Effect of a =X-NH-Fragment, (X = C, N), on Z/E Isomerization and ON/OFF Functionality of Isatin Arylhydrazones, ((Arylamino)Methylene)Indolin-2-Ones and Their Anions.

The subject of this work was the study of thermally and photochemically stimulated Z « E isomerization and hydrazo « 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.

ON/OFF Photostimulation of Isatin Bipyridyl Hydrazones: Photochemical and Spectral Study.

Four novel isatin hydrazones containing bipyridyl fragments were synthesized as potential ON/OFF switches. Hydrazone Z-isomers exhibit high thermal stability. The characteristic photochemical reaction for all studied hydrazones is the Z-E isomerization in CHCl3. After irradiation of hydrazones 1 and 2 in dimethylformamide (DMF), the photoreaction products are tautomers. When using light with the appropriate wavelength, the photo-tautomerization reaction is reversible. In these conditions, studied hydrazones have ON/OFF switch properties. In the case of hydrazones 1 and 2, by alternating heat and light stimulation it is possible to control the isomerization process reversibly. In the presence of fluoride ions, NH hydrogen from the studied hydrazones is cleaved, and the corresponding anions are formed. The resulting anions of Z-isomers are changed to the corresponding E-isomer at room temperature.

4-Azafluorenone and α-Carboline Fluorophores with Green and Violet/Blue Emission.

The emission properties of three 4-azafluorenone and five new α-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 α-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 α-carbolines were investigated in prepared organic field-effect transistors and organic light-emitting diodes, respectively.

Isatin-1,8-Naphthalimide Hydrazones: A Study of Their Sensor and ON/OFF Functionality.

Five novel hydrazones derived from substituted isatins were synthesized as potential anion sensors. Using UV-VIS, FTIR, NMR and fluorescence spectroscopy, these compounds' 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-, HSO4-, Br-, Cl-, NO3-, F- and CH3COO-) and these receptors' 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.

Tautomeric photoswitches: anion-assisted azo/azine-to-hydrazone photochromism.

The photoswitching properties of two easily synthesized isatin 4-nitrophenylhydrazones were investigated. Although the parent isatin 4-nitrophenylhydrazones exhibit low addressability which hampers their photochromic applications, the addition of strongly basic anions to phenylhydrazone solutions creates a new Vis-Vis photochromic system with the unusual azo/azine-to-hydrazone photo-tautomerization process as the photoswitching mechanism. To the best of our knowledge, this is the first report related to the anion-assisted azo/azine-to-hydrazone photo-tautomerism.

Effect of Structure on Charge Distribution in the Isatin Anions in Aprotic Environment: Spectral Study.

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.

7-Dialkylaminocoumarin Oximates: Small Molecule Fluorescent "Turn-On" Chemosensors for Low-Level Water Content in Aprotic Organic Solvents.

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.

Synthesis and Herbicidal Activity of New Hydrazide and Hydrazonoyl Derivatives.

Three new hydrazide and five new hydrazonoyl derivatives were synthesized. The chemical structures of these compounds were confirmed by 1H-NMR, IR spectroscopy and elemental analysis. The prepared compounds were tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts and growth of the green algae Chlorella vulgaris. IC50 values of these compounds varied in wide range, from a strong to no inhibitory effect. EPR spectroscopy showed that the active compounds interfered with intermediates Z•/D•, which are localized on the donor side of photosystem II. Fluorescence spectroscopy suggested that the mechanism of inhibitory action of the prepared compounds possibly involves interactions with aromatic amino acids present in photosynthetic proteins.

3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution and polymer matrices: Tuning their fluorescence via para-phenyl substitution.

The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethylamino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (RF, Br, CF3, CN or NO2) in the para-position on the phenyl ring were investigated in solvents and in polymer matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted Intra-molecular Charge-Transfer (TICT) state formation, specific solute-solvent interactions (hydrogen bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.

Isatinphenylsemicarbazones as efficient colorimetric sensors for fluoride and acetate anions - anions induce tautomerism.

The anion induced tautomerism of isatin-3-4-phenyl(semicarbazone) derivatives is studied herein. The interaction of F(-), AcO(-), H2PO4(-), Br(-) or HSO4(-) anions with E and Z isomers of isatin-3-4-phenyl(semicarbazone) and N-methylisatin-3-4-phenyl(semicarbazone) as sensors influences the tautomeric equilibrium of these sensors in the liquid phase. This tautomeric equilibrium is affected by (1) the inter- and intra-molecular interactions' modulation of isatinphenylsemicarbazone molecules due to the anion induced change in the solvation shell of receptor molecules and (2) the sensor-anion interaction with the urea hydrogens. The acid-base properties of anions and the difference in sensor structure influence the equilibrium ratio of the individual tautomeric forms. Here, the tautomeric equilibrium changes were indicated by "naked-eye" experiment, UV-VIS spectral and (1)H NMR titration, resulting in confirmation that appropriate selection of experimental conditions leads to a high degree of sensor selectivity for some investigated anions. Sensors' E and Z isomers differ in sensitivity, selectivity and sensing mechanism. Detection of F(-) or CH3COO(-) anions at high weakly basic anions' excess is possible.

7-(Dimethylamino)coumarin-3-carbaldehyde and its phenylsemicarbazone: TICT excited state modulation, fluorescent H-aggregates, and preferential solvation.

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.

Spectral properties of substituted coumarins in solution and polymer matrices.

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.

Influence of polarity of solvents on the spectral properties of bichromophoric coumarins.

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.

Synthesis and study of novel coumarin derivatives potentially utilizable as memory media.

Novel coumarin derivatives, 2-oxo-2H-chromenecarbaldehyde hydrazones were prepared by reaction of substituted 2-oxo-2H-chromenecarbaldehydes with N-aminoimides in ethanol in the presence of 4-toluenesulfonic acid as catalyst. The photochromic and thermochromic properties of the prepared compounds were investigated.

Spectroscopic study of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles and their N-allylbenzothiazolium bromides. Solvent and substituent effects on their ultraviolet-visible and fluorescence spectra.

UV-vis and fluorescence spectra of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles 1 and their N-allylbenzothiazolium bromides 2 have been measured and interpreted. The substitution and solvent effects on electronic structure and spectra have been investigated. The benzothiazolium salts substituted with saturated cyclamines show strong push-pull character and can be used as potential NLO materials. Formation of aggregated structures was observed at higher concentrations of the benzothiazolium bromides.