New meso substituted cyanine dyes in the 2-R-5H-[1,2,4]triazolo[5,1-a] isoindole series

meso-Substituted symmetrical monomethine cyanine dyes derived from the triazoloisoindole were obtained by reaction of 2-R-5H-[1,2,4]triazolo[5,1-a]isoindoles with acyl chlorides. The meso group can be varied in a wide range enhancing the interest of these dyes like biological probes. Spectral UV–vis properties are reported.