A series of novel 6-amino-4-(1-cyano-2-arylvinyl)-2-oxo-1,2-dihydropyridine-3,5-dicarbonitriles were synthesized via the reaction of functionalized 2-chloropyridines with salicylaldoxime. These cyanostilbene-pyridone hybrids are of significant interest as tunable fluorophores for the development of chemosensors targeting toxic heavy metal ions. The photophysical properties of compounds were studied, and structure-specific fluorescence sensing of both mercury(II) and silver(I) ions governed by distinct aggregation mechanisms was observed. Specifically, the p-dimethylamino-substituted derivative exhibited aggregation-caused quenching (ACQ) in the presence of Hg2 + and Ag+ ions, with higher affinity for mercury(II). In contrast, the p-diethylamino-substituted cyanostilbazole showed significant aggregation-induced emission (AIE) enhancement in aqueous media. The pH-dependence studies and interference ion screening were performed to establish optimal sensing conditions, enabling successful metal detection at sub-micromolar levels.

Convenient methods for synthesizing two isomeric nicotinonitrile-based building blocks with 2-amino-4-aryl- and 4-amino-2-arylpyridine-3,5-dicarbonitrile moieties were developed. These blocks were modified at the C6 position using N-, O-, or C-nucleophiles. The investigation of the effect of solvents on the spectral and luminescent properties of the synthesized chromophores revealed that the emission characteristics of 2-aryl derivatives are more significantly influenced by the polarity of the solvent, while 4-aryl-substituted molecules are primarily affected by acidity. The absorption and emission maxima of the starting 4-aryl- and 2-aryl-6-chloropyridines were observed at lower energy wavelengths than those of the N-, O-, and C-substituted derivatives. Chemosensory studies showed that the emission intensity of 6-amino-2-(dicyanomethylene)-4-(4-(dimethylamino)phenyl)-1,2-dihydropyridine-3,5-dicarbonitrile increased significantly in the presence of Ag+ ions in aqueous solution.

It was found that new colored ionic organic compounds are formed as a result of the reactions of 2-(4-aryl-5-cyano-[2,2′-bipyridin]-6(1H)-ylidene)malononitriles with triethylamine and pyrrolidine. These compounds are stable in air and show solid-state photoluminescence in the green-yellow region of the visible spectrum (λemmax 525–565 nm). The photophysical properties of the resulting powders were studied. The position of the emission maximum and the emission intensity depend on the structure of both the cation and the anion. The most intense photoluminescence was observed for the triethylammonium salt containing a methoxy group in the aromatic substituent of the anion. The results obtained can be used to develop a new method for luminescence detection of volatile organic amines.

Tripotassium 2-(1-cyano-2,2-disulfidoethenyl)-1,1,3,3-tetracyanopropenide was synthesized for the first time by the reaction of carbon disulfide and malononitrile trimer. Its further transformations afforded 2-amino-4-(dicyanomethylidene)-4H-thiopyran-3,5-dicarbonitrile derivatives.

A new approach to the synthesis of 2-amino-4-aroyl-6-halopyridine-3,5-dicarbonitriles using commercially available saturated solutions of hydrogen halides is proposed. The synthesized compounds demonstrated binding properties towards mercury(II) ions, which is manifested in fluorescence quenching. The limit of mercury(II) detection with a leading compound falls in the nanomolar range, which is comparable to the known reagents based on small molecule compounds.

A convenient approach for the dehydroxyalkoxylation of hydroxy derivatives of pyrrolo[3,4-c]pyridine into the corresponding alkoxy derivatives via refluxing in the presence of sulfuric acid in an excess of the corresponding alcohol as solvent has been proposed. The synthesized compounds have been investigated as reagents for quantitative determination of mercury(II) ions. The lead compound has shown the mercury(II) ions detection limit in the nanomolar range, which is comparable to the performance of known reagents based on compounds of small molecules.

The reaction of 4-amino-6-aryl-2-halopyridine-3,5-dicarbonitriles with thioglycolic acid ethyl ester was used to synthesize a series of new efficient fluorophores of thieno[2,3- b ]pyridine series. The long-wavelength absorption bands of DMSO solutions of the prepared compounds are at the boundary of the UV and visible regions of the spectrum (λabs 375-388 nm) and show an ambiguous influence of the substituent electronic effect, that was explained by quantum chemical calculations. The emission maxima are in the yellow-green region (λem 490- 510 nm) and they are blue-shifted in the presence of electron donor groups with slightly increasing intensity (Φem 37.8-60.6%). It was found that the nitro group presence causes a complete photoluminescence quenching both in solution and in the solid state. In addition, the position of the emission maximum (λem 473-505 nm) and its intensity (Φem 3.6-72.7%) strongly depend on the polarity and the basic properties of the medium, that was established using the Catalan empirical model.

A simple strategy for the synthesis of 2-oxo-1,2-dihydropyridine-3-carbonitrile derivatives (2-oxonicotinonitrile, 3-cyanopyridone) in good yields by substituting the halogen atom with an oxime under mild conditions was developed. The proposed approach makes it possible to avoid the problems associated with the hydrolysis of easily modified groups, since the reaction is carried out in the absence of water.

An approach based on the use of a silver salt with an organic anion based on nicotinonitrile containing a tricyanobutadiene fragment was proposed for the quantitative fluorimetric determination of a number of anions and thiols, including glutathione and cysteine.

(Z)-6-Alkylamino-2-amino-4-(2-aryl-1-cyanoethenyl)pyridine-3,5-dicarbonitriles were synthesized by the reaction of (Z)-2-amino-4-(2-aryl-1-cyanoethenyl)-6-chloropyridine-3,5-dicarbonitriles with various amines, including biologically relevant ones. The products showed solid state fluorescence with the emission maxima ranging from λ 472 to 562 nm and almost complete absence of fluorescence in solution. Increase of the volume fraction of water in binary solvents above a certain value led to the appearance of fluorescence due to formation of aggregates. Fluorescence enhancement upon addition of a viscous solvent (glycerol) indicated aggregation-induced emission of the synthesized compounds.

Facile approach to the synthesis of novel donor-acceptor chromophores containing a 1,4-diarylbuta-1,3-diene system was developed. Optical properties of compounds in various solvents and in solid state were studied. It was found that compounds with unsubstituted and methoxy-substituted phenyl moiety conjugated with 2-amino-6-chloropyridine-3,5-dicarbonitrile acceptor show moderate photoluminescence in powders and weak emission in solution. At the same time, the presence of dimethylamino group in the phenyl moiety led to stronger intramolecular charge transfer (ICT) emission of the chromophore in many organic solvents and amorphous solids as well as to interesting acidochromic properties.

Previously unknown 2-{4-aryl-5-cyano-[2,2′-bipyridin]-6(1 H )-ylidene}malononitriles were synthe­sized by reaction of 3-aryl-1-(pyridin-2-yl)prop-2-en-1-ones (azachalcones) with malononitrile dimer. Their colored solutions showed fluorescence in the yellow–orange region with the emission maxima located at λ 565 to 582 nm, depending on the substituent in position 4 of the pyridine ring bearing cyano groups. The synthesized compounds are promising for further study as chemosensors due to a unique combination of 2,2′-bipyridine and buta-1,3-diene-1,1,3-tricarbonitrile fragments in their molecules.

Bicyclic 6-6 systems with one bridgehead nitrogen atom can be classified as derivatives of quinolizinium ion, quinolizine, and quinolizidine. Compounds of this class often possess diverse and important biological activities. Many of these compounds, especially quinolizidines, are widely encountered in druglike compounds and natural products. In this chapter, preparation and chemical properties of these compounds over the past 10 years are systematized according to their level of unsaturation and the type of synthesis. Synthetic methods are based on the location of the newly formed bond (or bonds) with respect to the bridgehead nitrogen atom. At the end of the chapter the total synthesis of some important derivatives and their application are presented.

(Z)-2-Amino-4-(2-aryl-1-cyanoethenyl)-6-(piperidin-1-yl)pyridine-3,5-dicarbonitriles were synthe­sized by reaction of piperidine with (Z)-2-amino-4-(2-aryl-1-cyanoethenyl)-6-chloropyridine-3,5-dicarbonitriles. The synthesized compounds exhibited solid-state fluorescence with emission maxima in the range λ 472– 564 nm, whereas almost no fluorescence in solution was observed.

The synthesis of novel highly efficient fluorescent dyes of 4-amino-2-chloro-6-arylpyridine-3,5-dicarbonitrile series via heterocyclization of aryl(heteryl)methylidene derivatives of malononitrile dimer bearing electron-donor groups was described. Solvatochromic behavior and substituents effect on the spectral-luminescent properties were also investigated. Strong solvatochromism and high relative fluorescence quantum yields up to 0.92 despite the large Stokes shift values and were observed.

A series of novel 6-oxo-1,6-dihydro-[2,2'-bipyridine]-5-carbonitriles has been synthesized and characterized. Their photophysical properties in DMSO solution and aqueous medium as well as fluorescence response to the presence of metal ions have been investigated. The obtained 4-(4-methoxyphenyl)-6-oxo-1,6-dihydro-[2,2'-bipyridine]-5-carbonitrile has been shown as a selective fluorescent “turn-ON” probe for Cd2+ ions with LoD 0.359 µM, 1:1 metal–ligand ratio and binding constant of 5.2 × 104 M−1.

The novel turn-on fluorescent chemosensors for silver ion based on nicotinonitriles, containing a tricyanobutadiene moiety (tricyanopyridine, TCPy) were developed. The enchantment of fluorescent emission can be observed by naked eye, even in the presence of interference cations. The binding mode turned out to be a 1 : 1 ratio as determined using Job’s plot.

2-Alkylamino-4-amino-6-arylpyridine-3,5-dicarbonitriles were synthesized by the reaction of primary and secondary amines with 4-amino-6-aryl-2-chloropyridine-3,5-dicarbonitriles. The study of the spectral luminescent properties showed the presence of fluorescence in solutions with a maximum in the region of 399–471 nm and in the solid state with a maximum in the region of 393–502 nm.

The novel, selective and pH-resistant AIE type chemosensor, based on pyridine, containing a tetracyanobutadiene moiety (4-CN-TCPy) for turn on detection of Ag+, as well as for turn-off detection of I− and mercaptocarboxylic acids was developed. On the example of both tumor and non-tumor cells, it was shown that developed sensor can be used for fluorescent imaging of tissues.