Luminescent properties of new naphthylnitroxyl radicals

Method of time-resolved fluorescence was applied to study the luminescent properties of several 3-and 2-imidazoline derivatives of naphthalene. For 2-imidazoline derivatives in which the imidazoline fragment is directly bound to the naphthalene fragment, a weak (quantum yield φ < 0.001) luminescence of common π-system containing the radical group and the naphthalene core was recorded. 3-imidazoline derivatives, in which naphthalene and imidazoline fragments are separated by an ethylene bridge, demonstrate luminescence with the spectrum similar to that of free naphthalene. Quantum yield of luminescence and life-time of singlet excited state of 3-imidazoline derivatives are ca. 50 times less than for free naphthalene, because of intramolecular quenching of the luminophore luminescence by a stable radical.