Conformational switching induced by near-infrared laser irradiation.

This work describes a molecular system where it is possible to effectively control the interconversion between two different stable conformational states, using selective narrow-band near-infrared irradiation. Monomers of hydroxyacetone (HA) isolated in low temperature argon matrices at 15 K exist exclusively in the conformational ground state Cc. Narrow-band near-infrared vibrational excitation of the first OH stretching overtone of the Cc form resulted in conformational isomerization. The photoproduct was identified as the higher energy Tt conformer of HA, and it was found to be stable at 15 K. The reverse isomerization, converting Tt into Cc, could also be induced by laser excitation of the first OH stretching overtone of the Tt form. The interpretation of the experimental observations was supported by anharmonic and harmonic calculations of the vibrational spectra and barriers to intramolecular rotation.