The attempts at thermal imaging using a two-component system involving a combination of cyanine dye as a doping agent (Fig. ). This SCO-Cy7-BPEI nanocomposite (Fig. ) exhibited hysteretic SCO (Fig. ) and an unexpected reversible and strong luminescence intensity drop when switching the spin state from HS Fe(II) to the LS Fe(II) (Fig. ). The luminescenceintensity variation with SCO in the composite is attributed to the change in the crystal lattice (volume, stiffness, etc.) upon undergoing SCO. This study revealed the possibility of molecular spin-state switching affecting the luminescence behavior without any spectral overlap between the metal complex and the luminophore [102]. Then, in 2003, this phenomenon was observed with some Fe(II) complexes, as reported by Bousseksou and co-workers. Some previously synthesized complexes (52-57) were taken for this work, and their dielectric property at variable temperatures were measured, and then a correlation between the SCO and dielectric property was established . A dielectric hysteresis loop (Fig. ) is observed in the temperature dependence of dielectric property measurements. Among the six samples studied here, only one sample showed a decrease in the dielectric constant from LS to HS state (Fig. ), and others exhibited an increase in the dielectric constant (Fig. ).