Although azapentacenes have been widely demonstrated as promising candidates for n-type organic semiconductor devices, the exploration of larger azaacenes is still a challenge. In particular, theoretical studies on the electronic structures of larger azaacenes and the influence of N substitution on the ground states are still rare. Herein, we reported our investigation on the electronic ground-state characters of larger azaacenes through density functional theory (DFT) calculations. Our results indicated that larger azaacenes (fused aromatic rings larger than 6) would show open-shell singlet biradical characters and the introduction of more N atoms into the backbone of large acenes could favor their closed-shell ground states. Interestingly, azahexacenes with three or more N atoms (compounds N64–N68) and azaheptacenes (compound N74) with fourteen N atoms displayed closed-shell singlet ground states compared with the open-shell singlet diradical ground states for larger acenes. Our theoretical studies may guide the design and synthesis of larger azaacenes, which are the promising n-type organic semiconducting materials.