Cyclometalated Platinum(II) Terpyridylacetylide with a Bis(arylamine) Donor as a Proton-Triggered Luminescence Chemosensor for Zn2+

A cyclometalated Pt(II) acetylide derivative bearing a bis(arylamine) donor (D) and a terpyridine (TPY) receptor (A) was successfully synthesized and characterized. This three-component D-pi-A system displays an intense low-energy absorption band at lambda(max) = 470 nm, resulting from overlapping the d pi(Pt) -> pi*(C<^>N<^>N) metal-to-ligand charge transfer and pi( CAr) -> pi*(C<^>N<^>N) ligand-to-ligand charge transfer transitions with the pi(bis(arylamine)) -> pi*(C<^>N<^>N) intraligand charge transfer transition. Upon protonation of the bis(arylamine) donor, a strong emission from the phosphorescence Pt(II) complex unit is recovered at lambda(max) = 580 nm. With introduction of the TPY receptor, this complex possesses quite high affinity for Zn2+ (K-a = 6.86 x 109 mol(-2) dm(6)) to form the heterotrinuclear PtZnPt complex in CH2Cl2 solution. Though this coordination effect is seriously inhibited by protons in acidic medium, the 2.4-fold luminescence intensity enhancement is obtained yet, strongly suggesting the presence of the intramolecular energy transfer process from the Zn(II)-TPY complex core to the phosphorescence Pt(II) complex units at two ends. The H+-triggered and Zn2+-enhanced luminescence can be reversibly switched on and off upon successive additions of H+ and OH-. Furthermore, this complex displays an unexpected Zn2+-selective luminescence enhancement effect in acidic solution.