Charge transfer-triggered reversible spin-state switching

Abstract

Triggering the spin-state switching (SSS) in solutions at room temperature (RT) has attracted attention in the field of molecular switches. Herein, we report the preparation and switching properties of a ferrous complex Fe(H₂Bpz₂)₂(L-C₂H₅) (H₂Bpz₂ = dihydrobis(1-pyrazolyl)borate, L-C₂H₅ = (4,15-bis[4-(N,N-diethylamino)phenyl][1,2,5]thiadiazolo-[3,4-i]dipyrido[a,c]phenazine)). Upon near-infrared (NIR) laser on, the ferrous complex formed H-aggregation in the solution with enhanced ligand-to-ligand charge transfer, which thus achieved a high-spin state. Upon switching the NIR laser off, the ferrous complex changed to J-aggregation with enhanced intramolecular charge transfer, which resulted in the low-spin state; as a consequence, charge transfer triggered reversible SSS in the solution at RT. More interestingly, further confinement into the solid-state three-dimensional polymer sponge did not affect the SSS performance of the ferrous complex, suggesting the high potential of Fe(H₂Bpz₂)₂(L-C₂H₅) for practical applications in future molecular electronic and spintronic devices.