Triplet states in a series of Pt-containing ethynylenes

By use of optical steady state and time resolved spectroscopy, we studied t he evolution of the triplet excited state in a series of six ethynylenic po lymers 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 inclu sion of platinum in the polymer backbone induces a strong spin-orbit coupli ng such that triplet state emission (phosphorescence) associated with the c onjugated 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 decre asing optical gap, the intensity and lifetime of the triplet state emission were seen to reduce in accordance with the energy gap law. (C) 2000 Americ an Institute of Physics. [S0021-9606(00)71641-2].