Understanding the Electronic Structures and Absorption Properties of Porphyrin Sensitizers YD2 and YD2-o-C8 for Dye-Sensitized Solar Cells

The electronic structures and excitation properties of dye sensitizers determine the photon-to-current conversion efficiency of dye sensitized solar cells (DSSCs). In order to understand the different performance of porphyrin dye sensitizers YD2 and YD2-o-C8 in DSSC, their geometries and electronic structures have been studied using density functional theory (DFT), and the electronic absorption properties have been investigated via time-dependent DFT (TDDFT) with polarizable continuum model for solvent effects. The geometrical parameters indicate that YD2 and YD2-o-C8 have similar conjugate length and charge transfer (CT) distance. According to the experimental spectra, the HSE06 functional in TDDFT is the most suitable functional for describing the Q and B absorption bands of porphyrins. The transition configurations and molecular orbital analysis suggest that the diarylamino groups are major chromophores for effective CT excitations (ECTE), and therefore act as electron donor in photon-induced electron injection in DSSCs. The analysis of excited states properties and the free energy changes for electron injection support that the better performance of YD2-o-C8 in DSSCs result from the more excited states with ECTE character and the larger absolute value of free energy change for electron injection.     

Pharmacological Activities of Ruthenium Complexes Related to Their NO Scavenging Properties

Angiogenesis is considered responsible for the growth of primary tumours and of their metastases. With the present study, the effects of three ruthenium compounds, potassiumchlorido (ethylendiamminotetraacetate)rutenate(III) (RuEDTA), sodium (bis-indazole)tetrachloro-ruthenate(III), Na[trans-RuCl₄Ind₂] (KP1339) and trans-imidazoledimethylsulphoxidetetrachloro-ruthenate (NAMI-A), are studied in vitro in models mimicking the angiogenic process. The ruthenium compounds reduced the production and the release of nitrosyls from either healthy macrophages and immortalized EA.hy926 endothelial cells. The effects of NAMI-A are qualitatively similar and sometimes quantitatively superior to those of RuEDTA and KP1339. NAMI-A reduces the production and release of nitric oxide (NO) by the EA.hy926 endothelial cells and correspondingly inhibits their invasive ability; it also strongly inhibits the angiogenesis in matrigel sponges implanted subcutaneously in healthy mice. Taken together, these data support the anti-angiogenic activity of the tested ruthenium compounds and they contribute to explain the selective activity of NAMI-A against solid tumour metastases, the tumour compartment on which angiogenesis is strongly involved. This anti-angiogenic effect may also contribute to the inhibition of the release of metastatic cells from the primary tumour. Investigations on the anti-angiogenic effects of NAMI-A at this level will increase knowledge of its pharmacological properties and it will give a further impulse to the development of this class of innovative metal-based drugs.     

Passivating ligand and solvent contributions to the electronic properties of semiconductor nanocrystals

We examine in detail the impact of passivating ligands (i.e., amines, phosphines, phosphine oxides and pyridines) on the electronic and optical spectra of Cd(33)Se(33) quantum dots (QDs) using density functional theory (DFT) and time-dependent DFT (TDDFT) quantum-chemical methodologies. Most ligand orbitals are found deep inside in the valence and conduction bands of the QD, with pyridine being an exception by introducing new states close to the conduction band edge. Importantly, all ligands contribute states which are highly delocalized over both the QD surface and ligands, forming hybridized orbitals rather than ligand-localized trap states. In contrast, the states close to the band gap are delocalized over the QD atoms only and define the lower energy absorption spectra. The random detachment of one of ligands from the QD surface results in the appearance of a highly localized unoccupied state inside the energy gap of the QD. Such changes in the electronic structure are correlated with the respective QD-ligand binding energy and steric ligand-ligand interactions. Polar solvent significantly reduces both effects leading to delocalization and stabilization of the surface states. Thus, trap and surface states are substantially eliminated by the solvent. Polar solvent also blue-shifts (e.g., 0.3-0.4 eV in acetonitrile) the calculated absorption spectra. This shift increases with an increase of the dielectric constant of the solvent. We also found that the approximate single-particle Kohn-Sham (KS) approach is adequate for calculating the absorption spectra of the ligated QDs. Besides a systematic blue-shift, the KS spectra are in very good agreement with their respective counterparts calculated with the more accurate TDDFT method.     

In situ FTIR study of photocatalytic NO reaction on photocatalysts under UV irradiation

The photocatalytic reaction of nitric oxide (NO) on TiO₂ and transition metal-loaded M (Cu, V, and Cr)/TiO₂ catalysts was studied using in situ FTIR spectroscopy under UV irradiation. TiO₂ and M/TiO₂ catalysts were prepared by the sol–gel method via controlled hydrolysis of titanium (IV) butoxide. Copper, vanadium, or chromium was loaded onto TiO₂ during the sol–gel procedure. After treatment at 500 °C under air flow, a large amount of surface peroxo species and OH groups were detected on the TiO₂ and M/TiO₂ catalysts. Nitric oxide was adsorbed on TiO₂ and M/TiO₂ in the form of bidentate nitrites and nitrates by reacting with OH groups, peroxo, or MO species. In addition, NO can also be adsorbed on Mⁿ⁺ in the form of nitrosyls. Under UV irradiation, bidentate nitrite was oxidized to either monodentate or bidentate nitrate. Such oxidation was suggested to be induced by superoxo species generated by oxidizing peroxo species via photogenerated holes. The existence of nitrosyls deferred the oxidation of nitrites to nitrates due to the prior oxidation of nitrosyls by superoxo. The XRD and UV–vis spectra showed that the structures and the abilities of absorbing UV light of all catalysts were not influenced by the photocatalytic NO reaction. Possible mechanisms were proposed for the photocatalytic NO oxidation on TiO₂ and M/TiO₂ based on the intermediates found from the in situ FTIR study.     

Novel drug delivery system for photoinduced nitric oxide (NO) delivery

A hybrid material (AB-1) was obtained by immobilizing photolabile ruthenium nitrosyl complex [Ru(L^SBH)(PPh₃)₂(NO)Cl](ClO₄) (1) into alginate polymer. A controlled release of nitric oxide was observed when a suspension of AB-1 was exposed to visible light. The amount of photoreleased NO from polymeric hybrid material was estimated using Griess reagent assay.     

分子光开关钌配合物[Ru（phen）2（phehat）]^2＋的光谱研究

运用TDDFT方法,分子光开关钌配合物[Ru（phen）2（phehat）]^2＋的UV—Vis光谱得以计算和理论解释。计算表明在水溶液环境下对钌配合物进行计算,实验结果和计算结果一致。而且,溶液条件下计算的UV-Vis光谱的结果能较好的指认该配合物实验光谱的^1MLCT和^1LLCT性质。     

Binding and Docking Interactions of NO,CO and O2 in Heme Proteins as Probed by Density Functional Theory

Dynamics and reactivity in heme proteins include direct and indirect interactions of the ligands/substrates like CO, NO and O₂ with the environment. Direct electrostatic interactions result from amino acid side chains in the inner cavities and/or metal coordination in the active site, whereas indirect interactions result by ligands in the same coordination sphere. Interactions play a crucial role in stabilizing transition states in catalysis or altering ligation chemistry. We have probed, by Density Functional Theory (DFT), the perturbation degree in the stretching vibrational frequencies of CO, NO and O₂ molecules in the presence of electrostatic interactions or hydrogen bonds, under conditions simulating the inner cavities. Moreover, we have studied the vibrational characteristics of the heme bound form of the CO and NO ligands by altering the chemistry of the proximal to the heme ligand. CO, NO and O₂ molecules are highly polarizable exerting vibrational shifts up to 80, 200 and 120 cm⁻¹, respectively, compared to the non-interacting ligand. The importance of Density Functional Theory (DFT) methodology in the investigation of the heme-ligand-protein interactions is also addressed.     

Fluorene-based organic dyes containing acetylene linkage for dye-sensitized solar cells

New organic dyes based on diphenylaminofluorene donors, cyanoacrylic acid acceptors and either ethynylbenzene or ethynylthiophene π-spacers have been synthesized and characterized as sensitizers for dye-sensitized solar cells. The dye with thiophene in the conjugation pathway exhibited longer wavelength absorption due to the significant lowering of the LUMO level when compared to the phenyl analog. However, the dye with the phenylacetylene linker displayed promising DSSC characteristics such as short circuit current, open circuit voltage and fill factor indicative of efficient charge generation and injection. The solvatochromic behavior of the dyes were examined in solvents of different polarity and found to exhibit negative solvatochromism of the fluorescence emission suggestive of a nonpolar solvent stabilized excited state with a significant structural reorganization. The TDDFT computations were used to explain the optical properties of the dyes.     

Synthesis of Schiff Base‐Ruthenium Complexes and Their Applications in Catalytic Processes

The synthesis of various Schiff base mononuclear and binuclear ruthenium complexes, whose additional ligands around the metal core have been selected from an array of motifs, is described. These types of ruthenium complexes, conveniently prepared from commonly available ruthenium sources, are rather stable, display good tolerance towards diverse organic functionalities and also to air and moisture. Remarkably, they exhibit a high activity and chemoselectivity in a variety of catalytic processes such as ring‐closing metathesis (RCM), Kharasch addition, alkyne dimerization, enol ester synthesis, ring‐opening metathesis polymerization (ROMP) and atom‐transfer radical polymerization (ATRP). This review covers both homogeneous and heterogeneous hybrid Schiff base‐ruthenium complexes.     

NO–NH3 coadsorption on vanadia/titania catalysts: determination of the reduction degree of vanadium

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) has been used to study NH₃ and NO adsorption over a 15% w/w vanadia/titania catalyst. NH₃ is adsorbed as coordinate NH₃ and NH₄⁺ species over the oxidised catalyst, leading to the reduction of the vanadia surface. At 300°C, adsorbed nitrosyls species are detected, suggesting that the oxidation of gaseous or adsorbed ammonia species takes place over the V=O sites. Coadsorption experiments show that NO is able to reoxidise about the 57% of the reduced V=O groups, resulting in N₂, according to a NO+V_□→1/2N₂+V=O reaction. On the other hand, NO is only adsorbed over vanadia reduced surfaces. The measure of the area of the 2ν(V=O) bands results in an estimate of the oxidation state of vanadium. From this estimate it can be concluded that nitrosyls species are adsorbed on the catalyst surface for vanadium atoms having an oxidation state ranging from +4 to +3.1.     

Triphenylamine-based organic dyes containing benzimidazole derivatives for dye-sensitized solar cells

The synthesis and application to dye-sensitized solar cells of two new triphenylamine-based organic dyes containing benzimidazole derivatives as secondary donors together with a simple triphenylamine derived dye for the purpose of comparison is reported. The photophysical and electrochemical properties of the dyes were investigated by UV–vis spectroscopy and cyclic voltammetry. The introduction of benzimidazole derivatives in the phenyl ring of the triphenylamine core increases the molar extinction coefficients and λ_max because of the extension of the π-conjugation structures of the dyes. Overall conversion efficiencies of ∼2.5% under full sunlight (AM 1.5G, 100 mW cm⁻²) irradiation were obtained for DSSCs based on these new dyes, under the same conditions, the reference dye and di-tetrabutylammonium cis-bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) (N719) gave overall conversion efficiencies of 1.23% and 5.61%, respectively. Our findings demonstrate that the introduction of benzimidazole derivatives as secondary donors in triphenylamine-based dye can improve their photovoltaic performance compared to the unsubstituted reference dye in DSSCs.     

Ruthenium(II) and Platinum(II) Complexes with Biologically Active Aminoflavone Ligands Exhibit In Vitro Anticancer Activity

Continuing our studies on the mechanisms underlying the cytotoxicity of potential drugs, we have described several aspects of the in vitro anticancer activity of ruthenium(II) and platinum(II) complexes with bioactive, synthetic aminoflavone ligands. We examined the mechanism of proapoptotic activity of cis-dichlorobis(3-imino-2-methoxyflavanone)ruthenium(II), cis-dichlorobis(3-imino-2-ethoxyflavanone)ruthenium(II), and trans-dichlorobis(3-aminoflavone)platinum(II). Cisplatin was used as a reference compound. The cytotoxicity was investigated by MTT assay. The mechanism of proapoptotic activity of the tested compounds was investigated by evaluation of caspase-8 activity, cytometric analysis of annexin-V positive cells, and mitochondrial potential loss measurement. The results showed that ruthenium compounds break partially or completely the cisplatin resistance by activating the caspase 8-dependent apoptosis pathway and loss of mitochondrial membrane potential. Platinum compounds also have a cytostatic effect, but their action requires more exposure time. Potential mechanisms underlying drug resistance in the two pairs of cancer cell lines were investigated: total glutathione content, P-glycoprotein activity, and differences in the activity of DNA repair induced by nucleotide excision. Results showed that cisplatin-resistant cells have elevated glutathione levels relative to sensitive cells. Moreover, they indicated the mechanisms enabling cells to avoid apoptosis caused by DNA damage. Pg-P activity has no effect on the development of cisplatin resistance in the cell lines described.     

Metalloporphyrin-NO bonding: building bridges with organometallic chemistry

DFT calculations in our laboratory and elsewhere have elucidated fundamental aspects of the structure and bonding of a variety of metalloporphyrin-diatomic complexes, including the biologically important heme CO, NO, and O(2) complexes. We have also studied some more exotic species such as metalloporphyrin-dinitrosyl, -dialkyl, and -diaryl complexes. In the course of this research, we discovered a number of unexpected similarities (isolobal analogies) between the bonding in metalloporphyrin-NO and organometallic compounds. Equally important, DFT calculations have played a significant role in advancing our understanding of selective diatomic ligand binding by heme proteins.     

Chemical Activation in Blood Serum and Human Cell Culture: Improved Ruthenium Complex for Catalytic Uncaging of Alloc‐Protected Amines

Chemical (as opposed to light‐induced) activation of caged molecules is a rapidly advancing approach to trigger biological processes. We previously introduced the ruthenium‐catalyzed release of allyloxycarbonyl (alloc)‐protected amines in human cells. A restriction of this and all other methods is the limited lifetime of the catalyst, thus hampering meaningful applications. In this study, we addressed this problem with the development of a new generation of ruthenium complexes for the uncaging of alloc‐protected amines with superior catalytic activity. Under biologically relevant conditions, we achieved a turnover number >300, a reaction rate of 580 m ^?1 s^?1, and we observed high activity in blood serum. Furthermore, alloc‐protected doxorubicin, as an anticancer prodrug, could be activated in human cell culture and induced apoptosis with a single low dose (1 μm ) of the new catalyst.     

Ag nanocrystal as a promoter for carbon nanotube-based room-temperature gas sensors

We have investigated the room-temperature sensing enhancement of Ag nanoparticles (NPs) for multiwalled carbon nanotube (MWCNT)-based gas sensors using electrical measurements, in situ infrared (IR) microspectroscopy, and density functional theory (DFT) calculations. Multiple hybrid nanosensors with structures of MWCNTs/SnO(2)/Ag and MWCNTs/Ag have been synthesized using a process that combines a simple mini-arc plasma with electrostatic force directed assembly, and characterized by electron microscopy techniques. Ag NPs were found to enhance the sensing behavior through the "electronic sensitization" mechanism. In contrast to sensors based on bare MWCNTs and MWCNTs/SnO(2), sensors with Ag NPs show not only higher sensitivity and faster response to NO(2) but also significantly enhanced sensitivity to NH(3). Our DFT calculations indicate that the increased sensitivity to NO(2) is attributed to the formation of a NO(3) complex with oxygen on the Ag surface accompanying a charge rearrangement and a net electron transfer from the hybrid to NO(2). The significant response to NH(3) is predicted to arise because NH(3) is attracted to hollow sites on the oxidized Ag surface with the H atoms pointing towards Ag atoms and electron donation from H to the hybrid sensor.     

Hybrids as NO Donors

Cinnamic acid and its derivatives have been studied for a variety of biological properties, including anti-inflammatory, antioxidant, anticancer, antihypertensive, and antibacterial. Many hybrids of cinnamic derivatives with other bioactive molecules have been synthesized and evaluated as nitric oxide (NO) donors. Since NO plays a significant role in various biological processes, including vasodilation, inflammation, and neurotransmission, NO donor groups are incorporated into the structures of already-known bioactive molecules to enhance their biological properties. In this review, we present cinnamic hybrids with NO-donating ability useful in the treatment of several diseases.     

Electronic structure and spectral properties of the triarylamine-dithienosilole dyes for efficient organic solar cells

The recently synthesized high-performance triarylamine dyes with the dithienosilole π-conjugated spacer for efficient organic solar cells are calculated at the density functional theory (DFT) level with the Bader approach for the quantum theory of atoms in molecule (QTAIM) analysis. The presence of stabilizing intramolecular hydrogen bonds and Van der Waals interactions in the dye molecules is predicted and the energies of these interactions are estimated. The electronic bands nature in absorption spectra of the dyes is determined by the time-dependent DFT calculations with a linear response methodology using B3LYP and BMK hybrid functionals. Relations between incident light absorption intensity in the first long-wavelength band of the dye, its polarization, HOMO-LUMO orbital nature and the driving force of electron injection to the semiconductor are discussed.     

The Effect of Number of Porphyrin Polymer Units on Bandgap for ππ* Conjugation and Charge Transfer System Based on Simulation

This paper discusses the effect of number of units on bandgap for conjugation versus charge transfer system by using a conjugated polymer ([Zn])_n and an unconjugated planar push–pull one (AQ–[Zn])_n built upon 2,3-anthraquinone and bis(ethynyl)zinc(II)porphyrin. They are supported by DFT and TDDFT calculations, along with some experimental data. The position of the Q-bands is highly adjustable due to the presence of the twisted conformations in ([Zn])_n chain.     

功能性钌配合物[Ru(phen)_2(mdpz)]~(2+)的电子吸收光谱研究

运用含时密度泛函(TDDFT)方法,对功能性钌配合物[Ru(phen)2(mdpz)]2+的UV-Vis光谱进行计算和理论解释。计算结果表明在乙氰溶液环境下的计算结果与实验结果符合较好。并且,乙氰溶液条件下计算的UV-Vis光谱的结果能较好的指认该配合物实验光谱的1MLCT和1LLCT性质。     

Diazobenzo[a]fluorene derivatives as visible photosensitizers for free radical polymerization

Several benzophenazine dyes containing a diazobenzo[a]fluorene moiety have been synthesized and characterized by ¹H NMR spectroscopy and mass spectrometry (CI MS). The spectroscopic and electrochemical properties of these dyes were examined. These compounds were evaluated as potential light absorbing chromophores for free radical polymerization. The results are discussed on the basis of the free energy change for electron transfer from the diazobenzo[a]fluorene dyes to the electron donors/acceptors. The kinetic studies of the photoinitiated polymerization of trimethylolpropane triacrylate (TMPTA) using electron donors, such as phenylthioacetic acid, phenoxyacetic acid, N-phenylglycine and ethyl 4-N,N-dimethylaminobenzoate, and electron acceptors, such as 1-methoxy-4-phenylpyridinium tetrafluoroborate and 1-ethoxy-2-methylpyridinium hexafluorophosphate, have shown that these dyes are efficient photoinitiators for free radical polymerization in visible light. The heavy atoms present in the chemical structure may lead to excited triplet states within the dye facilitating electron transfer from these states.