Stong coupling of the single excitations in the Q-like bands of phenylene-linked free-bases and zinc bacteriochlorin dimers:a time-dependent density functional theory study

摘要

Time-dependent desity-functiional theory (TDDFT) calculations were carried out to predict the O-like bands of the two stucutral isomer of the phenylene-liked free-base (FBBC) and zinc (ZnBC) bacteriochlorin dimers.The calculated singlet excitation energies and oscillator strengths for the low-lying excited states of the reference monomers,FBBC and ZnBC,are quite consistent with recent ab initio calculation.The 1,3 and 1,4-phenylene-linked dimers have monomer-like Q bands and new Q' bands comprosed of the cross-likned (i.e.,charge transfer)excitatioins from the FBBC(ZnBC)ring to the ZnBC(FBBC)ring,whose excitation energies are slightly and considerable red-shifted by about 0.03eV and 0.5-0.7 compared to the monomer,respectively.The monomer-like Q_x bands are of the mixed highest occupied molecular orbital (HOMO)->lowest unoccupied molecular orbital (LUMO) excitations in the Q_x bands from the different bacteriochlorin ring is the coupling of the Q_x transition dipole moments trough the #alpha#-#alpha# interaction between the unreduced pyrroles situated across the phenylene group.This mixing character is still amintained in the monomers separated by the same distance in the dimer,which is quite different from previous TDDFT calculations for the phenylene-linked free-base and zinc prophyrin dimers.The present dimers may show a more efficient Q_x excitation energy transfer between the bacteriochlorins via each's throunth-space overlapped LUMOs than the conventional porphyrin dimers.