G. V. Mayer

Photonics of zinc complexes of 3,3′-bis(dipyrrolylmethenes)

We measure the spectral luminescence characteristics (absorption, fluorescence, lasing, phosphorescence, and luminescence excitation spectra; fluorescence and phototransformation quantum yields; lifetimes of long-lived radiation) and estimate the fluorescence radiation constants and lifetimes for new synthesized binuclear bihelical complexes of zinc(II) with 3,3′-bis(dipyrrolylmethenes) of different structure in liquid and solid solutions. We discuss possible applications of these compounds.

Photonics of zinc(II) and boron(III) chelates with methyl- and phenyl-substituted dipyrromethenes and azadipyrromethenes

A comparative study of spectral, luminescent, and photophysical parameters has been carried out for a series of zinc(II) and boron(III) chelates with dipyrromethene ligands of a similar structure: tetramethyl- and tetraphenylpyrrodimethenes bearing the substituents on the pyrrole rings and tetraphenylazapyromethene. In some cases, the luminescence efficiency of the chelates depends on the excitation wavelength. The replacement of the central atom boron(III) by zinc(II) results in not only a twofold increase in the number of coordinated chromophoric ligands and the absorption coefficient, but also an increase in the contribution of nonradiative processes to excitation energy deactivation and, hence, a decrease in the yield of fluorescence. The efficiency of intersystem crossing is higher in the zinc(II) dipyrromethene complexes than in the corresponding boron-chelated dipyrromethenes (BODIPYs), resulting in the appearance of phosphorescence in frozen solutions. It has been found that the replacement of the meso-spacer in the dipyrromethene ligand by the nitrogen atom not only shifts the absorption and fluorescence band maximums to longer wavelengths, but also decreases the fluorescence efficiency and leads to the appearance of long-lived luminescence even in aza-BODIPY. An analysis of the results has shown that these behavior can be due to involvement of the nπ* (πσ*, σπ*) states localized on the meso-nitrogen in the deactivation of excitation energy.

Spectroscopic and laser characteristics of new efficient luminophores for a wide spectral range based on complexes of dipyrrolylmethene derivatives with difluorine borate

We have studied the spectral-luminescent, lasing, photochemical, and endurance characteristics of a series of new efficiently emitting difluorine borate complexes with dipyrrolylmethenes of different structures. Experimental data have been obtained in polar and nonpolar organic solvents and in solid polymer films involving the participation of silicate structures. We have discussed relations of the structure of investigated compounds and formed solvates with their optical characteristics, and have given guidelines on the use of particular compounds as active media of tunable lasers for determining spectral ranges.

Optical Properties of Zinc(II) and Boron(III) Dipyrrinates with Different Structures

The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.

Spectral and luminescent properties of some porphyrin compounds in different electronic states

The spectral and luminescent properties of some derivatives of tetraphenylporphyrin are studied at different concentrations of these compounds; the spectra of neutral and ionic forms are interpreted; and the quantum yields of ordinary and, in some cases, short-wavelength fluorescence from highly excited states are determined. The spectra of transient absorption from excited states, existing in the time range of tens of nanoseconds, are measured, and the quantum yields of formation of triplet molecules are estimated. Hypotheses regarding the mechanism of phototransformations of some porphyrins in chloroform are put forth.

Luminescent characteristics of tetraphenylporphyrin and its derivatives with lutetium

The spectral and luminescent characteristics of new tetraphenylporphyrin derivatives that contain the lutetium atom in their structure are studied in comparison with the most completely studied unsubstituted tetraphenylporphyrin and its complex with zinc. The luminescence quantum yields in liquid and frozen solutions are measured. The specific features of luminescent characteristics of these compounds and their possible applications are discussed.

Emission of Concentrated Solutions of Organic Compounds Excited with High-Power Laser Radiation

Specific features of emission of concentrated (C ≤ 1.2·1019 cm–3) solutions of organic molecules (rhodamine 6G, rhodamine C, phenalemine 512, and substituted paraterphenyl (LOC-1)) are investigated as functions of the exciting photon energy (at λexc = 308 and 532 nm) and power density of exciting radiation (up to 1 GW/cm2). One of the observed emission types – band emission – is studied. The intensity of band emission (its short- and long-wavelength maxima) is investigated versus the exciting radiation power density, and its time and polarization characteristics are also analyzed. The results obtained together with the specific features of the emission spectrum of concentrated rhodamine-C solution, measured after passage of sounding radiation with maximum at the wavelength equal to that of the short-wavelength maximum of band emission, demonstrate that the band emission is simply superfluorescence.

Spectroscopic and proton-acceptor properties of biologically active molecules of benzoic acid and its derivatives

We have measured the absorption, fluorescence, fluorescence excitation spectra, fluorescence quantum yields, and IR Fourier-transform spectra of aromatic acids in solutions. We have considered spectroscopic particular features of benzoic acid, its hydroxylated and methoxylated derivatives. Using quantumchemistry methods, we have calculated and interpreted electronic spectra. Data of calculations have been compared with experimental results. We have ascertained the main channels and mechanisms of photophysical relaxation processes in the molecules under study. Proton-acceptor properties of molecules of aromatic acids have been evaluated. We have analyzed in detail mechanisms by which hydrogen bonds are formed, intramolecular charge redistribution is realized, and the electron density of oxygen atoms changes. Spectroscopic indications of participation of oxygen-containing groups in intramolecular interactions and in intermolecular interactions with the formation of cyclic dimers have been revealed.

Photophysical processes in dimers of thiacarbocyanine cations

The results of quantum-chemical calculations of absorption, fluorescence, and induced T-T absorption spectra and the rate constants of photophysical processes for the monomer and dimers of the 3,3′-diethylthiacarbocyanine cation are presented. It has been shown that the formation of the dimers leads to a substantial reduction in the efficiency of the radiative pathways and enhancement of the efficiency of the non-radiative pathways of deactivation of the fluorescent state, thereby resulting in a decrease in the quantum yield of fluorescence. The fluorescence quantum yield depends in this case on the relative orientation of the molecules in the dimer with respect to each other. The calculation results satisfactorily describe experimental data on the spectral and luminescent properties of the dimers of the 3,3′-diethylthiacarbocyanine cation and their photophysical processes.

Spectral, luminescent, and lasing characteristics of pyridyloxazole derivatives in inorganic and hybrid gel materials

The spectral, luminescent, lasing, and photochemical characteristics of two pyridyloxazole derivatives incorporated during the sol-gel synthesis into inorganic silicate and hybrid organic-inorganic xerogels in the form of bulk matrices and thin films are studied. It is found that organic molecules are fixed in nanopores of solid matrices by specific interactions between proton-accepting centers of molecules and proton-donating centers of silicate matrices and create cationic and dicationic forms under such interactions. It is shown that pyridyloxazoles are more photostable in solid xerogels than in solutions.