Photophysical properties of platinum(II) acetylides in tetrahydrofuran (THF) solutions and incorporated in poly(methyl methacrylate) (PMMA) glasses have been studied over a large concentration range from 10 mu M to 50 mM. In general, the luminescence properties of the studied chromophores in the liquid state were also maintained in the solid state, except for shorter decay times of 50-90 mu s of the triplet state in the glass compared with 200-300 mu s in solution at low concentrations. The phosphorescence line shapes were found to be independent of both the chromophore concentration and the environment (THF and PMMA). The triplet state lifetimes did not change with concentration in the solid-state case, whereas, in solution, the decay becomes shorter at increasing concentration. The latter effect could be modeled with an additional linear quenching rate, k(q), in the range of (1 to 7) x 10(7) M-1 s(-1). Excitation spectra of the triplet state at high concentrations, in both solutions and solid glasses, showed additional excitation bands on the long wavelength side compared with the corresponding measurements at low concentrations. This indicates enhanced singlet-triplet coupling due to intermolecular electronic interactions that become important at concentrations of 0.1 to 1 mM and above.