<p>In this study, the structural properties, energetic data, and classification of the chemical properties of <i>n,m</i>-diazaphenanthrine derivatives were studied by a density functional theory (DFT) method. The important and proper indices were applied in this investigation. The structures, electronic properties, and chemical reactivities of 25 isomeric <i>n,m</i>-diazaphenanthrenes were studied by a B3LYP/6–31+G(<i>d</i>) method/basis set. All the optimized geometries of these isomers kept good planarity. The structural properties such as bond lengths and dipole moments of these isomers were calculated. The energies of frontier orbitals (HOMO and LUMO) are used to determine several chemical reactivity parameters as a measure of their relative stabilities. These include total energy (<i>E</i>), ionization potential (<i>I</i>), electron affinity (<i>A</i>), chemical hardness (η), chemical softness (<i>S</i>), electronic chemical potentials (μ), and electrophilicity (ω). Based on these calculations, the heats of formation (Δ<i>H</i>°<i><sub>f</sub></i>) for all the <i>n,m</i>-diazaphenanthrine derivatives are predicted. Benzo[<i>h</i>]quinazoline (<b>P<sub>13</sub></b>) and benzo[<i>f</i>]cinnoline (<b>P<sub>34</sub></b>) are calculated to be the most stable and the least stable isomers, respectively. 1,10-Phenanthroline (<b>P<sub>110</sub></b>) possesses the minimum electrophilicity, while benzo[<i>c</i>]cinnoline (<b>P<sub>56</sub></b>) is calculated to have the highest electrophilicity among the isomeric structures. The largest and smallest dipole moments are calculated for benzo[<i>f</i>]phthalazine (<b>P<sub>23</sub></b>) and 3,8-phenanthroline (<b>P<sub>38</sub></b>), respectively. Linear relationships between the calculated <i>E</i><sub>LUMO</sub> (in eV) values and electrophilicity (ω) of the isomeric <i>n,m</i>-diazaphenanthrenes were observed.</p
