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Zn(II) complexes using La and Lb were synthesized. The Z-isomers of studied complexes were isolated from the reaction mixture. The structure of these complexes was determined by NMR spectroscopy and X-ray diffraction analysis. The Z-isomers of complexes are present in two conformations. The change in hydrazo = azo equilibrium of the complexes is achieved by light-stimulated photoreaction. The phototautomerization is a reversible process. By changing the wavelength used to stimulate photoreaction, the change is achieved in the tautomeric reaction equilibrium state in the desired direction. The studied complexes have the characteristics of ON/OFF switches. It is possible to use UV–vis and fluorescence spectroscopy to clearly define ON and OFF states and to measure the response of signals induced by photostimulation.

The light and thermally initiated mutual E- and Z-isomer transformations of two efficient isatin N-phenylsemicarbazone colorimetric sensors for strongly basic anions differing in sensitivity, selectivity and sensing mechanism were investigated in solvents of different polarity. The reaction mechanism of photochemically and thermally initiated E–Z isomerization and the absence of back Z–E isomerization is discussed in terms of self-aggregate formation, hydrazide-hydrazonol tautomeric equilibrium, the role of intra- and inter-molecular hydrogen bonds, excited-state proton transfer, solvent polarity and concentration effects. The effect of the activation energies related to conformational and geometric changes of the isomers and the possible analytical application were investigated. Theoretically calculated properties are in good agreement with obtained experimental results and support the proposed reaction mechanism.

This paper describes four photo-sonochemical reactors for simultaneous application of UV light and ultrasonic irradiation on the reaction mixture. Two of them allow a follow-up of the reaction course by UV–vis spectroscopy continuously and are therefore regarded as suitable for kinetic studies.

The photochemical behaviour of 6-X-4H-3(bicyclo[2.2.1]-5-heptene-2,3-dicarboimidoximinomethyl)-4-chromones (X=CH 3 , Cl, NO 2 ) was studied upon irradiation ( λ irr ≅310 nm) in CH 3 OH and benzene. Direct E–Z or Z–E photoisomerization and thermal Z–E isomerization were observed. The activation energies of Z–E isomerization were in the range 8.7–69.5 kJ mol −1 . Prolongation of the irradiation of the title compounds till the equilibrium is reached between E and Z isomers results in the irreversible process. The products of this irreversible process were identified. Fluorescence emission and excitation spectra were measured.

The ultrasound effect on two well-described photochemical reaction was studied. Ultrasound does not affect the initiated photoisomerization of 2-phenylindan-1,3-dione to 3-benzylidenephthalide in the case when any additive is present, which is a monomolecular process, but enhances the effect of quenchers on its photoisomerization, which is a bimolecular process. The photodimerization of acenaphthylene is considerably affected by simultaneous sonication, which results in different ratios of the stereoisomers in comparison with the silent process Sonication appears to affect the first reaction by homogeneous distribution of the excited states, or intermediates and possibly by quenching the excited triplet state of the second reaction. Two new reactors were designed allowing simultaneous irradiation of the reaction mixture by UV light and ultrasonic waves.

3-( N,N -dimethylamino)-2H-1-benzopyran-2-one (DMAC) exhibits a relatively strong shortlived emission (λ max ≈ 460 nm; lifetime, 0.2 ns) in non-polar solvents with a Stokes' shift of about 8000 cm −1 . In more polar solvents, the emission shifts bathochromically (Stokes' shift up to 10 000 cm −1 and lifetime of 0.5 ns). Polar protic solvents quench the fluorescence and the quenching can be quantitatively described by a Stern—Volmer dependence. The bimolecular quenching rate constants are lower than those controlled by diffusion. The monomethyl derivative 3-( N -methylamino)-2H-1-benzopyran-2-one (MAC) exhibits emission in non-polar and polar solvents which is hypsochromically shifted with respect to DMAC (λ max ≈ 400 nm; Stokes' shift around 4000 cm −1 ) and is short-lived (less than 0.1 ns). The fluorescence of DMAC and MAC originates in the intramolecular charge-transfer state.

2- N,N -dimethylamino-1,3-indanedione (DMAI) undergoes demethylation during photolysis (λ > 290 nm), producing 2- N -methylamino-1,3-indanedione (MAI) under conditions of direct or sensitized reaction. Ferrocene successfully quenches demethylation, while ethyl iodide accelerates the reaction rate. The yield and the rate of formation of MAI strongly depend on the reaction conditions, mainly on the solvent, the concentration of DMAI and the presence of an electron acceptor (substituted nitrobenzene). The UV, IR and NMR spectra support the donor—acceptor intramolecular interpretation in the ground state of DMAI and MAI.

3-( N , N -dimethylamino)-2 H -benzopyran-2-one (DMAC) sensitizes the decomposition of CCl 4 during the photolysis in the near UV region (λ > 290 nm). The products of the photolysis are 3-( N -methylamino)-2 H -1-benzopyran-2-one (MAC) as a result of the demethylation of DMAC and the compounds formed by the reaction of DMAC with the trichloromethyl radical 3-( N , N -dimethylamino)-3,4-bis(trichloromethyl)-2 H -3,4-dihydrobenzopyran-2-one and hydrochloride DMAC. Recombination of ·CCl 3 radicals yields hexachloroethane. The ratio of the products depends on the reaction conditions (the concentration of DMAC, the light intensity and the temperature). The primary step in the mechanism of the sensitization of CCl 4 is assumed to be the formation of the excited state, charge transfer (CT) complex of the type DMAC δ+ …CCl 4 δ− . Chloromethanes CH x Cl 4− x ( x = 0,1,2) quench the fluorescence of DMAC and MAC. The Stern—Volmer constant for MAC is related to the electron affinity of chloromethanes.