Symmetry-breaking enhanced emission of C ₆₀ upon nucleobase binding: Spectroscopic observation combined with TD-DFT mechanism

Low-dimensional nanocarbons such as fullerenes are important nano-bio model systems. Their non-covalent interactions with nucleic acid building blocks can enable molecular recognition and alter photophysical behavior, but the structural-activity relationship between nucleobases molecular structure and spectroscopy remains unclear. Here, steady-state photoluminescence (PL) spectroscopy and quantum chemical calculations were used to study C60 adsorption with five nucleobases (A, C, G, T, and U) in dimethyl sulfoxide. C60 shows a visible PL band at ∼409 nm under 301 nm excitation. Equal concentrations of nucleobases markedly enhance C60 emission with minor shifts, following T > U > A > G > C. Density functional theory (DFT) predicts stable π-stacking-like complexes with separations of ∼3.3 Å and binding energies of −0.23 to −0.38 eV. Reduced density gradient analysis reveals dispersion-dominated attraction, consistent with physisorption. Time-dependent DFT indicates that low-energy singlet excitations remain mainly localized on C60, while adsorption-induced symmetry breaking gives these states weak oscillator strength, explaining the enhanced emission. Correlation relationship for the molecular orbital transition was established, and a quantitative assessment and transition contribution were provided based on the orbital transition diagrams. These results clarify fullerene-nucleobase recognition and support adsorption-enhanced fluorescence as a probe of base-dependent interactions.