Bipyridyl Platinum Research Articles

Alkyl-substituted bipyridyl platinum (II) complexes bearing alkynyl-naphthalimide ligands: Synthesis, photophysical properties, and tunable aggregation-induced emission activity

Different alkyl chains were introduced into alkynyl-naphthalimide ligands and bipyridine ligands to synthesize five platinum complexes, their structures were characterized and the photophysical properties were systematically investigated. It was found that the introduction of alkyl chains had no obvious effect on the absorption and emission of these complexes in dilute solution, while influence aggregation-induced emission activity in aggregated state. In the mixed solvent system of tetrahydrofuran and ethylene glycol, the shorter alkyl chains on the bipyridine ligands strengthen the aggregation-induced phosphorescence emission (AIPE) properties of complexes, however, the introduction of different alkyl chains on the alkynyl-naphthalimide ligands makes no difference on their AIPE properties. Combining the single crystal results and Hirshfled surface analysis, the photophysical properties of these complexes in aggregated state were affected by the stacking modes, which is due to the different interactions. This research may broaden the scope for the design of multi-functional materials adopting different aggregation states.

Tuning excited state of bipyridyl platinum(II) complexes with bio-active flavonolate ligand: Structures, photoreactivity, and DFT calculations

Platinum(II) complexes with coordinated bio-active molecules that can undergo photo-induced oxygenation are finding applications in photoactivated chemotherapy (PCT). A series of bipyridyl(bpy) Pt(II) complexes with ligand flavonolate (fla-) [PtIIBpyFlaR][BF4] [BF4] (R = p- OMe (1), p-Me (2), p-H (3)) were prepared and characterized. Their photochemical and photophysical properties were investigated. Complexes 1–3 exhibit emission at ~530 nm, as compared to the analogous [PdIIBpyFlaR][BF4] with no emission upon irradiation. In addition, Pt(II) complexes undergo oxygenation reaction with oxygen with near visible light, indicating photocleavage of ligand flavonolate. Carbon monoxide(CO) release was observed by deoxymyoglobin from oxygenation of Pt(II) flavonolate complexes. Density functional theory calculations predict a mixed, Pt/fla- to bpy, metal/ligand-to-ligand charge transfer (ML-LCT) state in complexes 1–3.

New platinum(II)–bipyridyl corrole complexes: Synthesis, characterization and binding studies with DNA and HSA

A simple methodology giving access to the metal-free corroles of trans-A2B type, 5,15-bis(pentafluorophenyl)-10-{3-[2-(pyridin-4-yl)vinyl]phenyl}corrole and 5,15-bis(pentafluorophenyl)-10-{4-[2-(pyridin-4-yl)vinyl]phenyl}corrole, and to the corresponding bipyridyl platinum(II) complexes is described. These new positional isomers were fully characterized and spectroscopic studies demonstrated the ability of Pt(II)–corrole complexes to establish non-covalent interactions with calf-thymus DNA (ct-DNA) and human serum albumin (HSA). Additionally, gel electrophoresis experiments demonstrated that Pt(II)–corrole complexes are able to bind plasmid pMT123 DNA, inducing alterations on its secondary structure.

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

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±39ps in toluene solution. A triplet quantum yield of 0.06 was measured using relative actinometry. Excited-state absorption cross sections of 5.6×10−17cm2 (singlet) and 7.8×10−16cm2 (triplet) at 532nm 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 16.3μs 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.

Tuning excited states of bipyridyl platinum(II) chromophores with π-bonded catecholate organometallic ligands: synthesis, structures, TD-DFT calculations, and photophysical properties.

A series of bipyridyl (bpy) Pt(II) complexes with π-bonded catecholate (cat) [(bpy)Pt(LM)][BF4]n (2-5) (LM = Cp*Rh(cat), n = 2; Cp*Ir(cat), n = 2; Cp*Ru(cat), n = 1; and (C6H6)Ru(cat), n = 2) were prepared and fully characterized. The molecular structures of the four compounds were determined and showed that the solid-state packing is different and dependent on the π-bonded catecholate unit. For instance, while the (bpy)Pt(II) complexes 2 and 3 with rhodium and iridium catecholates did not show any Pt···Pt interactions those with the ruthenium catecholates 4 and 5 showed the presence of Pt···Pt and π-π interactions among individual units and generated one- and two-dimensional supramolecular chains. The photophysical properties of these compounds 2-5 were investigated and showed that all compounds are luminescent at low temperature, in contrast to the well-known parent compound [(C6H4O2)Pt(bpy)] (1), which is weakly luminescent at 77 K. Time-dependent density functional theory studies are advanced to explain this difference in behavior and to highlight the role of the π-bonded catecholate system.

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

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.

Cyclometalated platinum(ii) with ethynyl-linked azobenzene ligands: an original switching mode

The photophysical properties of 6-phenyl-2,2'-bipyridyl platinum(ii) complexes bearing different σ-alkynyl-linked azobenzene ancillary ligands were investigated. These complexes exhibited strong, broad, structureless charge-transfer bands in the visible region, which were red-shifted when the electron-donating ability of the para substituent on the azo-acetylide ligand increased. When excited at the charge-transfer absorption band, the complexes exhibited weak green emission, which was assigned to a triplet metal-to-ligand charge transfer/interligand charge transfer emission ((3)MLCT/(3)L'LCT). The presence of an amino substituent in the azobenzene moiety opened the possibility of protonation, which led to the formation of an azonium based derivative and resulted in drastic perturbations of the molecular orbitals and photophysical properties of the Pt-acetylide complex. These studies are fully supported by DFT and TD-DFT calculations.

Tuning Photophysics and Nonlinear Absorption of Bipyridyl Platinum(II) Bisstilbenylacetylide Complexes by Auxiliary Substituents

The photophysics of six bipyridyl platinum(II) bisstilbenylacetylide complexes with different auxiliary substituents are reported. These photophysical properties have been investigated in detail by UV-vis, photoluminescence (both at room temperature and at 77 K) and transient absorption (nanosecond and femtosecond) spectroscopies, as well as by linear response time-dependent density functional theory (TD-DFT) calculations. The photophysics of the complexes are found to be dominated by the singlet and triplet π,π* transitions localized at the stilbenylacetylide ligands with strong admixture of the metal-to-ligand (MLCT) and ligand-to-ligand (LLCT) charge-transfer characters. The interplay between the π,π* and MLCT/LLCT states depends on the electron-withdrawing or -donating properties of the substituents on the stilbenylacetylide ligands. All complexes exhibit remarkable reverse saturable absorption (RSA) at 532 nm for nanosecond laser pulses, with the complex that contains the NPh(2) substituent giving the strongest RSA and the complex with NO(2) substituent showing the weakest RSA.

Photophysics and Nonlinear Absorption of Cyclometalated 4,6-Diphenyl-2,2′-bipyridyl Platinum(II) Complexes with Different Acetylide Ligands

The photophysical properties of a series of 4,6-diphenyl-2,2'-bipyridyl platinum(II) complexes bearing different σ-alkynyl ancillary ligands (1a-1k) were systematically investigated. All complexes exhibit strong (1)π,π* absorption bands in the UV region; and broad, structureless charge-transfer band(s) in the visible region, which systematically red-shift(s) when the electron-donating ability of the para substituent on the phenylacetylide ligand increases. All complexes are emissive in solution at room temperature. When excited at the charge-transfer absorption band, the complexes exhibit long-lived orange emission (λ(max): 555-601 nm), which is attributed to a triplet metal-to-ligand charge transfer/intraligand charge transfer emission ((3)MLCT/(3)ILCT). Most of these complexes exhibit broad triplet transient difference absorption in the visible to the near-IR region, with a lifetime comparable to those measured from the decay of the (3)MLCT/(3)ILCT emission. The reverse saturable absorption (RSA) of these complexes were demonstrated at 532 nm using nanosecond laser pulses. The degree of RSA follows this trend: 1k ≈ 1a > 1c > 1f ≈ 1i > 1h ≈ 1b > 1e > 1d > 1g, which is mainly determined by the ratio of the triplet excited-state absorption cross section to that of the ground-state and the triplet excited-state quantum yield.

Excited-state absorption of a bipyridyl platinum(II) complex with alkynyl-benzothiazolylfluorene units

The singlet excited-state lifetime of a bipyridyl platinum(II) complex containing two alkynyl-benzothiazolylfluorene units was determined to be 145+/-105 ps by fitting femtosecond transient difference absorption data, and the triplet quantum yield was measured to be 0.14. A ground-state absorption cross section of 6.1 x 10(-19) cm(2) at 532 nm was deduced from UV-visible absorption data. Excited-state absorption cross sections of (6.7+/-0.1) x 10(-17) cm(2) (singlet) and (4.6+/-0.1) x 10(-16) cm(2) (triplet) 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. For this complex, the ratio of the triplet excited-state absorption cross section to the ground-state absorption cross section--long used as a figure of merit for reverse saturable absorbers--thus stands at 754, to our knowledge the largest ever reported at 532 nm wavelength.

Synthesis and kinetic studies of new bipyridyl platinum(II) phenoxide complexes by phase transfer catalysis: Crystal structure of [(bipy)Pt(OC6H4-4-OMe)2

Abstract The synthesis of new platinum bipy (bipy = 2,2′-bipyridyl) complexes containing phenoxide ligands is reported, together with kinetic studies of their oxidative addition reactions with MeI to produce phenoxo platinum(IV) complexes. Complexes of the form [(bipy)Pt(OC 6 H 4 -4-X) 2 ] (X = OCH 3 , CH 3 , H, Br, Cl) are prepared by the reaction of the chloro complex [(bipy)PtCl 2 ] with substituted phenols and KOH in a two phase system of water and chloroform in the presence of benzyl triphenylphosphonium chloride. Platinum(IV) complexes are formed by oxidative addition of MeI to the platinum(II) complexes obtained. The complexes are characterized by elemental analysis, UV–Vis, IR, mass spectrometry and 1 H and 13 C NMR spectroscopy. The reaction of methyl iodide with [(bipy)Pt(OC 6 H 4 -4-OMe) 2 ] to give [(bipy)PtMe(I)(OC 6 H 4 -4-OMe) 2 ] follows the rate law rate = k 2 [(bipy)Pt(OC 6 H 4 -4-OMe) 2 ][MeI]. The values of k 2 increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction.

An active catalyst system for proton reduction composed of a bipyridyl platinum complex and a polymer membrane

Electrocatalysis for the H+ reduction with bis(2,2′-bipyridyl) Pt complex (Pt(bpy)22+) incorporated in a polymer matrix was studied. When the cyclic voltammogram (CV) was measured at a basal-plane pyrolytic graphite (BPG) electrode coated with a Nafion® (Nf) membrane incorporating Pt(bpy)22+ (denoted as BPG/Nf[Pt(bpy)22+]), a remarkable growth of the cathodic current due to H+ reduction was observed below –0.4 V (vs. Ag/AgCl) in a repeated scanning. A much higher amount of H2 was obtained with the system BPG/Nf[Pt(bpy)22+] than by the conventional Pt-black. The XPS spectrum of Nf[Pt(bpy)22+] showed the formation of zero-valent Pt after the electrochemical process, indicating that H+ reduction begins to take place after formation of the catalytically active species. This work shows that a highly active catalyst system for H+ reduction can be fabricated from a noble metal complex and a polymer matrix.

An active catalyst system for proton reduction composed of a bipyridyl platinum complex and a polymer membrane

Electrocatalysis for the H + reduction with bis(2.2'-bipyridyl ) Pt complex (P((bpy 2 2+ in a polymer matrix was studied. When the cyclic voltammogram (CV) was measured at a basal-plane pyrolytic graphite (BPG) electrode coated with a Nafion® (Nf) membrane incorporating Pt(bpy) 2 2+ (denoted as BPG/Nf[Pt(bpy) 2 2+ ]), a remarkable growth of the cathodic current due to H + reduction was observed below -0.4 V (vs. Ag/AgCl) in a repeated scanning. A much higher amount of H 2 was obtained with the system BPG/Nf[Pt(bpy) 2 2+ ] showed the formation of zero-valent Pt after the electrochemical process, indicating that H + reduction begins to take place after formation of the catalytically active species. This work shows that a highly active catalyst system for H + reduction can be fabricated from a noble metal complex and a polymer matrix.

Synthesis, structures and antitumor activity of the first crown ester-linked bipyridyl platinum complexes

Three new crown ester-linked bipyridine homologs with three, four or five ethylene glycol units, which are bulky and soluble in both hydrophilic and lipophilic media, were synthesized. The reaction of the appropriate macrocycles with K 2PtCl 4 in water gave yellow cisplatin analogs in good yield. These complexes were converted to carboplatin analogs by exchange of the leaving group. All the compounds were characterized by elemental analysis and various spectroscopic methods. Carboplatin analogs showed good solubility in both hydrophilic and lipophilic media. The crystal structure of 2c, the carboplatin analog with macrocycles containing five ethylene glycol units, was determined by X-ray diffraction: space group P1, a = 9.798(1), b = 12.580(3), c = 13.945(2) Å, α = 108.62(2), β = 94.59(1), γ = 97.42(2)°, Z = 2, R = 0.0618. Some of platinum complexes showed a moderate cytotoxic effect on both murine leukemia L1210 and P388 even though they do not have any NH proton.

Synthesis of Transition Metal Complexes of the Unknown Chelate, Dithioacetylacetone

ACETYLACETONE (acacH), from which the unknown chelate, dithioacetylacetone, can theoretically be obtained by substitution of two oxygen atoms with sulphur, is one of the most versatile bidentate chelates known1. In the enol form the hydroxylic proton can readily be replaced by a great many metal ions to give neutral complexes of the composition M(acac)n. The co-ordination number of the metal is usually 2n and the resulting stereochemistry is tetrahedral, square planar or octahedral, although examples of square antiprismatic and square pyramidal co-ordination are known. The bonding to the metal is invariably through the two oxygen atoms, although it has been shown2 recently that the α-carbon atom can bond to platinum in the compound trimethyl (acetylacetonyl)-2 : 2′ bipyridyl platinum (IV). Certain of the metal acetylacetonates undergo reactions characteristic of aromatic systems and these have been reviewed by Prof. Collman3.