Global Optimization of a Spin-Crossover Molecule on Monolayer MoS₂: Spin Transition-Induced Band Edge Shift

We investigate the interaction between a Fe(II) spin-crossover molecule and a two-dimensional (2D) substrate. Using density functional theory combined with molecular dynamics simulations, we explore the configuration space and spin state energetics of the [Fe(py)2bpym(NCS)2] molecule adsorbed on the 2D semiconductor MoS2. We show that the deposited molecule can display a high-spin ground state, in contrast to the locking of a low-spin state observed on metallic substrates. The variation can be primarily attributed to the noncovalent interactions occurring at the interface. Furthermore, the molecular doping of the n-type is examined from an electronic structure point of view. Specifically, our calculations reveal a notable shift of the band edge that can reach 0.3 eV due to fluctuations in the electric dipole at the interface upon spin-state switching. This observation indicates the possibility of regulating the photocatalytic selectivity of hydrogen evolution and CO2 reduction reactions within the heterostructure by manipulating the molecular spin state using an external trigger.