Selenium-induced curvature control enables polymorphism in borabuckybowls

Selenium, a heavier congener of sulfur, has a larger atomic radius and higher polarizability, leading to distinct chemical reactivity and bonding. While these differences have been exploited in biological redox chemistry and materials science, their structural implications for molecular geometry and conformational adaptability remain underexplored. Such effects are particularly important for tuning solid-state properties of curved π-conjugated systems. Here we report a selenium-embedded borabuckybowl with shallow bowl geometry and enhanced shape adaptability. This structural flexibility enhances the redox stability and enables three distinct polymorphs depending on crystallization temperature. Differential scanning calorimetry revealed clear thermodynamic differences among these polymorphs in enthalpic and entropic contributions. The influence of crystal polymorphism on microscopic charge-transport properties was investigated computationally, and the structural adaptability and stability toward oxidation enabled the formation of suitable single crystals under I₂ doping conditions, allowing experimental evaluation of electrical conductivity. This study highlights sulfur-to-selenium substitution as an effective strategy for controlling molecular shape adaptability and solid-state properties of curved π-conjugated molecules.