Cd2+-selective fluorescence enhancement of N,N'-bis(2-quinolylmethyl)-N, N'-dimethyl-1,2-phenylenediamine derivatives

Reducing the basicity of aliphatic nitrogen atoms of BQDMEN (N,N'-bis(2-quinolylmethyl)-N,N'-dimethylethylenediamine) by replacement of ethylenediamine (EN) moiety with 1,2-phenylenediamine (PHEN) shifted the metal ion selectivity toward Cd2+ side in BQDMPHEN (N,N'-bis(2-quinolylmethyl)-N,N'-dimethyl-1,2-phe- nylenediamine). Further manipulation by methoxy and isopropyl substitutions on the quinoline rings and anilinic nitrogen atoms, respectively, affords TriMeOBQDIPHEN (N,N'-bis(5,6,7-trimethoxy-2-quinolylmethyl)-N,N'-diisopropyl-1,2-phenylenediamine) as a fluorescent Cd2+ sensor with excellent selectivity (IZn/ ICd = 0.05 with 40 equiv. of metal ions). In contrast to the significant fluorescence quenching of TriMeOBQDMEN around pH 8-12, the steady fluorescence intensity in wide pH window was successfully achieved by the 1,2-phenylenediamine skeleton of TriMeOBQDMPHEN in the presence of KCl.