Lewis acid and base sensing by platinum(II) polypyridines

This report describes platinum(II) complexes of 6-(2-pyridyl)-dipyrido[3,2-a:2',3'-c]phenazine (dppzp) and 6-phenyl-dipyrido[3,2-a:2',3'-c]phenazine (dppz phi). The [Pt(dppzp)Cl](+) (1) system exhibits an excited-state lifetime of 5.0 mu s in deoxygenated dichloromethane. Lewis bases quench the emission with rate constants on the order of 10(7) M-1 S-1; however, acetic acid is definitely not a quencher. The carbometalated [Pt(dppz phi)Cl] (2) complex is novel in that it is subject to quenching by acid as well. In deoxygenated 2-chloronaphthalene, the excited-state lifetime of 2 is 270 ns, and acetic acid quenches the emission with a rate constant of 2 x 10(8) M-1 S-1. In addition, Lewis bases like dimethyl sulfoxide and dimethylformamide quench the emission of 1 and 2 with similar efficiencies. The coordinatively unsaturated platinum center provides a logical place for attack by Lewis bases, whereas the phenazine extension of dppz phi introduces potentially acid-sensitive nitrogen centers. The emissive states of 1 and 2 exhibit mainly intraligand character, but enhanced charge-transfer character in 2 accounts for the differences in reactivity.