Ultrafast branching in intersystem crossing dynamics revealed by coherent vibrational wavepacket motions in a bimetallic Pt($$\mathrm{II}$$) complex
- Northwestern University, Evanston, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)
- University of Washington, Seattle, WA (United States)
- North Carolina State University, Raleigh, NC (United States)
Ultrafast excited-state processes of transition metal complexes (TMCs) are governed by complicated interplays between electronic and nuclear dynamics, which demand a detailed understanding to achieve optimal functionalities of photoactive TMC-based materials for many applications. Here, in this work, we investigated a cyclometalated platinum(II) dimer known to undergo a Pt-Pt bond contraction in metal-metal-to-ligand-charge-transfer (MMLCT) excited state using femtosecond broadband transient absorption (fs-BBTA) spectroscopy in combination with geometry optimization and normal mode calculations. Using sub-20 fs pump and broadband probe pulses in fs-BBTA spectroscopy, we are able to correlate coherent vibrational wavepacket (CVWP) evolution with stimulated emission (SE) dynamics of the 1MMLCT state. The results demonstrated that the 145 cm-1 CVWP motions with the damping times of ~ 0.9 ps and ~ 2 ps originate from coherent Pt-Pt stretching vibrations in the singlet and triplet MMLCT states, respectively. On the basis of excited-state potential energy surface calculations in our previous work, we rationalized that the CVWP transfer from Franck-Condon (FC) state to the 3MMLCT state was mediated by a triplet ligand-centered (3LC) intermediate state through two step intersystem crossing (ISC) on a time scale shorter than a period of the Pt-Pt stretching wavepacket motions. Moreover, it was found that the CVWP motion with 110 cm-1 frequency decays with the damping time of ~ 0.2 ps, well matching the time constant of 0.253 ps corresponding to a redshift in the SE feature at early time. This observation indicates that the Pt-Pt bond contraction changes the stretching frequency from 110 to 145 cm-1 and stabilize the 1MMLCT state relative to the 3LC state with the ~ 0.2 ps time scale. Thus, the ultrafast ISC from the 1MMLCT to the 3LC states occurs before the Pt-Pt bond shortening. The findings herein provide insight into understanding the impact of Pt-Pt bond contraction on ultrafast branching of the 1MMLCT population into the direct (1MMLCT → 3MMLCT) and indirect ISC pathways (1MMLCT → 3LC → 3MMLCT) in the Pt(II) dimer. These results revealed intricate excited state electronic and nuclear motions that could steer the reaction pathways with levels of details that have not achieved before
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF); USDOE
- Grant/Contract Number:
- AC02-06CH11357; CHE-1955806; CHE-1955795
- OSTI ID:
- 1923256
- Alternate ID(s):
- OSTI ID: 1870732
- Journal Information:
- Faraday Discussions, Vol. 237; ISSN 1359-6640
- Publisher:
- Royal Society of ChemistryCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Coherent Vibrational Wavepacket Dynamics in Platinum(II) Dimers and Their Implications
Ultrafast Excited-State Dynamics of Photoluminescent Pt(II) Dimers Probed by a Coherent Vibrational Wavepacket