The crystal structures and thermal profiles of three crystal polymorphs of tricyclic imidazonaphthyridine derivatives (INA) were investigated. The aniline derivative INA–AN, in which a 4-anilino moiety was introduced at position 9 of the imidazonaphthyridine framework, yielded a nonplanar curved structure between imidazonaphthyridine and aniline. Three crystals (INA–AN-α (I4₁/a with Z′ = 1) as an emissive polymorph, as well as INA–AN-β1 and INA–AN-β2 (Pc with Z′ = 4) as nonemissive polymorphs) were obtained. The polymorphs comprised multiple-hydrogen-bond networks. INA–AN-β1 and -β2 crystallized into different polymorphs via recrystallization: INA–AN-β1 and -β2 were obtained from the solvent, as well as via melting and recrystallization processes. Notably, the crystal structures and parameters of INA–AN-β1 and -β2 largely corresponded, although their thermal behaviors were significantly different: INA–AN-β1 underwent a thermal crystal transformation, yielding INA–AN-α at ∼185 °C, while INA–AN-β2 readily melted at ∼190 °C. These distinct profiles indicated that the subtle distinct molecular arrangements, as well as crystal packings, might account for the different thermal profiles of INA–INA-β polymorphs. Interestingly, in addition to INA–AN-β polymorphs, an imidazonaphthyridine framework bearing an N,N-dimethylamine moiety, INA–DMA, crystallized in the P1̅ space group with Z′ = 4, indicating that the INA framework containing an aromatic ring afforded high-Z′ crystal structures.