Hydrocarbon diradical 1, a new stable, 3-fold symmetric analogue of trimethylenemethane (TMM) with no heteroatom perturbation, is prepared and studied. Such diradicals should provide new building blocks for high-spin hydrocarbon polyradicals with very strong net ferromagnetic coupling, Magnetic studies (SQUID) and EPR spectroscopy indicate that 1 in tetrahydrofuran-d(8) (THF-d(8)) possesses a triplet (S = 1) ground state, with strong ferromagnetic coupling. After annealing at room temperature, the EPR spectra of 1 (similar to 0.02 M in frozen THF-d(8)) consist of a single narrow resonance (Delta H-pp center dot 1 G), and intermolecular antiferromagnetic coupling is increased by 1 order of magnitude. This behavior is consistent with the presence of exchange narrowing, thus suggesting aggregation of 1 in THF-d(8). Blue solutions of 1 in THF-d(8) possess a strong UV-vis absorption band at lambda(max) approximate to 640 nm. Diradical 1 in THF-d(8) is stable (or persistent) at room temperature, with no detectable decomposition for at least 2 days.