Systematic Investigation of Photoinduced Electron Transfer Controlled by Internal Charge Transfer and Its Consequences for Selective PdCl 2 Coordination

Fluoroionophores of fluorophore–spacer–receptor format were prepared for detection of PdCl 2 by fluorescence enhancement. The fluorescent probes 1 – 13 consist of a fluorophore group, an alkyl spacer and a dithiomaleonitrile PdCl 2 receptor. First, varying the length of the alkylene spacer (compounds 1 – 3 ) revealed a dominant through‐space pathway for oxidative photoinduced electron transfer (PET) in CH 2 ‐bridged dithiomaleonitrile fluoroionophores. Second, fluorescent probes 4 – 9 containing two anthracene or pyrene fragments connected through CH 2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential ( E Ox ) through electron‐withdrawing or ‐donating groups on the anthracene moiety regulates the thermodynamic driving force for oxidative PET (Δ G PET ) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields ( Φ f ), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl 2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10 – 13 were synthesized.