) is very close to the theoretical value of √2 (Eq 1 in the Supplementary Information, and Supplementary Fig. ). In addition, the intensity of the triplet species relative to the doublet species noticeably increases at 100 K compared to at 10 K (Fig. ). This observation further demonstrates that the triplet state is the thermally populated excited state of cg-2. Next, superconducting quantum interference device (SQUID) measurement was performed on freshly prepared crystalline powder of cg-2 to quantify the energy gap (∆ES-T) between the singlet ground state and the triplet excited state, more fundamentally, the coupling strength between the two spins in cg-2. The product value of the molar magnetic susceptibility and temperature (χm•T) rapidly increase from 25 K, and gradually approaches saturation after 200 K (Fig. ). This is the characteristic feature of thermally populated transition from the magnetically silent singlet state to the magnetically active triplet state. By fitting the χm•T -T curve with Bleaney-Bowers equation (Eq 3 in the Supplementary Information, the contribution from doublet impurities is treated as a constant in the fitting), ∆ES-T was determined to be -0.29 kcal/mol, which is consistent with DFTcalculated value -0.35 kcal/mol. This ∆ES-T value is considerably smaller than the energy gaps for many open-shell singlet diradicaloid systems , suggesting the coupling strength between the spatially segregated spins in cg-2 is much weaker than bonding interaction. In addition, χm•T value rapidly decreases below 25 K, indicating that the influence of intermolecular AFM coupling can no longer be ignored at extremely low temperatures. At present, the interaction between the two spatially segregated electrons in cg-2 has been clearly revealed: the two electrons can feel the existence of each other and keep their spins paired in the ground state, suggesting a spin entanglement in Clar's goblet. The singlet ground state can be thermally excited to triplet state. Theoretically calculated spin density distribution (Supplementary Fig. ) of the singlet state of cg-2 retains the same spin polarization feature as the pristine Clar's goblet, with the up and down spins separately localized on the two halves.