Ultrafast Excited-State Decays in [Re(CO)₃(N,N)(L)]ⁿ⁺: Nonadiabatic Quantum Dynamics

Abstract

The ultrafast luminescent decay of [Re(CO)(phen)(im)], representative of Re(I) carbonyl α-diimine photosensitizers, is investigated by means of wavepacket propagations based on the multiconfiguration time-dependent Hartree (MCTDH) method. On the basis of electronic structure data obtained at the time-dependent density functional theory (TD-DFT) level, the luminescence decay is simulated by solving a 14 electronic states multimode problem including both vibronic and spin-orbit coupling (SOC) up to 15 vibrational modes. A careful analysis of the results provides the key features of the mechanism of the intersystem crossing (ISC) in this complex. The intermediate state, detected by means of fs - ps time-resolved spectroscopies, is assigned to the T state corresponding to the triplet intraligand (IL) transition localized on the phen ligand. By switching off/on SOC and vibronic coupling in the model it is shown that efficient population transfer occurs from the optically active metal-to-ligand-charge-transfer1,3MLCT states to T and to the lowest long-lived phosphorescent MLCT (T) state. The early ultrafast SOC-driven decay followed by a T/T equilibration controlled by vibronic coupling underlies the photoluminescent properties of [Re(CO)(phen)(im)]. The impact of the axial and N,N ligands on the photophysics of this class of Re(I) complexes is further rationalized on the basis of their calculated optical properties. The relative position of the IL and upperMLCT states with respect to the optically active singlet state is influenced by the N,N ligand and affects the relaxation dynamics.

Excited‐State Reactivity of [Mn(im)(CO)3(phen)]+: A Structural Exploration

“…The six “spin–orbit free” low‐lying singlet and triplet excited states of [Re(im)(CO) 3 (phen)] + give rise to 14 largely mixed “spin–orbit” states when SOC is considered . Large SOC terms and mixings characterize the Re complex as expected for a heavy metal atom complex and the general trends when including SOC are observed in the SO simulated spectrum, that is a shift to the red of the lowest bands and a lowering of the intensities (Fig.…”

“…It can be seen that in both complexes the lowest singlets correspond to pure MLCT states, however in the case of [Mn(im)(CO) 3 (phen)] + the MC singlet states (S 5 -S 7 ) appear below the lowest LLCT (S 11 ) and IL (S 12 ) states, in contrast to [Re(im)(CO) 3 The six "spin-orbit free" low-lying singlet and triplet excited states of [Re(im)(CO) 3 (phen)] + give rise to 14 largely mixed "spin-orbit" states when SOC is considered. [12,13,17] Large SOC terms and mixings characterize the Re complex as expected for a heavy metal atom complex and the general trends when including SOC are observed in the SO simulated spectrum, that is a shift to the red of the lowest bands and a lowering of the intensities (Fig. 2).…”

“…This suggests that a further analysis has to include other important degrees of freedom, eventually breaking the symmetry that will assist the CO ax dissociation. Alternatively, an effective spinvibronic mechanism similar to the one revealed for [Re(im) (CO) 3 (phen)] + [17] could as well populate efficiently the low-lying dissociative triplet states.…”

“…The photo-reactivity of this class of first-row transition metal complexes on irradiation in the visible has been associated to the presence of low-lying metal-centered (MC) states in the vicinity of the MLCT absorbing states. [3][4][5][6][7] Whereas extensive work, both experimental and theoretical, has been achieved on third-row analogues to understand and interpret the spectroscopy and the photophysics of the usually nonreactive [Re(CO) 3 (bpy/phen)(L)] 0/+ compounds, [8][9][10][11][12][13][14][15][16][17][18][19] little is known on the optical and photophysical properties of [Mn(CO) 3 (bpy/phen)(L)] 0/+ complexes.…”

Performance of trajectory surface hopping method in the treatment of ultrafast intersystem crossing dynamics

“…[Re(Br)(CO)3bpy] thus provides a prototype system for the study of photochemistry and photophysics of transition metal complex systems. In recent years, Daniel, Gindensperger and coworkers have performed substantial work in this area 108,[112][113][114] , so we choose their model as our benchmark prototype. In their original paper 108 , a six-mode five-state model including two singlet states (S1, S2) and three sets of triplet states (T1, T2, T3) was constructed for the full-quantum MCTDH dynamics simulations.…”