Synthesis, Luminescence, and Structure of a Polymorphic Polyfluorinated Diiodoplatinum(II) Diimine Complex.

PtI(5,5'-bis(HCFCHOCH)-2,2'-bpy)], , is the first example of a substituted fluorinated diiodoplatinum diimine complex that exhibits polymorphism. The complex, upon recrystallization, forms two different polymorphs, denoted as α and β forms. The luminescence of the α and β forms are the same in glassy solution at 77 K; however, in the solid state, they differ significantly.

Oxidation Pathways Involving a Sulfide-Endcapped Donor-Acceptor-Donor π-Conjugated Molecule and Antimony(V) Chloride.

The oxidation pathways and products of a discrete, sulfide-endcapped donor-acceptor-donor (D/A/D) molecule, namely, propylenedioxythiophene-benzothiadiazole-propylenedioxythiophene, are investigated. The electrochemical and chemical oxidations proceed by two distinct routes. Specifically, electrochemical oxidation undergoes a sequential two-step, one-electron (1e) oxidation route with a 117 mV difference between consecutive half-wave potentials.

Photophysical Properties of Pt(II) Polypyridines with Five- versus Six-Membered Chelate Rings: Trade-Offs in Angle Strain.

This report describes the synthesis and characterization of a series of eight [Pt(NNN)X] complexes where the tridentate NNN ligand is (2,2'-bipyrid-6-yl)(pyrid-2-yl)sulfide (btp) or methyl(2,2'-bipyrid-6-yl)(pyrid-2-yl)amine (bmap) and X is OMe, Cl, phenylethynyl (CPh), or cyclohexylethynyl (CCy). The expectation was that inserting a heteroatom into the backbone of 2,2':6',2″-terpyridine (trpy) would expand the overall intraligand bite angle, introduce ILCT character into the excited states, and improve the photophysical properties. Crystal structures of [Pt(bmap)CPh] and [Pt(btp)Cl] reveal that atom insertion into the trpy backbone successfully expands the bite angle of the ligand by 8-10°.

DNA binding of Pd(TC3), a conformable cationic porphyrin with a long-lived triplet state.

The goal of this work has been to synthesize and investigate Pd(TC3), an intercalating porphyrin that has conformable substituents capable of groove binding to B-form DNA. (TC3 denotes the doubly deprotonated form of 5,10,15,20-tetra[3-(3'-methylimidazolium-1'-yl)prop-1-yl]porphyrin.) Palladium(ii) is an apt choice for the central metal ion because it remains strictly four-coordinate and provides for a luminescent triplet excited state with a long lifetime.

Cr(III)-HMC (HMC = 5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane) Alkynyl Complexes: Preparation and Emission Properties.

Presented here is the chemistry of Cr(III) alkynyl complexes based on the rac-HMC and meso-HMC ligands (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Thus far, two pairs of cis/trans-[Cr(rac/meso-HMC)(C2R)2]Cl (R = Ph, C2H/C2SiMe3) complexes have been synthesized from reactions between cis/trans-[Cr(rac/meso-HMC)Cl2]Cl and LiC2R. These complexes were characterized using single crystal X-ray diffraction, UV-vis spectroscopy, FT-IR spectroscopy, and fluorimetry.

Engineering Chemically Exfoliated Large-Area Two-Dimensional MoS2 Nanolayers with Porphyrins for Improved Light Harvesting.

Molybdenum disulfide (MoS2 ) is a promising candidate for electronic and optoelectronic applications. However, its application in light harvesting has been limited in part due to crystal defects, often related to small crystallite sizes, which diminish charge separation and transfer. Here we demonstrate a surface-engineering strategy for 2D MoS2 to improve its photoelectrochemical properties.

Tuning a Lanthanide Complex To Be Responsive to the Environment in Solution.

The f-f emissions of lanthanide-ion complexes have predictable emission energies and many practical applications, but the emitting states are generally impervious to the surroundings. This investigation explores ligand- and metal-centered emission processes for a series of mixed-ligand complexes of composition M(X-T)(NO3)3, where the metal ion is europium, gadolinium, terbium, or lutetium, and X-T denotes the tridentate ligand 2,2':6',2″-terpyridine (H-T), 4'-phenyl-2,2':6',2″-terpyridine (Ph-T), or 4'-pyrrolidin-N-yl-2,2':6',2″-terpyridine (pyrr-T). The presence of the pyrrolidinyl substituent imparts intraligand charge-transfer (ILCT) character to the ligand-based excited states and reduces the energy gap between the singlet and the triplet excited states.

Binding Studies of G-Quadruplex DNA and Porphyrins: Cu(T4) vs Sterically Friendly Cu(tD4).

This investigation explores binding interactions involving G-quadruplex DNA and two copper(II)-containing porphyrins (5,10,15,20-tetra(N-methylpyridinium-4-yl)porphyrinato)copper(II) and the sterically friendlier analogue (trans-5,15-di(N-methylpyridinium-4-yl)porphyrinato)copper(II), or Cu(T4) and Cu(tD4), respectively. The study incorporates five different DNA sequences that support the formation of unimolecular and bimolecular G-quadruplex hosts capable of exhibiting at least nine different structures in toto. Absorbance and emission results establish that G-quadruplex DNA is more adept at sequestering Cu(tD4) compared with the bulkier Cu(T4) ligand, even though the predominant mode of uptake is by end-capping, irrespective of the porphyrin or DNA sequence employed.

Regeneration of Light-Harvesting Complexes via Dynamic Replacement of Photodegraded Chromophores.

All-synthetic molecular donor-acceptor complexes are designed, which are capable of counteracting the effect of photoinduced degradation of donor chromophores. Anionic gallium protoporphyrin IX (GaPP) and semiconducting carbon nanotube (CNT) are used as a model donor-acceptor complex, which is assembled using DNA oligonucleotides. The GaPP-DNA-CNT complex produces an anodic photocurrent in a photoelectrochemical cell, which steadily decays due to photo-oxidation.

DNA-binding studies of a tetraalkyl-substituted porphyrin and the mutually adaptive distortion principle.

This investigation explores DNA-binding interactions of various forms of an alkyl-substituted cationic porphyrin, H2TC3 (5,10,15,20-tetra[3-(3'-methylimidazolium-1'-yl)]porphyrin). The motivating idea is that incorporating alkyl rather than aryl substituents in the meso positions will enhance the prospects for intercalative as well as external binding to DNA hosts. The ligands may also be applicable for photodynamic and/or anticancer therapy.

Internal versus external binding of cationic porphyrins to single-stranded DNA.

Absorbance, induced circular dichroism, and emission studies establish that the tetrasubstituted cationic porphyrin Cu(T4) preferentially binds externally to single-stranded (ss) DNA sequences, except in a purine-rich system like 5'-(dA)10-3' where a degree of internalization occurs. On the other hand, the sterically friendly, disubstituted Cu(tD4) system exclusively binds to ss DNA by internalization, that is, pseudointercalation. By and large the results show that double-stranded DNA hosts decisively outcompete more flexible ss hosts for the uptake of a porphyrin, regardless of the binding motif.

Accessibility and external versus intercalative binding to DNA as assessed by oxygen-induced quenching of the palladium(II)-containing cationic porphyrins Pd(T4) and Pd(tD4).

Studies reveal that it is possible to design a palladium(II)-containing porphyrin to bind exclusively by intercalation to double-stranded DNA while simultaneously enhancing the ability to sensitize the formation of singlet oxygen. The comparisons revolve around the cations [5,10,15,20-tetra(N-methylpyridinium-4-yl)porphyrin]palladium(II), or Pd(T4), and [5,15-di(N-methylpyridinium-4-yl)porphyrin]palladium(II), or Pd(tD4), in conjunction with A═T and G≡C rich DNA binding sequences. Methods employed include X-ray crystallography of the ligands as well as absorbance, circular dichroism, and emission spectroscopies of the adducts and the emission from singlet oxygen in solution.

Structure and emission studies of dimorphic crystals of [PtBr2(5,5'-bis(CF3CH2OCH2)-2,2'-bpy)] (1).

The yellow (1y) and orange (1o) crystalline polymorphs of [PtBr2(5,5'-bis(CF3CH2OCH2)-2,2'-bipyridine)] exhibit surprisingly short nearest neighbour Pt···Pt separations of 3.526 Å and 3.590 Å, respectively, at 295 K.

Varying substituents and solvents to maximize the luminescence from [Ru(trpy)(bpy)CN]+ derivatives.

Ruthenium(II) in combination with monodentate, bidentate, and tridentate ligands has proven to be a useful design for a variety of applications, but the majority of systems are virtually nonluminescent in solution. The goal of this work has been to design luminescent forms with practicable emission quantum yields, and the focus has been on [Ru(X-T)(dmeb)CN](+) systems, where X-T denotes 2,2':6',2″-terpyridine bearing substituent X at the 4'-position and dmeb denotes [2,2'-bipyridine]-4,4'-dicarboxylic acid, dimethyl ester. Results show that varying the π-electron-donating ability of the 4'-X substituent is an effective way to tune the energy and lifetime of the charge-transfer (CT) emission.

π donation and its effects on the excited-state lifetimes of luminescent platinum(II) terpyridine complexes in solution.

Introducing electron-donating groups extends the excited-state lifetimes of platinum(II)-terpyridine complexes in fluid solution. Such systems are of interest for a variety of applications, viz., as DNA-binding agents or as components in luminescence-based devices, especially sensors.

Arylated versus cyclometalated platinum(II) polypyridines: photoluminescence from Pt(4'-R-trpy)Ph+ systems (R = NMe2, N-pyrrolidinyl, or 1-pyrenyl).

Many platinum(II) polypyridine complexes are good luminophores, an enigmatic exception being Pt(trpy)Ph(+), where trpy denotes 2,2':6',2"-terpyridine. A new analysis suggests the complex is nonemissive due to (3)SBLCT (sigma-bond-to-ligand charge transfer) character in the lowest energy excited state. Bases for two distinct strategies for inducing emission from aryl derivatives become clear.

Cationic copper(II) porphyrins intercalate into domains of double-stranded RNA.

A cationic, copper(II)-containing ligand, derived from bulky 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin, Cu(T4), and two sterically friendlier forms, [trans-5,15-di(N-methylpyridinium-4-yl)porphyrinato]copper(II), Cu(tD4), and [cis-5,10-di(N-methylpyridinium-4-yl)porphyrinato]copper(II), Cu(cD4), bind to DNA and RNA hosts. Six hairpin-forming RNA 18-mer sequences and two previously studied DNA analogues serve as convenient binding platforms of programmable base composition. A crystal structure shows that the copper center of Cu(tD4) is four-coordinate, establishing compatibility with intercalative binding as well as susceptibility to solvent-induced emission quenching.

DNA oligonucleotide templated nanohybrids using electronic type sorted carbon nanotubes for light harvesting.

Light harvesting nanostructure hybrids have been designed and demonstrated using single-wall carbon nanotubes (SWCNTs) and porphyrin chromophores. DNA oligonucleotides are used to conjugate SWCNTs with light-absorbing chromophores for transparent films which generate photocurrents. High-purity semiconducting SWCNTs demonstrate significant enhancement in the photocurrent compared to metallic or unsorted tubes.

Regiospecific quenching of a photoexcited platinum(II) complex at acidic and basic sites.

The carbometalated complex Pt(dppzφ*)Cl, where dppzφ* denotes the 6-(4-tert-butylphenyl)-dipyrido[3,2-a:2',3'-c]phenazine ligand, exhibits emission in a dichloromethane solution at room temperature with a concentration-dependent excited-state lifetime. Extrapolation to zero Pt(dppzφ*)Cl concentration yields a limiting lifetime of 11.0 μs in the absence of dioxygen along with an impressive emission quantum yield of 0.

First emission studies of Tc2X8(2-) systems (X = Cl, Br).

The emission spectra of the solids [n-Bu(4)N](2)Tc(2)X(8) (X = Cl, Br) have been investigated at room temperature and 77 K. In each case, the emission originates in the (1)δ-δ* excited state, as with the rhenium homologues, but has a shorter lifetime.

A red-emitting light switch based on a heteroleptic ruthenium(II) complex containing a tridentate dppz analogue.

Delocalization of the charge-transfer excitation in the series [Ru(NNN)(bpy)CN](+) [bpy = 2,2'-bipyridine; 1, NNN = 2,2':6',2''-terpyridine; 2, NNN = 2-(2'-pyridyl)-1,10-phenanthroline or php; 3, NNN = 6'-(2''-pyridyl)dipyrido[3,2-a:2',3'-c]phenazine or dppzp] proves to be an effective way of tuning photophysical properties. Red-emitting 3 functions as a DNA "light switch", shows emission from a state with charge-transfer-to-phenazine character, and exhibits a significantly enhanced emission signal relative to 1 and other dppzp-containing ruthenium(II) complexes.

Steric effects direct the binding of porphyrins to tetramolecular quadruplex DNA.

The binding motifs of copper(II) porphyrins with G quadruplex DNA structures vary markedly depending on the steric demands of the ligand and the host structure.

DNA-binding and physical studies of Pt(4'-NR2-trpy)CN+ systems (trpy = 2,2':6',2''-terpyridine).

This paper focuses on DNA-binding interactions exhibited by Pt(dma-T)CN(+), where dma-T denotes 4'-dimethylamino-2,2':6',2''-terpyridine, and includes complementary studies of the corresponding pyrr-T complex, where pyrr-T denotes 4'-(N-pyrrolidinyl)-2,2':6',2''-terpyridine. The chromophores are useful for understanding the interesting and rather intricate DNA-binding interactions exhibited by these and related systems. One reason is that the terpyridine ligands employed provide intense visible absorption and enhanced photoluminescence signals.

Spectroscopic properties of orthometalated platinum(II) bipyridine complexes containing various ethynylaryl groups.

Neutral orthometalated platinum(II) complexes of the deprotonated 6-phenyl-2,2'-bipyridine ligand (bearing a trialkoxygallate, tolyl, ethynyltrialkoxygallate, or ethynyltolyl substituent) and a sigma-bonded Cl, ethynyltolyl, or ethynyltrialkoxygallate coligand have been prepared by a stepwise procedure based on copper-promoted cross-coupling reactions. The X-ray structure of the [2-(p-tolyl)ethynyl][4-{2-(p-tolyl)ethynyl}-6-phenyl-2,2'-bipyridyl)]platinum(II) complex revealed a coplanar arrangement of all residues bound to platinum, although the tolylethynyl groups exhibit position-dependent bending in the solid state. The complexes exhibit charge-transfer absorption in the visible region.

Lewis acid and base sensing by platinum(II) polypyridines.

This report describes platinum(II) complexes of 6-(2-pyridyl)-dipyrido[3,2- a:2',3'- c]phenazine (dppzp) and 6-phenyl-dipyrido[3,2- a:2',3'- c]phenazine (dppzphi). The [Pt(dppzp)Cl] (+) ( 1) system exhibits an excited-state lifetime of 5.0 micros in deoxygenated dichloromethane.