Luminescence of the nitronyl nitroxide radical group in a spin-labelled pyrazolylquinoline

The synthesis, structure and photoluminescence of a group of substituted 2-pyrazolylquinolines, including a spin-labelled derivative, are described. A comparative study of photoluminescence from the synthesized compounds demonstrates that introduction of a nitronyl nitroxide radical group results not only in the expected reduction in photoluminescence from the pyrazolylquinoline moiety, but also gives rise to a new red photoluminescence band (maximum at 692 nm in acetonitrile) from the radical fragment.