Synthesis, Photophysics, and Reverse Saturable Absorption of Bipyridyl Platinum(II) Bis(acetylide) Complexes Bearing Aromatic Electron-Withdrawing Substituents on the Acetylide Ligands

Abstract

Three platinum(II) bipyridyl bis((7-R-fluoren-2-yl)acetylide) complexes (R = benzoyl (Pt-1), 2-(N-phenylbenzimidazoly) (Pt-2), or 2-(3-phenylquinoxalinyl) (Pt-3)) are synthesized and characterized. Their photophysical properties and reverse saturable absorption are systematically investigated via UV-vis absorption, emission, transient absorption, and nonlinear transmission spectroscopy/technique. All three complexes possess ligand-centered (1)π,π* transitions below 400 nm, and a broad, featureless (1)MLCT/(1)LLCT absorption band in the region of 400-550 nm in CH2Cl2 solutions. They are emissive in a variety of fluid solutions at room temperature and at 77 K glassy matrix. On the basis of the emission lifetime, solvatochromic effect, and thermally induced Stokes shift, the emitting states are tentatively ascribed to (3)π,π*/(3)MLCT/(3)LLCT states for Pt-1, and predominantly (3)MLCT/(3)LLCT states for Pt-2 and Pt-3 in polar solvents like CH3CN. Pt-1-Pt-3 also exhibit broad triplet excited-state absorption, i.e., 425-800 nm for Pt-1 and Pt-3, and 425-725 nm for Pt-2, from the same excited states that emit. Strong reverse saturable absorption (RSA) occurs at 532 nm for ns laser pulses from all of the complexes due to the stronger triplet excited-state absorption at this wavelength, suggesting that the π-conjugated aromatic electron-withdrawing substituents at the fluorenylacetylide ligands enhance the RSA of the Pt(II) diimine bis(acetylide) complexes.