Dibenzobarallene was used as a key intermediate for the synthesis of 2-(3-hydroxy-2-naphthoyl)-3,4,4a,5,10,10a-hexahydro-1H-5,10-benzenobenzo[g]phthalazine-1,4-dione (2). The previous compound was coupled with the appropriate diazonium chloride to give the corresponding 4-arylazo-2-naphthol derivatives 3a–l. Also, nitration, nitrosation and bromination of compound 2 afforded the corresponding nitro, nitroso and bromo derivatives 4–6, respectively. The synthesized compounds were established and evaluated as antibacterial agents. The results showed clearly that compounds 2, 3a, 3c, 3d, 3g, 3i, 4, 5 and 6 exhibited interesting high activities compared with reference drugs. Also, these compounds were applied to polyester as disperse dyes in which their color measurement and fastness properties were evaluated.