1,4 '-Diazaflavone pigment ( 2) was synthesized by a simple environmentally friendly microwave-assisted one-pot method for the cyclization of 2 '-amino (E)-4 ''-aza-chalcone ( 1) under solventless conditions using K-10 clay. In addition, 10 new N-alkyl (C-5-12,C-14-15) substituted 1,4 '-diazaflavonium bromide pigments (3-12) were prepared from compound 2 or directly from compound 1, with corresponding alkyl halides in acetonitrile under reflux. The anti-microbial activity of compounds 1-12 was tested. The N-alkyl substituted 1,4 '-diazaflavonium bromides (3-12) showed good antimicrobial activity against the gram-positive bacteria tested with minimal bactericidal concentration (MBC) values for the reference antibiotic kanamycin. The optimum length of the alkyl chain for better and broader activity was 6-10 carbon atoms in the series of compounds (3-12).