Attached
Absorption and emission spectra of 5-hydroxy1,10-phenanthroline, 1 in acetonitrile shows that
maximum absorption and emission at 268 nm and 403
nm, respectively. The divalent cations of Fe, Co, Cd,
Pb and Mn showed the complex formation with 5-
hydroxy-l,10-phenanthroline with a single isobestic
point in the absorption spectra. However, divalent
cations of Ni, Cu and Zn did not show complex
formation. According to the gathered emission spectra,
Fe(II), Cd(II), Co(H) and Pb(II) were seemed to form
fluorescence active complexes with 1.
The Stem-Volmer plot of 1 in the presence of
Fe(II), Co(H), Cd(II), Pb(H) and Mn(II) indicated the
presence of both static and dynamic quenching by the
same quencher.1,1 However in the emission study no
such complex formation was observed with Mn(H)
and this is due to the non-fluorescent nature of the
complex formed. In the presence ofNi(II) and Zn(H), it
indicated the dynamic quenching of fluorescence of
the 1. In the presence of Cu(II) the study implies the
presence of accessible and inaccessible fluorqphores
to divalent copper ion.1 The divalent cations of Fe, Co
and Cd showed the formation of 1:3 complexes
whereas Pb and Mh showed the formation of 1:2
complexes.3
The static and dynamic quenching constants and
formation constants were calculated for different metal
ions. Out of all metal ions o f interest, it illustrates the
strongest static quenching towards the Fe(II) ions.
The ratiometric study of 1 revealed greater
sensitivity towards Fe(II) with a minimum detection
for 0.35 pmol dm'3 o f metal ion concentration. With
other metal ions it is a considerable concentration
which showed such deviation, i.e. for Cd(II), Co(II),
Pb(H) the concentrations were 2.55, 1.80, and 2.87
ptaol dm'3, respectively. This illustrates more
sensitivity of compound 1 towards Fe(H). According to
fluorescence study the ratiometric sensing of Fe(H)
using 1 appeared to be more reliable and accurate than
thestatic or dynamic quenching sensing.
However, the interference study by the other metal
ions on the unbound and Fe(H) bound 5-hydroxy-1,10-
phenanthroline indicates considerable interference
from other metal ions. Co(II) and Pb(TI) ions specified
the quenching of both bound and unbound forms
indicating the occurrence o f dynamic quenching.
Whereas Cd(II), N i(II) and M n(II) showed
fluorescence enhancement o f unbound form and
diminishment of bound form indicating a shift in the
equilibrium of formation of Fe(H) bound complex
more towards the reactants. Cu(H) and Zn(H) ions
illustrated a vast decrease in fluorescence intensity of
bound form with a insignificant change of unbound
form indicating the occurrence o f dynamic quenching
on bound form only
