On-surface regioselective cyclodehydrogenation of 1,3,6,8-tetra-o-tolylpyrene on Au(111)

On-surface reactions have emerged as a powerful strategy for engineering covalent nanoarchitectures with potential applications in electronics, optoelectronics, spintronics, and photovoltaics. Despite their expansion into various product categories, reactions involving methyl-phenyl functional groups remain limited due to cyclization competition between the methyl and benzene groups. Here, we investigate the regioselective cyclodehydrogenation of a pyrene core decorated with methyl-phenyl on an Au(111) substrate. Using bond-resolution scanning tunneling microscopy, we identify four cyclization pathways originating from the external methyl-phenyl groups in combination with the internal aryl group, yielding five products with diverse magnetic ground states. Statistical analysis indicates that closed-shell structures with methyl groups distributed clockwise or anticlockwise dominate (>60%), revealing a preferred configuration on the Au(111) surface. This selectivity is attributed to the cooperative influence of the underlying Au(111) template, which directs the cyclization pathways. Our study promotes the development of on-surface synthesis by elucidating substrate-templated regioselective behavior during competitive methyl-phenyl cyclodehydrogenation and establishing an atomically precise approach for fabricating non-benzenoid carbon nanostructures.