Aleksandr A. Ishchenko

Influence of interaction of chromophores, linked by the unconjugated chain, on the luminescence properties of biscyanine dyes

Abstract Deactivation of electronically excited state of chemically bound dimers – biscyanines with two chromophores linked by unconjugated chains and corresponding monomer dye was investigated. It was found that the quantum yield of dimer fluorescence is lower than that of a monomer dye. The amount of quantum yield of fluorescence decreases with the increase of chromophores interaction degree (the decrease of the isolating polymethylene bridge length). It is shown on the basis of the external heavy-atom effect studies that the decrease of biscyanines fluorescence ability is connected with the enhancment of singlet–triplet intersystem crossing ( S 1 ⤳ T 1 ). It has been established that the probability of the triplet states population in biscyanines with chromophores in parallel arrangement is considerably higher than that in similar compounds with an angular arrangement of chromophores. The delayed fluorescence was observed in the case of dyes with parallel arrangment of chromophores.

Investigation of Conformational and Electron Properties of Biscyanine Dyes

ABSTRACT The spectral and luminescent characteristics of four biscyanine dyes and corresponding monomer dye in ethanol solutions and in polyvinyl butyral have been investigated. The influence of angle between chromophores of biscyanine molecules on splitting and intensity of absorption bands has been discussed. It has been shown that the splitting of the biscyanine excited electron level S1 is caused both dipole and resonant chromophor interactions. It has been found that the fluorescence quantum yields of the biscyanines in ethanol at room temperature are 0.005–0.02. The introduction of biscyanines in a polymer matrix, which provides rigidity of a polymethine chain, results in reduction of molecules trans-cis isomerization and consequently increase of fluorescence quantum yields.

The length of the polymethine chain and the spectral-luminescent properties of symmetrical cyanine dyes

The general characteristics that relate the length of the polymethine chain of symmetrical cyanine dyes to their spectral-luminescent properties depending on the electron-donor character of the heterocycles and the nature of the solvent are formulated. For various types of symmetrical cyanines, the Stokes shifts decrease with the elongation of the polymethine chain due to weakening of the vibronic interactions. The vinylene shifts of the band maxima are essentially constant and fall within the range 100 to 130 nm depending on the nature of the heterocycles and the solvent. When the polymethine chain elongates the fluorescence quantum yields first increase and then decrease. The greater the effective length of the heterocycle the stronger the decrease. The fluorescence decay occurring when the polymethine chain gets longer is associated with intensification of the internal conversion. For symmetrical cyanines, the changes in the shapes of the electronic bands (their width, asymmetry, excess, and fine structure) as the chain elongates are governed by the competing effects of the vibronic and intermolecular interactions. The former decrease as the chain lengthens, causing the narrowing of the absorption bands for the lower vinylogs. On the other hand, the latter increase as chain lengthens, which leads to broadening of the bands for the higher vinylogs. The higher the solvent nucleophilicity and the greater the deviation of the electron-donor ability of the heterocycle from the average value the greater the broadening. Any elongation of the polymethine chain of symmetrical cyanines causes only narrowing of the bands and an increase in the asymmetry, excess, and structuring in the fluorescence spectra, which, unlike the absorption spectra, is independent of the electron-donor character of the heterocycles and the nature of the solvent. These effects are caused by the fact that, in contrast to absorption, changes in the shape of emission bands with increasing chain length are governed predominantly by vibronic rather than by intermolecular interactions.

A dye laser with a polyurethane matrix

A dye laser with a polyurethane matrix cured by polycondensation is studied. An increase in the conversion efficiency, service life, optical stability, and tuning range in comparison with lasing media produced by radical polymerization is demonstrated.

Relaxation Times of New Passive Polymer Switches for 1.06μm

The method of using a saturable absorber to mode-lock the solid state laser is now a well established and simple technique1, 2. A number of polymethine dyes are presently known to be useful for passive mode locking of the solid state lasers in the 1.06 μm range3, 4. So far, reports on application of these dyes for mode-locked operation consider mostly dyes in solution rather than in plastic, although the polymethine dyes in plastic have some advantages. First, they can simplify the design of a mode-locked laser and, second, increase reproducibility of temporal and energetic parameters of the radiation. But this can be achieved only in the case if spectral, luminescence, and nonlinear optical characteristics of the dyes in the polymer matrix are not significantly different from the characteristics in liquid solutions. It was a difficult problem for a long time, and only now it has been solved by appropriate selection of the dye structure and the nature of the matrix containing it5.

STRUCTURES OF TERMINAL HETEROCYCLIC GROUPS AND FLUORESCENCE-SPECTRAL PROPERTIES OF POLYMETHINE DYES

The fluorescence and absorption bands of carbocyanines containing pyrylium or benzoxazolium groups, their nitrogen-, sulfur-, and selenium-containing analogs, their benzohomologs, or isomeric analogs of pyrylium as terminal groups were mathematically processed using the method of moments. The regularities in the displacement of the absorption and fluorescence bands following the replacement of the heteroatom and variations of the positions of substituents in the terminal groups were explained using perturbation theory. Based on quantum-chemical calculations, the changes in the bond orders in the ground and excited states of the dyes were studied. The correlations between the moments of the experimental absorption and fluorescence bands and the frequency and the form of the chromophore vibrations were analyzed. The transition from pyrylo-4-cyanines to isomeric pyrylo-2-cyanines leads to substantial broadening of the bands, an increase in the Stokes shifts, decreases in the coefficients of asymmetry, kurtosis, and fine structure of the bands, as well as a decrease in the quantum yield of fluorescence.

Investigation of intermolecular interactions in solution polymer organic dye by method electronic spectroscopy

It has been shown that specific electrostatic interactions between charges of ion dyes and functional groups of polymer play main role in the cause of polar coulored matrices. These interaction prevent by formation tight ion pairs of dyes and their associates. Therefore, such matrices have practically the same electronic spectra as liquid solution of dyes. Electrostatic interactions between dye counterions dominate in low polarity polymer matrices. Process of formation tight ions pair is became easier. Such pairs cause quenching of the fluorescence and distortion of electronic spectra by comparison with liquids.