Well designed iridium-phosphinite complexes: Biological assays, electrochemical behavior and density functional theory calculations.

Mononuclear phosphinite Iridium complexes based on ferrocene group have been prepared and characterized by various spectroscopic techniques. The complexes were subjected to cyclic voltammetry studies in order to determine the energies of HOMO and LUMO levels and to estimate their electrochemical and some electronic properties. Organic complex-based memory substrates were immobilized using TiO2-modified ITO electrodes, and the memory functions of phosphinite-based organic complexes were verified by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). Extensive theoretical and experimental investigations were directed to gain a more profound understanding of the chemical descriptors and the diverse electronic transitions taking place within the iridium complexes, as well as their electrochemical characteristics. The quantum chemical calculations were carried out for the iridium complexes at the DFT/CAM-B3LYP level of theory in the gas phase. Furthermore, the antioxidant, antimicrobial, DNA binding, and DNA cleavage activities of the complexes were tested. Complex 2 exhibited the highest radical scavenging activity (67.5 ± 2.24 %) at 200.0 mg/L concentration. It was observed that the complexes formed an inhibition zone in the range of 8-15 mm against Gram + bacteria and in the range of 0-13 mm against Gram - bacteria. The agarose gel electrophoresis method was used to determine the DNA binding and DNA cleavage activities of the complexes. All of the tested complexes had DNA binding activity; however, complexes 1, 2, and 8 showed better binding activity than the others.

Exploring the potential of anthracene derivatives as fluorescence emitters for biomedical applications.

Two novel anthracene derivatives were synthesized, and detailed photo-physical and biological investigations were carried out using a variety of spectroscopy techniques. The effect of cyano (-CN) substitution was found to be effective to alter the charge population and frontier orbital energy levels via Density Functional Theory (DFT) calculations. Particularly, the introduction of styryl and triphenylamine groups attached to the anthracene core helped to increase the conjugation relative to the anthracene moiety. The results revealed that the molecules have intramolecular charge transfer (ICT) properties, occurring from the electron donating triphenylamine to the electron accepting anthracene moiety in solutions. In addition, the photo-physical properties are strongly cyano-dependent, where the cyano-substituted (E/Z)-(2-anthracen-9-yl)-3-(4'-(diphenylamino)biphenyl-4yl)acrylonitrile molecule showed stronger electron affinity due to the enhanced internal steric hindrance compared to the (E)-4'-(2-(anthracen-9-yl)vinyl)-N,N-diphenylbiphenyl-4-amine molecule, which resulted in a lower photoluminescence quantum yield (PLQY) value and a shorter lifetime in the molecule. Besides, the Molecular Docking approach was used to investigate possible cellular staining targets to confirm cellular imaging potential of the compounds. Moreover, cell viability analyses put forth that synthesized molecules do not exhibit significant cytotoxicity under 125 µg mL-1 concentration on the human dermal fibroblast cell line (HDFa). Moreover, both of the compounds showed great potential in cellular imaging of HDFa cells. Compared to Hoechst 33258, a common fluorescent dye used for nuclear staining, the compounds showed higher magnification of cellular structure imaging capacity by staining the whole cellular compartment. On the other hand, bacterial staining showed that ethidium bromide has higher resolution in monitoring Staphylococcus aureus (S. aureus) cell culture.

Increasing Sugar Content in Source for Biofuel Production Using Agrochemical and Genetic Approaches at the Stages of BioMass Preharvesting and Harvesting.

In order to optimize biofuel (including bioethanol) production processes, various problems need to be solved, such as increasing the sugar content of raw materials/biomass to gain a higher yield of the product. This task can be solved in several ways, with their own advantages and disadvantages, and an integrated approach, such as using a combination of ripening agents and phytohormones or application of a superabsorbent polymer with at least one sugar-enhancing agent, can be applied as well. Here, we reviewed several methods, including pre- and postharvest factors (light, temperature, partial replacement of potassium with magnesium, etc.), genetic modifications (traditional breeding, phytohormones, etc.), chemical ripening methods (Ethephon, Moddus, etc.), and some alternative methods (DMSO treatment, ionic liquids, etc.). The aim of this review was to provide a comprehensive, up-to-date summary of methods of increasing the carbohydrate level in plants/biomass for bioethanol production.

Halogenation of a twisted non-polar π-system as a tool to modulate phosphorescence at room temperature.

Halogenation of a twisted three-fold symmetric hydrocarbon with F, Cl or Br leads to strong modulation of triplet-triplet annihilation and dual phosphorescence, one thermally activated and the other very persistent and visible by eye, with different relative contributions depending on the halide. The room temperature phosphorescence is highly unusual given the absence of lone-pair-contributing heteroatoms. The interplay between the spin-orbit coupling matrix elements and the spatial configuration of the triplet state induces efficient intersystem crossing and thus room temperature phosphorescence even without relying on heteroatomic electron lone pairs. A ninefold increase of the ISC rate after introduction of three bromine atoms is accompanied by a much higher 34-fold increase of phosphorescence rate.

Generating Light from Upper Excited Triplet States: A Contribution to the Indirect Singlet Yield of a Polymer OLED, Helping to Exceed the 25% Singlet Exciton Limit.

The mechanisms by which light is generated in an organic light emitting diode have slowly been elucidated over the last ten years. The role of triplet annihilation has demonstrated how the "spin statistical limit" can be surpassed, but it cannot account for all light produced in the most efficient devices. Here, a further mechanism is demonstrated by which upper excited triplet states can also contribute to indirect singlet production and delayed fluorescence. Since in a device the population of these TN states is large, this indirect radiative decay channel can contribute a sizeable fraction of the total emission measured from a device. The role of intra- and interchain charge transfer states is critical in underpinning this mechanism.

Synthesis and investigation of intra-molecular charge transfer state properties of novel donor-acceptor-donor pyridine derivatives: the effects of temperature and environment on molecular configurations and the origin of delayed fluorescence.

A novel series of donor-acceptor-donor (D-A-D) structured pyridine derivatives were synthesised and detailed photo-physical investigations were made using mainly steady-state and time-resolved spectroscopy techniques at varying temperatures. The investigations showed that the molecules have solvent polarity and temperature dependent excited-state configurations, confirmed in two different polarity solvents (295-90 K), i.e. methyl cyclohexane (MCH) and 2-methyltetrahdrofurane (2-MeTHF). In MCH, the investigations revealed dual fluorescence over the temperature range of 295-90 K. At 295 K, the ground-state configuration of the molecules has a partially twisted geometry as determined by DFT calculation, yet the emission originates totally from a locally excited (LE) state, however once the temperature is lowered to 90 K, the twisted molecular configuration is stabilised, and the emission originates from a fully-relaxed intramolecular charge transfer state (ICT), this is contrary to the systems where structural reorganisation stabilises ICT and this is frozen out at low temperatures. The DFT calculations revealed different ground state molecular configurations due to the presence of different electron-donating groups, e.g. the molecule including anthracene groups has a near 90° twisted geometry whereas the triphenylamine including molecule has a pyramidal geometrical folding, therefore, the decrease in temperature restricts the donor degree of rotational freedom. In 2-MeTHF solution, the fluorescence spectrum of both molecules is always of ICT character, but gradually red-shifts through the fluid to glass transition temperature (∼135 K), in this case, the fluorescence occurs after structural and solvent-shell relaxations, however, upon cooling below 135 K, the spectra dramatically shift back to blue giving rise to strong emission from an ICT excited-state (but not the LE state) where the molecules have unrelaxed geometries. This significant change in the nature of the emitting species was explained with specific solvent-solute dynamic interactions in the vicinity of the solvation shell and the effect of thermal excitation of molecular vibrational modes of the C-C bond linking donor and acceptor units. Finally, we confirmed that the molecules have ICT ground-state geometry in the solid-state phase (spin-coated films), and the time-resolved decay dynamics were investigated comparing the spin-coated films (at RT and 25 K) and MCH solutions (at 295 K and 90 K).

Synthesis, spectroscopic and catalytic properties of some new boron hybrid molecule derivatives by BF2 and BPh2 chelation.

A new series of Schiff base ligands (L1-L3) and their corresponding fluorine/phenyl boron hybrid complexes [LnBF2] and [LnBPh2] (n=1, 2 or 3) have been synthesized and well characterized by both analytical and spectroscopic methods. The Schiff base ligands and their corresponding fluorine/phenyl boron hybrid complexes have been characterized by NMR ((1)H, (13)C and (19)F), FT-IR, UV-Vis, LC-MS, and fluorescence spectroscopy as well as melting point and elemental analysis. The fluorescence efficiencies of phenyl chelate complexes are greatly red-shifted compared to those of the fluorine chelate analogs based on the same ligands, presumably due to the large steric hindrance and hard π→π(∗) transition of the diphenyl boron chelation, which can effectively prevent molecular aggregation. The boron hybrid complexes were applied to the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. The catalytic studies showed that boron hybrid complexes are good catalytic precursors for transfer hydrogenation of aromatic ketones in 0.1M iso-PrOH solution. Also, we have found that both steric and electronic factors have a significant impact on the catalytic properties of this class of molecules.

The key role of geminate electron-hole pair recombination in the delayed fluorescence in rhodamine 6G and ATTO-532.

In this paper we investigate the delayed fluorescence (DF) phenomena in the widely used laser dye, rhodamine 6G, and its derivative ATTO-532 as a function of excitation energy using highly sensitive time-resolved gated nanosecond spectroscopy. Excitation with UV laser radiation results in delayed emission, which arises from singlet states created from geminate pair recombination, not triplet annihilation. For the first time the origins and photo-physical properties of delayed fluorescence in these highly fluorescent molecules are elucidated.