New unsymmetric diaminomaleonitrile-based azo dyes (H3Ln , n=1-3) have been synthesized via condensation reaction of 5-(4-X-phenyl)-azo-salicyladehyde (X=NO2, OMe and CH3) with 2-amino-3-(5-bromo-2-hydroxybenzylamino)maleonitrile. The solvatochromic behaviors of the dyes were probed by studying their UV–Vis spectra in five pure organic solvents of different polarities. The systematic DFT calculations have been carried out to investigate capability of the dyes to detect fluoride ion in gas phase and CH3CN solution. Furthermore, all prepared dyes were assayed for their in vitro antibacterial activities against Gram-positive (S. aureus, S. epidermidis and L. monocytogenes) and Gram-negative (E. coli, P. aeruginosa and K.pneumonia.) bacteria by disc diffusion method. The results indicated that all prepared dyes show good inhibition against Gram positive bacteria namely L. monocytogenes as compared to standard drugs. recognition ability
