Ultrafast Photophysics of a Dinitrogen-Bridged Molybdenum Complex

Shahnawaz Rafiq, Máté J. Bezdek, Marius Koch, Paul J. Chirik, Gregory D. Scholes

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Among the many metal-dinitrogen complexes synthesized, the end-on bridging (μ2, η1, η1 - N2) coordination mode is notoriously unreactive for nitrogen fixation. This is principally due to the large activation energy for ground-state nitrogen-element bond formation and motivates exploration of the photoexcited reactivity of this coordination mode. To provide the foundation for this concept, the photophysics of a dinitrogen-bridged molybdenum complex was explored by ultrafast electronic spectroscopies. The complex absorbs light from the UV to near-IR, and the transitions are predominantly of metal-to-ligand charge transfer (MLCT) character. Five excitation wavelengths (440, 520, 610, 730, and 1150 nm) were employed to access MLCT bands, and the dynamics were probed between 430 and 1600 nm. Despite the large energy space occupied by electronic states (ca. 1.2 eV), the dynamics were independent of the excitation wavelength. In the proposed kinetic model, photoexcitation from a Mo-N=N-Mo centered ground state populates the π∗-state delocalized over two terpyridine ligands. Due to a large terpyridine-terpyridine spatial separation, electronic localization occurs within 100 fs, augmented by symmetry breaking. The subsequent interplay of internal conversion and intersystem crossing (ISC) populates the lowest 3MLCT state in 2-3 ps. Decay to the ground state occurs either directly or via a thermally activated metal-centered (3MC) trap state having two time constants (10-15 ps, 23-26 ps [298 K]; 103 ps, 612 ps [77 K]). ISC between 1MLCT and 3MLCT involves migration of energized electron density from the terpyridine π∗ orbitals to the Mo-N=N-Mo core. Implication of the observed dynamics for the potential N-H bond forming reactivity are discussed.

Original languageEnglish
Pages (from-to)6298-6307
Number of pages10
JournalJournal of the American Chemical Society
Issue number20
StatePublished - May 23 2018

Bibliographical note

Funding Information:
S.R., M.K., and G.D.S. acknowledge support from the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy, through Grant No. DE-SC0015429. M.K. further acknowledges support from a Swiss National Science Foundation postdoctoral fellowship. M.J.B. and P J.C. acknowledge support from the U.S. Department of Energy, Office of Science, Basic Energy Science (DE-SC0006498). M.J.B. thanks the Natural Sciences and Engineering Research Council of Canada for a predoctoral fellowship (PGS-D) as well as Princeton University for an Edward C. Taylor Fellowship. S.R. thanks Daniel Oblinsky for assistance with low-temperature pump−probe measurements.

Publisher Copyright:
© 2018 American Chemical Society.

ASJC Scopus subject areas

  • Catalysis
  • Chemistry (all)
  • Biochemistry
  • Colloid and Surface Chemistry


Dive into the research topics of 'Ultrafast Photophysics of a Dinitrogen-Bridged Molybdenum Complex'. Together they form a unique fingerprint.

Cite this