Electronic structure and optical properties of germanium-bridged platinum(II)-containing diethynylfluorene monomer and oligomers: A theoretical investigation

We apply quantum-chemical techniques to investigate the structural, electronic, and optical properties of some platinum-containing fluorenyleneethynylenegermylene-derived monomers and oligomers. The aim of our quantum-chemical calculations is to investigate the role of the transition metal centers in the organometallic system in terms of electronic structure and to estimate the influence of metal on the optical properties of the monomer and oligomers. The results indicate that there is a weak electronic interaction between the metal-based fragment and the π-conjugated organic segments, and consequently the photophysical properties are mainly based on the fluorenyleneethynylene (TFT) π-conjugated fragment with little contribution from the metal center. The role of metal center can be described as weak delocalization coupled with strong localization characteristic along the organometallic backbone. The introduction of platinum ions into the π-conjugated structure leads to bathochromic shifts in the absorption features as compared to those for the free ligands.     

Self-assembly of luminescent alkynylplatinum(II) terpyridyl complexes: modulation of photophysical properties through aggregation behavior

Complexes of platinum(II) with polypyridine (that is, the multidentate ligands related to pyridine, such as bipyridine or terpyridine) have rich photophysical properties. These compounds are able to give different crystal forms in the solid state: this polymorphism is evident in the broad range of colors that can be observed in solid samples. Because of the square-planar coordination geometry of the metal center, Pt···Pt as well as π-π interactions between the chromophoric polypyridyl platinum(II) moieties are thought to contribute to the polymorphism. Owing to limited solubility, metal···metal interactions in platinum(II) polypyridyl systems had been mainly studied in the solid state, but our preparation of more soluble complexes has enabled detailed spectroscopic examinations in solution. In this Account, we describe our development of these alkynylplatinum(II) terpyridyl complexes and their unique spectral properties. A series of square-planar platinum(II) terpyridyl complexes with enhanced solubility due to the presence of the alkynyl group exhibited intense emission in solution. The lowest energy absorption and emission bands are suggested to originate from the dπ(Pt) → π*(terpy) metal-to-ligand charge transfer (MLCT) and π(C≡C-C(6)H(4)-R) → π*(terpy) ligand-to-ligand charge transfer (LLCT) transitions. In addition to polymorphism and a wide range of spectral properties, these complexes also exhibit "solvatochromism" and "solvatoluminescence". They show remarkable color changes and luminescence enhancement when the diethyl ether content in a solvent mixture is varied, even as the concentration of the platinum(II) complex is held constant. The dramatic color changes and luminescence enhancement are tentatively suggested to originate from a metal-metal-to-ligand charge transfer (MMLCT) transition: reduced solvation (caused by an increase in the fraction of diethyl ether, which is the nonsolvating component of the liquid) is thought to increase Pt···Pt and π-π stacking interactions that arise from ground-state self-assembly or aggregate formation. The absorbance and luminescence wavelengths in these solvent-induced self-assemblies are also found to be dependent on the nature of the anions. Thus, counterions play an important role in governing the degree of self-assembly and the extent of interactions within these aggregates. Several polymers carrying multiple negatively charged functional groups (under basic conditions) as well as oligonucleotides have been shown to induce the aggregation and self-assembly of the positively charged water-soluble alkynylplatinum(II) terpyridyl complexes. The driving force for the induced aggregation and self-assembly is electrostatic binding of the complex molecules to the polymer, which brings the cations into a close proximity that induces Pt···Pt and π-π interactions and gives rise to remarkable color changes and luminescence enhancement. The spectral changes are shown to be related to the properties of both the complexes and the polymers. Upon electrostatic interaction, the platinum(II) complex cations are also found to stabilize the polymers and biopolymers in a helical conformation through Pt···Pt and π-π interactions. The influence on their secondary structure is revealed by significant circular dichroism (CD) signal enhancement.     

Regioselective Addition of Organometallic Reagents to 2‐(1‐Alkynyl)‐2‐alken‐1‐ones for an Efficient Synthesis of Substituted 1,2‐Allenyl Ketones

Highly substituted 1,2‐allenyl ketones can be easily and efficiently prepared from organometallic reagents and readily available 2‐(1‐alkynyl)‐2‐alken‐1‐ones. The synthetic application of 1,2‐allenyl ketone products was also showcased by palladium‐catalyzed further transformation.     

Carbon-carbon bond formation involving reactions of alkynes with group 9 metals (Ir, Rh, Co): preparation of conjugated olefins

Stable alkynyl complexes of iridium(III) (L(n)Ir-triple bond-R) that are prepared from the reactions of terminal alkynes readily undergo the intramolecular C-C bond-forming reactions between the alkynyl and adjacent hydrocarbyl ligands to yield conjugated olefins. These reactions are initiated by electrophiles (H(+), Me(+)) that attack the beta carbon of the alkynyl ligand to increase the electrophilicity of the alpha carbon of the alkynyl ligand. The C-C bond is then formed between the alpha carbons of the alkynyl and adjacent hydrocarbyl ligands.     

Synthesis and Characterization of a Heteroleptic Ru(II) Complex of Phenanthroline Containing Oligo-Anthracenyl Carboxylic Acid Moieties

In an effort to develop new ruthenium(II) complexes, this work describes the design, synthesis and characterization of a ruthenium(II) functionalized phenanthroline complex with extended π-conjugation. The ligand were L(1) (4,7-bis(2,3-dimethylacrylic acid)-1,10-phenanthroline), synthesized by a direct aromatic substitution reaction, and L(2) (4,7-bis(trianthracenyl-2,3-dimethylacrylic acid)-1,10-phenanthroline), which was synthesized by the dehalogenation of halogenated aromatic compounds using a zero-valent palladium cross-catalyzed reaction in the absence of magnesium-diene complexes and/or cyclooctadienyl nickel (0) catalysts to generate a new carbon-carbon bond (C-C bond) polymerized hydrocarbon units. The ruthenium complex [RuL(1)L(2)(NCS)(2)] showed improved photophysical properties (red-shifted metal-to-ligand charge-transfer transition absorptions and enhanced molar extinction coefficients), luminescence and interesting electrochemical properties. Cyclic and square wave voltammetry revealed five major redox processes. The number of electron(s) transferred by the ruthenium complex was determined by chronocoulometry in each case. The results show that processes I, II and III are multi-electron transfer reactions while processes IV and V involved one-electron transfer reaction. The photophysical property of the complex makes it a promising candidate in the design of chemosensors and photosensitizers, while its redox-active nature makes the complex a potential mediator of electron transfer in photochemical processes.     

Neutral and Cationic Macromolecules based on Iron Sandwich Complexes

This article is one of a number of reviews in the special issue of the Journal of Inorganic and Organometallic Polymers and Materials, celebrating the 50th anniversary of the discovery of metallocene-based polymers. Since the first examples of polyferrocenes in 1955, research into the design of organometallic polymers has grown exponentially. Organoiron polymers have incorporated ferrocene and arene cyclopentadienyl complexes, and have been developed for materials, liquid crystals, and electrocatalysts. The focus of this review is on the synthesis, properties, and characterization of macromolecules based on ferrocene or arene cyclopentadienyliron cations. Ferrocene-based polymers in which the ferrocene moieties are in or pendent to the backbone are described, as well as, the use of arene cyclopentadienyliron complexes in the design of polymeric materials. The design of star-shaped macromolecules and dendrimer materials that contain ferrocene and/or arene cyclopentadienyliron units will be discussed as well.     

Organometallic Compounds: An Opportunity for Chemical Biology?

Organometallic compounds are renowned for their remarkable applications in the field of catalysis, but much less is known about their potential in chemical biology. Indeed, such compounds have long been considered to be either unstable under physiological conditions or cytotoxic. As a consequence, little attention has been paid to their possible utilisation for biological purposes. Because of their outstanding physicochemical properties, which include chemical stability, structural diversity and unique photo- and electrochemical properties, however, organometallic compounds have the ability to play a leading role in the field of chemical biology. Indeed, remarkable examples of the use of such compounds-notably as enzyme inhibitors and as luminescent agents-have recently been reported. Here we summarise recent advances in the use of organometallic compounds for chemical biology purposes, an area that we define as "organometallic chemical biology". We also demonstrate that these recent discoveries are only a beginning and that many other organometallic complexes are likely to be found useful in this field of research in the near future.     

Coumarin-Tagged Dinuclear Trithiolato-Bridged Ruthenium(II)⋅Arene Complexes: Photophysical Properties and Antiparasitic Activity

The synthesis, characterization, photophysical and biological properties of 13 new conjugate coumarin-diruthenium(II)⋅arene complexes against Toxoplasma gondii are presented. For all conjugate organometallic unit/coumarins, an almost complete loss of fluorescence efficacy was observed. However, the nature of the fluorophore, the type of bonding, the presence and length of a linker between the coumarin dye and the ruthenium(II) moiety, and the number of dye units influenced their biological properties. The in vitro activity against a transgenic T. gondii strain grown in human foreskin fibroblasts (HFF) leads to IC₅₀ values for T. gondii β-gal from 105 to 735 nM. Of note is that nine compounds displayed lower IC₅₀ than the standard drug pyrimethamine. One compound applied at its IC₅₀ did not affect B-cell proliferation but had an impact on T-cell proliferation in murine splenocyte cultures. Transmission electron microscopy of T. gondii β-gal-infected HFF showed that treatment predominantly affected the parasites’ mitochondrion.     

Water-soluble quaternized mercaptopyridine-substituted zinc-phthalocyanines: Synthesis, photophysical, photochemical and bovine serum albumin binding properties

The synthesis and characterization of the new zinc phthalocyanine derivatives, tetra- (non-peripheral, 5) and octa-(peripheral, 6) substituted with 2-mercaptopyridine and their respective quaternized derivatives (8 and 9) are reported. Photochemical and photophysical properties of the new complexes are compared with those of the previously reported peripherally tetra-substituted complexes 7 and 10. The quaternized compounds exhibit excellent solubility in water, making them potential photosensitizers for use in photodynamic therapy (PDT) of cancer. Spectroscopic, aggregation, photophysical and photochemical properties of these complexes are also investigated and compared. Photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yield) properties of these phthalocyanine photosensitizers are very important for the assessment of these complexes as PDT agents. In this study, the effects of the position of the substituents and quaternization of the substituents on the photophysical and photochemical parameters of the zinc phthalocyanines are also reported. This study also showed that the water-soluble quaternized zinc phthalocyanines strongly bind to blood plasma proteins such as bovine serum albumin (BSA).     

Tropolone-Conjugated DNA: A Fluorescent Thymidine Analogue Exhibits Solvatochromism,Enzymatic Incorporation into DNA and HeLa Cell Internalization

Tropolone is a non-benzenoid aromatic scaffold with unique photophysical and metal-chelating properties. Recently, it has been conjugated with DNA, and the photophysical properties of this conjugate have been explored. Tropolonyl-deoxyuridine (tr-dU) is a synthetic fluorescent DNA nucleoside analogue that exhibits pH-dependent emissions. However, its solvent-dependent fluorescence properties are unexplored owing to its poor solubility in most organic solvents. It would be interesting to incorporate it into DNA primer enzymatically. This report describes the solvent-dependent fluorescence properties of the silyl-derivative, and enzymatic incorporation of its triphosphate analogue. For practical use, its cell-internalization and cytotoxicity are also explored. tr-dU nucleoside was found to be a potential analogue to design DNA probes and can be explored for various therapeutic applications in the future.     

A New Class of Luminescent Platinum(II) Complexes of 1,3-Bis(N-alkylbenzimidazol-2′-yl)benzene-Type Ligands and Their Application Studies in the Fabrication of Solution-Processable Organic Light-Emitting Devices

A novel class of luminescent platinum(II) bzimb (1,3-bis(N-alkylbenzimidazol-2′-yl)benzene) complexes has been designed and synthesized. With the incorporation of various substituents on the anionic phenyl ring of the bzimb ligand, the emission color can be readily tuned. Their photophysical, electrochemical and electroluminescence properties have been studied. These platinum(II) bzimb complexes have been demonstrated to be capable of serving as phosphorescent dopants. Efficient solution-processable OLEDs (organic light-emitting devices), with a maximum external quantum efficiency of up to 4.85 %, can be achieved. This class of platinum(II) bzimb complexes represents a promising class of phosphorescent dopants for solution-processable OLEDs.     

Conception and Evaluation of Fluorescent Phosphine-Gold Complexes: From Synthesis to in vivo Investigations

A phosphine gold(I) and phosphine-phosphonium gold(I) complexes bearing a fluorescent coumarin moiety were synthesized and characterized. Both complexes displayed interesting photophysical properties: good molar absorption coefficient, good quantum yield of fluorescence, and ability to be tracked in vitro thanks to two-photon imaging. Their in vitro and in vivo biological properties were evaluated onto cancer cell lines both human and murine and into CT26 tumor-bearing BALB/c mice. They displayed moderate to strong antiproliferative properties and the phosphine-phosphonium gold(I) complex induced significant in vivo anti-cancer effect.     

Complexes of Ir(III)-octaethylporphyrin with peptides as probes for sensing cellular O2

Ir(III)-porphyrins are a relatively new group of phosphorescent dyes that have potential for oxygen sensing and labeling of biomolecules. The requirement of two axial ligands for the Ir(III) ion permits simple linkage of biomolecules by a one-step ligand-exchange reaction, for example, using precursor carbonyl chloride complexes and peptides containing histidine residue(s). Using this approach, we produced three complexes of Ir(III)-octaethylporphyrin with cell-penetrating (Ir1 and Ir2) and tumor-targeting (Ir3) peptides and studied their photophysical properties. All of the complexes were stable and possessed bright, long-decay (unquenched lifetimes exceeding 45 μs) phosphorescence at around 650 nm, with moderate sensitivity to oxygen. The Ir1 and Ir2 complexes showed positive staining of a number of mammalian cell types, thus demonstrating localization similar to endoplasmic reticulum and ATP- and temperature-independent intracellular accumulation (direct translocation mechanism). Their low photo- and cytotoxicity allows intracellular oxygen to be probed.     

Photophysical Properties of BADAN Revealed in the Study of GGBP Structural Transitions

The fluorescent dye BADAN (6-bromoacetyl-2-dimetylaminonaphtalene) is widely used in various fields of life sciences, however, the photophysical properties of BADAN are not fully understood. The study of the spectral properties of BADAN attached to a number of mutant forms of GGBP, as well as changes in its spectral characteristics during structural changes in proteins, allowed to shed light on the photophysical properties of BADAN. It was shown that spectral properties of BADAN are determined by at least one non-fluorescent and two fluorescent isomers with overlapping absorbing bands. It was found that BADAN fluorescence is determined by the unsolvated “PICT” (planar intramolecular charge transfer state) and solvated “TICT” (twisted intramolecular charge transfer state) excited states. While “TICT” state can be formed both as a result of the “PICT” state solvation and as a result of light absorption by the solvated ground state of the dye. BADAN fluorescence linked to GGBP/H152C apoform is quenched by Trp 183, but this effect is inhibited by glucose intercalation. New details of the changes in the spectral characteristics of BADAN during the unfolding of the protein apo and holoforms have been obtained.     

Synthesis, Optical Properties and Photophysics of Group 10–12 Transition Metal Complexes and Polymer Derived from a Central Tris(p-ethynylphenyl)amine Unit

A new series of luminescent group 10–12 metal alkynyl complexes and polyyne polymer containing a central tris(p-ethynylphenyl)amine bridging chromophore were prepared. The regiochemical structures of these triangular-shaped trinuclear compounds and polymer were studied by various spectroscopic and photophysical analyses. Upon photoexcitation, each of them emits an intense purple-blue fluorescence emission in the near UV region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions observed in the low-energy region harnessed through the strong heavy-atom effects of group 10–12 transition metals was examined and the results were compared among these three neighboring late transition metal elements. The influence of group 15 nitrogen-based heteroatom on the intersystem crossing rate and the spatial extent of the lowest singlet and triplet excitons was fully elucidated and a comparison was made to the nearest group 14 and 16 neighbors in the same row of the Periodic Table. Dedicated to Professor Takakazu Yamamoto in recognition of his outstanding contribution to the area of transition metal-based coordination polymers.     

Synthesis and electronic properties of double pincer-type cyclometalated iridium complexes

Double pincer-type cyclometalated iridium complexes were prepared based upon a few assumptions and their photophysical properties were examined.     

The Curious Case of the Allyl Ligand: A Study in Applying the 18-Electron Rule

The 18-electron rule is an incredibly powerful tool for explaining the properties and reactivities of organometallic complexes. With the rule, however, comes the difficulty of choosing a method of implementing it, i.e. what many popular texts refer to as the “donor-pair” (ionic) method or the “neutral-ligand” method. The choice becomes particularly difficult when ligands can be counted in multiple ways via the donor-pair method, as in the case of the allyl ligand. In this investigation we hope to show that a choice of counting method can be chosen based on experimental intuition, as supported by a density functional theory (DFT) investigation. The natural electronic charge of metals, the η³-π-allyl (or simply the allyl) ligand, and the η³-cyclopropenyl ligand are discussed for a variety of organometallic complexes. A variety of DFT exchange-correlation functionals and basis sets, coupled with the Natural Population Analysis method of Landis and Weinhold, reveal the allyl ligand’s charge in a complex can be traced back to its experimental precursor. These results emphasize that the 18-electron rule is not merely a bookkeeping device and that the donor-pair method in the case of the allyl ligand holds more utility than the neutral-ligand method.     

BODIPY-based polymeric dyes as emerging horizon materials for biological sensing and organic electronic applications

The design, synthesis, and characterization of BODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene)-based small molecules has undergone tremendous progress in the past two decades. BODIPYs and their dipyrrin precursors have been recently reviewed with emphasis placed on their syntheses, reactions and applications including biochemical labelling, fluorescent switches, chemosensors, and electroluminescent devices. Compared to other dye classes, these systems offer unique attractions such as excellent thermal/photochemical stability, intense absorption/emission profiles, negligible triplet-state formation, and small Stokes shifts. Their optoelectronic and semiconductor properties can be finely tuned via facile synthetic modifications on the dipyrromethene core, while their optical characteristics are relatively insensitive to medium polarity and the pH of the environment. On the contrary, the optoelectronic and photophysical properties of BODIPY-based polymeric semiconductors the newest developed family in BODIPY-based organic materials (the first BODIPY based conjugated polymers were published in 2008) are still not well understood. For fully resolving these open questions, it will be shown in this review that the optoelectronic and photophysical properties of the BODIPY-based conjugated polymers are depending on various parameters including: (i) the positions where the BODIPY core will be attached into the polymer backbone (α-, β-, meso positions, or fluorine substitution) and (ii) the number of methyl substituents on 1, 2, 3, 5, 6, and 7 positions and finally (iii) if BODIPY functions as electron rich or electron deficient building block in “donor-acceptor” (D-A) conjugated polymers. This is a very significant advance in the emerging field of BODIPY chemistry since it opens the path for further optimization of the recent and new developed BODIPY-based polymeric semiconductors with predetermined optoelectronic and photophysical properties by providing new design rules to organic and material chemists as well as physical (bio)chemistry and device (bio)engineering scientists.     

Voltammetric, EQCM, and in situ conductivity studies of 3,6-bis(2-thienyl)-N-ethyl carbazole

3,6-Bis(2-thienyl)-N-ethylcarbazole (Th-ECz-Th) was obtained by using organometallic polycondensation mediated by organotransition metal complexes. The properties of electrochemically obtained polymer films from this monomer were characterized by simultaneous voltametric and in situ conductivity and electrochemical quartz microbalance techniques.     

Investigation of ring-opening polymerization of 5-[2-{2-(2-methoxyethoxy)ethoxy}-ethoxymethyl]-5-methyl-1,3-dioxa-2-one by organometallic catalysts

To develop new polymer-based materials, the design of aliphatic carbonate has received attention and become a well-known cyclic monomer. In view of carbonate ring polymer scope, poly(trimethylene carbonate) (PTMC) has been continuously developed for further applications due to its unique degradability. PTMC bearing oligo ethylene glycol units, PTMCM-MOE3OM, were typically prepared via ring-opening polymerization (ROP) using amidine-based catalysts such as 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) and benzyl alcohol (BnOH) as an initiator. To improve the polymer molecular weight or other properties, several know-how synthetic catalysts based on organometallic complexes are under consideration as potential catalysts. With the existence of diverse classes of metallic complexes, the inorganic complexes were investigated for their catalytic activity based on tris(dimethylsilyl)amido chelating, bis(phenolate) chelating, and macrocyclic tetradentate (NNNN)-type cyclen chelating with a metal-core of tin (II), scandium (III), lutetium (III), and zinc (II). In this study, we found that involving a Zn(II) dimethylcyclen/alkoxide ligand and Mg complexes could accelerate the reaction and finish the polymerization under ambient conditions within 2 hr. Molecular weight reached 11,000 g/mol (40%) and 8,100 g/mol (> 96%). Subsequently, we concluded that Zn and Mg complexes were high reactivity for initiating the ROP of TMCM-MOE3OM upon steadily degree of polymerization.