Spectroscopic Studies. To study the change in optical property with temperature, UV-vis-NIR spectroscopic studies have been carried out for this sample in the visible region of the spectrum at the temperature ranging from 303 ̶ 413 K. At 303 K, the spectrum exhibits a shoulder at around 420 nm and a broad band centered at around 700 nm (Figure , right). This result matches well with the previously reported data. The 420 nm band is described as the ligand-to-metal chargetransfer (LMCT) transition originating from the [Fe II (Tp)(CN)3] 2-unit, while the 700 nm band is ascribed as the metal-to-metal charge transfer (MMCT) transition band coming from Fe II LS to Co III LS center. As expected, the MMCT transition band decreased while increasing the temperature, and a new band at 540 nm started to appear above 343 K (Figure ). This is due to the conversion of green colored diamagnetic (Fe II LS-CN-Co III LS) state into red colored paramagnetic (Fe III LS-CN-Co II HS) state. The 540 nm band is arising due to the metal-to-metal charge transfer transition from Co II HS to Fe III LS center which matches well with the literature value. pair and/or paramagnetic Co(II) → Fe(III) pair through the cyanide bridge in this system. Thus, the process of electrical conductivity can be better analyzed by understanding the dielectric property of the system across the phase transition temperatures for 1. The real part of the dielectric constant (′) has been shown as a function of temperature ranging from 296 K up to 420 K (sweep rate 1 K min -1 ) at different selected frequencies (Figure , left) and the corresponding imaginary (″) dielectric behavior is plotted in Figure (right). The dielectric constant increases monotonically as a function of temperature and a characteristic jump (a sudden fall) occurs at 408 K corresponding to the transition temperature (dia to para) as evidenced in the DSC and magnetic measurements (vide supra, Figure ) followed by a slow rise in nature. The transition around 332 K seen in the DSC data and magnetic measurements is weakly visible in the dielectric measurement (Figure ), which could occur if the transition involves isostructural transformation or a low-energy structural transition. The Cole-Cole plot at low temperatures (before the transition) shows two semi-circular behaviors, one complete and another just beginning of the semi-circular nature (Figure ). This characteristic indicates the dimeric nature of the system, which upon heating gradually converts the diamagnetic {Fe system, which relaxes back to the diamagnetic-dipolar state upon lowering the temperature. We have utilized this dielectric bistability in the device based application.