Peripheral structural modifications of arenes are widely used to control or improve the optoelectronic properties, molecular assembly, and stability of aromatic pi-materials as well as to explore new functions. However, known modifications are often tedious and complex; therefore, a simple yet powerful modification strategy is needed. We discovered that annulation with a simple adamantane scaffold exerts a significant impact on the properties, alignment, and stability of aromatic pi-systems. This unprecedented adamantane annulation was achieved by a two-step transformation of metalated arenes and 4-protoadamantanone, generating a range of adamantane-annulated arenes. Analysis on structural and electronic property uncovered unique effects of the process, such as high solubility and enhanced conjugation. The oxidation of adamantane-annulated perylenes produced strikingly stable cationic species with emission extended to near-infrared region. This simple property modulation of aromatic pi-systems would not only create potentially ground-breaking oi-materials but also novel nanocarbon materials, such as diamond-graphene hybrids.