Solvatochromic and pH Switch Properties of a D–π–A Dye with benzo[b]thiophene as Donor Moiety

A charge transfer dye with the D–[Formula: see text]–A structure was synthesized by Pd catalyzed Hartwig–Buchwald coupling and Knoevenagel condensation reaction, using N, N-dihexylbenzo[b]thiophen-6-amine as donor and 2-(3-cyano-4, 5, 5-trimethylfuran-2 (5H)-ylidene)malononitrile (TCF) as acceptor. The solvatochromic and pH switch properties of the as-synthesized dye were investigated through UV-vis absorption and fluorescence emission spectra. A positive solvatochromism of the dye in different polar solvents was observed along with a visible color change of the solution. By adding acid/base into the DMSO solution of the dye, the color as well as the absorption and emission spectra of the solution exhibited outstanding characteristics of pH switch.

Push-Pull Chromophores Based on the Naphthalene Scaffold: Potential Candidates for Optoelectronic Applications

A series of ten push-pull chromophores comprising 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as the electron-withdrawing group have been designed, synthesized, and characterized by UV-visible absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The solvatochromic behavior of the different dyes has been examined in 23 solvents and a positive solvatochromism has been found for all dyes using the Kamlet-Taft solvatochromic relationship, demonstrating the polar form to be stabilized in polar solvents. To establish the interest of this polyaromatic electron acceptor only synthesizable in a multistep procedure, a comparison with the analog series based on the benchmark indane-1,3-dione (1H-indene-1,3(2H)-dione) has been done. A significant red-shift of the intramolecular charge transfer band has been found for all dyes, at a comparable electron-donating group. Parallel to the examination of the photophysical properties of the different chromophores, a major improvement of the synthetic procedure giving access to 1H-cyclopenta[b]naphthalene-1,3(2H)-dione has been achieved.

SPECTORPHOTOMETRIC AND PROTOLYTIC PROPERTIES OF FUSED CYANOPIRIDINES

Development of new optical probes is a promising trend that has been actively implemented in recent years. A rational design of the probes should consider a number of parameters that contribute to the ability of the probe to exhibit highly selective optical response to the analyte. The obvious criteria are the chemical stability and reactivity of the probe, its photostability and the possibility of its reusable application. In this work, new probes based on fused benzothiazoles with different heterocyclic substituents were studied. The spectrophotometric characteristics of compounds in dimethylsulfoxide, acetonitrile and ethanol solutions were obtained. The probes exhibited the absorption in the near UV region and the blue part of the visible spectrum. Absorption spectra of the molecules are characterized by broad band with absorption maximum around 391–400 nm. The selected compounds demonstrated a slight positive solvatochromism. The blue shift of absorption maxima is due to the formation of protonated form of the probe in the presence of hydrochloric acid. Further, in basic conditions, the absorbance maxima of the probes are localized at longer wavelength (Δλ around 80 nm). Reversibility of compounds in the reactions of deprotonation-protonation was studied. Formal protonation constants of compounds (lgKpf) in water-organic solutions were calculated using the UV-Vis spectrophotometry titration method. Protonation constants of probes are in the range: lgKpf = 2.67–4.95. The obtained values of the protonation constants are in good agreement with the data calculated using the software ACD Labs. The presence of the amidine fragment in the structure of the chromophore core leads to an increase in its basicity, with respect to heterocyclic substituents. It was shown that the presence of a substituent more basic than benzothiazole leads to the destruction of the probe in solution with a pH 11. It occurs due to the opening of the iminopyridine cycle into its synthetic precursor. Based on the results, 2-(1,3-benzothiazol-2-yl)-3-(3-hydroxypropyl)-1-imino-1H-pyrido[2,1-b][1,3]benzothiazole-4-carbonitrile was selected for further use as sensitive pH probe.

Synthesis and evaluation of novel antibacterial monoazo disperse dyes based on sulfonamide derivatives on polyester

Purpose This paper aims to present the design and synthesis of a series of novel antibacterial monoazo disperse dyes based on sulfonamide derivatives to combine the dyeing and functional finishing steps on polyester into one process. Design/methodology/approach The diazoniom salts of sulfonamides, namely, 4-amino-N-(2-pyrimidinyl) benzenesulfonamide, 4-amino-N-(4-methyl-2-pyrimidinyl) benzenesulfonamide and 4-amino-N-(4,6-dimethyl-2-pyrimidinyl) benzenesulfonamide were prepared and then coupled to N,N-diethyl aniline, N,N-dicyanoethyl aniline and N,N-dihydroxy ethyl aniline, respectively, to produce the dyes. Findings The structures of the dyes were characterized using their spectral data (FTIR, 1H-NMR, UV-Vis) and elemental analysis. The results indicated that all the dyes exhibit positive solvatochromism in more polar solvents. Dispersion of the dyes was prepared in water and applied to polyester fabrics. The synthesized dye 3a which had good exhaustion on the fabric (89.98 per cent) and were tinctorially stronger (28899 l/mol.cm) showed higher visual colour yield (16.51). The antibacterial efficacy of the dyes was assessed, and they showed activity against both gram-positive and gram-negative bacteria but in different levels depending on their structures. Research limitations/implications A simple way to combing functional finishing and dyeing in one process was successfully performed via design and synthesis of disperse dyes with an antibacterial moiety incorporated into dye molecules. The dyes were fully charaterized and evaluated on polyester. Originality/value A series of novel antibacterial monoazo disperse dyes based on sulfonamide derivatives were synthesized. The authors studied their application for dyeing of polyester fabric. The dyes offered good results in terms of preparation, yield, purity, visual colour yield, fastness properties and activity against bacteria.

New electroactive asymmetrical chalcones and therefrom derived 2-amino- / 2-(1H-pyrrol-1-yl)pyrimidines, containing an N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment: synthesis, optical and electrochemical properties

In this paper we present a synthetic approach to six new D–π–A–D conjugated chromophores containing the N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment. Such readily functionalizable heterocycle as carbazole was used as a main starting compound for their preparation. The investigation of the optical properties has shown that the positive solvatochromism is inherent to the chromophores containing an electron-withdrawing prop-2-en-1-one fragment, while the compounds containing a 2-aminopyrimidine moiety exhibit both positive and negative solvatochromism. The fluorescence quantum yields were experimentally determined for some of the synthesized chromophores; e.g., 1-(5-arylthiophen-2-yl)ethanones quantum yields were found to lie in an interval of 60–80%. Electrochemical oxidation of the synthesized chromophores has resulted in the formation of colored thin oligomeric films that became possible due to the presence of carbazole or pyrrole fragments with free electron-rich positions.

Assembly of New Merocyanine Chromophores with a 1,8-Naphthalimide Core by a New Method for the Synthesis of the Methine Function

A new method for the synthesis of the monomethine group using nitro as a leaving group in an SN-Ar reaction is described. A series of novel merocyanine dyes has been synthesised and their photophysical properties have been elucidated. The longest wavelength absorption occurs in the range 519–619 nm and the molar absorptivities vary with the substituents and are in the range 1000–47700 L mol–1 cm–1. The dyes show high chemical and photostability. One example from the series has the ability to distinguish methanol from ethanol. The introduction of a quinoid fragment into the structure leads to a pronounced intramolecular charge transfer and hence a noticeable positive solvatochromism. The structures and electronic properties of the compounds have been studied by density functional theory (DFT) and time-dependent DFT.

Effect of Counterion on the Solvatochromic Properties of Heteroleptic Chelate Copper(II) Complexes

A series of heteroleptic chelate copper(II) complexes of the type [Cu(L)(acac)]X where acac = acetylacetonate; L = N,N′-1,6-bis(2-fluorophenyl)-2,5-diazahexane;X=CIO4-,BPh4-,PF6-, andBF4-have been prepared and characterized by elemental analyses, IR and UV-Vis spectroscopies, and molar conductance measurements. The prepared complexes are fairly soluble in a large number of organic solvents and show positive solvatochromism. Among the complexes [Cu(L)(acac)]ClO4, it is demonstrated the most solvatochromism. A multiparametric equation has been utilized to explain the solvent effect on the d-d transition of the complexes using SPSS/PC software. To explore the mechanism of interaction between solvent molecules and the complexes, different solvent parameters such as DN, AN,α,ET(30),π*, andβusing stepwise multiple linear regression (SMLR) method were employed. The results demonstrated that the donor power of the solvent plays the most important role in the solvatochromism of the compounds.

Synthesis, Characterization, and Tautomeric Properties of Some Azo-azomethine Compounds

The primary azo compound 1-(3-formyl-4-hydroxyphenylazo)-4-nitrobenzene reacts with some aliphatic and aromatic diamines and yields the corresponding azo-azomethine compounds. These compounds were characterized by elemental analysis, IR, UV/Vis, and NMR spectroscopy. The primary azo compound exists entirely in the azo form in solution as well as in the solid phase. The tautomeric structure of azo-azomethine compounds heavily depends on the solvent and the substituents. Aliphatic diamine-based compounds favor the enol-imine tautomer while aromatic diamine-based compounds have structures that lie between the two enol-imine and keto-amine tautomers due to a relatively strong intramolecular hydrogen bond. The compounds exhibit positive solvatochromism (bathochromic shift) so that their absorption bands move toward longer wavelengths as the polarity of the solvents increases. In addition, UV/Vis spectrophotometry has shown that the studied compounds have molar extinction coefficients larger than 40000.