Theoretical analysis of singlet and triplet excited states of nickel porphyrins

摘要

Local density and generalized gradient approximation time-dependent density functional methods have been used for calculation of the singlet and triplet excited states of nickel-porphine,Ni-tetraphenyloporphine,and Ni-octaethyloporphyrine.Special attention is paid to metal-ligand transitions and d-d transitions.It is shown that the lowest exited singlet states of the three compounds can be described as a transfer of an electron from the porphine ring to the d_x2_(-y)2 orbital of the nickel atom.On the other hand,the lowest excited triplet state arises from promotion of an electron between two nickel d orbitals,an occupied d_z2 and an empty d_x2_(-y)2.It is proposed that a rapid quenching of the excited singlet states is due to an ultrafast intersystem crossing between ~1E_g and ~3E_g or ~3B_(Ig) states.