Stabilization of G‐Quadruplex DNA with Platinum(II) Schiff Base Complexes: Luminescent Probe and Down‐Regulation of c‐myc Oncogene Expression

The interactions of a series of platinum(II) Schiff base complexes with c‐myc G‐quadruplex DNA were studied. Complex [PtL ^1a ] ( 1 a ; H₂L ^1a =N,N′‐bis(salicylidene)‐4,5‐methoxy‐1,2‐phenylenediamine) can moderately inhibit c‐myc gene promoter activity in a cell‐free system through stabilizing the G‐quadruplex structure and can inhibit c‐myc oncogene expression in cultured cells. The interaction between 1 a and G‐quadruplex DNA has been examined by ¹H NMR spectroscopy. By using computer‐aided structure‐based drug design for hit‐to‐lead optimization, an in silico G‐quadruplex DNA model has been constructed for docking‐based virtual screening to develop new platinum(II) Schiff base complexes with improved inhibitory activities. Complex [PtL ³ ] ( 3 ; H₂L ³ = N,N′‐bis{4‐[1‐(2‐propylpiperidine)oxy]salicylidene}‐4,5‐methoxy‐1,2‐phenylenediamine) has been identified with a top score in the virtual screening. This complex was subsequently prepared and experimentally tested in vitro for its ability to stabilize or induce the formation of the c‐myc G‐quadruplex. The inhibitory activity of 3 (IC₅₀=4.4 μM ) is tenfold more than that of 1 a . The interaction between 1 a or 3 with c‐myc G‐quadruplex DNA has been examined by absorption titration, emission titration, molecular modeling, and NMR titration experiments, thus revealing that both 1 a and 3 bind c‐myc G‐quadruplex DNA through an external end‐stacking mode at the 3’ terminal face of the G‐quadruplex. Such binding of G‐quadruplex DNA with 3 is accompanied by up to an eightfold increase in the intensity of photoluminescence at λ_max=652 nm. Complex 3 also effectively down‐regulated the expression of c‐myc in human hepatocarcinoma cells.     

New Energetic Copper(II) Complexes With Pyrazolyl Type Ligands

Nine Cu^II complexes ( I – IX ) containing the azide ion and bis‐2,6‐(pyrazol‐1‐yl)pyridine (pp), bis‐2,6‐(pyrazol‐1‐yl)pyridine (dmpp), and 2‐(pyrazol‐1‐yl)‐6‐(3,5‐dimethylpyrazol‐1‐yl)pyridine (mpp), which are derivatives of pyrazolylpyridine, were prepared in nonaqueous medium. These complexes were characterized by elemental analyses and IR spectroscopy. Crystals of one of these complexes [CumppClN₃ ( VII )] were prepared in suitable size, and a molecular structure of this complex was obtained with X‐ray diffraction method. Complexes were examined by thermogravimetry and differential scanning calorimetry methods. Thermal decomposition was observed in complexes including two azide groups similar to that seen in explosives. In the complexes containing one azide group, formation of the Cu^I complexes was observed after thermal decomposition of the azide group.     

Stabilization of Human Telomeric G‐Quadruplex and Inhibition of Telomerase Activity by Propeller‐Shaped Trinuclear PtII Complexes

Two novel propeller‐shaped, trigeminal‐ligand‐containing, flexible trinuclear Pt^II complexes, {[Pt(dien)]₃(ptp)}(NO₃)₆ ( 1 ) and {[Pt(dpa)]₃(ptp)}(NO₃)₆ ( 2 ) (dien: diethylenetriamine; dpa: bis‐(2‐pyridylmethyl)amine; ptp: 6′‐(pyridin‐3‐yl)‐3,2′:4′,3′′‐terpyridine), have been designed and synthesized, and their interactions with G‐quadruplex (G4) sequences are characterized. A combination of biophysical and biochemical assays reveals that both Pt^II complexes exhibit higher affinity for human telomeric (hTel) and c‐myc promoter G4 sequences than duplex DNA. Complex 1 binds and stabilizes hTel G4 sequence more effectively than complex 2 . Both complexes are found to induce and stabilize either antiparallel or parallel conformation of G4 structures. Molecular docking studies indicate that complex 1 binds into the large groove of the antiparallel hTel G4 structure (PDB ID: 143D) and complex 2 stacks onto the exposed G‐quartet of the parallel hTel G4 structure (PDB ID: 1KF1). Telomeric repeat amplification protocol assays demonstrate that both complexes are good telomerase inhibitors, with IC₅₀ values of (16.0±0.4) μM and (4.20±0.25) μM for 1 and 2 , respectively. Collectively, the results suggest that these propeller‐shaped flexible trinuclear Pt^II complexes are effective and selective G4 binders and good telomerase inhibitors. This work provides valuable information for the interaction between multinuclear metal complexes with G4 DNA.     

Metal‐Ion‐Binding Analogs of Ribonucleosides: Preparation and Formation of Ternary Pd2+ and Hg2+ Complexes with Natural Pyrimidine Nucleosides

Four metal‐ion‐binding nucleosides, viz. 2,6‐bis(1‐methylhydrazinyl)‐9‐(β‐D ‐ribofuranosyl)‐9H‐purine ( 2a ) and its N‐acetylated derivative, 2b , 2,4‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐5‐(β‐D ‐ribofuranosyl)pyrimidine ( 3 ), and 2,4‐bis(1‐methylhydrazinyl)‐5‐(β‐D ‐ribofuranosyl)pyrimidine ( 4 ) have been synthesized. The ability of these nucleosides and the previously prepared 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐9‐(β‐D ‐ribofuranosyl)‐9H‐purine to form Pd²⁺‐ and Hg²⁺‐mediated complexes with uridine has been studied by ¹H‐NMR spectroscopy. To obtain additional support for the interpretation of the NMR data, comparative measurements on the ternary‐complex formation between pyridine‐2,6‐dicarboxamide ( 5 ), pyrimidine nucleosides, and K₂PdCl₄ were carried out.     

Near‐Infrared‐III‐Absorbing and ‐Emitting Dyes: Energy‐Gap Engineering of Expanded Porphyrinoids via Metallation

The synthesis of organometallic complexes of modified 26π‐conjugated hexaphyrins with absorption and emission capabilities in the third near‐infrared region (NIR‐III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis‐Pd^II and bis‐Pt^II complexes of hexaphyrin via N‐confusion modification led to substantial metal d_π–p_π interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO–LUMO energy gap. A remarkable long‐wavelength shift of the lowest S₀→S₁ absorption beyond 1700 nm was achieved with the bis‐Pt^II complex, t ‐Pt₂‐3 . The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t ‐Pt₂‐3 potentially useful as a NIR‐III PA contrast agent. The rigid bis‐Pd^II complexes, t ‐Pd₂‐3 and c ‐Pd₂‐3 , are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR‐III‐emissive and photoacoustic‐response capabilities.     

The crystal structure,luminescence and nitrobenzene‐sensing properties of a two‐dimensional MnII coordination polymer based on 2,6‐bis(imidazol‐1‐yl)pyridine

A two‐dimensional Mn^II coordination polymer (CP), poly[bis[μ₂‐2,6‐bis(imidazol‐1‐yl)pyridine‐κ²N³:N^3′]bis(thiocyanato‐κN)manganese] [Mn(NCS)₂(C₁₁H₉N₅)₂]_n, (I), has been obtained by the self‐assembly reaction of Mn(ClO₄)₂·6H₂O, NH₄SCN and bent 2,6‐bis(imidazol‐1‐yl)pyridine (2,6‐bip). CP (I) was characterized by FT–IR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction. The crystal structure features a unique two‐dimensional (4,4) network with one‐dimensional channels. The luminescence and nitrobenzene‐sensing properties were explored in a DMF suspension, revealing that CP (I) shows a strong luminescence emission and is highly sensitive for nitrobenzene detection.     

Luminescent Cyclometalated Alkynylplatinum(II) Complexes with a Tridentate Pyridine‐Based N‐Heterocyclic Carbene Ligand: Synthesis,Characterization, Electrochemistry,Photophysics, and Computational Studies

A new class of luminescent alkynylplatinum(II) complexes with a tridentate pyridine‐based N‐heterocyclic carbene (2,6‐bis(1‐butylimidazol‐2‐ylidenyl)pyridine) ligand, [Pt^II(C^N^C)(C?CR)][PF₆], and their chloroplatinum(II) precursor complex, [Pt^II(C^N^C)Cl][PF₆], have been synthesized and characterized. One of the alkynylplatinum(II) complexes has also been structurally characterized by X‐ray crystallography. The electrochemistry, electronic absorption and luminescence properties of the complexes have been studied. Nanosecond transient absorption (TA) spectroscopy has also been performed to probe the nature of the excited state. The origin of the absorption and emission properties has been supported by computational studies.     

Synthesis,structure and biological activity of diorganotin derivatives with pyridyl functionalized bis(pyrazol‐1‐yl)methanes

Three pyridyl functionalized bis(pyrazol‐1‐yl)methanes, namely 2‐[(4‐pyridyl)methoxyphenyl] bis(pyrazol‐1‐yl)methane (L¹), 2‐[(4‐pyridyl)methoxyphenyl]bis(3,5‐dimethylpyrazol‐1‐yl)methane (L²) and 2‐[(3‐pyridyl)methoxyphenyl]bis(pyrazol‐1‐yl)methane (L³) have been synthesized by the reactions of (2‐hydroxyphenyl)bis(pyrazol‐1‐yl)methanes with chloromethylpyridine. Treatment of these three ligands with R₂SnCl₂ (R = Et, n‐Bu or Ph) yields a series of symmetric 2:1 adducts of (L)₂SnR₂Cl₂ (L = L¹, L² or L³), which have been confirmed by elemental analysis and NMR spectroscopy. The crystal structures of (L²)₂Sn(n‐Bu)₂Cl₂·0.5C₆H₁₄ and (L³)₂SnEt₂Cl₂ determined by X‐ray crystallography show that the functionalized bis(pyrazol‐1‐yl)methane acts as a monodentate ligand through the pyridyl nitrogen atom, and the pyrazolyl nitrogen atoms do not coordinate to the tin atom. The cytotoxic activity of these complexes for Hela cells in vitro was tested. Copyright © 2010 John Wiley & Sons, Ltd.     

Flat vs. Folded Chelate Rings in cis‐PtIIa2 (a = NH3, a2 = en,a2 = 2, 2′‐bpy) Complexes of Twofold Substituted Diazine Ligands

Acid‐base and ligating properties of three bis(substituted)pyrazine (pz) and pyrimidine (pym) ligands (pyrazine‐2, 5‐dicarboxylic acid, 2, 5‐pzdcH2, 2, 3‐bis(pyridine‐2‐yl)pyrazine, 2, 3‐bppz, pyrimidine‐4, 6‐dicarboxylic acid, 4, 6‐pmdcH₂) toward cis‐Pt^IIa₂ (a = NH₃, a₂ = en, a₂ = 2, 2′‐bpy) have been studied. Combinations of pz‐N/pym‐N with donor atoms of the substituents lead to 5‐membered platinum chelates, but exclusive N, N‐coordination through the pyridyl substituents of 2, 3‐bppz can lead to a 7‐membered platinum chelate with a characteristic L‐shape of the resulting cation. It is observed for Pt^II(2, 2′‐bpy), yet not for Pt^II(en), and is a consequence of differences in sterical interactions between the 2, 3‐bppz ligand and the coligands of Pt^II.     

Synthesis and Structure of Copper(II) Nitrate Complexes with 2, 6‐Bis(pyrazolyl)pyridine

Three mononuclear copper(II) complexes of copper nitrate with 2, 6‐bis(pyrazol‐1‐yl)pyridine ( bPzPy ) and 2, 6‐bis(3′,5′‐dimethylpyrazol‐1‐yl)pyridine ( bdmPzPy ), [Cu(bPzPy)(NO₃)₂] ( 1 ), [Cu(bPzPy)(H₂O)(NO₃)₂] ( 2 ) and [Cu(bdmPzPy)(NO₃)₂] ( 3 ) were synthesized by the reaction of copper nitrate with the ligand in ethanol solution. The complexes have been characterized through analytical, spectroscopic and EPR measurements. Single crystal X‐ray structure analysis of complexes 1 and 2 revealed a five‐coordinate copper atom in 1 , whereas 2 contains a six‐coordinate (4+2) Cu^II ion with molecular units acting as supramolecular nodes. These neutral nodes are connected through O–H ··· O(nitrate) hydrogen bonds to give couples of parallel linear strips assembled in 1D‐chains in a zipper‐like motif.     

[Bis(3,5‐dimethylpyrazol‐1‐yl‐κN2)hydro(pyrazol‐1‐yl‐κN2)borato][(3,5‐dimethylpyrazol‐1‐yl‐κN2)dihydro(pyrazol‐1‐yl‐κN2)borato]nickel(II)

The title compound, [Ni(C₈H₁₂BN₄)(C₁₃H₁₈BN₆)] or Bp′Tp′Ni^II, where Bp′ is (3,5‐dimethylpyrazol‐1‐yl)dihydro(pyrazol‐1‐yl)borate and Tp′ is bis(3,5‐dimethylpyrazol‐1‐yl)hydro(pyrazol‐1‐yl)borate, contains a divalent Ni^II centre bound by the chelating N atoms of the polysubstituted pyrazolylborate ligands. It is shown to lack a strong agostic B—H...Ni interaction, implying that the sixth coordination site is unoccupied in the solid state. This square‐pyramidal complex is the only known crystal structure where the Ni^II centre is pentacoordinated while bonded exclusively to pyrazolyl units. This is of interest with respect to electrochemical and catalytic properties.     

Design,synthesis, pharmacological evaluation and DNA interaction studies of binuclear Pt(II) complexes with pyrazolo[1,5‐a]pyrimidine scaffold

Substituted pyrazolo[1,5‐a]pyrimidine ligands were synthesized by cyclization, using 3‐(thiophen‐2‐yl)‐1H‐pyrazol‐5‐amine with substituted enones (3‐phenyl‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐one) in presence of KOH and DMF as solvent to form cyclic aromatic compounds. The substituted pyrazolo[1,5‐a] pyrimidine based binuclear Pt^II complexes containing neutral tetradentated ligands have general formula [Pt₂(5a–5f)Cl₄], (where, (5a ‐5f) = pyrazolo[1,5‐a] pyrimidine ligand). This compounds were characterized by physicochemical and spectroscopic method like elemental analyses, UV‐Visible, FT‐IR, EDX, TGA, molar conductivity, magnetic susceptibility measurements, mass spectroscopy, ¹H and ¹³C NMR method. The square planar geometry was predicted by electronic spectral study. All Pt^II compounds were evaluated by antimicrobial assay, in vitro brine shrimp assay, in vivo cellular level bioassay using S. Pombe cells and anti‐tuberculosis study. LC₅₀ (50% lethal concentration) values of compounds are observed between 6.450 ‐ 102.07 μg/mL. UV‐vis absorption titration, competitive displacement assay, molecular docking and viscosity measurement were carried out to examine the binding type and binding strength of complexes. The binding studies suggest partial intercalative binding mode of the complexes and the observed binding constant (K_b) values are found in the order of 6d > 6b > 6c > 6a > 6e > 6 f. The anti‐proliferative cytotoxicity of the synthesized Pt^II complexes (6a‐6f) were tested against the HCT‐116 (Human Colorectal Carcinoma) cancer cell line.     

2,6‐Bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine and its octahedral copper complex

In the tridentate ligand 2,6‐bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine, C₂₃H₁₉N₇, both sets of triazole N atoms are anti with respect to the pyridine N atom, while in the copper complex aqua[2,6‐bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine](pyridine)(tetrafluoroborato)copper(II) tetrafluoroborate, [Cu(BF₄)(C₅H₅N)(C₂₃H₁₉N₇)(H₂O)]BF₄, the triazole N atoms are in the syn–syn conformation. The coordination of the Cu^II atom is distorted octahedral. The ligand structure is stabilized through intermolecular C—H...N interactions, while the crystal structure of the Cu complex is stabilized through water‐ and BF₄‐mediated hydrogen bonds. Photoluminiscence studies of the ligand and complex show that the ligand is fluorescent due to triazole–pyridine conjugation, but that the fluorescence is quenched on complexation.     

In situ synthesis of mononuclear copper(II) complexes of the new tridentate ligand bis[(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)methyl]amine

Two mononuclear copper complexes, {bis[(3,5‐dimethyl‐1H‐pyrazol‐1‐yl‐κN²)methyl]amine‐κN}(3,5‐dimethyl‐1H‐pyrazole‐κN²)(perchlorato‐κO)copper(II) perchlorate, [Cu(ClO₄)(C₅H₈N₂)(C₁₂H₁₉N₅)]ClO₄, (I), and {bis[(3,5‐dimethyl‐1H‐pyrazol‐1‐yl‐κN²)methyl]amine‐κN}bis(3,5‐dimethyl‐1H‐pyrazole‐κN²)copper(II) bis(hexafluoridophosphate), [Cu(C₅H₈N₂)₂(C₁₂H₁₉N₅)](PF₆)₂, (II), have been synthesized by the reactions of different copper salts with the tripodal ligand tris[(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)methyl]amine (TDPA) in acetone–water solutions at room temperature. Single‐crystal X‐ray diffraction analysis revealed that they contain the new tridentate ligand bis[(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)methyl]amine (BDPA), which cannot be obtained by normal organic reactions and has thus been captured in the solid state by in situ synthesis. The coordination of the Cu^II ion is distorted square pyramidal in (I) and distorted trigonal bipyramidal in (II). The new in situ generated tridentate BDPA ligand can act as a meridional or facial ligand during the process of coordination. The crystal structures of these two compounds are stabilized by classical hydrogen bonding as well as intricate nonclassical hydrogen‐bond interactions.     

Synthesis and crystal structure of an M4L6 tetrahedral cage with outward‐facing pockets from a substituted pyrazolyl–pyridine ligand

The self‐assembly of metal–polydentate ligands to give supramolecular tetrahedral complexes is of considerable current interest. A new ligand, 4‐benzyl‐2‐[1‐(2‐{[3‐(4‐benzylpyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]methyl}benzyl)‐1H‐pyrazol‐3‐yl]pyridine (L), with chelating pyrazolyl–pyridine units substituted on the 4‐position of the pyridyl ring with benzyl units, has been synthesized and fully characterized. The self‐assembly of L with cobalt(II) gave rise to a tetrahedral cage (hexakis{μ‐4‐benzyl‐2‐[1‐(2‐{[3‐(4‐benzylpyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]methyl}benzyl)‐1H‐pyrazol‐3‐yl]pyridine}perchloratotetracobalt(II) octakis(perchlorate) acetonitrile undecasolvate, [Co₄(ClO₄)(C₃₈H₃₂N₆)₆](ClO₄)₇·11CH₃CN) with approximate T symmetry. The X‐ray crystal structure of the cage, i.e. [Co₄L₆ClO₄](ClO₄)₇, shows that the substituted benzyl groups are oriented away from the centres of their respective ligands towards the Co^II vertices, making small outward‐facing pockets from three benzyl rings at the corners of the tetrahedron.     

Vectorial Electron Transfer in Donor–Photosensitizer–Acceptor Triads Based on Novel Bis‐tridentate Ruthenium Polypyridyl Complexes

The first examples of rodlike donor–photosensitizer–acceptor arrays based on bis‐2,6‐di(quinolin‐8‐yl)pyridine Ru^II complexes 1 a and 3 a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time‐resolved absorption spectroscopy reveals long‐lived, photoinduced charge‐separated states (τ_CSS ( 1 a )=140 ns, τ_CSS ( 3 a )=200 ns) formed by stepwise electron transfer. The overall yields of charge separation (≥50 % for complex 1 a and ≥95 % for complex 3 a ) are unprecedented for bis‐tridentate Ru^II polypyridyl complexes. This is attributed to the long‐lived excited state of the [Ru(dqp)₂]²⁺ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.     

Synthesis,Characterization, Self‐Assembly,Gelation, Morphology and Computational Studies of Alkynylgold(III) Complexes of 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Derivatives

A novel class of alkynylgold(III) complexes of the dianionic ligands derived from 2,6‐bis(benzimidazol‐2′‐yl)pyridine (H₂bzimpy) derivatives has been synthesized and characterized. The structure of one of the complexes has also been determined by X‐ray crystallography. Electronic absorption studies showed low‐energy absorption bands at 378–466 nm, which are tentatively assigned as metal‐perturbed π–π* intraligand transitions of the bzimpy^2? ligands. A computational study has been performed to provide further insights into the nature of the electronic transitions for this class of complexes. One of the complexes has been found to show gelation properties, driven by π–π and hydrophobic–hydrophobic interactions. This complex exhibited concentration‐ and temperature‐dependent ¹H NMR spectra. The morphology of the gel has been characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Binuclear and chain‐structure zinc(II) complexes constructed from 3,4‐dimethoxy‐trans‐cinnamic acid and N‐donor coligands 4‐(1H‐pyrazol‐3‐yl)pyridine and 4,4′‐bipyridine

3,4‐Dimethoxy‐trans‐cinnamic acid (Dmca) reacts with zinc sulfate in the presence of 4‐(1H‐pyrazol‐3‐yl)pyridine (L₁) or 4,4′‐bipyridine (L₂) under hydrothermal conditions to afford two mixed‐ligand coordination complexes, namely tetrakis(μ‐3,4‐dimethoxy‐trans‐cinnamato‐κ²O:O′)bis[[4‐(1H‐pyrazol‐3‐yl)pyridine]zinc(II)] heptahydrate, [Zn₂(C₁₁H₁₁O₄)₄(C₈H₇N₃)₂]·7H₂O or [Zn₂(Dmca)₄(L₁)₂]·7H₂O, (I), and catena‐poly[[bis(3,4‐dimethoxy‐trans‐cinnamato‐κO)zinc(II)]‐μ‐4,4′‐bipyridine‐κ²N:N′], [Zn(C₁₁H₁₁O₄)₂(C₁₀H₈N₂)]_n or [Zn(Dmca)₂(L₂)]_n, (II). The Zn^II centres in the two compounds display different coordination polyhedra. In complex (I), the Zn^II cation is five‐coordinated with a pseudo‐square‐pyramidal geometry, while in complex (II) the Zn^II cation sits on a twofold axis and adopts a distorted tetrahedral coordination environment. Complex (I) features a centrosymmetric binuclear paddle‐wheel‐like structure, while complex (II) shows a chain structure. This study emphasizes the significant effect of the coordination mode of both carboxylate‐group and N‐donor coligands on the formation of complex structures.     

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

Conjugated Polyelectrolyte‐Induced Self‐Assembly of Alkynylplatinum(II) 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Complexes

Water‐soluble cationic alkynylplatinum(II) 2,6‐bis(benzimidazol‐2′‐yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal–metal‐to‐ligand charge transfer (MMLCT) absorptions and triplet MMLCT (³MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non‐conjugated polyelectrolytes, driven by Pt???Pt and π–π interactions among the complex molecules. Interestingly, the two‐component ensemble formed by [Pt(bzimpy‐Et){C?CC₆H₄(CH₂NMe₃‐4)}]Cl₂ ( 1 ) with para‐linked conjugated polyelectrolyte (CPE), PPE‐SO₃^?, shows significantly different photophysical properties from that of the ensemble formed by 1 with meta‐linked CPE, mPPE‐Ala. The helical conformation of mPPE‐Ala allows the formation of strong mPPE‐Ala– 1 aggregates with Pt???Pt, electrostatic, and π–π interactions, as revealed by the large Stern–Volmer constant at low concentrations of 1 . Together with the reasonably large Förster radius, large HOMO–LUMO gap and high triplet state energy of mPPE‐Ala to minimize both photo‐induced charge transfer (PCT) and Dexter triplet energy back‐transfer (TEBT) quenching of the emission of 1 , efficient Förster resonance energy transfer (FRET) from mPPE‐Ala to aggregated 1 molecules and strong ³MMLCT emission have been found, while the less strong PPE‐SO₃^?– 1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of ³MMLCT emission in the PPE‐SO₃^?– 1 ensemble.