We have synthesized two ligand systems, N(SO
2
)(R
1
)dpa (L1) and N(SO
2
)(R
2
)dpa
(L2), where
R
1
= biphenyl and R
2
= azobenzene, which are
sulfonamide derivatives of the NNN-donor chelating dipicolylamine.
Both L1 and L2 can be used as sensors for detecting Fe
3+
and are highly sensitive and selective over a wide range of common
cations. Time-dependent density functional theory (TDDFT) calculations
confirmed that the key excitations of L2 and the [Fe(L2)(H
2
O)
3
]
3+
model complex involve −R
2
-unit-based π and π* charge transfer. L2 demonstrates
a relatively high photostability, a fluorescence turn-on mechanism,
and a detection limit of 0.018 μM with 1.00 μM L2 concentration,
whereas L1 has a detection limit of 0.67 μM. Thus, both ligands
have the potential to be used as fluorosensors for the detection of
Fe
3+
in aqueous solutions.
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