text: Efforts to elucidate the excited states of diphosphenes is important and valuable to realize the application of PP double bonds in molecular electronics. In triplets trans-HPPH, the P-P bond length is predicted to be 2.291 Å. It is not only longer than the P-P double bond in ground state trans-bis(2,4,6-tri-tert-butylphenyl)diphosphene, but also longer than that of P-P single bond in HPPH. Calculation of the dihedral angle of trans-HPPH suggests that it is almost 90 degree, which means the formation of  and  P-P bonds is forbidden and σ bond is enhanced.