Monitoring spin-crossover phenomena via Re(i) luminescence in hybrid Fe(ii) silica coated nanoparticles

Abstract

Bare (1) and silica coated (1@SiO₂) spin crossover (SCO) nanoparticles based on the polymer {[Fe(NH₂Trz)₃](BF₄)₂}_n have been prepared following a water-in-oil synthetic procedure. For 1, the critical temperatures of the spin transition are T_C↓ = 214.6 K and T_C↑ = 220.9 K. For 1@SiO₂, the abruptness of the transition is enhanced and the critical temperatures are centred at room temperature (T_C↓ = 292.1 K and T_C↑ = 296.3 K). An inert Re(I) complex of formula [Re(phen)(CO)₃(PETES)](PF₆) (phen = 1, 10-phenanthroline; PETES = 2(4-pyridylethyl)triethoxysilane) (Re) was also synthesized yielding intense green emission centred at λ_em = 560 nm. The grafting of this complex on the silica shell of 1@SiO₂ led to a bifunctional SCO-luminescence composite (1@SiO₂/Re) whose luminescence properties were tuned by the spin state switching. Temperature-variable photophysical studies showed that luminescence and spin transition were synchronized through a radiative (trivial) energy transfer mechanism between the Re(I) and the Fe(II)-LS (LS, Low Spin) centres.