Resolving the ultrafast intersystem crossing in a bimetallic platinum complex

Abstract

Bimetallic platinum complexes have interesting luminescent properties and feature long-lasting vibrational coherence and ultrafast intersystem crossing (ISC) after photoexcitation. Ultrafast triplet formation is driven by very strong spin-orbit coupling in these platinum (II) systems, where relativistic theoretical approaches beyond first-order perturbation theory are desirable. Using a fully variational relativistic theoretical method recently developed by the authors, we investigate the origins of ultrafast ISC in the [Pt(ppy) (μ-tBu2pz)]2 complex (ppy = phenylpyridine, pz = pyrazolate). Spin-orbit coupling values, evaluated along a Born-Oppenheimer molecular dynamics trajectory, are used to propagate electronic populations in time. Using this technique, we estimate ultrafast ISC rates of 15–134 fs in this species for the possible ISC pathways into the three low-lying triplet states.

Ultrafast Excited-State Dynamics of Photoluminescent Pt(II) Dimers Probed by a Coherent Vibrational Wavepacket

“…In comparison, Pt3 has an optimal CI of S 1 and T 2 near the FC region, but the PES energy difference between T 2 and T 1 is slightly larger than that of Pt4 so that it has dual pathways. Furthermore, our recent theoretical study has examined the ISC dynamics on a pyrazolate-bridged Pt­(II) dimer by a fully variational relativistic method, demonstrating the consistent result that the high-lying 3 LC state with its energy adjacent to the 1 MMLCT state enables ultrafast ISC to the 3 MMLCT state …”

“…Furthermore, our recent theoretical study has examined the ISC dynamics on a pyrazolate-bridged Pt(II) dimer by a fully variational relativistic method, demonstrating the consistent result that the high-lying 3 LC state with its energy adjacent to the 1 MMLCT state enables ultrafast ISC to the 3 MMLCT state. 40 On the basis of the STFT analyses (Figure 5) and the calculated excited-state PESs (Figure 6), Figure 7 depicts the ISC trajectories projected onto the Pt−Pt stretching vibrational coordinate for Pt3 and Pt4. The Pt−Pt stretching CVWP is first launched by the ground state to the 1 MMLCT PES transition at the FC region with an increased Pt−Pt bond order and a corresponding oscillation frequency of ∼150 cm −1 (220 fs period).…”

Photophysical Properties of Phosphorescent Mono- and Bimetallic Platinum(II) Complexes with C∧C* Cyclometalating NHC Ligands

“…For example, the metallophilic interaction can be controlled by the steric hindrance of the bridging ligands. Different classes of bridging ligands can be used to obtain bimetallic platinum­(II) complexes; − bispyrazolate complexes in particular have received considerable attention from the scientific community as they are readily available and allow for a change of the intermetallic distance. ,− When the steric demand at the pyrazolate is small, the Pt–Pt distance is long enough to prevent the formation of any Pt–Pt interaction ( 2 in Scheme ). In contrast, when the steric demand is increased, the ligand pushes the platinum­(II) centers closer together.…”

Nonadiabatic instanton rate theory beyond the golden-rule limit

“…One expects to also find systems with intermediate values of the diabatic coupling, lying in a "grey area" where neither Born-Oppenheimer nor golden-rule rate theory are valid. [34][35][36][37][38] This intermediate regime has always been of great interest, and the search for a corresponding practical nonadiabatic rate theory is ongoing. 39 Considerable progress [40][41][42][43][44] has been made for dissipative systems that can be mapped onto a spin-boson model, 45 of which electron transfer in solution is a typical example.…”