Spin-polarized currents induced in antiferromagnetic polymer multilayered field-effect transistors.

A theoretical construction of an antiferromagnetic polymer multilayered field-effect transistor with polymers stretched between the source and drain contacts was undertaken. The model employed a quantum approach to the on-chain spin-charge distribution, which was self-consistently coupled with the charge distribution controlled by the gate voltage. Contrary to standard field-effect transistors, we found that the current firstly increased superlinearly with the drain voltage, then it achieved the maximum for drain voltages notably lower than the gate voltage, and after that, it decreased with the drain voltage with no saturation. Such effects were coupled with the formation of the current spin-polarization ratio, where the on-chain mobility of respective spin-polarized charges was significantly dependent on the applied drain voltage. These effects arise from competition among the antiferromagnetic coupling, the intra-site spin-dependent Coulomb interaction, and the applied drain and gate voltages, which strongly influence the on-chain spin-charge distribution, varying from an alternating spin configuration to a spin-polarized configuration at both ends of the chain. Substantial control over the magnitude of spin-polarized currents was achieved by manipulating gate and drain voltages, showcasing the feasibility of practical applications in spintronics.

Formation of spin-polarized current in antiferromagnetic polymer spintronic field-effect transistors.

We have theoretically investigated the feasibility of constructing a spintronic field-effect transistor with the active channel made of a polymer chain with the antiferromagnetic coupling oriented in the source-to-drain direction. We found two different device function regimes controlling the on-chain spin-charge carrier density by tuning the gate voltage. At higher charge carrier densities, the source-drain current linearly increases with decreasing charge carrier densities. In this regime, no polymer spin-polarized current is observed. Upon reaching a critical gate voltage, the current decreases with decreasing charge densities. It is accompanied by the formation of spin-polarized current, generated by an on-chain process, which can be related to spin-charge spatial distribution symmetry breaking caused either by an application of the source-to-drain voltage (higher spin polarization near the drain), or the breakdown of the Peierls dimerization near chain ends. Numerical simulation of the transistor characteristics suggests that the design of a polymer spintronic field-effect transistor is in principle feasible.

Gate voltage impact on charge mobility in end-on stacked conjugated oligomers.

We present a model of the charge transport in thin film organic field-effect transistors with the active channel made of linear conjugated chains stacked on the substrate with end-on-orientation. The transport was simulated in a box consisting of 25 polymer chains, in which the delocalized quantum orbital eigenstates of the on-chain hole distribution were calculated. The inter-chain charge transfer was solved semi-classically. The full self-consistent distribution of charge density and electric field was determined for various applied gate and source-drain voltages. We found that the dependence of charge mobility on gate voltage is not monotonic: it first increases with increasing gate voltage for a limited interval of the latter, otherwise it decreases with the gate voltage. Next, we found formation of the second resonant peak for higher gate voltages. The mobility dependence on the gate voltage confirmed that the current flowing through the active semiconductor layer should be described not only as the hole transfer between adjacent repeat units of the neighbouring chains, but also as the transfer of coherences among on-chain repeat units. The presented model can also give a new insight into the charge transport in organic field-effect transistors with a novel vertical architecture.

Effect of the substituent position on the electrochemical, optical and structural properties of donor-acceptor type acridone derivatives.

Three new donor-acceptor (D-A) compounds, positional isomers of phenoxazine-substituted acridone, namely 1-phenoxazine-N-hexylacridone (o-A), 2-phenoxazine-N-hexylacridone (m-A) and 3-phenoxazine-N-hexylacridone (p-A), were synthesized. The synthesized compounds showed interesting, isomerism-dependent electrochemistry. Their oxidation was reversible and their potential (given vs. Fc/Fc+) changed from 0.21 V for o-A to 0.36 V for p-A. In contrast, their reduction was irreversible, isomerism-independent and occurred at rather low potentials (ca. -2.25 to -2.28 V). The electrochemical results led to the following values of the ionization potentials (IPs) and electron affinities (EAs): 5.03 eV and -2.14 eV, 5.15 eV and -2.20 eV, and 5.20 eV and -2.28 eV for o-A, m-A and p-A, respectively. The experimentally obtained values were in very good agreement with those predicted by DFT calculations. All three isomers readily formed single crystals suitable for their structure determination. o-A and p-A crystallized in P1[combining macron] and P21/n space groups, respectively, with one molecule per asymmetric unit, while m-A crystallized in the P21/c space group with two molecules in the asymmetric unit accompanied by disordered solvent molecules. The UV-vis spectra of the studied compounds were isomerism and solvent independent, yielding absorption maxima in the vicinity of 400 nm. Their photoluminescence spectra, in turn, strongly depended on isomerism and the used solvent showing smaller Stokes shifts for the emission bands registered in toluene as compared to the corresponding bands measured in dichloromethane. The photoluminescence quantum yields (φ) were systematically higher for toluene solutions reaching the highest value of 20% for p-A. For all three isomers studied, stationary and time-resolved spectroscopic investigations carried out in toluene at different temperatures revealed spectral features indicating a contribution of thermally activated delayed fluorescence (TADF) to the observed spectroscopic behaviour. The measured photoluminescence quantum yields (φ) were higher for solid state films of pure compounds and for their dispersions in solid matrices (zeonex) than those recorded for toluene and dichloromethane solutions of the studied phenoxazine-N-hexylacridone isomers. The obtained experimental spectroscopic and structural data were confronted with theoretical predictions based on DFT calculations.

On the methodology of the determination of charge concentration dependent mobility from organic field-effect transistor characteristics.

We developed a new methodology for determining charge concentration dependent mobility from organic field-effect transistor (OFET) characteristics, applicable for semiconducting polymers with structural and energy disorder. We show that basic formulae recommended by the "IEEE Standard for Test Methods for the Characterization of Organic Transistors and Materials" for the determination of the field-effect mobility as obtained from the slope ISD1/2vs. VSG (in the saturation regime) or from the transconductance dISD/dVSG (in the linear regime) are not suitable for materials with concentration dependent charge carrier mobility. We propose alternative expressions, which can be directly analytically derived from the drift-diffusion equation with the mobility explicitly dependent on the charge concentration. This methodology for mobility determination was used for analysis of the experimental data obtained for a poly(3-hexylthiophene)-based OFET with the bottom gate-bottom SD electrode configuration.

Modelling of the charge carrier mobility in disordered linear polymer materials.

We introduced a molecular-scale description of disordered on-chain charge carrier states into a theoretical model of the charge carrier transport in polymer semiconductors. The presented model combines the quantum mechanical approach with a semi-classical solution of the inter-chain charge hopping. Our model takes into account the significant local anisotropy of the charge carrier mobility present in linear conjugated polymers. Contrary to the models based on the effective medium approximation, our approach allowed avoiding artefacts in the calculated concentration dependence of the mobility originated in its problematic configurational averaging. Monte Carlo numerical calculations show that, depending on the degree of the energetic and structural disorder, the charge carrier mobility increases significantly with increasing charge concentration due to trap filling. At high charge carrier concentrations, the effect of the energetic disorder disappears and the mobility decreases slightly due to the lower density of unoccupied states available for the hopping transport. It could explain the experimentally observed mobility degradation in organic field-effect transistors at high gate voltage.

Roles of octabutoxy substitution and J-aggregation in stabilization of the excited state in nickel phthalocyanine.

Nickel phthalocyanine (NiPc) complexes are known to show a rapid nonradiative deactivation of the photoexcited state through the internal conversion. This could be exploited in practical applications, such as photoprotection and photodynamic therapy. The butoxy substitution of NiPc plays an important role for drug delivery but also greatly influences its photophysics. We prepared novel peripherally substituted 2,3,9,10,16,17,23,24-octabutoxy nickel(II) phthalocyanine and characterized the deactivation pathway of its photoexcited state in solution by femtosecond transient absorption spectroscopy and quantum chemical calculations. We bring experimental evidence for the kinetic model, in which the photoexcitation evolves in two independent branches. In the first branch, assigned to the monomer, it undergoes ultrafast intersystem crossing to a triplet state, which subsequently decays to the ground state through a pathway involving lower-lying triplet states, with a ground-state recovery lifetime of 814 ps. It is about three-times longer than the lifetime published for unsubstituted NiPc. In the second branch, the photoexcitation decayed to a triplet state with an orders of magnitude longer lifetime, with the quantum yield of about 4%. This state showed spectral features of J-aggregates. These findings are important for the applications that rely on singlet oxygen formation or fast nonradiative deactivation of the excited state.

Naphthalene bisimides asymmetrically and symmetrically N-substituted with triarylamine--comparison of spectroscopic, electrochemical, electronic and self-assembly properties.

Two semiconducting naphthalene bisimides were comparatively studied: NBI-(TAA)(2), symmetrically N-substituted with triaryl amine and asymmetric NBI-TAA-Oc with triaryl amine and octyl N-substituents. Both compounds show very similar spectroscopic and redox properties but differ in their supramolecular organization. As evidenced by STM, in monolayers on HOPG they form ordered 2D structures, however of different packing patterns. NBI-(TAA)(2) does not form ordered 3D structures, yielding amorphous thin films whereas films of NBI-TAA-Oc are highly crystalline. DFT calculations predict the ionization potential (IP) of 5.22 eV and 5.18 eV for NBI-TAA-Oc and NBI-(TAA)(2), respectively, as well as the electron affinity values (EA) of -3.25 eV and -3.22 eV. These results are consistent with the cyclic voltammetry data which yield similar values of IP (5.20 eV and 5.19 eV) and somehow different values of EA (-3.80 eV and -3.83 eV). As judged from these data, both semiconductors should exhibit ambipolar behavior. Indeed, NBI-TAA-Oc is ambipolar, showing hole and electron mobilities of 4.5 × 10(-5) cm(2)/(V s) and of 2.6 × 10(-4) cm(2)/(V s), respectively, in the field effect transistor configuration. NBI-(TAA)(2) is not ambipolar and yields field effect only in the p-channel configuration. This different behavior is rationalized on the basis of structural factors.

Theoretical study on the protonation of cucurbit[7]uril.

By using quantum mechanical DFT calculations, the most probable structures of the cucurbit[7]urilH3O+ and cucur-bit[7]uril'(H3O+)2 cationic complex species were derived. In these two complexes having a plane symmetry, each of the considered H3O+ cations is bound by relatively strong hydrogen bonds to the corresponding carbonyl oxygens of the parent cucurbit[7]uril macrocycle.

Bambus[6]uril as a novel macrocyclic receptor for the nitrate anion.

By using quantum mechanical DFT calculations, the most probable structure of the bambus[6]uril x NO3(-) anionic complex species was derived. In this complex having C3 symmetry, the nitrate anion NO3(-), included in the macrocyclic cavity, is bound by twelve weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the considered NO3(-) ion.

Complexation of the ammonium cation with dibenzo-18-crown-6: extraction and DFT study.

From extraction experiments and gamma-activity measurements, the extraction constan corresponding to the equilibrium NH4(+)(aq) + 1*Na(+)(nb) <=> 1*NH4(+)(nb) + Na(+)(aq) taking place in the two-phase water - nitrobenzene system (1 = dibenzo-18-crown-6, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K(ex) (NH4(+),1*Na(+)) = -0.1 +/- 0.1. Further, the stability constant of the 1*NH4(+) complex species in water-saturated nitrobenzene was calculated for a temperature 25 degrees C as log beta (1*NH4(+)) = 5.7 +/- 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1*NH4(+) cationic complex was derived. In this complex, the "central" cation NH4(+) is bound by three strong linear hydrogen bonds to the three corresponding ethereal oxygen atoms of the parent crown ligand 1. The interaction energy of the resulting complex 1*NH4(+) was found to be -796.1 kJ/mol, confirming the formation of the considered complex species.

Extraction and DFT study on the complexation of Zn(2+) with beauvericin.

From extraction experiments and g-activity measurements, the exchange extraction constant corresponding to the equilibrium Zn2+(aq) + 1 . Sr2+(nb) <-> 1 . Zn2+(nb) + Sr2+(aq) taking place in the two-phase water-nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (Zn2+, 1 . Sr2+) = -0.3 ± 0.1. Further, the stability constant of the beauvericin - zinc complex (abbrev. 1 . Zn2+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log ßnb (1 . Zn2+) = 9.1 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1 . Zn2+ complex species was predicted.

In vitro assessment of alkylglyceryl-functionalized chitosan nanoparticles as permeating vectors for the blood-brain barrier.

A series of O-substituted alkylglyceryl chitosans with systematically varied alkyl chain length and degree of grafting has been employed for the formulation of aqueous nanoparticulate systems, which were in turn investigated for their effects on a modeled blood-brain-barrier system of mouse-brain endothelial cells. Barrier function measurements employing electric cell-substrate impedance sensing and analyses of tight junction-specific protein profiles have indicated that the alkylglyceryl-modified chitosan nanoparticles impact upon the integrity of the model blood-brain barrier, whereas confocal microscopy experiments have demonstrated the efficient cellular uptake and the perinuclear localization of these nanoparticles. The application of nanoparticles to the model blood-brain barrier effected an increase in its permeability, as demonstrated by following the transport of the tracer molecule fluorescein isothiocyanate.

Experimental and Theoretical Study on the Complexation of the Thallium Cation with Dibenzo-18-crown-6.

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Tl+(aq) + 1.Na+(nb) <-> 1.Tl+(nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (1 = dibenzo-18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex(Tl+, 1.Na+) = 2.1. Further, the stability constant of the complex 1.Tl+ in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log ßnb (1.Tl+) = 6.6. Finally, by using quantum mechanical DFT calculations, the most probable structure of the resulting complex 1.Tl+ was solved.

Experimental and theoretical study on the complexation of beauvericin with the ammonium cation.

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium NH4+(aq) + NaL+ (nb) <-> NH4L+(nb) + Na+ (aq) taking place in the two-phase water-nitrobenzene system (L = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (NH4+, NaL+) = 1.5 ± 0.1. Further, the stability constant of the NH4L+ complex in water-saturated nitrobenzene was calculated for a temperature of 25 °C as log ßnb (NH4L+) = 4.6 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the NH4L+ cationic complex species was derived. In this complex having C3 symmetry, the ammonium cation NH4+ is bound by three strong linear hydrogen bonds to the three corresponding oxygen atoms of the parent beauvericin ligand L. The interaction energy of the resulting complex NH4L+ was found to be -828.8 kJ/mol, confirming the formation of the considered complex NH4L+.

Complexation of the Silver Cation with Dibenzo-30-crown-10: Extraction and DFT Study.

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag+(aq) + 1.Cs+(nb) <-> 1.Ag+ (nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (1 = dibenzo-30-crown-10; aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex (Ag+, 1.Cs+) = -1.7 ± 0.1. Further, the stability constant of the complex 1.Ag+ in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log ßnb (1.Ag+) = 6.0 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the resulting complex 1.Ag+ was solved.

Extraction and DFT Study on the Complexation of the TRIS+ Cation with a Hexaarylbenzene-Based Receptor.

From extraction experiments and -activity measurements, the exchange extraction constant corresponding to the equilibrium TRIS+(aq) + 1.Cs+(nb) <-> 1.TRIS+(nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (TRIS+ = (HOCH2)3C-NH3+, 1 = hexaarylbenzene - based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (TRIS+, 1.Cs+) = -2.0 ± 0.1. Further, the stability constant of the hexaarylbenzene - based receptor .TRIS+ complex (abbrev. 1.TRIS+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C : log ßnb (1.TRIS+) = 6.0 ± 0.2. By using quantum mechanical calculations, the most probable structure of the 1.TRIS+ complex species was solved. In this complex having C3 symmetry, the cation TRIS+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation - π interaction.

D-A-D Compounds Combining Dithienopyrrole Donors and Acceptors of Increasing Electron-Withdrawing Capability: Synthesis, Spectroscopy, Electropolymerization, and Electrochromism.

Five D-π-A-π-D compounds consisting of the same donor unit (dithieno[3,2-b:2',3'-d]pyrrole, DTP), the same π-linker (2,5-thienylene), and different acceptors of increasing electron-withdrawing ability (1,3,4-thiadiazole (TD), benzo[c][1,2,5]thiadiazole (BTD), 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP), 1,2,4,5-tetrazine (TZ), and benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI)) were synthesized. DTP-TD, DTP-BTD, and DTP-DPP turned out to be interesting luminophores emitting either yellow (DTP-TD) or near-infrared (DTP-BTD and DTP-DPP) radiation in dichloromethane solutions. The emission bands were increasingly bathochromically shifted with increasing solvent polarity. Electrochemically determined electron affinities (|EA|s) were found to be strongly dependent on the nature of the acceptor changing from 2.86 to 3.84 eV for DTP-TD and DTP-NDI, respectively, while the ionization potential (IP) values varied only weakly. Experimental findings were strongly supported by theoretical calculations, which correctly predicted the observed solvent dependence of the emission spectra. Similarly, the calculated IP and EA values were in excellent agreement with the experiment. DTP-TD, DTP-BTD, DTP-TZ, and DTP-NDI could be electropolymerized to yield polymers of very narrow electrochemical band gap and characterized by redox states differing in color coordinates and lightness. Poly(DTP-NDI) and poly(DTP-TD) showed promising electrochromic behavior, not only providing a rich color palette in the visible but also exhibiting near-infrared (NIR) electrochromism.

Affinity capillary electrophoresis and density functional theory employed for the characterization of hexaarylbenzene-based receptor complexation with alkali metal ions.

In this study, affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations were combined to investigate non-covalent binding interactions between the hexaarylbenzene-based receptor (R) and alkali metal ions, Rb(+) and Cs(+) , in methanol. The apparent binding (stability) constants (K(b) ) of the complexes of receptor R with alkali metal ions in the methanolic medium were determined by ACE from the dependence of effective electrophoretic mobility of the receptor R on the concentration of Rb(+) and Cs(+) ions in the BGE using a non-linear regression analysis. The receptor R formed relatively strong complexes both with rubidium (log K(b) =4.04±0.21) and cesium ions (log K(b) =3.72±0.22). The structural characteristics of the above alkali metal ion complexes with the receptor R were described by ab initio density functional theory calculations. These calculations have shown that the studied cations bind to the receptor R because they synergistically interact with the polar ethereal fence and with the central benzene ring via cation-π interaction.

Affinity capillary electrophoresis and quantum mechanical calculations applied to the investigation of hexaarylbenzene-based receptor binding with lithium ion.

In this study, two complementary approaches, affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations, have been employed for quantitative characterization and structure elucidation of the complex between hexaarylbenzene (HAB)-based receptor R and lithium ion Li(+) . First, by means of ACE, the apparent binding constant of LiR(+) complex (K LiR +) in methanol was determined from the dependence of the effective electrophoretic mobilities of LiR(+) complex on the concentration of lithium ions in the 25 mM Tris/50 mM chloroacetate background electrolyte (BGE) using non-linear regression analysis. Prior to regression analysis, the effective electrophoretic mobilities of the LiR(+) complex were corrected to reference temperature 25 °C and constant ionic strength 25 mM. The apparent binding constant of the LiR(+) complex in the above methanolic BGE was evaluated as logK LiR + = 1.15±0.09. Second, the most probable structures of nonhydrated LiR(+) and hydrated LiR(+)·3H(2)O complexes were derived by DFT calculations. The optimized structure of the hydrated LiR(+)·3H(2)O complex was found to be more realistic than the nonhydrated LiR(+) complex because of the considerably higher binding energy of LiR(+)·3H(2)O complex (500.4 kJ/mol) as compared with LiR(+) complex (427.5 kJ/mol).