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Abstract
Light-induced spin crossover (LISCO) in transition metal complexes has drawn attention to the researcher due to its various application in science and technologies. The interplay of LISCO with single molecular magnetism (SMM) is interesting in view of its application towards photoregulated storage devices, magnetic photoswitches. Herein, we have studied the interplay between LISCO and SMM of a Fe(II) complex ([Fe(Tp)(CN)3]-2) which is an ultimate miniature of potential building block of SMM using density functional theory (DFT) and time-dependent DFT method. The molecular structure and energy in low-spin singlet, high-spin quintet as well as intermediate spin triplet is calculated. It is found that the molecule is stable in its LS state but can undergo spin crossover upon irradiation of UV-vis light via triplet excited states. The singlet excited states are close-lying, forming a band structure. The detailed mechanism of LISCO is proposed based on the calculated potential energy cuts and spin-orbit coupling values. While the LS state of the complex has Ms=0 and diamagnetic, the HS state has Ms=±2 and paramagnetic. The calculations suggest a positive zero field splitting parameter and a reasonably small E/D value with a high magnetic relaxation barrier of 96 cm-1. Therefore, for a good SMM, the complex has to be trapped in its HS state after the SCO and reverse spin-crossover (rSCO) has to be stopped. On the other hand, the complex can be used as photoregulated magnetic switch if both the SCO and rSCO happens at the similar time scale.
