further elucidated through magnetic measurements supported by density functional theory (DFT) calculations. This work represents a significant progress toward overcoming the long-standing challenge of stabilizing large acenes, opening new avenues for their exploration and integration into functional materials and device applications.