wherein R₁ to R₁₂ are substituents each independently selected from the group consisting of hydrogen, linear or branched alkyl group having 1 to 24 carbon atoms, linear or branched alkoxy group having 1 to 24 carbon atoms, linear or branched acyl group having 2 to 24 carbon atoms, aldehyde group, carboxyl group, linear or branched carboxylic ester group having 2 to 24 carbon atoms, sulfonic group, linear or branched sulfonic ester group having 1 to 24 carbon atoms, cyano group, hydroxyl group, nitro group, amino group, amide group, and halogen group, providing that the cases where all of R₁ to R₁₂ are hydrogen and where all of R₂, R₆ and R₁₀ are substituted by the same substituent and the rest of the substituents are all hydrogen are excluded;

X^a− is at least one anion selected from the group of monovalent to tervalent anions consisting of chlorine ion, bromine ion, iodine ion, fluorine ion, nitrate ion, sulfate ion, hydrogen sulfate ion, phosphate ion, fluoroborate ion, perchlorate ion, thiocyanate ion, acetate ion, propionate ion, methane sulfonate ion, p-toluene sulfonate ion, trifluoroacetate ion, and trifluoeomethane sulfonate ion;

a is an integral number in the range from 1 to 3 indicating the ionic valence of the ion X; and

m is a number in the range from 0.001 to 0.5.