Modulating the properties of buckybowls containing multiple heteroatoms

Abstract

Embedding heteroatoms in buckybowls is an effective approach to alter their electronic structures and physicochemical properties. However, buckybowls with heteroatoms situated at both the peripheral rim and the central core to modulate the properties are quite rare. Herein, we report buckybowls containing sulfur atoms at the rim and nitrogen atoms in the center with tunable properties according to the state of the sulfur atoms. When the sulfur atoms are in the form of electron-donating sulfide, the buckybowl demonstrates weak fluorescence. It shows a low oxidative potential and elevated frontier molecular orbital energy levels due to the increased electron density. The electron-rich heterobuckybowl can be chemically oxidized to generate monocations and dications with gradually planarized structures according to the oxidation state. Moreover, it can assemble with electron-deficient fullerene C₆₀ to form a 1 : 1 complex in toluene solution and a 2 : 1 complex in the crystalline state with strong intermolecular attractive interactions. After the oxidation of the sulfur atom to an electron-withdrawing sulfonyl group, the buckybowl shows the strongest photoluminescence in both solution and solid states in the regime of heterobuckybowls thus far. A decline in frontier molecular orbital energy levels and weak association behavior with fullerene C₆₀ to generate a 1 : 1 complex in toluene solution are also observed due to the reduced electron density.