The molecular structure, thermal stability, detonation properties and impact sensitivity of nitrogen-rich tetrazine-based designed high energy density molecules are examined. The effective stability of the designed molecules in terms of electronic structure, thermal excitation, photo-excitation and in presence of water are predicted. The topography of the excited and ground state (S-1 and S-0) of those molecules along the C-NO2 bond dissociation coordinate are studied. The existence of the double minima at the S-1 state and the S-1-S-0 intersection produces a probabilistic path for molecules B1, B2 and A1, to revert back to their respective S-0 state from the S-1 state via both radiative and non-radiative deactivation mechanism. The energy content (in terms of heats of formation), detonation velocities and detonation pressure of tetrazine-based molecules are measured. Interestingly, the thermal stability of these designed molecules is higher than the two well-known high energy density molecules: RDX and HMX. The detonation velocities and the detonation pressure of these molecules are higher than RDX, however, are lower than HMX. In addition, the safety, reliability and stability of these high energy density molecules have been measured by formulating semi-empirical equations of impact sensitivity based on linear and multiple linear regression method and the present study is ended with the discussion of most probable synthetic routes to the designed molecules.