White light emission from a green cyclometalated platinum(II) terpyridylphenylacetylide upon titration with Zn(II) and Eu(III)

The cyclometalated Pt(II) acetylide derivative with a 1,3-bis(N-octyl-benzimidazol-2-yl)benzene (N<^>C<^>N) ligand and a free terpyridine (TPY) receptor has been successfully synthesized and characterized. X-ray crystallography shows its inefficient conjugation degree between the [(N<^>C<^>N)Pt] and TPY planes. This bifunctional complex shows an enhanced (MLCT)-M-1/LLCT absorption band (epsilon= 3.30 x 10(4) dm(3) mol(-1) cm(-1)) centered at lambda(max)= 365 nm, and the well-resolved vibronic-structured (MLCT)-M-3/LLCT emission bands (phi= 0.08, tau= 3.43 mu s) in the range ofca. 475-700 nm. Consecutive titrations show that added Zn2+ and Eu(HFA)(3) bond to its free TPY receptor with 1 : 2 and 1 : 1 stoichiometry to form the heterotrinuclear Pt-Zn-Pt (K-a= 3.48 x 10(4) mol(-1) dm(3)) and heterodinuclear Pt-Eu (K-a= 1.73 x 10(4) mol(-1) dm(3)) complexes, respectively. A sensitizing effect of Zn2+ on the TPY unit, and the incomplete d -> f energy transfer from the [(N<^>C<^>N)Pt(ii)] antenna donor to the Eu(iii) center with maximum efficiency of 51.8% are observed. Using anin situmixed titration strategy, the R/G/B emission triads consisted of red [(TPY)Eu(HFA)(3)] and green [(N<^>C<^>N)Pt(II)] dual phosphorescence and blue [(TPY)Zn(TPY)] fluorescence, which can be well balanced to realize the white-light-emission with CIE coordinates (x= 0.36, y= 0.36) by precisely controlling the molar ratio (9 : 1 : 2) of the parent complexes, Eu(HFA)(3) and Zn(ClO4)(2).