A cyclometalated platinum(II) 4,6-diphenyl-2,2'-bipyridyl pentynyl complex (1) has been synthesized and structurally characterized. Its photophysical and third-order nonlinear optical properties have been systematically investigated. This complex exhibits a metal-to-ligand charge-transfer ((MLCT)-M-1) absorption band between 400 and 500 nm and a (MLCT)-M-3 emission band at similar to 591 nm at room temperature with a lifetime of similar to 100 ns. At 77 K, the emission band blue shifts. Both UV-vis absorption and emission spectra show solvent dependence. Low-polarity solvents cause a bathochromic shift of the absorption and emission bands. This complex also exhibits a broad and strong transient absorption from the near-UV to the near-IR spectral region, with a triplet absorption coefficient of 4933 L center dot mol(-1)center dot cm(-1) at 585 nm and a quantum yield of 0.51 for the formation of the triplet excited state. Nonlinear transmission and Z-scan techniques were employed to characterize the third-order nonlinearities of this complex. A strong and broadband reverse saturable absorption was observed for nanosecond and picosecond laser pulses due to the reduced ground-state absorption in the visible spectral range. It also exhibits a self-defocusing effect at 532 nm for nanosecond laser pulses. The excited-state absorption cross section deduced from the open-aperture Z-scan increases at longer wavelengths, with an exceptionally large ratio of excited-state absorption to ground-state absorption of 160 at 570 nm for picosecond laser pulses.