6
16
S.C. Mohapatra, P. Mathur / Spectrochimica Acta Part A 78 (2011) 612–616
Table 3
study confirms the binding of amide carbonyl rather than amide-
NH a result supported by crystal data on similar bis-benzimidazolyl
diamide ligands. EPR work suggests a highly distorted copper(II)
geometry in solution state as evidenced by low A|| values, further
N-SHF structure on one of the complexes, implicates the binding
Fluorescence spectra of copper(II) complexes with O-GBGA in concentration of
.0 × 10− M in HPLC grade CH2Cl2.
6
7
Complexes
Quantum yield (photon)
O-GBGA
0.029
0.010
0.022
0.021
0.012
[
[
[
[
Cu(O-GBGA)(CH3COO)2]
Cu(O-GBGA)Cl2]
Cu(O-GBGA)(NO3)2]
Cu(O-GBGA)(C6H5COO)2]
of imine N-atoms of the benzimidazole, giving a N O2 donor envi-
2
ronment on copper(II). The ligand and its copper(II) complexes give
fluorescence quantum yield which is higher than for some nitrogen
containing fluorophores implying that the lone pair of the benz-
imidazole N-atom is only weakly involved in PET to the aromatic
fluorophore. The relative fluorescence intensity change reveals that
The fluorescence spectrum of 7 M solution in dichloromethane
for O-GBGA shows two groups of bands, one group (F1) arising
between 350 and 385 nm, while the other arising between 400 and
− −
3 6
5
it is larger for larger anions like CH COO and C H COO while
−
−
smaller for anions like Cl and NO3 . Thus, fluorescence of these
copper(II) compounds can distinguish between small and large
anions.
4
65 nm (F2). The short wave length fluorescence bands within (F1)
are found to be red shifted with respect to simple benzimidazole
and bis benzimidazole type ligands [20,21]. The fluorescence quan-
tum yield of the present ligating system is similar to that reported
for bis benzimidazole type ligand but quite higher than for some of
the nitrogen containing fluorophores [22], implying that the lone
pair of the benzimidazole nitrogen is only weakly involved in photo
induced electron transfer (PET) to the aromatic fluorophore. The
fluorescence spectra of the copper(II) complexes of O-GBGA show
only very slight shift in the ꢁmax of the bands in 350–465 nm region,
as compared to the ligand. However, the total area under the curve
between these wavelength regions does change. This change is
reflected in the quantum yields as reported in Table 3. The quantum
yields have been calculated by utilizing the formula:
Acknowledgement
Authors are grateful to the University of Delhi, Delhi, for a special
grant.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.11.033.
References
areacomp εanth
˚
= 0.292
areaanth εcomp
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[
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. Conclusion
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