title: Bond shortening (1.4 Å) in the singlet and triplet excited states of [Ir2(dimen)4]2+ in solution determined by time-resolved X-ray scattering.
abstract: Ground- and excited-state structures of the bimetallic, ligand-bridged compound Ir2(dimen)4(2+) are investigated in acetonitrile by means of time-resolved X-ray scattering. Following excitation by 2 ps laser pulses at 390 nm, analysis of difference scattering patterns obtained at eight different time delays from 250 ps to 300 ns yields a triplet excited-state distance between the two Ir atoms of 2.90(2) Å and a triplet excited-state lifetime of 410(70) ns. A model incorporating the presence of two ground-state structures differing in Ir–Ir separation is demonstrated to fit the obtained data very well, in agreement with previous spectroscopic investigations. Two ground-state isomers with Ir–Ir separations of 3.60(9) and 4.3(1) Å are found to contribute equally to the difference scattering signal at short time delays. Further studies demonstrate the feasibility of increasing the effective time resolution from the 100 ps probe width down to the 10 ps regime by positioning the laser pump pulse at selected points in the X-ray probe pulse. This approach is used to investigate the structures of both the singlet and the triplet excited states of Ir2(dimen)4(2+).
authors.affiliation: Centre for Molecular Movies, Technical University of Denmark, Risø National Laboratory, Materials Department, Roskilde, Denmark. hald@risoe.dtu.dk
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Haldrup
authors.forename: Tobias
authors.initials: T
authors.lastname: Harlang
authors.forename: Morten
authors.initials: M
authors.lastname: Christensen
authors.forename: Asmus
authors.initials: A
authors.lastname: Dohn
authors.forename: Tim Brandt
authors.initials: TB
authors.lastname: van Driel
authors.forename: Kasper Skov
authors.initials: KS
authors.lastname: Kjær
authors.forename: Niels
authors.initials: N
authors.lastname: Harrit
authors.forename: Johan
authors.initials: J
authors.lastname: Vibenholt
authors.forename: Laurent
authors.initials: L
authors.lastname: Guerin
authors.forename: Michael
authors.initials: M
authors.lastname: Wulff
authors.forename: Martin Meedom
authors.initials: MM
authors.lastname: Nielsen