Charge-transfer plasmons with narrow conductive molecular bridges: A quantum-classical theory.

We analyze a new type of plasmon system arising from small metal nanoparticles linked by narrow conductive molecular bridges. In contrast to the well-known charge-transfer plasmons, the bridge in these systems consists only of a narrow conductive molecule or polymer in which the electrons move in a ballistic mode, showing quantum effects. The plasmonic system is studied by an original hybrid quantum-classical model accounting for the quantum effects, with the main parameters obtained from first-principles density functional theory simulations. We have derived a general analytical expression for the modified frequency of the plasmons and have shown that its frequency lies in the near-infrared (IR) region and strongly depends on the conductivity of the molecule, on the nanoparticle-molecule interface, and on the size of the system. As illustrated, we explored the plasmons in a system consisting of two small gold nanoparticles linked by a conjugated polyacetylene molecule terminated by sulfur atoms. It is argued that applications of this novel type of plasmon may have wide ramifications in the areas of chemical sensing and IR deep tissue imaging.

Estimation of the thermal and photochemical stabilities of pheromones.

The correlation between the kinetic stability of molecules against temperature and variations in their geometric structure under optical excitation is investigated by the example of different organic pheromone molecules sensitive to temperature or ultraviolet radiation using the density functional theory. The kinetic stability is determined by the previously developed method based on the calculation of the probability of extension of any structural bond by a value exceeding the limit value Lмах corresponding to the breaking of the bond under temperature excitation. The kinetic stability calculation only requires the eigenfrequencies and vibrational mode vectors in the molecule ground state to be calculated, without determining the transition states. The weakest bonds in molecules determined by the kinetic stability method are compared with the bond length variations in molecules in the excited state upon absorption of light by a molecule. Good agreement between the results obtained is demonstrated and the difference between them is discussed. The universality of formulations within both approaches used to estimate the stability of different pheromone molecules containing strained cycles and conjugated, double, and single bonds allows these approaches to be applied for studying other molecules. Graphical Abstract Estimation of the thermal and photochemical stabilities of pheromones.

[Stability of lepidopterous pheromone molecules of forest insects to environmental factors].

The interactions of the pheromones of some representatives of the Lepidoptera order with each other and with materials contained in the forest air, as well as the effect of electromagnetic radiation on pheromone have been studied. It was found that the reactions of pheromones with substances contained in the forest air are irreversible and proceed with the liberation of heat. Electromagnetic radiation affects very strongly the structure of pheromones. In this case, a pheromone molecule is activated and can readily enter into reaction.

[The mechanism of formation of emitter by fluorescence of calcium-discharged obelin].

It is known that bioluminescence of obelin is triggered by Ca2+ the binding of which to the protein induces the decarboxylation of 2-hydroperoxycoelenterazine. The molecular mechanism of fluorescence of obelin, which determines the fluorescence of see hydroid Obelia Longissima, has been investigated with the use of quantum chemical calculations. According to quantum chemical calculations, the emitter of the reaction is the ion-pair state of phenolate-anion of coelenteramide. It has been shown that the fluorescence spectrum of this state depends on the position of the proton between the oxygen atoms of the phenol group of coelenteramide and the nitrogen atom of His22. The agreement of the calculated absorption and fluorescence spectra with the experimental spectrum shows the accuracy of the quantum chemical calculations and conclusions.