Triplet states in a series of Pt-containing ethynylenes

By use of optical steady state and time resolved spectroscopy, we studied the evolution of the triplet excited state in a series of six ethynylenic polymers of the structure [-Pt(PBu3n)(2)-C=C-R-C=C-](n) where the spacer unit R is systematically varied to give optical gaps from 1.7-3.0 eV. The inclusion of platinum in the polymer backbone induces a strong spin-orbit coupling such that triplet state emission (phosphorescence) associated with the conjugated system can be detected. Throughout the series we find the S-1-T-1 (singlet-triplet) energy splitting to be independent of the spacer R, such that the T-1 state is always 0.7 +/-0.1 eV below the S-1 state. With decreasing optical gap, the intensity and lifetime of the triplet state emission were seen to reduce in accordance with the energy gap law. (C) 2000 American Institute of Physics. [S0021-9606(00)71641-2].