A 1,4-azaborine derivative fused by two naphthalene rings, a dinaphthoazaborine was synthesized, and its molecular structure was revealed by X-ray crystallographic analysis. UV vis absorption and fluorescence spectra of the dinaphthoazaborine indicated a decrease in the HOMO-LUMO energy gap compared with that of dibenzoazaborines. Electrochemical measurements elucidated the enhanced electron-accepting characteristics of the dinaphthoazaborine.