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Deactivation of the excited states of 1-anthrol by aromatic N-heterocycles

1976; Elsevier BV; Volume: 5; Issue: 6 Linguagem: Inglês

10.1016/0047-2670(76)85047-2

1873-2658

Sadaaki Yamamoto, Kôichi Kikuchi, Hiroshi Kokubun,

Synthesis and Biological Evaluation

The interactions of the excited 1-anthrol with pyridine, quinoline, and acridine have been investigated in cyclohexane. Fluorescence of 1-anthrol is quenched dynamically by pyridine and quinoline at about a diffusion controlled rate. 1-Anthrol hydrogen bonded with pyridine or quinoline in the ground state does not produce any transient species detectable by a conventional flash apparatus and is non-fluorescent. The bimolecular interaction between the excited singlet 1-anthrol and pyridine leads to neither the enhancement of intersystem crossing nor reaction. The triplet 1-anthrol is not deactivated by pyridine, but by quinoline and acridine with the rate constants of 1.1 – 1.4 × 109 and 1.1 × 109 M−1 s−1, respectively, yielding 1-anthroxyl radical. By means of the triplet energy transfer to the hydrogen bonded species, it was found that the radical is formed from the triplet state of the hydrogen bonded 1-anthrol. Acid dissociation constants of 1-anthrol were determined as pK = 10.0, ∼10, and −0.07 for the ground, the triplet, and the singlet excited states, respectively. It was suggested that the acidities of both the hydrogen bonding donor and acceptor are closely correlated with the facility of the hydrogen atom transfer reaction in the excited states.