Perturbing the spin state and conduction of Fe (II) spin crossover complexes with TCNQ

Abstract

We investigated modifications driven by 7,7,8,8-tetracyanoquinodimethane (TCNQ) to the spin state configuration of [Fe(3-bpp)2](TCNQ)2 co-crystal and both spin state and electric conductivity of [Fe{H2B(pz)2}2(bipy)] and TCNQ mixtures. The Fe2+ site in the [Fe(3-bpp)2](TCNQ)2 co-crystal has a sizable orbital moment. During X-ray absorption measurements, the iron ion is partially excited to the high spin state and strong surface effects are indicated. Mixing TCNQ with the [Fe{H2B(pz)2}2(bipy)] spin crossover complex leads to a molecular combination with increased conductivity and drift carrier lifetimes. [Fe{H2B(pz)2}2(bipy)] thin films with TCNQ, grown using dimethylformamide (DMF), are to great extent locked mainly in the low spin (LS) state across a broad temperature range and exhibit drift carrier lifetimes approaching 0.5 s. When deposited onto a ferroelectric polyvinylidenefluoride-hexafluoropropylene thin film substrate, [Fe{H2B(pz)2}2(bipy)], shows enhanced transistor carrier mobility, likely associated with the increasing cationic character of [Fe{H2B(pz)2}2(bipy)] thin films with TCNQ.