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Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1 H -pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5- a ]pyrimidines.

Diarylethene-derived molecules alter their electronic structure upon transformation between the open and closed forms of the diarylethene core, when exposed to ultraviolet (UV) or visible light. This transformation results in a significant variation of electrical conductance and vibrational properties of corresponding molecular junctions. We report here a combined experimental and theoretical analysis of charge transport through diarylethene-derived single-molecule devices, which are created using the mechanically controlled break-junction technique. Inelastic electron tunneling (IET) spectroscopy measurements performed at 4.2 K are compared with first-principles calculations in the two distinct forms of diarylethenes connected to gold electrodes. The combined approach clearly demonstrates that the IET spectra of single-molecule junctions show specific vibrational features that can be used to identify different isomeric molecular states by transport experiments.

We report on an experimental study of the charge transport through tunnel gaps formed by adjustable gold electrodes immersed into different solvents that are commonly used in the field of molecular electronics (ethanol, toluene, mesitylene, 1,2,4-trichlorobenzene, isopropanol, toluene/tetrahydrofuran mixtures) for the study of single-molecule contacts of functional molecules. We present measurements of the conductance as a function of gap width, conductance histograms as well as current–voltage characteristics of narrow gaps and discuss them in terms of the Simmons model, which is the standard model for describing transport via tunnel barriers, and the resonant single-level model, often applied to single-molecule junctions. One of our conclusions is that stable junctions may form from solvents as well and that both conductance–distance traces and current–voltage characteristics have to be studied to distinguish between contacts of solvent molecules and of molecules under study.

Catalyst- and template-free condensation of photochromic difurylethene bisaldehyde with o-phenylenediamine led to selective formation of macrocyclic Schiff base [AB]2 product. Application of the same difurylethene bisaldehyde in the McMurry reaction resulted in cyclic dimer formation in moderate yield. No linear oligomers were observed in both approaches.

Bis(benzothienyl)ethene sulfones are very interesting molecules for super‐resolution microscopy due to their photoswitching properties. However, functionalization of the ‘classical’ bis(benzothienyl)ethene sulfones with a five‐membered central ring leads to significant decrease of quantum yields of photoconversion of the fluorescent closed form of the dye to the non‐fluorescent open form that limits their application in microscopy. Here, we designed and synthesized diarylethenes with a fluorinated four‐membered central ring that adds extra strain to the closed form of the dye. The reaction mechanism of their formation was studied, and byproducts formed upon structural rearrangement of the benzothiophene fragment were characterized. The photochromic properties of the new molecules were investigated by NMR and absorption spectroscopy. Some of these compounds show enhanced tendency to ring opening and have quantum yields of the ring‐opening reaction in the range of 0.2–0.5. Strained switching: Fluorescent photoswitchable dyes are essential for several super‐resolution microscopy techniques. Dyes with enhanced photoswitching performance based on diarylethenes containing sterically constrained perfluorocyclobutene ring have been developed. The mechanism of the reaction of thianaphthenes with hexafluorocyclobutene leading to the target dyes was studied and formed byproducts were characterized. The photoswitching reaction was investigated using both optical and NMR‐based methods and quantum yields of photoconversion were measured.

Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines.Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines.

The chemical properties of 3-amino-5-methylisoxazole in the reactions involving pyruvic acid derivatives are reported. The multicomponent condensation of 3-amino-5-methylisoxazole, aromatic aldehyde, and pyruvic acid was not effective while the treatment of the starting amine with pyruvic acid derivatives led to suitable synthetic procedures for selective synthesis of furanones and pyrrolones. It was established that only NH2-nucleophilic center of 3-amino-5-methylisoxazole takes part in the heterocyclizations with pyruvic acid derivatives.

Using scanning tunneling microscopy and spectroscopy we investigate the adsorption properties and ring-closing reaction of a diarylethene derivative (C5F-4Py) on a Ag(111) surface. We identify an electron-induced reaction mechanism, with a quantum yield varying from \\(10^-14-10^-9\\) per electron upon variation of the bias voltage from \\(1-2\\) V. We ascribe the drastic increase in switching efficiency to a resonant enhancement upon tunneling through molecular orbitals. Additionally, we resolve the ring-closing reaction even in the absence of a current passing through the molecule. In this case the electric-field can modify the reaction barrier, leading to a finite switching probability at 4.8 K. A detailed analysis of the switching events shows that a simple plate-capacitor model for the tip-surface junction is insufficient to explain the distance dependence of the switching voltage. Instead, describing the tip as a sphere is in agreement with the findings. We resolve small differences in the adsorption configuration of the closed isomer, when comparing the electron- and field-induced switching product.