Two Schiff bases: 2-(1-(methylimino)methyl)-phenol (SMA) and its chlorosubstituted derivative 2-(1-(methylimino)methyl)-6-chlorophenol (SMAC), and SMA complexes with water were studied by infrared matrix isolation spectroscopy and DFT/B3LYP/6-311G++(2d,2p) quantum chemical calculations. SMA and SMAC bases trapped in an argon matrix from the vapor above the liquid and solid samples have the most stable enol conformation with intramolecular O-H···N bonding. Irradiation (λ > 320 nm) leads in both bases to a rotational isomerization reaction in which the scission of the O-H···N bond occurs and the C(H)NCH(3) and OH groups are turned by 180° around the C-C and C-O bonds, respectively. In SMAC a competitive photoreaction channel yields the trans-keto tautomer. The identification of the two SMAC photoproducts evidences that in the excited enol form of this compound two processes compete with each other: the rotational isomerization and intramolecular proton transfer (ESIPT). In the argon matrices doped with SMA and H(2)O the SMA-water complexes were identified and characterized spectroscopically. Interaction of SMA with one or two water molecules does not affect the photochemistry of SMA.

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The photochemistry of salicylaldoxime in solid argon has been investigated by FTIR spectroscopy and DFT calculations. The salicylaldoxime molecule trapped in the matrix from the vapor above the solid sample has the most stable syn1 conformation with an intramolecular hydrogen bond. Irradiation (λ Ͼ 320 nm) leads to conversion of the syn1 conformer into the syn3 one, in which the C(H)NOH and (C)OH groups are rotated around the C-C and C-O bonds, respectively, and the intramolecular hydrogen bond is broken. The photochemistry of syn3 involves three possible routes: (i) conversion of syn3 into anti2 conformer, this process requires rearrangement of the NOH group with respect to the

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