Cyclometalated Platinum(II) Complex with Strong and Broadband Nonlinear Optical Response

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 (1MLCT) absorption band between 400
and 500 nm and a 3MLCT emission band at ∼591 nm at room temperature with a lifetime of ∼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·mol-1·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.