Chromophoric Ligand Research Articles

Tartrate‐Anchored Tetranuclear Titanium‐Oxo Clusters Functionalized by Chromophore Ligands Exhibiting Photoelectric Response and Photodegradation Performances of Methylene Blue

ABSTRACTIn recent years, researchers have devoted considerable effort to the study of high crystalline titanium‐oxo clusters (TOCs), because TOCs are considered to be the molecular analogs of TiO2 nanoparticles and have the potential to be utilized as effective cleaning and catalytic materials. Two new tartrate‐anchored tetranuclear TOCs functionalized with chromophore ligand of p‐nitrobenzoate (NB)/p‐toluenesulfonate (TS), namely, [Ti4(TA)(NB)2(OiPr)10] (1, H4TA = tartaric acid) and [Ti4(TA)(TS)2(OiPr)10] (2), were synthesized and their structures were characterized by various methods. The molecular structure analyses indicated that 1 and 2 are all tetranuclear {Ti4} TOCs, in which tartrate appears as a hexadentate μ4‐bridging ligand while p‐nitrobenzoate/p‐toluenesulfonate acts as a bidentate μ2‐bridging ligand. TOCs 1 and 2 are of good thermal and solvent stability. Furthermore, their photocurrent responses and photocatalytic degradation activities towards methylene blue (MB) were also investigated. In the presence of H2O2, the photocatalytic degradation efficiencies of MB by 1 and 2 are about 84.43% and 71.00%, respectively, at room temperature under visible light irradiation for 60 min. These findings shed light on designing efficient polycarboxylate‐based TOCs photocatalysts.

Octocrylene carboxylate as an antenna in a luminescent Europium(III) complex: Experimental and theoretical insights

A new carboxylic acid, 2-cyano-3,3-diphenyl-2-propenoic acid, CLN, a chromophore ligand, was obtained by an alkaline hydrolysis reaction from the octocrylene, a commercial type B ultraviolet (UVB) radiation absorber. The CLN structure was elucidated by single-crystal X-ray diffraction (SCXRD) as being tetragonal with space group P4‾21/c and the presence of a carboxylic acid group was confirmed by mass, infrared (IR), and proton nuclear magnetic resonance (1H NMR) spectroscopy. In this way, coordination compounds were developed between CLN and Ln(III), Ln = being Gadolinium (Gd) and Europium (Eu), with a stoichiometry of 4:13 metal:ligand, confirmed by thermal and elemental analyses, corroborating with the metal cluster predicted by Sparkle/AM1 semi-empirical model. Photoluminescence data indicated that Eu(III) is efficiently sensitized by CLN due to its triplet excited state, determined using the emission spectrum of the Gd(III) mimic complex (T = 25,477 cm−1), being suitable for this purpose. Therefore, the emission spectrum of the Eu(III) complex exhibited a 5D0 → 7FJ transitions characteristic of the lanthanide ion. Furthermore, the Judd-Ofelt intensity parameters, the radiative and non-radiative decay rates, and the intrinsic quantum yield evaluated using the software LUMPAC software were in good agreement with the experimental values.

Crystal Structure of the Native Chromoprotein from Pleurotus salmoneostramineus Provides Insights into the Pigmentation Mechanism.

The pink-colored protein from the fungus Pleurotus salmoneostramineus (PsPCP) possesses unusual primary sequences with little resemblance to those of known proteins and exhibits a red color in aqueous solution. To understand the pigmentation mechanism of PsPCP, we elucidated the X-ray crystal structure of the native PsPCP. We identified a highly conjugated polyene ligand 2-dehydro-3-deoxylaetiporic acid A as a chromophore ligand, whose solution exhibits yellow. The crystal structure of PsPCP indicated that the ligand is secured in the central cavity and anchored at both termini by hydrophilic interactions and that surrounding residues show CH-pi and C-H···O hydrogen bondings. Geometrical analyses of the bound ligand demonstrated that the conjugated C-C and C═C bonds exhibit similar bond distances. The result indicated enhanced electron delocalization within the conjugated CC bond system, resulting in a redshift of the chromophore ligand. The computational estimates of the UV-vis spectra support the view that the electron delocalization within the conjugated CC bonds system of the bound ligand, induced by the specific ligand geometry within a limited space of PsPCP cavity, is responsible for the red pigmentation of PsPCP. Thus, we propose that the coloring mechanism of PsPCP, which constrains the geometry of a highly conjugated polyene ligand, is a novel type of pigment chemistry.

Layer-Ordered Organooxotin Clusters for Extreme-Ultraviolet Photolithography.

Extreme-ultraviolet (EUV) photolithography, which enables the high-throughput production of well-defined patterns with critical dimensions on the scale of several nanometers, is essential for the fabrication of a highly integrated semiconductor. The full exploitation of EUV lithographic techniques necessitates the development of photoresist (PR) materials with both high EUV sensitivity and a long shelf-life. However, despite notable advances, the available library of EUV PR materials remains limited. Here we report EUV PRs capable of forming preorganized layers consisting of ladder-structured tetranuclear stannoxanes. Single-crystal X-ray structure analyses reveal a close interlayer distance of 8.5 Å through interdigitation of the pseudoaxial butyl chains. The developed EUV PR materials exhibit high solubility in organic solvents commonly used in semiconductor processing, enabling the preparation of PR solutions with superior wettability and uniform film-forming ability on Si wafer substrates. These PR solutions also demonstrate notable resistance to hydrolytic decomposition for as long as 1 month, indicating a long shelf-life. Our PR materials enabled negative-tone patterning processes that involved a solubility decrease upon irradiation. The presence of chromophoric ligands makes our PR materials compatible with conventional UV photolithography, through photochemical reactions involving carbonyl units. In addition, e-beam and EUV lithography could produce fine line patterns of our PRs, with critical dimensions of 20 and 15 nm, respectively. Our research showcases the potential of layer-ordered organooxotin clusters for EUV PR applications.

Assessing the Character of the C6F5 Ligand from the Electrochemical and Photophysical Properties of [Ni(C6F5)2(N∧N)] Complexes.

Organonickel complexes containing α-diimine ligands [Ni(C6F5)2(N∧N)] (N∧N = 2,2'-bipyridine (bpy), 2,9-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), dipyrido[3,2-a:2',3'-c]phenazine (dppz), 1,4-bis(isopropyl)-1,4-diazabutadiene (iPr-DAB), and 1,4-bis(2,6-dimethylphenyl)-1,4-diazabutadiene (Xyl-DAB) were prepared and studied structurally, spectroscopically, and electrochemically. Their molecular structures from single-crystal X-ray diffraction show near-perfect square planar Ni(II) coordination except in the case of dmphen. Primary reversible electrochemical reductions in the range from -1 to -2 V vs ferrocene/ferrocenium couple lead to mainly diimine-localized radical anion complexes, while secondary reductions in the range from -2 to -2.5 V lead to dianion complexes, as shown through spectroelectrochemistry. Irreversible metal-centered oxidations at around 0.7 V result in rapid aryl-aryl reductive elimination and formation of decafluorobiphenyl. No photoluminescence was detected for the complexes containing chromophoric α-diimine ligands at room temperature. At 77 K in frozen glassy 2-Me-THF matrices, weak photoluminescence was detected for the dmphen and tmphen derivatives, with broad emission bands peaking around 570 nm. All results are rationalized with the support of (TD-)DFT calculations, highlighting the role of the C6F5 ligand in different systems.

Proton Domino Reactions at an Imidazole Relay Control the Oxidation of a TyrZ-His190 Artificial Mimic of Photosystem II.

A close mimic of P680 and the TyrosineZ-Histidine190 pair in photosystem II (PS II) has been synthesized using a ruthenium chromophore and imidazole-phenol ligands. The intramolecular oxidation of the ligands by the photoproduced Ru(III) species is characterized by a small driving force, very similar to PS II where the complexity of kinetics was attributed to the reversibility of electron transfer steps. Laser flash photolysis revealed biphasic kinetics for ligand oxidation. The fast phase (τ<50 ns) corresponds to partial oxidation of the imidazole-phenol ligand, proton transfer within the hydrogen bond, and formation of a neutral phenoxyl radical. The slow phase (5-9 μs) corresponds to full oxidation of the ligand which is kinetically controlled by deprotonation of the distant 1-nitrogen of the imidazolium. These results show that imidazole with its two protonatable sites plays a special role as a proton relay in a 'proton domino' reaction.

Novel composite based on cellulose nanomaterial for detection and selective removal of cadmium (II) ions from wastewater

In this study, we made a sustainable composite material from wheat straw agriculture waste. This material is environmentally friendly and has unique surface properties. We used it as a substrate because of its network and ability for surface modifications. To make this material, we embedded 2-(2-(di(thiophen-2-yl)methylene)hydrazineyl)-4-methylphenol (TMHM) chromophoric ligand on its surface. This enabled preconcentration, spectrophotometric determination, and removing of Cd2+ ions from real wastewater effluent samples. The resulting CNF-TMHM composite material displays exceptional sensitivity towards Cd2+ ions in aqueous solutions, accomplishing a remarkable detection limit as low as 4.17 ppb. Thus, sensitivity permits efficient naked-eye detection. Significantly, the CNF-TMHM composite material has a rapid and clear color change, shifting from pale yellow to wine red color, within less than two minutes when exposed to variable concentrations of Cd2+ ions. Furthermore, this developed CNF-TMHM composite material reveals remarkable effectiveness for Cd2+ ions detection and removal from wastewater samples. These dual potential addresses the serious environmental interests related to the pollution of water and achieving the sustainability development goals related to clean water.

Toward the Rational Design of Organic Catalysts for Organocatalysed Atom Transfer Radical Polymerisation.

Thanks to their diversity, organic photocatalysts (PCs) have been widely used in manufacturing polymeric products with well-defined molecular weights, block sequences, and architectures. Still, however, more universal property-performance relationships are needed to enable the rational design of such PCs. That is, a set of unique descriptors ought to be identified to represent key properties of the PCs relevant for polymerisation. Previously, the redox potentials of excited PCs (PC*) were used as a good descriptor for characterising very structurally similar PCs. However, it fails to elucidate PCs with diverse chromophore cores and ligands, among which those used for polymerisation are a good representative. As showcased by model systems of organocatalysed atom transfer radical polymerisation (O-ATRP), new universal descriptors accounting for additional factors, such as the binding and density overlap between the PC* and initiator, are proposed and proved to be successful in elucidating the experimental performances of PCs in polymerisation. While O-ATRP is exemplified here, the approach adopted is general for studying other photocatalytic systems.

Lanthanide complexes with an azo-dye chromophore ligand: syntheses, crystal structures, and near-infrared luminescence by long-wavelength excitation.

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by single-crystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing.

Circularly polarized luminescence activity in the near infrared spectral region of a water-soluble ytterbium(iii) complex containing a conjugated chromophoric ligand

A chiral Yb(iii) complex bearing a conjugated chromophoric ligand exhibits potential as NIR-to-NIR chiroptical probe for biological purposes.

Truxene-to-Fluorenone Energy Transfer in a Robust Mesoporous Zn-MOF.

A new metal-organic framework (MOF; [Zn4O(hett)4/3(fluo)1/2(bdc)1/2]n; TFT-MOF) constructed on chromophoric ligands 5,5',10,10',15,15'-hexaethyltruxene-2,7,12-triacetate (hett), 9-fluorenone-2,7-dicarboxylate (fluo), terephthalate (bdc), and the Zn4O node has been prepared and identified by powder X-ray diffraction. This luminescent MOF exhibits large mesoporous pores of 2.7 nm based on computer modeling using density functional theory (DFT) calculations. The steady-state and time-resolved fluorescence spectra and photophysical parameters of TFT-MOF have been investigated and compared with those of the free ligands and their basic chromophores. All in all, TFT-MOF exhibits particularly efficient singlet-singlet energy-transfer processes described as 1(hett)* → (fluo) and 1(bdc)* → (fluo), leading to fluorescence arising for the fluo lumophore operating only through Förster resonance energy transfer (FRET) with an efficiency of transfer of up to >95%. This experimental conclusion was corroborated by DFT and time-dependent DFT (TDDFT). For the 1(hett)* → (fluo) process, the approximated overall rate constant of energy transfer was evaluated to be at most 2.04 × 1010 s-1 (using a Stern-Volmer approach of solution data and the relationship between distance and concentration). This process was analyzed using the Förster theory, where two intrapore energy transfer paths of center-to-center distances of 13 and 25 Å have been identified. TFT-MOF photosensitizes the formation of singlet oxygen (1O2 (1Σg)) as detected by its phosphorescence signal at 1275 nm.

Enhancing the Circularly Polarized Luminescence of Europium Coordination Polymers by Doping a Chromophore Ligand into Superhelices.

Lanthanide-based molecular materials showing efficient circularly polarized luminescence (CPL) activity with a high quantum yield are attractive due to their potential applications in data storage, optical sensors, and 3D displays. Herein we present an innovative method to achieve enhanced CPL activity and a high quantum yield by doping a chromophore ligand into a coordination polymer superhelix. A series of homochiral europium(III) phosphonates with a helical morphology were prepared with the molecular formula S-, R-[Eu(cyampH)3-3n(nempH)3n]·3H2O (S/R-Eu-n, n = 0-5%). The doping of chromophore ligand S- or R-nempH2 into superhelices of S/R-Eu-0% not only turned on the CPL activity with the dissymmetry factor |glum| on the order of 10-3 but also increased the quantum yield by about 14-fold. This work may shed light on the development of efficient CPL-active lanthanide-based coordination polymers for applications.

Optimizing cellulose nanofiber composite for Co2+ ions recovery from lithium-ion battery wastes and removal from wastewater: A green environmental solution

In this study, we have introduced an advanced composite material that combines the remarkable properties of cellulose nanofibers (CNFs) with a tailored surface to enable the concentration, spectrophotometric detection, removal of Co2+ ions from wastewater samples and recovery of Co2+ ions from lithium-ion battery waste. CNFs, known for their eco-friendly nature and exceptional surface characteristics, serve as an ideal substrate for immobilizing the (3,3′-((1E,1′E)-((4-nitro-1,2-phenylene) bis(azaneylylidene)) bis(methaneylylidene)) bis(2-hydroxybenzoic acid) (NAMH) chromophoric ligand. The resulting CNFs-NAMH composite displays extraordinary sensitivity to Co2+ ions in aqueous solutions, achieving an impressive limit of detection (LOD) as 0.87 ppb. This exceptional sensitivity allows for straightforward visual detection with the naked eye.A noteworthy feature of the CNFs-NAMH composite is its rapid and distinct color change in approximately a minute upon exposure to varying concentrations of Co2+ ions. Moreover, this composite demonstrates high efficiency in removing Co2+ in polluted wastewater samples and recovering Co2+ ions from lithium-ion batteries, with a high efficiency of up to 79.5 % for Co2+ ions recovery from lithium-ion batteries and removal efficiency of 97.35 % for Co2+ from wastewater samples. This capability addresses critical environmental concerns associated with wastewater treatment and lithium-ion battery waste and provides a practical and sustainable approach for reclaiming valuable Cobalt ions.

Synthesis, characterization and photo-physical studies of naphthalamide-based Ir(III) complexes

Interest in tuning the emission towards deep-red (DR) and near-infrared (NIR) regions is enhanced due to their fascinating applications in the field of organic light-emitting diodes (OLEDs), night-vision display and bio-imaging. In this regard, Naphthalimide based bidentate chromophoric ligand (L1, NIPy, 2‑butyl‑6-(pyridin-2-yl)-1H-benzo[de]isoquinoline-1,3(2H)‑dione) was utilized to prepare the DR emitting Ir(III) complexes [Ir(L1)2(L2)] (1) and [Ir(L1)2(L3)] (2) where L2 = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine and L3 = 1-(4-fluorophenyl)-3-methyl-1H-3λ4-imidazole). Complexes have been characterized by various analytical and spectroscopic methods, and 2 was further confirmed by a single crystal X-ray diffraction method. Strong intermolecular π···π interactions between the naphthalamide units in complex 2 lead to the formation of a multi-dimensional framework. These complexes show emissions in the range of 650–700 nm at room temperature, which extends up to the near-infra-red region (800 nm). The photophysical studies were supported by DFT and TD-DFT calculations. These types of naphthalimide-based Ir(III) complexes tend to show emissions in the NIR region which has potential applications in the field of photodynamic therapy and OLEDs.

Influence of the position of the N-methyl group in tetra-(N-methylpyridyl)porphyrin on the features of its interaction with oligonucleotides. Spectral and thermochemical study

We studied the influence of the position of the N-methyl group in tetra-(N-methylpyridyl)porphyrin on the features of its interaction with oligonucleotides using experimental physicochemical methods. Spectral methods detecting changes in the photophysical properties of chromophore ligands made it possible to prove the mechanism of binding to poly[d(AT)2] and poly[d(GC)2]. The thermochemical method made it possible to evaluate the structural consequences of ligation of oligonucleotides, and in the case of tetra-(3-N-methyl-pyridyl)porphyrin, to clarify the mechanism of binding to oligonucleotides. The combination of spectral and thermochemical analysis is useful for elucidating the structure of ligand complexes with synthetic and natural DNA.

Functional organogold(III) complexes with bidentate cyclometalating ligands

The advancement of organometallic chemistry over the past decades has accelerated the development of functional materials based on metal complexes. In particular, organometallic complexes based on the gold(III) system have been attracting increasing attention. The square planar gold(III) metal center can coordinate to different chromophoric ligands as in related iridium(III) and platinum(II) systems, allowing the synthesis of another library of metal-based functional materials. Bidentate cyclometalating ligands such as 2-phenylpyridine derivatives are amongst the most commonly used class of ligands for the synthesis of transition metal complexes and they have been used for the preparation of gold(III) complexes with tunable photophysical properties. In this review, the recent progress in the development of organometallic gold(III) complexes based on these bidentate cyclometalating ligands will be discussed, with specific foci on the applications of these gold(III) complexes as emitters for organic light-emitting diodes as well as their biological applications.

Bifunctional Supertetrahedral Chalcogenolate Cluster-Based Assembly Materials Constructed by a Photoactive Ligand.

The assembly of supertetrahedral chalcogenolate clusters (SCCs) and multifunctional organic linkers could lead to the formation of tunable structures and synergistic properties. Two SCC-based assembled materials (SCCAM-1 and -2) constructed by a triangular chromophore ligand, tris(4-pyridylphenyl)amine, were successfully synthesized and characterized. The SCCAMs demonstrate unusually long-lived afterglow at low temperatures (83 K) and efficient activities for the photocatalytic degradation of organic dye in water.

Observation of long-lived phosphorescence in Au(i) complexes bearing chromophoric (N-heterocyclic carbene) ligands

Long-lived phosphorescence has been observed at room temperature in two gold(i) complexes of a fluorenyl-substituted N-heterocyclic carbene.

9-Borafluoren-9-yl and diphenylboron tetracoordinate complexes of F- and Cl-substituted 8-quinolinolato ligands: synthesis, molecular and electronic structures, fluorescence and application in OLED devices.

Six new four-coordinate tetrahedral boron complexes, containing 9-borafluoren-9-yl and diphenylboron cores attached to orthogonal fluorine- and chlorine-substituted 8-quinolinolato ligand chromophores, have been synthesised, characterised, and applied as emitters in organic light-emitting diodes (OLEDs). An extensive steady-state and time-resolved photophysical study, in solution and in the solid state, resulted in the first-time report of delayed fluorescence (DF) in solid films of 8-quinolinolato boron complexes. The DF intensity dependence on excitation dose suggests that this emission originates from triplet-triplet annihilation (TTA). Density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies give insight into the ground and excited state geometries, electronic structures, absorption energies, and singlet-triplet gaps in these new organoboron luminophores. Finally, given their highly luminescent behaviour, organic light-emitting diode (OLED) devices were produced using the synthesised organoboron compounds as emissive fluorescent dopants. The best OLED displays green-blue (λmaxEL = 489 nm) electroluminescence with an external quantum efficiency (EQE) of 3.3% and a maximum luminance of 6300 cd m-2.

Synthesis and Photophysical Studies of Copper(I) CAAC Half-Sandwich Complexes as a Highly Modifiable Class of Emitters.

Cyclopentadienyls are well-known strong donor ligands and have been successfully employed in catalysis as they tolerate a variety of substituents to adjust their steric and electronic properties. Although such highly modifiable ligands are of great interest for luminescence and photocatalytic applications, studies of CpR-containing photoactive transition-metal complexes are quite rare. In this work, we present a structural, electrochemical, and first elaborated photophysical investigation of a series of copper(I) half-sandwich complexes bearing cyclic alkyl(amino)carbenes (CAACs) as chromophore ligands and compare them with [Cu(Cp)(IDipp)] and [Cu(Cp*)(IDipp)] bearing a traditional N-heterocyclic carbene. Furthermore, we present the first molecular structure derived from single-crystal X-ray diffraction of a copper(I) indenyl complex, which can be described as an η2 (σ, π)-coordination. The CuI half-sandwich complexes show blue-green to orange phosphorescence with a photoluminescence quantum yield of up to 59% and radiative rate constants kr of up to 4 × 104 s-1 in the solid state, depending on the substitution pattern of the CpR ligand. Our TD/DFT calculations suggest that the emitting excited states are of 3MLCT/LLCT character. We determined the excited-state lifetime of the CuI half-sandwich complexes in solution to be as long as 600 ns, which in combination with the large π-surface of the CpR ligands allows for Dexter energy transfer for photocatalytic applications. In addition, the chiroptical properties of chiral [Cu(Cp/Cp*)(CAACMenthone)] were studied and compared to [CuCl(CAACMenthone)], of which we demonstrate that its circular polarized luminescence is the result of excimer formation and not, as previously reported, attributed to the monomeric C1-symmetric structure.