New diketopyrrolopyrrole (DPP) derivative as fluorescent probe for Zn2+

• We developed a new “turn on” fluorescent chemosensor DPPL2 for Zn2+.
• It showed photoinduced electron transfer and intramolecular charge transfer effects.
• This was the first DPP-based fluorescent chemosensor for heavy metal ions.
• We provided an effective platform for developing new fluorescent probes.

New turn-on fluorescent probe DPPL2, was rationally designed and synthesized based on the skeleton of diketopyrrolopyrrole (DPP), which presented sensitivity, selectivity for Zn2+ over other metal ions except some disturbance with Cd2+. Particularly, results demonstrated fluorescence enhancement and blue shift of DPPL2 upon Zn2+ binding. This phenomenon was a typical photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) process which was attributed to diminishing the electron of the nitrogen lone pair delocalization on the DPP core upon Zn2+ binding. For comparison, DPPL3 (acylation of nitrogen atom of DPPL2) was synthesized and no fluorescence enhancement was observed, which further indicated that lone pair electrons of nitrogen atoms attached to DPP core were ascribed to PET process. 1H NMR titrations and DFT calculations also proved that PET and ICT process of system.

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