Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

Abstract

Special Issue: Special Issue to Honour Professor Dr. Rudi van Eldik on the occasion of his 70th birthda

Structural Dynamics of Spin Crossover in Iron(II) Complexes with Extended-Tripod Ligands

“…The trigonal twist angle θ amounts to 60 • for a regular octahedron and gives 0 • for a trigonal prism. With a value of θ = 43.4 (8) • , the coordination pattern of [FeL] 2+ is well within the range observed for ls-iron(II) complexes of N 6 ligands of the extended tripod type and closely mimics structure analogues with pyridine derivatives [26,51]. As the experimental data are closely matched by a DFT-derived vacuum structure of the isolated complex with respect to bond lengths and angles (see Table 2), only minor matrix effects may be expected.…”

“…Around ambient temperature, however, the exchange reactions are very rapid, leading to randomizing spin states within a few nanoseconds in most iron(II) complexes [13][14][15][16][17][18][19][20][21][22][23][24]. Our serendipitous observation of spin state lifetimes in the microsecond range for a number of six-coordinate iron(II) complexes therefore marks a notable exception that demands rationalization [25,26]. Ligands of the extended-tripod type with a unique thiophosphoryl capping unit (L in Scheme 1 and derivatives thereof) were found to harbor hindered SCO kinetics, irrespective of solvent nature and the presence of dioxygen.…”

“…Respective effects on the SCO kinetics of these systems have not been reported yet. In this context, it is interesting to note that the SCO kinetics of a hydroxyl-substituted congener of [FeL] 2+ have been previously found to vary significantly with solvent [26].…”

“…Ultra-fast depopulation of the MLCT-like Franck-Condon state concomitant with quintet-state population generally occurs on the sub-ps timescale, greatly independent of ligand nature. Accordingly, the MLCT-state in a structure analogue of [FeL] 2+ is depopulated within few hundreds of femtoseconds [26]. We note in passing that there is much current interest in "taming" of MLCT states, aiming at longer MLCT-state lifetimes [24,59,60].…”

“…Recovery of the equilibrium is recorded via transient absorption spectroscopy [13][14][15][16][17][18][19][20][21][22][23][24]. This acquisition scheme has been shown previously to be applicable for a number of iron(II) complexes [25][26][27]. Transient-absorption spectra recorded directly after ns-laser excitation of solutions of Both the transient spectra and decay kinetics are only marginally affected by the solvent.…”