Abstract
The optically-controllable reversible single-molecule photoswitching in 2-thiobenzimidazole (C7H6N2S; 2TBI) is experimentally demonstrated. Monomers of the target compound were isolated in low temperature argon matrices and investigated by infrared spectroscopy. After matrix deposition, only the thione tautomer of the compound was observed. Such result is in accordance with the predicted relative energy of the two tautomers (thione and thiol forms; ΔE(thiol-thione) = 44.6 kJ mol−1, as obtained at the DFT(B3LYP)/6−311 + +G(d,p) level of approximation). In situ irradiation of the initially deposited matrix at λ = 307 nm, using an UV tunable narrowband light source, led to conversion of the thione form of 2TBI into the thiol tautomer. In turn, subsequent irradiation at λ = 246 nm resulted in the reverse, thiol→thione, photoconversion, demonstrating that the two tautomers can be selectively interconverted through optical control. Noteworthy, both photoprocesses take place without simultaneous significant photodecomposition of the compound, thus making this chemical system a promising candidate for acting as a molecular switch. The observed phototautomerizations are rationalized in terms of the Photo-Induced hydrogen-atom Detachment-Association (PIDA) mechanism.
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