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Taking account of special features of the diazotization of vic-aminonitro-1-methylpyrazoles, conditions have been found for synthesizing from them the isomers of arylazo-1-methylnitropyrazoles. The different behavior of these compounds under reducing conditions has been confirmed by polarographic data. The electronic absorption spectra of vic-arylazonitropyrazoles are interpreted.

1. The process of transfer of hydrogen from ketyl radicals to azomethine dyes proceeds through a transition state (or intermediate complex) with charge transfer from ketyl radicals to the dyes. 2. Azomethine dyes — derivatives of anilides of acylacetic acids — are far less active in the reaction with ketyl radicals than pyrazolone dyes. 3. The reducing activity of the radicals with respect to azomethine dyes decreases in the series: ketyl of acetone > ketyl of acetophenone > ketyl of benzophenone > neutral semiquinone radicals.

New 8-chloro-, 9-cyano-, and 8-methyl-9-carboxy-substituted (in the outer polymethine chain), indolo-3,3′-trimethinecyanines containing substituents in the 2, 5, or 7 position of the indole heteroresidues were synthesized, and their spectral, polarographic, and photographic properties were studied. It is shown that electron-acceptor substituents in the 2 and 2′ positions of the indole heteroresidues and the 8 and/or 9 positions of the polymethine chain of the dye molecules that do not have steric hindrance give rise to a bathochromic shift of their absorption maxima. 8-Chloro-, 9-cyano- and 8-methyl-9-carbethoxyindolo-3,3′-trimethinecyanines with electron-acceptor groups in the 2 and 2′ positions are ineffective sensitizers of direct positive silver halide emulsions.

Investigation by spectral and polarographic measurement as well as quantum-chemical calculations were carried out in order to estimate the relative and absolute positions of the frontier energy levels of γ-pyrylocyanines and their heteroanalogues. Correlations between the theoretical energy levels and the redox potentials as well as between the calculated energy gaps and the transition energies have been established. A new parameter—electron donor ability Φo—has been used for the characterization of the relative position of the frontier MO.