Tuning Photophysical Properties and Improving Nonlinear Absorption of Pt(II) Diimine Complexes with Extended π-Conjugation in the Acetylide Ligands

Abstract

Two new Pt(II) 4,4'-di(5,9-diethyltridecan-7-yl)-2,2'-bipyridine complexes (1 and 2) bearing 9,9-diethyl-2-ethynyl-7-(2-(4-nitrophenyl)ethynyl)-9H-fluorene ligand and N-(4-(2-(9,9-diethyl-7-ethynyl-9H-fluoren-2-yl)ethynyl)phenyl)-N-phenylbenzeneamine ligand, respectively, were synthesized and characterized. Their photophysical properties were investigated systematically by UV-vis absorption, emission, and transient absorption (TA) spectroscopy, and the nonlinear absorption was studied by nonlinear transmission technique. Theoretical TD-DFT calculations using the CAM-B3LYP functional were carried out to determine the nature of the singlet excited electronic states and to assist in the assignment of significant transitions observed in experiments. Complex 1 exhibits an intense, structureless absorption band at ca. 397 nm in CH2Cl2 solution, which is attributed to mixed metal-to-ligand charge transfer ((1)MLCT)/ligand-to-ligand charge transfer ((1)LLCT)/intraligand charge transfer ((1)ILCT)/(1)π,π* transitions, and two (1)MLCT/(1)LLCT transitions in the 300-350 nm spectral region. Complex 2 possesses an intense acetylide ligand localized (1)π,π* absorption band at ca. 373 nm and a moderately intense (1)MLCT/(1)LLCT tail above 425 nm in CH2Cl2. Both complexes are emissive in solution at room temperature, with the emitting state being tentatively assigned to the predominant (3)π,π* state for 1, whereas the emitting state of 2 exhibits a switch from (3)π,π* state in high-polarity solvents to (3)MLCT/(3)LLCT state in low-polarity solvents. Both 1 and 2 exhibit strong singlet excited-state TA in the visible to NIR region, where reverse saturable absorption (RSA) is feasible. The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these Pt complexes can be tuned drastically by extending the π-conjugation of the acetylide ligands. In addition, strong RSA was observed at 532 nm for nanosecond (ns) laser pulses from 1 and 2, demonstrating that the RSA of the Pt(II) diimine complexes can be improved by extending the π-conjugation of the acetylide ligands.

How to assess good candidate molecules for self-activated optical power limiting

“…[80][81][82] These measurements split the femtosecond to picosecond pulses into a pump and probe beam. The probe beam is delayed by a variable delay line.…”

Photophysical Properties of Visible‐Light‐Harvesting PtII Bis(acetylide) Complexes

“…Similar complexes were prepared by Sun's group (Figure ). [8b] These complexes show stronger visible‐light harvesting than complex 13 . For example, the molar absorption coefficient of complex 16b is up to 91700 m –1 cm –1 .…”

“…Sun's group also prepared 43 – 46 , a series of N ^ N Pt II bis(acetylide) complexes that show RSA (Figure ). [8a] In the UV/Vis absorption spectra, all of the complexes exhibit intense absorption in the UV region. For complex 43 the molar absorption coefficient is 71300 m –1 cm –1 at 397 nm, whereas that of complex 44 is 150000 m –1 cm –1 at 373 nm.…”

“…For applications of transition‐metal complexes in areas such as photocatalysis, TTA upconversion, nonlinear optics, etc., the improvement of visible‐light‐harvesting ability and the prolongation of triplet excited state lifetimes of Pt II complexes are crucial. To achieve these goals, the attachment of appropriate organic chromophores – showing strong visible‐light absorption – to the Pt II coordination centre is an effective approach.…”

Mononuclear zinc(II), cadmium(II), cobalt(III) and di-nuclear nickel(II) complexes of a 14pi electron diimine ligand: Syntheses, structures, photoluminescence and DFT investigations

“…Calc. for C 18 H 13 N 2 OZnCl: C,57.78;H,3.50;N,7.49;Found: C,57.42;H,3.39;N,7 (2) To 2-benzoyl pyridine (366 mg, 2 mmol) and 2-aminophenol (218 mg, 2 mmol) in a round bottom flask, methanol (25 mL) was added and the resulting solution was heated to reflux for 1.5 h. The reaction mixture was cooled at 298 K. To this solution, a solution of anhydrous zinc bromide (400 mg, 2 mmol) in methanol (15 mL) was added. The reaction mixture was allowed to evaporate slowly in air.…”