The electronic, magnetic, and optical characteristics of hexaazabipyH2 molecule (HA) and the 3d transition metal complexes for hexaazabipyH2 (TMHA) are investigated utilizing DFT and TD-DFT calculations. The stability of the investigated complexes is confirmed by the binding energy, molecular dynamic, and vibrational frequencies. The calculated HOMO-LUMO gap values show that the HA and TMHA are semiconductors. The magnetic moment (µ) for the investigated complexes is estimated, and the greatest µ value (3.76 µB) is recorded for the CrHA complex. The existence of the TM atom influences the UV–Vis spectrum of HA, where a redshift has occurred for the TMHA complexes except the ZnHA. The MnHA complex has a high light harvesting efficiency value of 0.403. The HA and TMHA complexes have refractive indices in the range of 2.311 to 3.323. Our results show that the HA as well TMHA complexes might be promising materials for solar cells and optoelectronics applications.