Tuning the diradical character of pentacene derivatives via non-benzenoid coupling motifs

The development of functional organic molecules requires structures of increasing size and complexity, which are typically obtained by the covalent coupling of smaller building blocks. Herein, with the aid of high-resolution scanning tunneling microscopy/spectroscopy and density functional theory, the coupling of a sterically demanded pentacene derivative on Au(111) into fused dimers connected by non-benzenoid rings was studied. The diradical character of the products was tuned according to the coupling section. In particular, the antiaromaticity of cyclobutadiene as the coupling motif and its position within the structure play a decisive role in shifting the natural orbital occupancies toward a stronger diradical electronic character. Understanding these structure–property relations is desirable not only for fundamental reasons but also for designing new complex and functional molecular structures.This work was funded by the Spanish MCIN/AEI/10.13039/501100011033 (PID2019-107338RB-C63, TED2021-132388B-C43, PID2019-109555GB-I00), the European Union’s Horizon 2020 research and innovation program (Marie Skłodowska-Curie Actions Individual Fellowship no. 101022150) and the Basque Government (IT1591-22), M.K. D.S. and P.J. acknowledge the financial support of Czech Science Foundation project no. 20-13692X, the CzechNanoLab Research Infrastructure supported by MEYS CR (LM2023051) and computational resources provided by the project “e-Infrastruktura CZ” (e-INFRA CZ LM2018140) supported by MEYS CR.Peer reviewe