Abstract
A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible “on” and “off” switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in “on” and “off” luminescence signal.
Highlights
We report the synthesis of a novel organoimido hexamolybdate containing 6-nitroquinoline moiety, which exhibits reversible stimuli-response to protons
6-nitro quinoline in the ratio of 1:1 using the well-established DCC (N,N′-dicyclohexylcarbodiimide) protocol[33] can conveniently give rise to the corresponding monosubstituted organoimido derivative, (Bu4N)2[Mo6O18(NC9H5N-NO2)] (Mo6-Q-NO2), which is crystallized as orange lamellar-like crystals when diethyl ether diffuses into their solution of acetonitrile
In light of the structural analysis as above, fluorescence enhancement upon gradual addition of dilute HCl into the 50% aqueous acetonitrile solution of Mo6-Q-NO2 is due to the protonation at the heterocyclic nitrogen atom leading to the Mo-N changing from triple bond to single bond, resulting in the effective channel of photo-induced electron transfer from the organic 6-nitroquinoline moiety to the hexamolybdate cluster that is blocked
Summary
We report the synthesis of a novel organoimido hexamolybdate containing 6-nitroquinoline moiety, which exhibits reversible stimuli-response to protons. All these changes of structure indicate that the Mo-N bond exhibits much more like single bond, largely decreasing the d-πinteraction between inorganic hexamolybdate cluster and organic quinoline aromatic ring.
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