Figure 4.

Dearomatization of MB⁺ after a 2e^–/1H⁺ transfer. (a) MB⁺ is a planar aromatic molecule that absorbs strongly in the visible light spectrum (λ_max = ∼650 nm). (b) LMB is a photoproduct of a 2e^–/1H⁺ transfer in MB⁺/DIPEA PET reaction. After a 2e^–/1H⁺ transfer, the thiazine ring in LMB is dearomatized and is significantly bent from the original planar structure. Time-dependent DFT (TD-DFT, Experimental Section) using ωB97XD/LANL2dz/CPCM-methanol predicts that LMB absorbs at λ_max = ∼300 nm, which corroborates the observed blue-shift of λ_max to ∼250 nm and explains the bleaching of the solution to its colorless form.