Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

Abstract

Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H](2-) after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet (1)A2u state and concomitant rise in population of the triplet (3)A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet (1)A2u state takes only a few picoseconds, ESETD from the triplet (3)A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H](2-) is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

Vibrational coherence transfer in the ultrafast intersystem crossing of a diplatinum complex in solution

“…This species exhibits the same absorption bands as Pt(pop) in solution, suggesting very similar energetics of the lowest triplet and singlet states, but also of the higher-lying UV bands. Ultrafast experiments (67) showed that the S 1 state undergoes a decay accompanied by a concomitant rise in population of the T 1 state with the same rate as the ISC in MeCN. While this may be fortuitous, it does raise an in-teresting question.…”

“…Pt(pop) is unstable in the gas phase, but the protonated [Pt(pop) + 2H] 2− anionic species is stable and was recently characterized by mass spectrometry and time-resolved pump-probe photoelectron spectroscopy (66,67). This species exhibits the same absorption bands as Pt(pop) in solution, suggesting very similar energetics of the lowest triplet and singlet states, but also of the higher-lying UV bands.…”

Ultrafast Intersystem Crossing in Isolated Ag29(BDT)123– Probed by Time-Resolved Pump–Probe Photoelectron Spectroscopy

“…The Ag 29 (BDT) 12 (TPP) 4 solid was synthesized following a previously reported method and used without further purification . Approximately 5 μM of clusters in dimethylformamide (DMF) was electrosprayed and probed using an ion beam apparatusparts of which have been previously described. − It has recently been modified to incorporate a velocity map imaging (VMI) setup and a new femtosecond laser system.…”

Ultrafast X-Ray Scattering Measurements of Coherent Structural Dynamics on the Ground-State Potential Energy Surface of a Diplatinum Molecule

“…Here we show how hard X-ray Free Electron Laser (XFEL) sources [13] now make it possible to directly map the structural dynamics of an ensemble of molecules as it evolves on the ground-state potential surface. illustrating this approach we investigate how the ground-state population of the much-studied di-platinum anion Pt- (Figure 1) [14][15][16][17][18][19][20][21][22][23] evolves following Pt-Pt distance-dependent photo-depletion of the ground-state population.…”