Fig. 3.

Redox behaviour of molecular tunnelling junction VI (methyl-viologen). a Chemical structures of different redox states of VI. b DFT-calculated Raman spectra and c experimental Raman from bulk solutions in which VI ²⁺ (red) is chemically reduced to VI ¹⁺ (purple) using dithionite, and VI ⁰ (triplet, blue) using NaBH₄ or Na₂S₂O₄ in the presence of Au nanoparticles (see Supplementary Fig. 10). The singlet VI ⁰ state (blue dotted line) is intermittently observed in NPoM experiments