An experimental and theoretical investigation was performed to study the photostability of cytosine and isocytosine. The experimental UV irradiation of acetonitrile solutions of the two compounds showed that the amino-oxo tautomer of cytosine is photostable while the amino-oxo tautomer of isocytosine tautomerizes to the amino-hydroxy form. The theoretical investigations were carried out at the CC2 level of theory. They were performed to explain the experimental observations. It was found that the (1)ππ(*) excited states of the ring deformation mechanisms of cytosine and isocytosine relax (internal conversion) to the ground states of the amino-oxo forms of the compounds. We propose a channel for the radiationless deactivation of the repulsive (1)πσ(*) excited state of the amino-oxo form of isocytosine to the ground state of the amino-hydroxy tautomer.

ABSTRACT:The nonlinear optical (NLO) properties of novel styrylquinolinium dye thin films for photonic applications have been studied by the Z-scan, second harmonic generation (SHG), and third harmonic generation (THG) techniques, providing both the second-and third-order nonlinear optical parameters. The styrylquinolinium dye (E)-1-ethyl-4-(2-(4-hydroxynaphthalen-1-yl)vinyl)quinolinium bromide was synthesized by the Knoevenagel condensation, and its structure and physicochemical properties were determined by 1 H NMR, 13 C NMR, FTIR, UV−vis spectroscopy, and elemental analysis. Functional thin films were deposited by pulsed laser deposition (PLD) using UV TEA N 2 laser onto glass substrates and KCl, NaCl monocrystals at room temperature and vacuum at 10 −3 mbar/0.1 Pa. Further characterization of the films and target from native material by FTIR spectroscopy revealed that there was no difference between the deposited films and the initial material. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements have been also performed in order to provide information about the morphology and topology of the thin films.

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Linear-dichroic infrared spectra (IR-LD) of 3-ethoxy-4-(N-norcodeino-)cyclobutene-1,2-dione (1) and codeine dihydrogenphosphate (Codeinum phosphoricum) (2), oriented as solid suspensions in nematic liquid crystals, have been measured. IR characteristic band assignments were made, and used in stereo-structural predictions. The results were compared with crystallographic structures of similar organic systems, and found to be in good agreement.

The title compound (systematic name: 6α‐acet­oxy‐4,5α‐ep­oxy‐3‐meth­oxy‐17‐meth­yl‐morphin‐7‐ene), C20H23NO4, crystallizes with one mol­ecule in the asymmetric unit. The mol­ecular structure exhibits features typical of morphine derivatives with a T configuration. The three‐dimensional packing is stabilized by inter­molecular C—H⋯N and C—H⋯π inter­actions.