Long-lifetime reverse saturable absorption in a bipyridyl platinum(II) complex bearing naphthalimidylethynyl-substituted fluorenylacetylide ligands

• We report photophysical parameters of a novel platinum(II) 2,2′-bipyridyl complex.
• The complex has an extremely large triplet excited-state absorption cross section.
• The complex features naphthalimidylethynyl-substituted fluorenyl-acetylide ligands.
• Including these substituents results in a 20-fold increase in the triplet excited-state lifetime.

By fitting femtosecond transient difference absorption time series at multiple wavelengths, the singlet excited-state lifetime of a particular platinum(II) 2,2′-bipyridyl complex bearing naphthalimidylethynyl-substituted fluorenyl-acetylide ligands was determined to be 83.5 ± 39 ps in toluene solution. A triplet quantum yield of 0.06 was measured using relative actinometry. Excited-state absorption cross sections of 5.6 × 10−17 cm2 (singlet) and 7.8 × 10−16 cm2 (triplet) at 532 nm were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies. Most significantly, fits of nanosecond transient difference absorption decay data yield a value of 16.3 μs for the triplet excited-state lifetime of the complex in deoxygenated toluene solution, longer by a factor of almost 20 than the lifetime of the analogous complex with benzothiazolyl-substituted ligands.