Characterization of new mesomeric betaines arising from methylation of imidazo[2,1-c][1,2,4]triazin-4(1H)-one, pyrazolo[5,1-c][1,2,4]triazin-4(1H)-one, and 1,2,4-triazolo[5,1-c][1,2,4]triazin-4(1H)-one