A luminescent Pt₂Fe spin crossover complex

Abstract

A heterotrinuclear [PtFe] spin crossover (SCO) complex was developed and synthesized employing a ditopic bridging bpp-alkynyl ligand L and alkynyl coordinated Pt terpy units: [Fe(L-Pt)](BF) (1). We identified two different types of crystals of 1 which differ in their molecular packing and the number of co-crystallized solvent molecules: 1H (1·3.5CHCl in P1[combining macron]) and 1L (1·10CHCl in C2/c); while 1L shows a reversible SCO with a transition temperature of 268 K, the analogous compound 1H does not show any SCO and remains blocked in the HS state. The temperature-dependent magnetic properties of 1H and 1L were complementarily studied by Mössbauer spectroscopy. It has been shown that 1L performs thermal spin crossover and that 1L can be excited to a LIESST state. The vibrational properties of 1 were investigated by experimental nuclear resonance vibrational spectroscopy. The experimentally determined partial density of vibrational states (pDOS) was compared to a DFT-based simulation of the pDOS. The vibrational modes of the different components were assigned and visualized. In addition, the photophysical properties of 1 and L-Pt were investigated in the solid state and in solution. The ultrafast transient absorption spectroscopy of 1 in solution was carried out to study the PL quenching channel via energy transfer from photoexcited Pt terpy units to the Fe-moiety.

Monitoring the Spin States of Ferrous Ions by Fluorescence Spectroscopy in Spin‐Crossover–Fluorescent Hybrid Materials

“…Instead, the fluorescence intensity is dominated by thermal quenching effects in the whole temperature range, except that at the critical temperature of the SCO the fluorescent intensity is suddenly enhanced. We notice that several recent papers have reported interesting results on SCO fluorescence, which together with our works may shed light on different mechanisms underlying the SCO–fluorescence correlation.…”

Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties

“…This isotope sensitivity implies certain limitations, but can also provide advantages. Notably, in the case of iron‐based SCO complexes, this feature was used at several instances to analyze vibrational modes of the coordination octahedron . As an example, Figure shows the partial VDOS of the SCO complex [Fe(HB(tz) 3 ) 2 ] in the two spin states extracted from NIS experiments .…”

Fluorescence modulation via photoinduced spin crossover switched energy transfer from fluorophores to FeII ions

“…When compared with the photoisomerization of organic molecules, the photoswitchable electron rearrangement of metal ions, such as spin crossover (SCO) and electron transfer, has been realized in the solid state with a fast response rate and good reversibility, accompanied by drastic changes in the electronic and crystal structure of the materials. 21 – 23 Such drastic changes should sufficiently perturb the environment of the fluorophore and further allow a fluorescent response; 24 – 34 thus providing a promising candidate for a light-responsive unit with which to construct photoswitchable fluorescent molecular devices. However, two challenges remain in achieving the goal in this system.…”