Organometallic Chromophores Research Articles

Designing a novel organometallic chalcone with an enormous second-harmonic generation response

Density Functional Theory (DFT) and the Hyper-Rayleigh scattering formalism are applied to investigate the frequency-dependent nonlinear optical (NLO) behavior of a novel organometallic chromophore composed of two chalcones bonded by a silver atom. In this investigation, the appropriate LanL2DZ and 6-311++G(d,p) basis sets are applied to describe the metal and the remaining elements, respectively. DFT-based methods which include an accurate description of the exchange Hartree–Fock term are essential to the description of the electrical α, β, and γ properties, which are the optical coefficients discussed. The results indicate that low polarity solvents like benzene improves β and γ values. For instance, from benzene to the water environment, the M06-2X DFT method indicates a decrease from 81.94×103 to 7.12×103 a.u. Moreover, the results in benzene are quite superior to that obtained for urea (0.04×103 a.u.) or 4-nitroaniline (0.73×103 a.u.), which are more standard for NLO materials. The prediction for the second hyperpolarizability (35.37×106 a.u.) is ca. 4.5 times greater than that reported for a single chalcone. The material is suitable for NLO applications.

Refine the evaluation of photophysical properties of organometallic chromophores under confined molecular crystal conditions

Many impressive results have been achieved in the researches and developments of luminescent chromophore materials by combining experimental synthesis and characterization with the cooperative theoretical calculation. However, the existing theoretical studies are usually based on the intrinsic properties of isolated molecules and extend their properties to the whole molecular material directly, which will lead to the persistence of errors and affect the computational design of molecular materials with different morphology. Therefore, the study of multimolecular systems needs to further consider the environmental effects on molecules. This work is based on the calculation of a series of crystalline Ir(III) complexes under background charge conditions to reveal how the surrounding charge affects the photophysical properties of a series of transition metal Ir(III) complex materials. Through this method, the study of crystalline complexes is found to be more authentically reproduced the charge transfer state, energy level, and reorganization energy, etc., and shows the changes of luminescence characteristics and efficiency. The change of the electronic structure of the target molecule would be characterized more comprehensively, thus obtaining more accurate results for the excited states properties of molecular materials.

Light-Harvesting Two-Photon-Absorbing Polymers

A series of atactic polystyrene-based polymers was synthesized that contains grafted π-conjugated organic and organometallic chromophores to investigate two-photon light-harvesting properties. The ...

Applications of Photoswitches in the Storage of Solar Energy

AbstractPhotoswitches are organic or organometallic chromophores that undergo a reversible chemical transformation upon absorption of light. Among the most commonly studied photoswitches are stilbenes and azobenzenes, capable of efficient interconversion between cis and trans isomers. When one isomer is significantly less thermodynamically stable than the other, photoisomerization of the stable to the metastable isomer converts a fraction of the absorbed photon energy into excess free energy (chemical potential). If the metastable isomer is sufficiently inert at room temperature, its photoconversion provides a means of storing solar energy, which is recovered by triggering heat‐releasing thermal conversion of the metastable to the stable isomer. In other words, such a photoswitch acts as a battery that captures solar energy, stores it as chemical potential and releases it on demand as heat. This process is known as molecular solar thermal energy storage or a molecular solar thermal battery. Unlike the more established conventional solar thermal storage, which uses sunlight to heat, melt or vaporize material, molecular solar thermal energy storage does not require thermal insulation to prevent discharge but relies on the kinetic activation barrier separating the two isomers. Unlike solar‐to‐chemical energy conversion by photosplitting of H2O or photoreduction of CO2, which comprise open‐system cycles, photoswitches are thermodynamically closed storage media. Successful deployment of molecular solar thermal energy storage requires new photoswitches that combine a seemingly contradictory set of molecular parameters: a large difference in the free energies of the two isomers separated by a large kinetic barrier; a high quantum yield of photogeneration of the metastable isomer that itself is either photochemically inactive or transparent to sunlight; highly selective isomerizations that allow many charge/discharge cycles without accumulation of side‐products even at high discharge temperatures. While the optimal photoswitch for molecular solar thermal energy storage remains to be invented, a large body of empirical observations acquired in the past decade provides several potentially valuable starting points for such a search.

Generic Classification Scheme for Second-Order Dipolar Nonlinear Optical Organometallic Complexes That Exhibit Second Harmonic Generation.

The molecular design rules of organic nonlinear optical (NLO) materials are well established, especially those pertaining to the first-order molecular hyperpolarizability, β, which governs second-harmonic generation (SHG): a phenomenon that is responsible for the frequency doubling processes in many optical applications. The availability of these rational guidelines has propelled the development of new organic SHG chromophores. Conversely, the development of organometallic SHG-active complexes has not been steered so clearly. Many reports on individual series of complexes suggest a singular correlation between their structure and SHG properties. Several reviews have catalogued such results, but these have only distinguished compounds by chemical type, while their SHG properties are described one-by-one for each chemical. We herein propose a generic classification scheme that can systematically rationalize dipolar SHG properties for all organometallic complexes. This classification method stands to provide the holistic information that is needed to generate a rational set of guidelines for the systematic molecular design of dipolar SHG-active organometallic chromophores. Our scheme shows that only a simple set of molecular design rules is required to relate the chemical structure of an organometallic complex to its second-order dipolar SHG properties. This is despite the fact that these molecular design rules are rooted in a complicated panoply of ligand- and crystal-field theory, resonance structures, intramolecular charge transfer considerations, metal oxidation states, and metal coordination attributes. While the roots of these rules can be derived at the individual chemical level, their derivation via our workflow of simple decision-making processes which connect these rules within a simple classification scheme, stands to facilitate a rational molecular design approach toward the materials discovery of organometallic complexes for SHG applications.

Electron Transfer from Photoexcited Naphthalene Diimide Radical Anion to Electrocatalytically Active Re(bpy)(CO)3Cl in a Molecular Triad

Electron donor–acceptor photosensitizers having long charge separation lifetimes and high-reducing potentials that can be easily appended to thermodynamically difficult to reduce catalysts hold great promise for driving CO2 reduction. This study presents a new molecular triad utilizing a naphthalene diimide radical anion (NDI•–) donor chromophore appended to a 9,10-diphenylanthracene (DPA) acceptor, which is in turn linked to Re(bpy)(CO)3Cl. The NDI•– chromophore is readily generated by mild chemical or electrochemical reduction, absorbs at wavelengths as long as 800 nm, and has an excited state oxidation potential (−2.1 V vs SCE), which rivals or exceeds those of metalorganic and organometallic chromophores. Photoexcitation of NDI•– to *NDI•– is followed by ultrafast reduction of DPA to DPA•–, which then rapidly reduces the metal complex. The overall quantum yield for reduction of Re(bpy)(CO)3Cl is approximately 90% using visible light. The overall time constant for the forward electron transfer to reduc...

Multiphoton spectroscopy: An optical window into molecular electrostatics

Quantitative knowledge about static molecular electric dipole moments is essential for understanding of intramolecular charge transfer as well as nanometer-scale static electric interactions. However, measuring or determining the molecular electrostatic properties with sufficient accuracy remains a challenging task. In our experiments, we measure the femtosecond two-photon absorption spectra- and cross sections of a range of organic- and organometallic chromophores in solution and use these data to determine the electric dipole moment change in corresponding lowest-energy dipole-allowed transition. Good correspondence of our experimental dipole moments with the quantum-chemical calculations as well as reports by other groups using conventional dipole moment measurement methods suggests that quantitative multiphoton spectroscopy may offer all-optical alternative to the traditional techniques such as Stark effect and electrochromism.

Enantioselective Excited-State Photoreactions Controlled by a Chiral Hydrogen-Bonding Iridium Sensitizer.

Stereochemical control of electronically excited states is a long-standing challenge in photochemical synthesis, and few catalytic systems that produce high enantioselectivities in triplet-state photoreactions are known. We report herein an exceptionally effective chiral photocatalyst that recruits prochiral quinolones using a series of hydrogen-bonding and π-π interactions. The organization of these substrates within the chiral environment of the transition-metal photosensitizer leads to efficient Dexter energy transfer and effective stereoinduction. The relative insensitivity of these organometallic chromophores toward ligand modification enables the optimization of this catalyst structure for high enantiomeric excess at catalyst loadings as much as 100-fold lower than the optimal conditions reported for analogous chiral organic photosensitizers.

Isophorone‐based organometallic chromophores: Synthesis, characterization and investigation of electro‐optical properties

A series of hybrid donor–acceptor complexes with a ferrocene moiety and isophorone derivatives were synthesized. Data from 1H NMR, 13C NMR, Fourier transform infrared, atomic absorption and mass spectroscopies and CHN analysis supported the predicted structure of the products. A comparative investigation was performed using UV–visible, cyclic voltammetry and fluorescence measurements. Density functional theory was used to optimize the chromophore structure and calculation of highest occupied and lowest unoccupied molecular orbital energy levels. The ferrocene/isophorone hybrids show useful properties for further development and studies as electro‐optic materials.

Printable Fluorescent Hydrogels Based on Self-Assembling Peptides

Fluorescent hydrogels (FH) have a variety of potential applications in the field of soft electronics. However, fabrication of mechanically stable and printable fluorescent hydrogels remains challenging. Here, we report a kind of fluorescent hydrogel based on the co-assembly of peptide motif and transition metal ions. The metal ions are captured in the hydrogel network at specific positions through covalently linked ligands on the peptide hydrogelators. This efficiently prevents the aggregation and self-quenching of organometallic chromophores. In addition, the formation of metal-ligand complexes introduces additional interactions to stabilize the hydrogel network, making the FH even more stable after the incorporation of metal ions. The FH is optically transparent but highly fluorescent. By using three different metal ions, the white light fluorescent supramolecular hydrogel has been achieved. As a proof-of-principle, we demonstrate the printability of the hydrogels to various patterns. We anticipate that with the improved fluorescent performance and stability, this kind of FH can find broad applications in extrusion-based 3D printing for the construction of soft electronics.

Photochemical Water-Splitting with Organomanganese Complexes.

Certain organometallic chromophores with water-derived ligands, such as the known [Mn(CO)3(μ3-OH)]4 (1) tetramer, drew our attention as possible platforms to study water-splitting reactions. Herein, we investigate the UV irradiation of various tricarbonyl organomanganese complexes, including 1, and demonstrate that dihydrogen, CO, and hydrogen peroxide form as products in a photochemical water-splitting decomposition reaction. The organic and manganese-containing side products are also characterized. Labeling studies with 18O-1 suggest that the source of oxygen atoms in H2O2 originates from free water that interacts with 1 after photochemical dissociation of CO (1-CO) constituting the oxidative half-reaction of water splitting mediated by 1. Hydrogen production from 1 is the result of several different processes, one of which involves the protons derived from the hydroxido ligands in 1 constituting the reductive half-reaction of water splitting mediated by 1. Other processes that generate H2 are also operative and are described. Collectively the results from the photochemical decomposition of 1 provide an opportunity to propose a mechanism, and it is discussed within the context of developing new strategies for water-splitting reactions with organomanganese complexes.

Photophysics and non-linear absorption of Au(I) and Pt(II) acetylide complexes of a thienyl-carbazole chromophore.

In order to understand the photophysics and non-linear optical properties of carbazole containing π-conjugated oligomers of the type ET-Cbz-TE (E = ethynylene, T = 2,5-thienylene, Cbz = 3,6-carbazole), a detailed investigation was carried out on a series of oligomers that feature Au(i) or Pt(ii) acetylide "end groups", as well as a Pt(ii)-acetylide linked polymer (CBZ-Au-1 and CBZ-Pt-1, CBZ-Poly-Pt). These organometallic chromophores were characterized by UV-visible absorption and variable temperature photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, open aperture nanosecond z-scan and two photon absorption (2PA) spectroscopy. The Au(i) and Pt(ii) oligomers and polymer exhibit weak fluorescence in fluid solution at room temperature. Efficient phosphorescence is observed from the Pt(ii) systems below 150 K in a solvent glass; however, the Au(i) oligomer exhibits only weak phosphorescence at 77 K. Taken together, the emission results indicate that the intersystem crossing efficiency for the Pt(ii) chromophores is greater than for the Au(i) oligomer. Nonetheless, nanosecond transient absorption indicates that direct excitation affords moderately long-lived triplet states for all of the chromophores. Open aperture z-scan measurement shows effective optical attenuation can be achieved by using these materials. The 2PA cross section in the degenerate S0→S1 transition region was in the range 10-100 GM, and increased monotonically toward shorter wavelengths, reaching 800-1000 GM at 550 nm.

Functionalization of a ruthenium-diacetylide organometallic complex as a next-generation push-pull chromophore.

The design and preparation of an asymmetric ruthenium-diacetylide organometallic complex was successfully achieved to provide an original donor-π-[M]-π-acceptor architecture, in which [M] corresponds to the [Ru(dppe)2] (dppe: bisdiphenylphosphinoethane) metal fragment. The charge-transfer processes occurring upon photoexcitation of the push-pull metal-dialkynyl σ complex were investigated by combining experimental and theoretical data. The novel push-pull complex, appropriately end capped with an anchoring carboxylic acid function, was further adsorbed onto a semiconducting metal oxide porous thin film to serve as a photosensitizer in hybrid solar cells. The resulting photoactive material, when embedded in dye-sensitized solar cell devices, showed a good spectral response with a broad incident photon-to-current conversion efficiency profile and a power conversion efficiency that reached 7.3 %. Thus, this material paves the way to a new generation of organometallic chromophores for photovoltaic applications.

Antenna Effect by Organometallic Chromophores in Bimetallic d–f Complexes

The nature of the intermetallic bond in a series of complexes of the type [Cp2-TM-M-Cp2] (where TM = Re and M = Y, La, Lu, Yb, Ac; also TM = Os and M = Th; Cp = cyclopentadienyl ligand) have been studied by relativistic two-component density functional theory (DFT) calculations. The results obtained in this work show that the interaction between the transition metal and lanthanide atoms is mainly ionic in all cases, while for the case of actinide atoms this interaction becomes significantly more covalent. The effective direction of the electron transfer between the Re→Ac or Os→Th centers allows us to propose that the [Cp2ReAcCp2] and [Cp2OsThCp2] complexes are ideal candidates for near-infrared (NIR) technologies since their absorption spectra show some transitions over 600 nm. We also observed a shifting of the absorption spectrum of around 100 nm of the [Cp2Re] fragment when is compared against the absorption spectrum of the entire complex. This behavior allows us to argue that the [Cp2Re] fragment is a good antenna chromophore due to the possibility of charge transfer transitions from this fragment to the f shell in lanthanide or actinide elements studied here.

114 Nanoscale composites with ytterbium porphyrin metallocomlexes for luminescence diagnostics and photothermal therapy of tumours

In the course of the recent development of new sol-gel derived materials for optics, organically modified metal oxide matrices have widely demonstrated their great potential. Most of the work performed in this area has been concentrated on embedding organic or organo-metallic chromophores in an oxide network to make optical devices. The main advantages of the use of hybrid organic—inorganic nanocomposites result from their high versatility in offering a wide range of possibilities to fabricate tailor-made materials in terms of their chemical and physical properties, and macroscopic shape molding. Such materials emerging in this field are known as ‘sol-gel photonics’. There have been some striking examples of the use of room temperature processed hybrids to design materials with emission, absorption, second-order nonlinear optical and photochromic properties.

ChemInform Abstract: Organoplatinum Chromophores for Application in High‐Performance Nonlinear Absorption Materials

AbstractReview: 81 refs.

Mechanism Insights into Second-Order Nonlinear Optical Responses of Anionic Metal Clusters

We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of two typical inorganic trinuclear anionic clusters, [MoCu2S4(SPh)2]2− and [Mo2CuS4]1−(edt)2(PPh3) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal–metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal–metal bonding strength, and the understanding will benefit to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means of the conscious tuning of metal–metal interactions and metal-core structures of inorganic polynuclear clusters.

Organoplatinum Chromophores for Application in High-Performance Nonlinear Absorption Materials

Chromophores and materials that exhibit nonlinear absorption over a broad spectrum and with high temporal dynamic range are of interest for application in materials engineering and biology. Recent work by a number of research groups has led to the development of a new family of organometallic chromophores and materials featuring interesting and useful nonlinear absorption properties. These systems contain the platinum acetylide moiety as a fundamental molecular unit, combined with delocalized, π-conjugated electron systems. These organometallic chromophores provide a unique combination of properties, such as negligible ground state absorption in the visible region, large spin-orbit coupling giving rise to high triplet excited state yield, triplet lifetime in the microsecond domain, high two-photon cross-section in the visible and near-infrared regions, and high triplet-triplet absorption cross-section in the visible and near-infrared region. This Spotlight on Application highlights recent developments in this area, combining background and review on nonlinear absorption in platinum acetylide chromophores and describing significant recent results from our own laboratory.

Substituent Effects on the Intramolecular Charge Transfer and Fluorescence of Bimetallic Platinum Complexes

An investigation of a series of platinum-containing organometallic complexes for the study of fluorescence phenomena in organometallic chromophores controlled by the intramolecular charge transfer (ICT) is presented in this work. We report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the substituent effects on the ICT and fluorescence emission. We demonstrate that the fluorescence maximum and lifetimes greatly depend on different substituents and the presence of bimetallic platinum donor. This work paves the way for an understanding of the fluorescence phenomena controlled by molecular ICT characters of these kinds of platinum-containing organometallic complexes.

Solvent effect on quadratic hyperpolarizability of 4-(dimethylamino-4′-stilbazole)tungsten pentacarbonyl: A revisit of mechanism for second-order response

The quadratic hyperpolarizability ( β) of 4-(dimethylamino-4′-stilbazole)tungsten pentacarbonyl (W(CO) 5DAS) organometallic chromophore has been studied by DFT/TDDFT methods. The intrinsical mechanism for the second-order response has been ascribed to the contribution from metal-to-ligand charge transfer. The consideration of the solvent effect quantitatively improves the consistency of the calculated data with the experimental data, and switches the β vec sign. The β vec value is remarkably sensitive to the polarized solvent and even exhibits the different mechanisms for the second-order response in gas and solution phases. The possibilities of using this intriguing effect in the perspective of a molecular switch device are evaluated.