In this work, a novel rigid chromophore was synthesized by the fusion of 9,9-dimethyl-9H-fluorene with indolocarbazole (ICz) for the development of deep-blue fluorescent emitters with high efficiencies and long lifetimes. The 10,10-dimethyl-10H-indeno[2,1-b]indolo[3,2,1-jk]carbazole (IDCz) was utilized as the chromophore for two deep-blue fluorescent emitters synthesized by mono- or di-substitution of electron-donating diphenylamine (DPA) auxochromophore. The systematic investigation of electroluminescence properties of IDCz, IDCz-DPA, and IDCz-2DPA revealed that the external quantum efficiency (EQE), device lifetime, and maximum luminance (L_max) were increased by increasing the number of DPA units. Moreover, the efficiency roll-off and full width at half maximum (FWHM) were also improved by the DPA substitution. The IDCz-2DPA emitter showed the best performances with a maximum EQE of 5.6%, L_max of above 47 000 cd m⁻², FWHM of 35 nm with little EQE roll-off at high luminance. Additionally, the IDCz-2DPA emitter outperformed the mono-substituted IDCz-DPA in terms of device lifetime by displaying an augmented lifetime (LT₈₀: above 140 h) as compared to that of IDCz-DPA (LT₈₀: 50 h).