Two state “ON–OFF” NLO switch based on coordination complexes of iron and cobalt containing isomeric ligand: a DFT study

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values. Moreover, switchable NLO response is also important in coordination complexes. Herein, we report two state ON–OFF switchable NLO contrast of coordination complexes of Fe and Co containing isomeric ligands. The optical, UV-visible, and electronic properties besides the “ON–OFF” switching effect are calculated using the CAM-B3LYP/6-31+G (d) method. The NLO responses of ligand–metal isomers are qualitatively evaluated through variation in charge transference (CT) style through TD-DFT. The higher β(o) in each isomeric pair is strongly dependent on the HOMO–LUMO gap. The isomer 4b with lowest HOMO–LUMO gap shows the highest NLO response. The charge transfer pattern in these complexes results in variation of their β(o) values. The notable β(o) contrast of 21.15 in isomeric pairs 3a and 3b makes these complexes a favorable material for genuine NLO switches. Hence, the outcome of the current investigation reveals that these ligand–metal isomeric complexes exhibit a two-state switch “ON–OFF” effect.