Photophysical and redox properties of new donor-acceptor-donor (DAD) compounds containing benzothiadiazole (A) and dimethyldihydroacridine (D) units: a combined experimental and theoretical study.

Four donor-acceptor-donor compounds consisting of 9,9-dimethyl-9,10-dihydroacridine donors differently linked to a benzothiadiazole acceptor were designed using DFT calculations and synthesized, namely 4,7-bis(4-(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (1), 4,7-bis(2,5-dimethyl-4-(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (2), 4,7-bis(3,5-di(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (3), and 4-(3,5-di(9,9-dimethyl-9,10-dihydroacridine)phenyl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (4). As predicted theoretically, all studied compounds were electrochemically active both in the reduction as well as in the oxidation modes. They underwent one electron quasi-reversible reduction. Oxidation of 1 and 2 involved a two electron process transforming them into dications and carrying out, in parallel, their dimerization. Oxidation of 3 and 4 resulted in their oligomerization (polymerization). The electrochemically determined ionisation potentials (IP) of 1-4 were similar, covering a narrow range of 5.28-5.33 eV and were consistent with DFT calculations. Larger differences were found for experimentally determined electron affinity (EA) values, being significantly lower for 2 (|EA| = 2.59 eV) as compared to 1, 3 and 4 whose |EA| values were higher by 0.15-0.25 eV, again consistent with DFT calculations. DFT calculations predict positive values of ΔE(S1-T1) for all compounds i.e. in the range of 0.18 eV to 0.43 eV for 1, 3 and 4 and a significantly lower value for 2 (0.06 eV), indicating a possible RISC process in this case. DFT calculations of ΔE(S1-T2) lead to negative and very small values for 2-4 implying a possible involvement of higher lying triplets in the generation of singlet excitons. The investigated derivatives exhibited fluorescence in the orange-red spectral range (550-770 nm) and were strongly dependent on the solvent polarity. The highest PLQY value of 37% was measured for 1 in toluene. The PLQY values significantly improved upon deoxygenation of the studied solutions. Solid state samples also exhibited higher PLQY values as compared to those determined for DCM solutions. These findings were rationalized by partial suppression of the vibrationally induced emission quenching in the solid state due to the intermolecular interaction confinement.

The importance of anchoring ligands of binuclear sensitizers on electron transfer processes and photovoltaic action in dye-sensitized solar cells.

The relatively low photon-to-current conversion efficiency of dye-sensitized solar cells is their major drawback limiting widespread application. Light harvesting, followed by a series of electron transfer processes, is the critical step in photocurrent generation. An in-depth understanding and fine optimization of those processes are crucial to enhance cell performance. In this work, we synthesize two new bi-ruthenium sensitizers with extended anchoring ligands to gain insight into underlying processes determining photovoltaic action mechanisms. The structure of the compounds has been confirmed, and their properties have been thoroughly examined by various techniques such as NMR, IR, elemental analysis UV-Vis, cyclic voltammetry, and electroabsorption. The experimental characterization has been supported and developed via extensive quantum-chemical calculations, giving a broad view of the presented molecules' properties. Finally, the DSSC devices have been assembled utilizing obtained dyes. The photovoltaic and EIS measurements, combined with performed calculations and fundamental dyes characterization, unraveled an intramolecular electron transfer as an initial step of the electron injection process at the dye/semiconductor interface. The overall photovoltaic action mechanism has been discussed. Our study demonstrates the significance of the anchoring group architecture in the molecular design of new sensitizers for DSSC applications.

Molecular Dynamics Simulation of Hydrogels Based on Phosphorylcholine-Containing Copolymers for Soft Contact Lens Applications.

The structure and dynamics of copolymers of 2-hydroxyethyl methacrylate (HEMA) with 2-methacryloyloxyethyl phosphorylcholine (MPC) were studied by molecular dynamics simulations. In total, 20 systems were analyzed. They differed in numerical fractions of the MPC in the copolymer chain, equal to 0.26 and 0.74, in the sequence of mers, block and random, and the water content, from 0 to 60% by mass. HEMA side chains proved relatively rigid and stable in all considered configurations. MPC side chains, in contrast, were mobile and flexible. Water substantially influenced their dynamics. The copolymer swelling caused by water resulted in diffusion channels, pronounced in highly hydrated systems. Water in the hydrates existed in two states: those that bond to the polymer chain and the free one; the latter was similar to bulk water but with a lower self-diffusion coefficient. The results proved that molecular dynamics simulations could facilitate the preliminary selection of the polymer materials for specific purposes before their synthesis.

Computational and Experimental Study of Nonlinear Optical Susceptibilities of Composite Materials Based on PVK Polymer Matrix and Benzonitrile Derivatives.

Theoretical and experimental investigations of the linear and nonlinear optical properties of composite materials based on the (Z)-4-(1-cyano-2-(5-methylfuran-2-yl)vinyl)benzonitrile molecule named as A, the (Z)-4-(2-(benzofuran-2-yl)-1-cyanovinyl)benzonitrile named as B and the (Z)-4-(2-(4-(9H-carbazol-9-yl)phenyl)-1-cyanovinyl)benzonitrile molecule named as C embedded into poly(1-vinylcarbazole) (PVK) polymer matrix were performed. The electronic and optical properties of A, B, and C molecules in a vacuum and PVK were calculated. The guest-host polymer structures for A, B, and C molecules in PVK were modeled using molecular dynamics simulations. The spatial distribution of chromophores in the polymer matrix was investigated using the intermolecular radial distribution (RDF) function. The reorientation of A, B, and C molecules under the influence of the external electric field was investigated by measuring the time-dependent arrangement of the angle between the dipole moment of the chromophore and the external electric field. The polarizabilities and hyperpolarizabilities of tested compounds have been calculated applying the DFT/B3LYP functional. The second- and third-order nonlinear optical properties of the molecule/PVK thin film guest-host systems were investigated by the Maker fringes technique in the picosecond regime at the fundamental wavelength of 1064 nm. The experimental results were confirmed and explained with theoretical simulations and were found to be in good agreement. The modeling of the composites in volumetric and thin-film form explains the poling phenomena caused by the external electric field occurring with the confinement effect.

Electronic States of Tris(bipyridine) Ruthenium(II) Complexes in Neat Solid Films Investigated by Electroabsorption Spectroscopy.

We present the electric field-induced absorption (electroabsorption, EA) spectra of the solid neat films of tris(bipyridine) Ru(II) complexes, which were recently functionalized in our group as photosensitizers in dye-sensitized solar cells, and we compare them with the results obtained for an archetypal [Ru(bpy)3]2+ ion (RBY). We argue that it is difficult to establish a unique set of molecular parameter values by discrete parametrization of the EA spectra under the Liptay formalism for non-degenerate excited states. Therefore, the experimental EA spectra are compared with the spectra computed by the TDDFT (time-dependent density-functional theory) method, which for the first time explains the mechanism of electroabsorption in tris(bipyridine) Ru complexes without any additional assumptions about the spectral lineshape of the EA signal. We have shown that the main EA feature, in a form close to the absorption second derivative observed in the spectral range of the first MLCT (metal-to-ligand charge transfer) absorption band in Ru(bpy)3(PF6)2, can be attributed to a delocalized and orbitally degenerate excited state. This result may have key implications for the EA mechanism in RBY-based systems that exhibit similar EA spectra due to the robust nature of MLCT electronic states in such systems.

How Can the Introduction of Zr4+ Ions into TiO2 Nanomaterial Impact the DSSC Photoconversion Efficiency? A Comprehensive Theoretical and Experimental Consideration.

A series of pure and doped TiO2 nanomaterials with different Zr4+ ions content have been synthesized by the simple sol-gel method. Both types of materials (nanopowders and nanofilms scratched off of the working electrode's surface) have been characterized in detail by XRD, TEM, and Raman techniques. Inserting dopant ions into the TiO2 structure has resulted in inhibition of crystal growth and prevention of phase transformation. The role of Zr4+ ions in this process was explained by performing computer simulations. The three structures such as pure anatase, Zr-doped TiO2, and tetragonal ZrO2 have been investigated using density functional theory extended by Hubbard correction. The computational calculations correlate well with experimental results. Formation of defects and broadening of energy bandgap in defected Zr-doped materials have been confirmed. It turned out that the oxygen vacancies with substituting Zr4+ ions in TiO2 structure have a positive influence on the performance of dye-sensitized solar cells. The overall photoconversion efficiency enhancement up to 8.63% by introducing 3.7% Zr4+ ions into the TiO2 has been confirmed by I-V curves, EIS, and IPCE measurements. Such efficiency of DSSC utilizing the working electrode made by Zr4+ ions substituted into TiO2 material lattice has been for the first time reported.

A study of the effect of X-ray irradiation on the structure of Narafilcon A biopolymer soft contact lenses.

BACKGROUND: The effects of external factors such as X-ray irradiation on the structure and physical properties of contact lenses are very important for both the patients using contact lenses and medical personnel. OBJECTIVES: The aim of the study was to investigate the effect of X-rays on the structure of Narafilcon A silicone-hydrogel contact lenses. MATERIAL AND METHODS: In order to study the structural changes caused by X-rays in Narafilcon A polymer contact lenses, the following spectroscopy methods were used: positron annihilation lifetime spectroscopy (PALS), Fourier transform middle infrared spectroscopy (FTIR) and Raman spectroscopy (RS). Irradiation of the investigated sample was carried out using an Elekta Synergy accelerator. The contact lenses were irradiated with the following total doses of X-rays: 0.05 Gy, 0.5 Gy, 0.8 Gy, and 1.0 Gy. RESULTS: The PALS measurements showed that X-ray irradiation caused slight changes in the size of the free volume and the fractional free volume in the structure of the polymer contact lenses examined. However, the FTIR and RS measurements showed that X-rays did not break the monomer bonds in the polymeric structure of the sample. CONCLUSIONS: The changes revealed by the PALS method may be related to possible displacement of monomer chains, resulting in changes in the dimensions and numbers of free volumes. The finding that X-ray radiation does not affect or damage polymer bonds can in the future contribute to the use of X-ray and gamma radiation to sterilize contact lenses.

Optical and vibrational properties of phosphorylcholine-based contact lenses-Experimental and theoretical investigations.

The Raman, MIR and UV-vis spectroscopy have been used to characterize Omafilcon A material constructing the one of the Proclear family contact lenses. The Omafilcon A is hydrogel material composed of 2-hydroxyethyl methacrylate (HEMA) and 2-methacryloyloxyethyl phosphorylcholine (PC) polymers crosslinked with ethyleneglycol dimethacrylate (EGDMA). Vibrational and electronic properties of the Omafilcon A material were also investigated by quantum chemical calculations. Experimentally obtained Raman, MIR and optical spectra were compared to the theoretical ones calculated applying RHF and DFT methodology. The quantum chemical calculations were performed for isolated monomers of lenses compounds as well as for their dimers and trimers to elucidate the effect of Omafilcon A polymerization and the role of an individual components.

Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces.

The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.

Comparison of Occurrence of Free Volumes for Rigid Gas Permeable and Soft Contact Lenses.

BACKGROUND: The polymeric materials: hydrogel, silicone--hydrogel and methacrylic acid are used in ophthalmology for the manufacture of contact lenses. It is important to research the structure of these materials, mainly the prevalence of free volumes. OBJECTIVES: The study has been conducted in order to comparison the presence of free volume gaps in the structure of the polymer soft contact lenses: Etafilcon A (hydrogel), Narafilcon A (silicone-hydrogel) and the polymer rigid gas permeable (RGP) contact lens (Fluor-Silicon-Methacrylat-Copolymer). In addition, to demonstrate differences in the occurrence of free volumes between types of represented contact lenses. MATERIAL AND METHODS: Three types of polymer contact lenses were used as materials: Etafilcon A, Narafilcon A and Fluor-Silicon-Methacrylat-Copolymer. The study was done by means of positron annihilation lifetime spectroscopy (PALS). RESULTS: As a result of the performed measurements, a graphical curve resulted which describes the relationship between the number of the annihilation acts in the time function. Significant changes were observed in the ortho-positronium long life component τ3 and their intensities between the examined polymer contact lenses. CONCLUSIONS: The conducted study using the Tao-Eldrup model indicates the presence of free volume holes in all research materials. There is a clear difference in the free volume sizes and their fractions between measured contact lenses are connected with oxygen permeability in these lenses. The results lead to the following connection: contact lenses of higher oxygen permeability coefficients and a water content of less, have more and larger free volumes than contact lenses of less oxygen permeability coefficient.

First principle calculations of the electronic and vibrational properties of the 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole molecule.

Results of first principle quantum chemical calculations of electronic and vibrational properties of the push-pull 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecule are reported and discussed. The structure of DCNP was optimized with HF/6-311G methodology and found to be planar. On the basis of obtained geometry, infrared absorption and Raman spectra were computed within the HF/6-311++G** formalism. They allow to conclude that the changes of molecule dipole moment and variation of its polarizability appear at the same vibrational mode and affect the optical properties of the DCNP. Four different methodologies: time-dependent HF and time-dependent DFT method with B3LYP, LC-BLYP, and CAM-B3LYP potentials were used to compute the optical absorption spectra of DCNP. Influence of solvent on molecular electronic structure was studied within the C-PCM model. It predicts the DFT/B3LYP methodology as the best one to compute the NLO properties of the DCNP. The computed HOMO and LUMO orbitals show evidence that the ground state of the molecule is located at its aromatic part. The discussion of charge transfer during the excitation process for the transition S0-S1 was performed. The charge transfer parameter calculated in vacuum and in solvent gives the evidence that the solvent environment weakly enhance the molecular charge transfer. It confirms the tendency of an occurrence of the intermolecular charge transfer in DCNP which is crucial for its hyperpolarizability magnitude. It was proved that the second-order susceptibility corresponding to SHG may be calculated for host-guest polymer/DCNP composite using the simple oriented gas model and the rigorous local field approach should not necessarily be applied.

Solid-state NMR correlation experiments and distance measurements in paramagnetic metalorganics exemplified by Cu-cyclam.

We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the (13)C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the (1)H signals was done by means of (1)H-(13)C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct (1)H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic (1)H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording (1)H-(1)H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the (1)H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu-cyclam by means of (13)CR2 relaxation experiments combined with the electronic relaxation determined by EPR.