Effects of Entangled IR Radiation and Tunneling on the Conformational Interconversion of 2-Cyanophenol

The conformers of 2-cyanophenol (2CP) and their interconversions were studied by infrared (IR) spectroscopy after trapping the monomers of the gaseous compound into low-temperature (15 K) argon (Ar) and nitrogen (N₂) matrixes. To assist in the interpretation of the experimental results, B3LYP, MP2, and QCISD electronic structure calculations were carried out for the 2CP molecule. Two planar conformers, cis and trans (orientation of OH with respect to the cyano group), are predicted with gas-phase populations at the sublimation temperature of ∼98 and ∼2%, respectively. The most stable form (cis) was experimentally identified in both cryomatrixes, whereas the less stable one (trans) was not detected in Ar but could be observed in the N₂ matrix with an abundance of ∼15%. Selective and bidirectional conversion between the two identified conformers was achieved upon irradiating the compound trapped in N₂ matrix with near-infrared (NIR) laser light tuned at the wavenumbers of the 2ν(OH) transitions of the respective conformers. The conformational composition of 2CP was also found to be affected by the broad-band IR radiation emitted by the spectrometer source. This effect could be suppressed, partially or completely, by using different long-pass IR filters, with cutoff values of approximately 2200, 1590, and 1170 cm^-1. The observed conformational changes are rationalized in terms of a competition between the over-the-barrier (light-induced) and through-the-barrier (hydrogen atom tunneling) effects. Very interestingly, both effects occur on the same time scale.