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Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+)

Pižl, Martin and Hunter, Bryan M. and Greetham, Gregory M. and Towrie, Michael and Záliš, Stanislav and Gray, Harry B. and Vlček, Antonín (2017) Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+). Journal of Physical Chemistry A, 121 (48). pp. 9275-9283. ISSN 1089-5639. doi:10.1021/acs.jpca.7b10215.

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Binuclear complexes of d^8 metals (Pt^(II), Ir^I, Rh^I,) 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* → pσ excitation. We report the bridging ligand dynamics of Ir2(1,8-diisocyanomenthane)_4^(2+)(Ir(dimen)), investigated by fs–ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000–2300 cm^(–1). The ν(C≡N) IR band of the singlet and triplet dσ*pσ 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 ^1dσ*pσ 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 ∼5 ps bond shortening combined with vibrational cooling. Intersystem crossing (70 ps) follows, populating a ^3dσ*pσ state that lives for hundreds of nanoseconds. During the first 2 ps, the ν(C≡N) IR bandwidth oscillates with the frequency of the ν(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 (∼400 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Hunter, Bryan M.0000-0001-8559-9304
Gray, Harry B.0000-0002-7937-7876
Vlček, Antonín0000-0002-6413-8311
Additional Information:© 2017 American Chemical Society. Received: October 15, 2017; Published: November 13, 2017. This work was supported by the Czech Science Foundation Grant 17-011375, NSF CCI Solar Fuels Program (CHE-1305124) and STFC (UK). B.M.H. is a Fellow of the Resnick Sustainability Institute at Caltech. Additional support was provided by the Arnold and Mabel Beckman Foundation, the Ministry of Education of the Czech Republic (Grant LTC17052), and COST Action CM1405. The authors declare no competing financial interest.
Group:CCI Solar Fuels, Resnick Sustainability Institute
Funding AgencyGrant Number
Czech Science Foundation17-011375
Science and Technology Facilities Council (STFC)UNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Arnold and Mabel Beckman FoundationUNSPECIFIED
Ministry of Education (Czech Republic)LTC17052
European Cooperation in Science and Technology (COST)CM1405
Issue or Number:48
Record Number:CaltechAUTHORS:20171115-101044605
Persistent URL:
Official Citation:Ultrafast Wiggling and Jiggling: Ir2(1,8-diisocyanomenthane)42+. Martin Pižl, Bryan M. Hunter, Gregory M. Greetham, Michael Towrie, Stanislav Záliš, Harry B. Gray, and Antonín Vlček. The Journal of Physical Chemistry A 2017 121 (48), 9275-9283. DOI: 10.1021/acs.jpca.7b10215
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83220
Deposited By: Tony Diaz
Deposited On:15 Nov 2017 22:02
Last Modified:15 Nov 2021 19:56

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