Several Cu(II) complexes were reported as fluorescent nitric
oxide sensors based on the strategy involving the reduction of a
metal center by nitric oxide [31–37]. A fluorescent ligand is
expected to be quenched on coordination to the paramagnetic Cu
(II) center. Nitric oxide reduction of a paramagnetic Cu(II) center
to a diamagnetic Cu(I) will restore the quenched fluorescence of
a ligand fluorophore [31–37]. Since, in the present case nitrite
selectively reduces Cu(II) center to Cu(I), the same strategy of
restoring the quenched fluorescence intensity of the ligand in the
complex was adopted. Fluorescence spectroscopic study at 298 K
suggested the significant quenching (>90%) of fluorescence intensity
of L in presence of equivalent amount of Cu(II) owing to paramagnetic
effect in methanol or acetonitrile solution (Fig. 6 and
Supporting information).