Ultrafast Wiggling and Jiggling: Ir2(1,8-diisocyanomenthane)42+

Martin Pižl, Bryan M. Hunter, Gregory M. Greetham, Michael Towrie, Stanislav Záliš*, Harry B. Gray, Antonín Vlček

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Binuclear complexes of d8 metals (PtII, IrI, RhI,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M-M bonding is strengthened upon dσ∗ â' pσ excitation. We report the bridging ligand dynamics of Ir2(1,8-diisocyanomenthane)42+ (Ir(dimen)), investigated by fs-ns time-resolved IR spectroscopy (TRIR) in the region of C=N stretching vibrations, 2000-2300 cm-1. The v(C=N) IR band of the singlet and triplet dσpσ excited states is shifted by-22 and-16 cm-1 relative to the ground state due to delocalization of the pσ LUMO over the bridging ligands. Ultrafast relaxation dynamics of the 1dσpσ state depend on the initially excited Franck-Condon molecular geometry, whereby the same relaxed singlet excited state is populated by two different pathways depending on the starting point at the excited-state potential energy surface. Exciting the long/eclipsed isomer triggers two-stage structural relaxation: 0.5 ps large-scale Ir-Ir contraction and 5 ps Ir-Ir contraction/intramolecular rotation. Exciting the short/twisted isomer induces a â5 ps bond shortening combined with vibrational cooling. Intersystem crossing (70 ps) follows, populating a 3dσpσ state that lives for hundreds of nanoseconds. During the first 2 ps, the Î(C=N) IR bandwidth oscillates with the frequency of the Î(Ir-Ir) wave packet, ca. 80 cm-1, indicating that the dephasing time of the high-frequency (16 fs)-1 C=N stretch responds to much slower (â400 fs)-1 Ir-Ir coherent oscillations. We conclude that the bonding and dynamics of bridging di-isocyanide ligands are coupled to the dynamics of the metal-metal unit and that the coherent Ir-Ir motion induced by ultrafast excitation drives vibrational dephasing processes over the entire binuclear cation.

Original languageEnglish (US)
Pages (from-to)9275-9283
Number of pages9
JournalJournal of Physical Chemistry A
Issue number48
StatePublished - Dec 7 2017

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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