Platinum diimine bis(acetylide) complexes: Synthesis, characterization, and luminescence properties

A new set of luminescent platinum(II) diimine complexes has been synthesize d and characterized. The anionic ligands in these complexes are arylacetyli des. The complexes are brightly emissive in fluid solution with relative em ission quantum yields phi(em) ranging from 3 x 10(-3) to 10(-1). Two series of complexes have been investigated. The first has the formula Pt(Rphen)(C =CC6H5)(2) where Rphen is 1,10-phenanthroline substituted in the 5-position with R = H, Me, Cl, Br, NO2, or C=CC6H5, while the second has the formula Pt(dbbpy)(C=CC6H4X)(2) where dbbpy = 4,4'-di(tert-butyl)bipyridine and X = H, Me, F, or NO2. From NMR, IR, and electronic spectroscopies, all of the c omplexes are assigned a square planar coordination geometry with cis-alkyny l ligands. The crystal structure of Pt(phen)(C=CC6H4CH3)(2) confirms this a ssignment. All of the complexes exhibit an absorption band at ca. 400 nm th at corresponds to a Pt d --> pi*(diimine) charge-transfer transition. The v ariation of a,, for this band with substituent variation supports this assi gnment. From similar changes in the energy of the solution luminescence as a function of substituents R and X, the emissive excited state is also of M LCT origin, but with spin-forbidden character on the basis of excited-state lifetime measurements (0.01-5.6 mu s). The complexes undergo electron-tran sfer quenching, showing good Stem-Volmer behavior using 10-methylphenothiaz ine and N,N,N',N-tetramethylbenzidine as reductive quenchers. Excited-state reduction potentials are estimated on the basis of a simple thermochemical analysis. Crystal data for Pt(phen)(C=CC6H4CH3)(2): monoclinic, space grou p C2/c, a = 19.0961(1) Angstrom, b = 10.4498(1) Angstrom, c = 11.8124(2) An gstrom, beta = 108.413(1)degrees, V = 2236.49 Angstrom(3), number of reflec tions 1614, number of variables 150, R1 = 0.0163, wR2 (I > 2 sigma) = 0.041 0.