To understand platinum acetylide molecular structure changes upon conversion to the triplet state, we measured time-resolved infrared (TRIR) spectra of the platinum acetylide complex trans-bis(tributylphosphine) bis(4-ethynyl-1-(2-phenylethynyl) benzene)platinum (abbreviated as PE2). We used density functional theory (DFT) methods to calculate the geometry, molecular orbitals and vibrational spectra of the ground and lowest energy triplet state of PE2. Solutions of PE2 were excited upon us pulsed laser excitation at 355 nm and TRIR spectra were collected. The TRIR data show cumulenic vibrations in the triplet state as well as evidence for photoproduct formation. The DFT results support the experimental data, suggesting PE2's triplet state has quinone character. (C) 2004 Elsevier B.V. All rights reserved.