Laser Flash Photolysis Study of the Magnetic Field Effects on the Biradicals Generated from Aromatic Ketone-Xanthene Bifunctional Chain Molecules

The external magnetic field effects (MFE) on the biradicals generated from the intramolecular photoreactions of bifunctional chain molecules, α-(xanthone-2-carbonyloxy)-ω-(xanthene-2-carbonyloxy)alkanes (XO-n-XH, n=2–12) and Ar-12-XH (Ar=anthraquinone-4-carbonyloxy (AQ), 4-benzoylphenoxy (BP), and 4-acetylphenoxy (AP)) were studied by laser flash photolysis. All biradicals exhibit significant MFE. The simultaneous observation of the effects on the two radicals at the ends of the chain, generated from XO-12-XH, AQ-12-XH, and BP-12-XH, presents unequivocal evidence that the respective two radical centers correlate magnetically each other. The n dependence of the effects on biradicals generated from XO-n-XH indicates that the singlet–triplet degeneracy of the biradical occurs at the chain length of around n=6, i.e., the interradical distance of about 15 Å.