Search

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 water sensing properties of four new efficient two-component colorimetric and fluorescent “turn-on” chemosensors based on the coumarin phenylsemicarbazone skeleton bearing different acceptor/donor functional groups on aniline structural subunits were investigated and are discussed in terms of their photophysical properties, interaction mechanism, sensitivity and substituent effects. Due to the sensing mechanism based on reversible acid–base keto/enolate (hydrazide/hydrazonolate) equilibrium, all the studied coumarin phenylsemicarbazone chemosensors provided rapid and reversible response to low-level water content in polar aprotic solvents. To the best of our knowledge, the determined detection limits for water by studied chemosensors are among the lowest published detection limits in the literature and have competitive sensitivity with chemodosimeters. Their deficiency is, however, the necessity of F− base presence.

The photochromic properties of isatin N2-diphenylhydrazones as a new type of molecular switch were investigated. Interestingly, dimerization stabilizes the formation of only E-isomers in the synthesis, even without a Z-isomer presence in the mother liquor. The irradiation of E-isomers in solution at their absorption maxima leads to the formation of the corresponding Z-isomers. Although the shift in the absorption maximum is not large and photochemical quantum yields are lower compared to in commonly used photoswitches, the absorbance changes are sufficient for potential practical use of these compounds as On-Off switches when the readout wavelength is optimally selected. The process is reversible and switching cycles can be repeated many times in both directions. The determined thermodynamic parameters and calculated geometry of the transition state clearly indicate the inverse mechanism of the thermally initiated slow back Z–E isomerization. Due to the Vis-Vis character of molecular photoswitching and significant geometric changes during the switching process, isatin N2-diphenylhydrazones are eminently suitable for molecular switching in biological/biotechnological applications. Moreover, the interaction of isatin N2-diphenylhydrazones with strongly basic anions increases their functionality and creates a four-state On-Off switch in one molecule. This four-state switch includes the unique E–Z isomerization induced photochemical switching between two stable tautomeric forms of organic amide anions. Simple synthesis of these derivatives and their sufficiently sensitive response to external stimuli promote isatin N2-diphenylhydrazones as suitable candidates for both discussed photochemistry areas (molecular switching and actinometry).

The effect of substituent and concentration on anion sensing selectivity and sensitivity of nine new easily synthesized isatin N-phenylsemicarbazone E-isomer sensors IIIa–XIa was investigated. The substantial difference between the association constants for IIIa–XIa interaction with strongly and weakly basic anions allows detection of F− or CH3COO− anions even at high weakly basic anion excess. Substitution in position 5- of the isatin ring and para-substitution on the phenyl ring in the phenylsemicarbazide chain influence sensor:anion complex stoichiometry and thus also sensor sensitivity. Detection limits of 3–4 × 10−7 mol dm−3 for F− and CH3COO− anions by sensors IVa and Va bearing electron-withdrawing substituents are among the lowest published detection limits for these anions in organic solvents. The high selectivity and sensitivity of sensor VIa allows confident F− detection at tolerated fluoride drinking-water level. The solution dilution leads to a dramatic change in sensor selectivity. Consequently, one E-isomer can be used to sense both strongly and weakly basic anions. On the other side, higher sensor solution concentrations increase the F− and CH3COO− anion detection range, similar to the additional Z-isomer utilization.

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.

In this work, the effect of inter- and intramolecular interactions of reactants and products, reactants concentration as well as the solvent effect on the ratio of E and Z isomers of isatinphenylsemicarbazones in the reaction mixture is examined. Theoretical calculations proved that Z isomers are more stable than E isomers. Experimental results confirmed the noncovalent intermolecular donor-acceptor interactions of the reactants in the reaction mixture at concentrations above 0.1 mol L−1. The E/Z isomer ratio of isatin-3-(4-phenyl)semicarbazone (I) and N-methylisatin-3-(4-phenyl)semicarbazone (II) depends on the initial concentrations of 3-amino-1-phenylurea (phenylsemicarbazide; V) and 1H-indole-2,3-dione (isatin; III), or 3-methylindol-2,3(1H)-dion (3-methylisatin; IV), respectively. Both isomers exhibit high thermal stability. Thermal E-Z isomerization takes place at temperatures above 70°C in N,N-dimethylformamide.

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.

A detailed investigation of infrared spectra was used to distinguish the structure of 3-(N,N-dimethylamino)coumarin from the structure of hypothetic 2-(N,N-dimethylamino)-1,3-indanedione suggested earlier as the product of the reaction between salicylaldehyde, acetanhydride and betaine.

Enantiopure 10,10′-bi(naphtho[2,3-b]pyran) (5a) has been prepared from (R)-BINOL by using the attachment of 1,1-diphenylallyl alcohol to positions 3 and 3′ of the binaphthalene via Heck coupling as a key step. The irradiation of 5a in solution with UV light at 313 nm caused photochemical opening of only one of the pyran rings, accompanied by minor changes in the CD spectrum. Thermal ring closure occurred spontaneously with an activation barrier of 74 kJ mol−1. When 5a was immobilised in a polystyrene film, an improved switching performance, both in terms of fatigue resistance (>10 cycles) and CD signal amplitude (>100 mdeg, >6:1 signal ratio of open/closed forms), was observed.

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.

The photochemical isomerizations have been studied of 2-phenyl-1,3-indanedione to mixture of E- and Z-benzalphthalide and of E-benzalphthalide to Z-benzalphthalide depending on the solvent used, concentration, and the light wavelength. The attempts at the reverse photochemical isomerization of E-benzalphthalide to 2-phenyl-1,3-indanedione have failed. Quantum yields of the isomerization of 2-phenyl-1,3-indanedione decrease in the following solvent series: cyclohexane acetonitrile benzene tetrachlormethane methanol. The isomerization quantum yield of 2-phenyl01,3-indanedione is inversely proportional to concentration of the starting substance, but the dependence of 1/φ on the concentration is not linear.