Size Effect on Ultrafast Dynamics of the Photoexcited ⁷Be Electron in ⁷Be@C_2n (2n = 60, 70, and 80)

The ultrafast excited-state dynamics of endohedral fullerenes are crucial in their photophysical and photochemical processes when they are employed as photovoltaic devices, photocatalytic devices, and single-molecule devices. In this study, by employing the ab initio non-adiabatic molecular dynamics simulations based on the time-dependent Kohn-Sham (TD-KS) method, we theoretically studied the size effect on ultrafast excited-state decay dynamics of the photoexcited ⁷Be electron in endohedral fullerenes ⁷Be@C_2n (2n = 60, 70, and 80). These excited-state decay dynamics, which involve the charge-transfer process, occur in an ultrafast time scale of about 3 ps. The larger fullerene cage delays the excited-state decay process because the presence of significant energy gaps and phonon modes in large endohedral fullerenes slows the non-radiative electron transitions among energy levels. Those findings not only provide physical insights into the excited-state decay dynamics of confined atoms but also stimulate further research to develop efficient endohedral-fullerene-based photoelectric and photocatalytic devices.