Single Crystal X-ray Diffraction studies were performed at 100 K and 300 K for the complex 18. The system crystallizes in the Monoclinic P21/c space group at both temperatures. The Fe(II) centers reside in a hexa-coordination environment with four equatorial N atoms coming from two L12 units and two N atoms from two coordinating NCS -ions in a trans fashion (Fig. ). At 100 K, the average Fe-N bond distances fall in the range of 1.941(5)-2.004(5) Å, suggesting the presence of Fe(II) LS state. The average Fe-N bond distances increase by 0.186 Å from 100 K to 300 K, suggesting switching from LS to HS state. This also accords with a large change in octahedral distortion index |ΔΣ| of 21.67 o while going from 100 K to 300 K. To inquire into the magnetic properties of the complex 18, solid-state magnetic susceptibility measurements were performed 18 to get T vs. T plot. At 300 K, the T value of 3.74 cm 3 mol -1 K is consistent with one Fe(II) HS state (S=2) (Fig. ). Upon decreasing the temperature, the T value slowly decreases up to 200 K, following a steep drop to reach the T value of 0.11 cm 3 K mol -1 at 2 K. To study the synergy between the spin state switching and fluorescence properties, variable temperature fluorescence emission spectra for both complex 18 and ligand L12 were recorded with the excitation wavelength of 310 nm. For the free ligand, the 394 and 412 nm fluorescence peaks show brighter emission with temperatures from 80 K to 300 K coming from the singlet to triplet state and reabsorption with delayed fluorescence. For complex 18, two distinct emission bands at 390 and 408 nm were found (Fig. ). The emission band at 390 K was found to be SCO independent with increasing the temperature, whereas the integrated intensity at 408 nm with variable temperature shows a sigmoidal nature which can be attributed to the effect of SCO phenomena. This complex 18 has a potential to be applied in ratiometric fluorescence thermosensing based on SCO considering luminescence intensity ratio (LIR), where I390 (T) can serve as a reference while I408 (T) is the SCO response. As the temperature increases, Fe(II) LS centers (strong quencher) get replaced with Fe(II) HS centers (weak quencher), changing the spinstate equilibrium as well as the LIR of complex 18, which exhibits a sharp increase. . The Sr Variable temperature PL measurements revealed that complex 19 exhibits an emission maximum centered at 350 nm, corresponding to radiative deexcitation of the excited enol* form at 80 K, which shifted to 414 nm with a bathochromic shift of ∼20 nm along with the appearance of another band at 510 nm (radiative relaxation of the excited cis-keto* form upon increasing the temperature to 300 K). In contrast, emission spectra of the ligand L13 show the above-mentioned two bands at 444 and 526 nm in the temperature range of 80 -289 K, describing a significant effect of the coordination environment around the iron centers with the ligands. Moreover, the temperature dependence of the shift of enol* band (max enol*) as max enol* vs T shows a sharp jump of 20 nm in between 135 and 179 K (from ∼395 nm below 150 K to 415 nm above 200 K).