TQPHEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)-1,2-phenylenediamine) derivatives as highly selective fluorescent probes for Cd2+?

Dalton Transactions Pub Date: 2014-09-15 DOI: 10.1039/C4DT02177K

Abstract

TQPHEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)-1,2-phenylenediamine) and its methoxy-substituted derivatives, 6-MeOTQPHEN (N,N,N′,N′-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-phenylenediamine) and TriMeOTQPHEN (N,N,N′,N′-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-phenylenediamine), were examined as fluorescent Cd2+ sensors. Although the TQPHEN exhibits a negligible fluorescence response toward Zn2+ due to weak binding affinity in DMF–H2O (1?:?1), a 6-fold fluorescence enhancement at 392 nm was observed in the presence of 1 equiv. of Cd2+. Comprehensive X-ray crystallographic analyses of TQPHEN-Zn2+ and TQPHEN-Cd2+ complexes reveal that significant distortion in the Zn2+ complex plays a key role in the Cd2+ specificity of TQPHEN. The TriMeOTQPHEN exhibits excellent sensitivity and selectivity for Cd2+ detection (ICd/I0 = 44, ICd/IZn = 20 and LODCd = ～10 nM (LOD = limit of detection)). On the other hand, the trans-1,2-cyclohexanediamine derivative TQDACH (N,N,N′,N′-tetrakis(2-quinolylmethyl)-trans-1,2-cyclohexanediamine) exhibits high Zn2+ specificity in the fluorescence response and extremely high Zn2+ binding affinity (Dalton Trans., 2013, 42, 9688). Subtle differences in the PHEN and DACH backbone significantly alter the stability with a specific metal and the fluorescence response of tetrakisquinoline-based fluorescent probes.

Graphical abstract: TQPHEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)-1,2-phenylenediamine) derivatives as highly selective fluorescent probes for Cd2+
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