Transient studies are used to examine the radiative decay dynamics in a series of phosphorescent platinum binuclear complexes. The complexes studied consist of square planar (2-(4',6'-difluorophenyl) pyridinato-N,C-2')Pt units bridged by either pyrazole or thiopyridine ligands. We observe an increase in radiative lifetime as temperature is reduced from 300 K to 4 K when the binuclear complexes, named 1, 2 and 3 with Pt-Pt spacings 3.19 angstrom, 3.05 angstrom, and 2.83 angstrom, respectively, are doped into a p-bis(triphenylsilyly) benzene wide energy gap host. The lifetimes for 1, 2 and 3 are tau = 6.3 +/- 0.1 mu s, tau = 2.3 +/- 0.1 mu s, and tau = 2.0 +/- 0.1 mu s at T = 295 K, respectively. At T = 4 K, those values increase to tau = 8.6 +/- 0.1 mu s, tau = 14.4 +/- 0.1 mu s, and tau = 17.0 +/- 0.1 mu s, suggesting that the neighboring heavy metal centers in compounds 2 and 3 have significant orbital overlap. A three-level zero-field splitting model yields the lowest triplet energy splittings of 28 +/- 3 cm (1), 142 +/-9 cm (1), and 113 +/- 10 cm (1) for compounds 1, 2 and 3, respectively. (c) 2008 Elsevier B.V. All rights reserved.