Photobehavior of (alpha-diimine)dimesitylplatinum(II) complexes

The photobehavior of complexes of the type Pt(diimine)(mes)(2) is investiga ted (where diimine = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4 ,7,8-tetramethyl-1,10-phenanthroline (tmp), 2,9-dimethyl-1,10-phenanthrolin e (2,9-dmp), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), and-4,7-diphenyl-1 ,10-phenanthroline (dpp)and mes the mesityl (2,4,6-trimethylphenyl) anion). For all compounds studied, solution RT emission is observed to be weak and excited-state lifetimes;are found to be short (120 ns) regardless of solve nt choice. Evidence is presented for energy-transfer quenching of Pt(dpp)(m es)(2) luminescence in toluene by dissolved O-2 (primarily producing single t oxygen) with an observed quenching rate constant of k(q) greater than or equal to 1.3 x 10(9) M-1 s(-1). Electron-transfer quenching is also observe d in the presence of 3,5-dinitrobenzonitrile, yielding a quenching rate con stant of k(q) greater than or equal to 1.6 x 10(9) M-1 s(-1). The latter ob servation suggests that these Pt(II) systems may have future value as excit ed-state reductants. All of the complexes display a much more intense and l onger-lived luminescence in the solid state at room temperature. Several po ssible explanations for this dependence on phase are proposed, with the mos t probable mechanism involving radiationless deactivation in solution via r otation of the o-methyl groups of the mesityl ligands.