Synthesis and properties of indolo-3,3′-trimethinecyanines substituted in the polymethine chain and heterorings

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.