Spin–Orbit Coupling Drives Femtosecond Nonadiabatic Dynamics in a Transition Metal Compound

Abstract

Transient absorption measurements conducted using broadband, 6 fs laser pulses reveal unexpected femtosecond dynamics in the [IrBr] model system. Vibrational spectra and the X-ray crystal structure indicate that these dynamics are not induced by a Jahn-Teller distortion, a type of conical intersection typically associated with the spectral features of transition metal compounds. Two-dimensional electronic spectra of [IrBr] contain 23 cross peaks, which necessarily arise from spin-orbit coupling. Real-valued 2D spectra support a spectroscopic basis where strong nonadiabatic coupling, ascribed to multiple conical intersections, mediates rapid energy relaxation to the lowest-energy excited state. Subsequent analysis gives rise to a more generalized description of a conical intersection as a degeneracy between two adiabatic states having the same total angular momentum.

A new family of one-dimensional bromo-bridged Ir(iv)–Cu(ii) complexes based on the hexabromoiridate(iv) metalloligand

“…The crystal structure of compound 1 was published elsewhere, 25 which is described as well-isolated [IrBr 6 ] 2− anions that are separated from each other by bulky NBu 4 + cations in its crystal lattice. 25 Compounds 2 , 3 and 4 crystallise in the triclinic, monoclinic and orthorhombic crystal systems with space groups P 1̄, C 2/ c and Pccn , respectively (Table 1). The crystal structure of 3 is isostructural to that of the previously reported {IrCl 5 (μ-Cl)Cu(Viim) 4 } n chain.…”

“…Therefore, no significant differences are seen in between these values, which are in agreement with those found in the literature for the [IrBr 6 ] 2− unit. 25…”

“…The (NBu 4 ) 2 [IrBr 6 ] compound was prepared as described in the literature. 25 Anal. calcd for C 32 H 72 N 2 Br 6 Ir ( 1 ): C, 33.2; H, 6.3; N, 2.4.…”

Characterizing divergent spin-orbit coupling effects on ultrafast nonradiative decay in transition-metal compounds

“…The complete coupling of all LMCT bands in the chromophore produces several dozen individual peaks, and the stimulated emission signal in the low frequency, 390 -460 THz, range of the 100 fs spectrum rapidly converts to excited state absorption (ESA) signal. Indeed, the ultrafast dynamics of [IrBr6] 2are best explained as interactions between spin-orbit coupled, adiabatic potential energy surfaces resulting in nonradiative decay of all LMCT transitions into the lowest excited state [13]. The observation of persistent vibrational coherence during this LMCT energy relaxation suggested conical intersection mediated nonradiative decay.…”

“…The schematic representation (right) was constructed using a simple group theory model in the total angular momentum basis. This figure has been adapted from ref 13…”