Search

The subject of this work was the study of thermally and photochemically stimulated Z &laquo, E isomerization and hydrazo &laquo, azo tautomerism of Z- and E-isomers of isatin arylhydrazones and ((arylamino)methylene)indolin-2-ones and their anions. Using NMR, UV-Vis spectroscopy, kinetic measurements, and HPLC, we studied the relationship of structure, (Z- and E-isomers), of these compounds and hydrazo=azo tautomerism. The ON/OFF functionality of these compounds and their anions using light to stimulate switching between ON and OFF states was investigated. We pointed out the characterization of the effect of =N- and =CH- structural fragments and aryl structure on ON and OFF states of isatin arylhydrazones and ((arylamino)methylene)indolin-2-ones.

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.

Five novel hydrazones derived from substituted isatins were synthesized as potential anion sensors. Using UV-VIS, FTIR, NMR and fluorescence spectroscopy, these compounds&rsquo, tautomeric equilibrium and Z-E photoisomerization were studied in DMF and CHCl3, depending on the hydrazone concentrations, the presence of basic anions and light stimulation. Anion recognition aspects (PF6&minus, HSO4&minus, Br&minus, Cl&minus, NO3&minus, F&minus, and CH3COO&minus, ) and these receptors&rsquo, detection limits were also studied. We also tested the light-stimulated ON-OFF functionality of these compounds in the presence or absence of these anions.

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).

Five isatin anions were prepared by deprotonation of initial isatins in aprotic solvents using basic fluoride and acetate anions (F− and CH3COO−). The F− basicity is sufficient to deprotonate isatin NH hydrogen from all the studied compounds. This process is reversible. In the presence of proton donor solvents, the anions form the corresponding isatins. The isatin hydrogen acidity depends on the overall structure of the isatin derivatives. The anions were characterized by ultraviolet–visible (UV–Vis), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Interestingly, the anions form aggregates at concentrations above 10−3 mol·dm−3. Further, the effect of cations on the UV–Vis spectra of the studied anions was studied. Charge transfer and its distribution in the anion depends on the radius and the cation electron configuration. The alkali metal cations, tetrabutylammonium (TBA+), Mg2+ and Ag+, interact with the C-2 carbonyl oxygen of the isatin anion. The interaction has a coulombic character. On the other hand, Cd2+, Zn2+, Hg2+, Co2+, and Cu+ cations form a coordinate bond with the isatin nitrogen.

The water sensing properties of two efficient two-component fluorescent “turn-on” chemo-sensors based on the 7-dialkylaminocoumarin oxime acid-base equilibrium were investigated. Interestingly, although simple frontier orbital analysis predicts an intramolecular photoinduced electron transfer quenching pathway in conjugated oximates, TD-DFT (Time-dependent density functional theory) quantum chemical calculations support non-radiative dark S1 excited state deactivation as a fluorescence quenching mechanism. Due to the acid-base sensing mechanism and sensitive “turn-on” fluorescent response, both studied coumarin aldoxime chemosensors exhibit rapid response to low-level water content in polar aprotic solvents, with detection limits comparable to chemodosimeters or chemosensors based on interpolymer π-stacking aggregation.

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.

The emission properties of three 4-azafluorenone and five new &alpha, carboline fluorophores in both solution and thin solid films were investigated. Fluorescence of the azafluorenone is clearly enhanced in thin solid films due to the presence of phenyl/biphenyl rotors, and these derivatives can be classified as green Aggregation-Induced Emission luminogens (AIEgens) with a non-emissive heteroaromatic core structure. Compared to azafluorenones, emission of &alpha, carbolines is hypsochromically shifted to the blue region of the electromagnetic spectrum, and most of these derivatives exhibit strong violet-blue fluorescence in both solution and thin solid film layers. Further, the effective mobility and electroluminescence of new &alpha, carbolines were investigated in prepared organic field-effect transistors and organic light-emitting diodes, respectively.

The photophysical properties of 7-(dimethylamino)coumarin-3-carbaldehyde 3 and its phenylsemicarbazone 4 were investigated in solvents of various polarity and in differing solvent mixtures. The different fluorescent quantum yield (ΦF) behavior of 3 and 4 in highly polar solvents is discussed in terms of Twisted Intramolecular Charge-Tranfer (TICT) state formation and the specific solute-solvent interactions. Because of the weak intermolecular hydrogen bonding ability of both the radiative ICT and nonradiative TICT excited state of 3 and the linear steep decrease in ΦF from a medium to high polarity region, coumarin 3 could be a useful polarity probe for microenvironments containing hydrogen bonding groups. Compared to 3, coumarin 4 exhibits the highest ΦF values in highly polar solvents with strong hydrogen bond acceptor ability. The high quantum yield of fluorescence in DMSO, DMF, and alcohols qualifies coumarin 4 as a laser dye in the given medium, with kF higher than k(nr). Contrary to previous reports that many H-aggregates are nonfluorescent in nature, coumarin 3 forms highly fluorescent H-aggregates in MeOH and EtOH. On the basis of the restrictions of the Kasha-exciton theory model, we assume that the formation of fluorescent H-dimer aggregates of 3 is driven by π(+)-π(-) interactions. To the best of our knowledge, this is the first report on aggregation of coumarin dye in alcoholic solutions. In addition, restrictions in the fitting procedure relating to determination of the solvation number, n, using the Covington-Newman model of preferential solvation and also the solvent nonideality parameter, h', are discussed in this article.

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH₃, OCH₃ and N(CH₃)₂, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH₃)₂ in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH₃)₂ substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5-4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have k(F) higher than k(nr) in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.

Absorption and fluorescence spectra of bichromophoric coumarins were investigated in different solvents and in polymer matrices. These bichromophoric coumarins were composed of a coumarin dimethylamino-substituted at position 7 or unsubstituted coumarin and phthalimide or a 1,8-naphthylimide linked with an iminomethyl bridge to the position 3 or 8 of the coumarin ring. Absorption spectra of 7-dimethylamino derivatives in position 3 of coumarin were quite similar, exhibiting broad bands around 430-440 nm like the parent compound 7-dimethylaminocoumarin-3-carbaldehyde. For coumarin derivatives substituted in position 8, the absorption maximum was shifted to shorter wavelength as for derivatives without position 7 dimethylamino substitution. The most intense fluorescence was observed for 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin in polar solvent, while intense fluorescence was observed for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxobenz[de]isoquinolinyl)iminomethyl]-coumarin in non polar solvent (chloroform), comparable with the fluorescence of 7-amino-4-methylcoumarin. Spectral measurements of bichromophoric coumarins in polymer matrices revealed that the maxima lies in between those for chloroform and methanol yielding more intense fluorescence then in solutions. Completely different solvent effects were observed for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxobenz[de]isoquinolinyl)imino-methyl]coumarin and 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin. With addition of polar methanol the intensity of fluorescence decreases, yielding a Stern-Volmer-like constant of 0.54 dm3 mol−1 for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxo-benz[de]isoquinolinyl)iminomethyl]coumarin and an even higher one of 1.08 dm3 mol−1 for 7-dimethylaminocoumarin-3-carbaldehyde compared to the rather low one of 0.024 dm3 mol−1 for 7-amino-4-methylcoumarin. Contrary to this, addition of methanol under identical conditions brings about an increase in fluorescence intensity of 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin (about 60-fold). The reasons for these different solvent effects are discussed.

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.

Reaction of 2,5-dimethyl-3,4-diphenylcyclopent-2-enone ( 1 ) with Ph 3 PCH 2 in THF gave 2,5-dimethyl-3,4-diphenylcyclopent-2-enel-ylidene ( 2 ) in 75% yield. Treatment of 2 with one equivalent Br 2 , followed by twp equivalents of triethylamine gave 1,4-dimethyl-2,3-diphenylfulvene ( 3 ) in 60% overall yield. Treatment of 3 with LiCH 3 and LiC 6 H 5 followed by FeCL 2 gave [ η 5 -1-CH 3 CH 2 -2,5-(CH 3 ) 2 -3,4-(C 2 H 5 ) 2 -3,4-(C 6 H 5 )C 2 ] 2 Fe and [ η 5 -1-C 6 H 5 CH 2 -2,5-(CH 3 ) 2 -3,4-(C 6 H 5 ) 2 C 5 ] 2 Fe, respectively, in good yield. Treatment of 3 with LiNHC(CH 3 ) 3 and LiP(C 6 H 5 ) 2 followed by FeCl 2 gave [ η 5 -1-(CH 3 ) 3 CNHCH 2 -2,5-(CH 3 ) 2 -3,4-(C 6 H 5 ) 2 -3,4-(C 6 H 5 ) 2 C 5 ] 2 Fe and [ η 5 -1-(C 6 H 5 ) 2 PCH 2 -2,5-(CH 3 ) 2 -3,4-(C 6 H 5 ) 2 C] 2 Fe, respectively, in good yield. Treatment of 3 with (R)-LiNHCH(CH 3 )C 6 H 5 followed by FeCl 2 gave the corresponding enantiomerically pure ferrocene complex (R,R)-[ η 5 -1-C 6 H 5 CH(CH 3 )NHCH 2 -2,5-(CH 3 ) 2 -3,4-(C 6 H 5 ) 2 C 5 ] 2 Fe in 44% yield.

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.

The method described herein this review compares the efficiency of ultrasound irradiation in sonochemical experiments in organic solvents. This method was shown to be independent of the shape and volume of the reaction vessel. The principle of this method is based on the fact that the concentration of dissolved oxygen in the entire reaction volume during acoustic cavitation depends on the ultrasound power or intensity of ultrasound field respectively. The concentration of dissolved oxygen is determined by the measurement of the fluorescence intensity with fluorescence probes.

Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Buchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction.

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.