Photoinduced amino–imino tautomerism of 2-aminopyridine in a low-temperature argon matrix

Photoinduced amino–imino reversible tautomerism between 2-aminopyridine and 2(1H)-pyridinimine in a low-temperature argon matrix was observed by infrared (IR) spectroscopy and density functional theory (DFT) calculation. The former molecule (amino tautomer) changed to the latter (imino tautomer) by UV irradiation (340 > λ ⩾ 300 nm), and the reverse reaction occurred by that with a longer wavelength (370 > λ ⩾ 340 nm). Photoinduced transient IR bands assigned to the amino tautomer in the T1 state were also observed.