Computational Insights Into Light‐Induced Spin Crossover and Magnetic Properties of [Fe ^<i>II</i> (Tp)(CN) ₃ ] ⁻² Complex

ABSTRACT Light‐induced spin crossover (LISCO) in transition metal complexes has gathered interest from researchers due to its diverse usage in science and technologies. The interplay of LISCO with single molecular magnetism (SMM) is intriguing because of its application toward photoregulated storage devices and magnetic photoswitches. Herein, we have studied the LISCO of an Fe(II) complex ([Fe(Tp)(CN) 3 ] −2 ), which is a monometallic part of a potential building block of SMM, using density functional theory (DFT) and the time‐dependent DFT methods. Furthermore, we have computed the magnetic characteristics of the molecule to elucidate its magnetic behavior, employing wave function‐based approaches. The molecular structure and energy in low‐spin (LS) singlet, high‐spin (HS) quintet, and intermediate‐spin triplet are 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 = 0 and is diamagnetic, the HS state has = and is paramagnetic. The calculations suggest a positive zero‐field splitting parameter and a non‐zero value. Therefore, to exhibit paramagnetic behavior, the complex has to be trapped in its HS state after the SCO, and reverse spin‐crossover (rSCO) has to be stopped. However, the complex, being a non‐Kramer's system, does not show the magnetic bistability in the high‐spin state and requires additional extension to function as a potential building block of a single‐molecule magnet.