Relationship between halogen-halogen interaction and electric conductivity in thiazolo[2,3-a]isoquinolin-7-ium triiodides

•Different X-X interactions in thiazolo[2,3-a]isoquinolin-7-ium triiodides.•Larger electric conductivity in the compounds bearing phenyl substituent.•Gain of higher HOMO energies in the case of larger electric conductivity.•Observation of higher HOMO energies from type II interaction in same ion pair. We studied crystal structures and electric conductivities of thiazolo[2,3-a]isoquinolin-7-ium triiodide synthesized from 2-(2-(phenylethynyl)-1-phenyl)thiazoles with 2 mol-equivalent of iodine molecules. Type I interaction of the halogen-halogen interactions were observed in the crystal structures of the compounds bearing phenyl group on thiazole ring. There is a clear difference in the crystal structures of the methyl substituted compounds with halogen bonds (Type II interaction). Larger electric conductivity under exposure of iodine vapor was achieved by the compounds with Type I interaction. They also have higher HOMO energies than other interactions. It would lead to increase the oxidized ability and the amount of hole species, which derive to larger electric conductivity. [Display omitted]