A strong charge-transfer effect in surface-enhanced Raman scattering induced by valence electrons of actinide elements

Abstract

The 6d electrons of Ac atom involved in excited transitions induce a strong CT-SERS enhancement which can be tuned by changing the conformation of pyridine-Ac@Au7 complexes.

Coupling effect on charge‐transfer mechanism of surface‐enhanced resonance Raman scattering

“…For the pyrazine–Ac@Au 7 (P) and pyrazine–Ac@Au 7 (V) structures, their SERS and SERRS spectra excited at different wavelengths reveal that there are stronger Raman intensities for pyrazine–Ac@Au 7 (V) complex, because of different bond length of Au―N, and the degree of charge transfer at ground state and orientation of charge transfer between pyrazine and Ac@Au 7 . The conclusion is similar to that presented in prior research by Gao et al . For the electronic transitions around 520 nm, both the charge‐transfer transitions from Ac@Au 7 to pyrazine and intrametallic charge redistribution are included for the pyrazine–Ac@Au 7 (V) complex, while the charge transfer is from pyrazine to Ac@Au 7 for the pyrazine–Ac@Au 7 (P) complex.…”

“…For the pyrazine–Ac@Au 7 (V) and pyrazine–Ac@Au 7 (P) complexes without coupling effect and resonant electronic transitions, their SERS intensities excited at the same incident lights are enhanced 1 × 10 3 and 5 times, respectively (see Figs S2(c) and S3(b)). In addition, the SERRS intensity of Ac@Au 7 –pyrazine–Ac@Au 7 (V/P) at 665 nm is about 3 times larger than the strongest SERRS intensity of V‐complex and 3 × 10 2 times larger than the strongest SERRS intensity of P‐complex presented in the prior work by Gao et al . The results above reveal that the vertical structure and coupling effect are important for the SERRS enhancement.…”

“…While without the coupling effect, the SERS enhancement factor is only 7 × 10 2 at 681 nm. Additionally, the SERRS intensity of Ac@Au 7 –pyrazine–Ac@Au 7 (V) is in the order of 10 7 A 4 /amu, which is 1 order of magnitude higher than the strongest SERRS intensity of V‐complex presented in the prior work by Gao et al . Thus, the coupling effect on the charge‐transfer mechanism plays an important role in SERRS spectroscopy.…”

“…Compared with the normal Raman spectrum of pyrazine excited at 513 nm, those SERRS spectra are enhanced about 1 × 10 5 times by the coupling effect, 3 × 10 2 times for the vertical structure and 10 times for the plane structure without coupling effect, respectively. In addition, the SERRS intensity of Ac@Au 7 –pyrazine–Ac@Au 7 (V/P) excited at 513 nm is about 3 × 10 6 A 4 /amu, which is 3 times than the strongest SERRS intensity of V‐complex and 3 × 10 2 times than the strongest SERRS intensity of P‐complex presented in the prior work by Gao et al . So, it is concluded that, for the SERRS spectra, the coupling effect and vertical structure are two core factors for the charge‐transfer mechanism of SERRS.…”

“…It is expected that the degree and orientation of charge transfer between molecule and substrate can significantly influence the enhanced intensity and profile of SERRS. Furthermore, the coupling effect on charge‐transfer mechanism can significantly enhance the SERRS intensity of Ac@Au 7 –pyrazine–Ac@Au 7 (V) up to the order of 10 7 A 4 /amu, which is 1 order of magnitude higher than the SERRS intensity of V‐complex presented in the prior work by Gao et al . The different coupling ways can result in different degrees of charge transfer on electronic transitions, also different intensities of charge‐transfer absorption peaks, and both of them can strongly influence the enhancement of charge‐transfer mechanism of SERRS.…”