Dibromohydantoin: A Convenient Brominating Reagent for 1,4,5,8-Naphthalenetetracarboxylic Dianhydride

An efficient and economical reagent for the bromination of 1,4,5,8-naphthalenetetracarboxylic dianhydride under mild reaction conditions is reported. 1,4,5,8-Naphthalenetetracarboxylic dianhydride was smoothly brominated by treatment with 5,5-dimethyl-1,3-dibromohydantoin (DBH) in concentrated H2SO4 as a solvent under ambient conditions. Mono-, di-, and tetrabrominated products were obtained in good-to-excellent yield by varying the equivalents of brominating reagent used, and the products were purified by crystallization. The mild reaction conditions and simple workup procedure make this method a practical and commercially viable route for the synthesis of pure mono-, di-, and tetrabrominated 1,4,5,8-naphthalenetetracarboxylic dianhydrides. Condensation of these dianhydrides with n-octylamine gives the corresponding imide (N,N') substituted mono-, di-, and tetrabromonaphthalene diimides, which are versatile precursors for the synthesis of core-functionalized naphthalene diimides. Toluene as a solvent significantly improves the efficiency of nucleophilic core substitution of these bromonaphthalene diimides with n-octylamine to afford core-substituted mono-, di-, and tetra-(n-octylamino)-naphthalene diimides. The core substitution reactions are clean, without any side products, and give excellent yields. The UV/vis absorbance and fluorescence properties of the core functionalized naphthalene diimides were studied and found to be dependent on the number of core substituents.