As explained in the introduction, the two electrons in Clar's goblet are spatially segregated and cannot be paired by forming a chemical bond. The long-standing question is: how do these two individual electrons interact with each other? In principle, a two-spin system can exist in a magnetically active triplet state when the spins are aligned, or in a magnetically silent singlet state when the spins are opposite. Alternatively, if spin-spin interaction is very weak, the system might behave like an almost independent doublet state. Thus, the key to addressing this question is to distinguish the spin ground state of Clar's goblet. Continuous-wave electron paramagnetic resonance (cw-EPR) measurement was first used to probe the interaction between the two spins. At 170 K, the spectrum of cg-2 in the frozen toluene-d8 solution shows resonance signals composed of two components: zero-field splitting (ZFS) from a triplet (S = 1) component and central peaks from a doublet (S = 1/2) component, which can be readily separated by simulation (Fig. , simulation parameters are attached in the Supplementary Information). A forbidden transition (|∆𝑚𝑚 s | = 2 ) signal is also observed (ms refers to magnetic quantum number). The characteristic ZFS and half-field absorption provide solid evidence for the existence of triplet state in Clar's goblet and rule out the possibility that the two spins are weakly interacted. Furthermore, ZFS parameters of |𝐷𝐷| = 114.5 MHz and |𝐸𝐸| = 15.7 MHz are obtained from simulations. Using the equation D = 1.39 × 10 4 (𝑔𝑔 𝑟𝑟 3 ⁄ ) where unpaired electrons are considered as point-dipoles , the average spin-spin distance in cg-2 is determined as 8.7 Å, further supporting the spatial segregation of the two spins (Fig. ). Additionally, the doublet component in cw-EPR spectrum is proposed to be monoradical impurities with structures similar to cg-2. The observation of doublet signals in the EPR measurement of diradicals is very common, and the origin of the monoradical impurities includes the interactions or reactions with oxygen, solvents, light or intermolecular interactions .