Excited high-spin quartet (S=3/2) state of a novel pi-conjugated organic spin system, pyrene-verdazyl radical

The excited high-spin quartet (S = 3/2) state of the intramolecular triplet-radical pair between the excited triplet state of pyrene and a dangling verdazyl radical was reported. A novel verdazyl radical with the pyrene moiety was designed and synthesized. The time-resolved ESR spectrum and a DFT calculation show the photo-induced ferromagnetic spin alignment between the excited triplet state of the pyrene moiety and the dangling verdazyl radical. This is the first observation of the high-spin (S > 1) excited state of the pi-conjugated pyrene-radical pair.