M. A. Kudinova

Syntheses and photophysical properties of a series of cation-sensitive polymethine and styryl dyes

The syntheses and photophysical properties of 20 cation-sensitive fluoroionophores carrying the tetraoxa monoaza 15-crown-5 receptor are described and discussed. Whereas complexation induces only weak effects for the positively charged hemicyanine probes, the closely related styryl dyes show stronger changes in their photophysical properties upon cation binding in the analytically advantageous near-infrared (NIR) region. The strongest effects in both cation-induced spectral effects and complex stability constants are observed for the uncharged probes of styryl base-type, but these probes usually absorb and emit at shorter wavelengths in the UV/VIS region. For both styryl dyes and styryl bases, in some cases cation-induced fluorescence enhancement or quenching is found.

Nature of the absorption bands of pyrylocyanines: heteroanalogues and isomers

Abstract The investigation of electron transition nature in pyrylocyanines and their heteroanalogues was carried out by spectral and quantum-chemical methods. The electron distribution diagrams have been used in order to determine the transition localization. The first transition is localized within the polymethine chain, and the higher ones are mainly localized within the end groups. It has been shown that the D 2h symmetry of the Huckel hamiltonian of γ-isomeric dyes had lead to quasi-generation of higher electron transitions, contrary to α-isomers being of C 2v symmetry.

Molecular and crystal structure of pyrylium squarylium dyes

The crystal structures of new dyes: 4-[[3-[[2,6-bis-(tert-butyl)-4H-pyran-4-ylidene]methyl]-2-oxido-4-oxo2-cyclobuten-]-ylidene]methyl]2,6-bis(tert-butyl)pyrylium (I) and its thio analog (II) were determined. Crystal data: space group P1 (I), P21/n (II); a = 5.960(9) Å (I), 10.400(4) Å (II); b = 9.366(3) Å (I), 12.242(4) Å (II); c = 13.948(3) Å (I), 14.482(6) Å (II); α = 70.43(2)° (I), 90.0° (II); ß = 84.82(9)° (I), 94.65(3)° (II); γ = 79.10(9)° (I), 90.0° (II); V = 720.0 Å3 (I), 1837.7 Å3 (II); Z = I (I), 2 (II); dcalc = 1.131 g/cm3 (I), 086 g/cm3 (II); R1(F) 0.049 (I), 0.045 (II). The substituents are trans-oriented relative to the planar 4-membered ring. Bond length distribution points to a considerable electron density delocalization over the whole molecule except the But groups. The pyrane rings are oriented differently relative to the central group; in II the rings lie in the same plane which is rotated through 7.7° with respect to the central fragment, whereas in I they lie in parallel planes which are 1.38 Å apart and deviate from the central fragment to opposite sides, forming with it dihedral angles of 12.8°. These conformational differences are possibly the result of the action of crystal field forces. In I molecules are arranged as overlapping stacks, whereas in II the pairwise parallel dye molecules are oriented in such a way that their long molecular axes are perpendicular to the long axes of the neighboring pair, resulting in a herringbone packing.

Nature of the absorption bands of pyrylocyanines.2. Influence of t-Bu, Ph and Th ring substituents

Abstract The effects of t-Bu, Ph and Th substituents on the absorption spectra of α-and γ-pyrylocyanines and their heteroanalogues have been investigated using experimental and quantum-chemical methods. It has been found that changes in the position of the absorption band depend on the electronegativity of the ring heteroatom (O, S, N CH3), polymethine length, and the position of the bond between the chain and the end group. In the case of dye molecules, the effect of two substituents was additive, in contrast to the corresponding salts of the intial heterocycles. An explanation for the significant shifts in the absorption maximum of the thienylcyanines has been presented.