Abstract

Iterative syntheses—repeating sequences of the same reactions to construct complex molecules—can facilitate the synthesis of specific classes of small molecules with structural redundancies, including acenes. Despite the prevalence of zigzag edges in the structures of acenes, few examples that effectively manipulate the edge configurations of acenes exist. In this study, the rationally designed iterative synthesis of three pentacene derivatives with continuous boron–oxygen bonds at the zigzag edges is reported. The simple and efficient two-step iteration employed ipso iodination with a trimethylsilyl group as the directing group and Suzuki cross-coupling/condensation reactions. Because of the fundamental role of pentacene derivatives in a broad spectrum of electronic applications, these findings are valuable across a diverse range of chemical and physical disciplines.

Researchers at UNIST have introduced a new, efficient way to alter the backbone of organic semiconductors, giving researchers finer control over the molecules used in flexible displays, sensors, solar cells, and other electronic devices.

Led by Professors Young S. Park and Seung Kyu Min from the Department of Chemistry, the team created an iterative synthesis method that places boron–oxygen bonds along the edge of pentacene, a well-known organic semiconductor made of five fused benzene rings.

Organic semiconductors are valued because they are light, flexible, and chemically tunable. Small changes in a molecule's length, shape, or atomic makeup can shift how it absorbs light, emits light, or transports charge. But chemists have usually tuned these materials by attaching groups to the outside of the molecule. Changing the carbon framework itself has remained much harder.

The new method works inside that framework. It inserts oxygen and boron atoms into the pentacene backbone, reshaping the molecule rather than simply decorating its edges.

Dr. Sunghwa Jung, the study's first author, said the process relies on a repeated two-step cycle. “Each cycle begins with iodination at a specific site, followed by ring closure using a boron reagent,” he said. “By repeating the sequence, we can build pentacene structures with consecutive boron–oxygen bonds along the molecular edge.”

By carefully controlling these cycles, the team synthesized three different pentacene derivatives, each with distinct boron–oxygen arrangements. The molecules absorbed and emitted light at different wavelengths, showing that their optical properties could be tuned through structure. All three also showed fluorescence quantum yields above 0.70, a sign of efficient light emission. The results point to possible uses in light-emitting organic semiconductors, fluorescent sensors, and optoelectronic materials that require bright, efficient emission.

“This work gives us a stepwise way to build new acene molecules with consecutive boron–oxygen bonds,” Professor Park said. “Because the process can control both molecular length and arrangement, it expands the structures available for organic semiconductor design.”

The study was published online in Angewandte Chemie International Edition on April 16, 2026. It was supported by funding from the National Research Foundation of Korea (NRF) and the Ministry of Trade, Industry and Energy (MOTIE).

Journal Reference

Seonghwa Jeong, Si-In Kim, Jonghwan Lee, et al., “Iterative Synthesis of Pentacene Derivatives with Continuous Boron–Oxygen Bonds,” Angew. Chem. Int. Ed. , (2026).