Modulation of spin states and electronic excitation via molecular doping with Fe(II)-porphyrin in 2D gallium nitride

2D gallium nitride possesses distinctive electronic states, making it ideal for future optoelectronic devices because of the quantum confinement and enhanced many-body interactions inherent in its atomically thin form. This study explores the impact of molecular doping with Fe(II)-porphyrin (FeP) on these characteristics using first-principle calculations. Contact of the magnetic center Fe with the nitrogen site causes a 17% decrease in the energy barrier for the transition from intermediate spin (S = 1) to high spin (S = 2) state, highlighting the sensitivity of spin dynamics to doping sites. Molecular diffusion barriers increase by 9.6 kJ/mol upon spin transition, suggesting that the spin state influences molecular mobility within the material. Exploring spectral functions reveals that FeP doping introduces spin-dependent molecule levels within the bandgap, which may play a role in electron-hole separation and spin injection. In addition, we show that the molecule-substrate coupling lowers the exciton binding energy by 0.1 eV, with further reduction during spin transitions. This weakening is attributed to increased electron mobility, quantified by static polarizability. These results indicate that the molecular spin state can control electronic excitations within substrate materials, presenting a promising strategy for designing spintronic devices.