Circularly polarized luminescence from helically chiral N,N,O,O-boron-chelated dipyrromethenes

Helically chiral N,N,O,O-boron chelated dipyrromethenes showed solution-phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λem(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5-ortho-phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|glum| up to 4.7 ×10−3) and fluorescence quantum yields (ΦF up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL-based bioimaging

Thermally-Activated, Delayed Fluorescence in O,B,O- and N,B,O-Strapped Boron Dipyrromethene Derivatives

A small series of boron dipyrromethene (BODIPY) dyes has been synthesized whereby the boron atom is constrained in a five-membered ring formed from either <i>o</i>-dihydroxypyridine or <i>o</i>-aminophenol. In the latter case, the amino group has been converted into the corresponding amide derivative so as to curtail the possibility for light-induced charge transfer from strap to BODIPY. These compounds are weakly emissive in fluid solution but cleavage of the strap, by treatment with a photoacid generator, restores strong fluorescence. Surprisingly, the same compounds remain weakly fluorescent in a rigid glass at 80 K where light-induced charge transfer is most unlikely. In fluid solution, the fluorescence quantum yield increases with increasing temperature due to a thermally activated step but does not correlate with the thermodynamics for intramolecular charge transfer. It is proposed that the strap causes rupture of the potential energy surface for the excited state, creating traps that provide new routes by which the wave packet can return to the ground state. Access to the trap from the excited state is reversible, leading to the delayed emission. Analysis of the temperature dependent emission intensities allows estimation of the kinetic parameters associated with entering and leaving the trap

Synthesis and Computational Characterization of Organic UV-Dyes for Cosensitization of Transparent Dye-Sensitized Solar Cells

The fabrication of colorless and see-through dye-sensitized solar cells (DSCs) requires the photosensitizers to have little or no absorption in the visible light region of the solar spectrum. However, a trade-off between transparency and power conversion efficiency (PCE) has to be tackled, since most transparent DSCs are showing low PCE when compared to colorful and opaque DSCs. One strategy to increase PCE is applying two cosensitizers with selective conversion of the UV and NIR radiation, therefore, the non-visible part only is absorbed. In this study, we report synthesis of novel five UV-selective absorbers, based on diimide and Schiff bases incorporating carboxyl and pyridyl anchoring groups. A systematic computational investigation using density functional theory (DFT) and time-dependent DFT approaches was employed to evaluate their prospect of application in transparent DSCs. Experimental UV/Vis absorption spectra showed that all dyes exhibit an absorption band covering the mid/near-UV region of solar spectrum, with a bathochromic shift and a hyperchromic shifts for Py-1 dye. Computational results showed that the studied dyes satisfied the basic photophysical and energetics requirements of operating DSC as well as the stability and thermodynamical spontaneity of adsorption onto surface of TiO2. However, results revealed outperformance of the thienothiophene core-containing Py-1 UV-dye, owing to its advantageous structural attributes, improved conjugation, intense emission, large Stokes shift and maximum charge transferred to the anchor. Chemical compatibility of Py-1 dye was then theoretically investigated as a potential cosensitizer of a reference VG20-C2 NIR-dye. By the judicious selection of pyridyl anchor-based UV-absorber (Py-1) and carboxyl anchor-based NIR-absorber (VG20), the advantage of the optical complementarity and selectivity of different TiO2-adsorption-site (Lewis- and Bronsted-acidic) can be achieved. An improved overall PCE is estimated accordingly

Mesomorphic, Optical and DFT Aspects of Near to Room-Temperature Calamitic Liquid Crystal

A new liquid crystalline, optical material-based Schiff base core with a near to room-temperature mesophase, (4-methoxybenzylideneamino)phenyl oleate (I), was prepared from a natural fatty acid derivative, and its physical and chemical properties investigated by experimental and theoretical approaches. The molecular structure was confirmed by elemental analysis, FT-IR (Fourier-Transform-Infrared Spectroscopy) and NMR (nuclear magnetic resonance) spectroscopy. Optical and mesomorphic activities were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results show that compound (I) exhibits an enantiotropic monomorphic phase comprising a smectic A phase within the near to room-temperature range. Ordinary and extraordinary refractive indices as well as birefringence with changeable temperatures were analyzed. Microscopic and macroscopic order parameters were also calculated. Theoretical density functional theory (DFT) calculations were carried out to estimate the geometrical molecular structures of the prepared compounds, and the DFT results were used to illustrate the mesomorphic results and optical characteristics in terms of their predicted data. Three geometrical isomers of the prepared compound were investigated to predict the most stable isomer. Many parameters were affected by the geometrical isomerism such as aspect ratio, planarity, and dipole moment. Thermal parameters of the theoretical calculations revealed that the highest co-planar aromatic core is the most stable conformer

Improvement of dye-sensitized solar cells' performance via co-sensitization of new azo thiazole organic dyes with ruthenium (II) based N-719 dye

Three novel azo thiazole organic dyes, NA-1–3, have been synthesized and utilized as co-sensitizers in dye-sensitized solar cells (DSSCs). These co-sensitizers were designed with a thiazole ring π-bridge that mediates between the diazo (–N = N–) functional group and carboxylic acid anchoring unit. They possess a rod-like molecular structure and exhibit strong UV–vis absorption near 600 nm. Co-sensitization studies were also conducted with the ruthenium complex N719. The co-sensitized DSSCs showed enhanced short-circuit and open-circuit photocurrents (Jsc) and voltages (Voc), resulting in more efficient photovoltaic performance compared to N719 (PCE 7.25%). Electrochemical impedance spectroscopy (EIS) and incident photon to current efficiency (IPCE) were employed to investigate the underlying reasons for these improvements. It was found that co-sensitization effectively reduced electron recombination, resulting in a higher Voc without compromising photocurrent loss

Synthesis, molecular modeling and bioactivity of new bis-thiazole, thiazole-pyrazole, and thiazole-pyridine analogues

Several new thiazole derivatives linked pyrazole and/or pyridine rings were synthesized based on the versatile precursor 2-(5-acetyl-4-methyl-3-phenylthiazol-2(3H)-ylidene)acetonitrile (1). The synthesized derivatives were optimized using DFT approach in order to inspect the configurations and energies of the HOMO-LUMO orbitals. The data disclosed low energy gap (ΔEH-L), 0.99–2.54 eV, following the order 9 < 3 = 4 ≈ 2 ≈ 8 < 5 < 1 < 7 ≈ 6. The in vitro anticancer activity of the new thiazole hybrids was tested against three cancer cell lines (HepG2, HCT-116, and MCF-7) as well as standard fibroblast cells (WI38) using Doxorubicin as a reference drug. The thiazole-pyridine hybrids 8 and 9 exhibited high cytotoxic efficacies against the MCF-7 cell line, IC50 28.53 ± 0.39 and 25.47 ± 0.54 µM. Moreover, the synthesized hybrids were docked against the crystal structure of (PDB: 3rcd) as a representative protein for the human epidermal growth factor receptor (HER2) to approve the relationship between the in vitro cytotoxicity results and inhibitor binding interactions. The docking study showed that thiazole-pyridine hybrids 8 and 9 displayed the highest score of bindings, which was compatible with the results of the cytotoxicity results

Binary Liquid Crystal Mixtures Based on Schiff Base Derivatives with Oriented Lateral Substituents

Binary mixtures of the laterally substituted Schiff base/ester derivatives, namely 4-((2- or 3-) substituted phenyl imino methyl) phenyl-4&rdquo;-alkoxy benzoates, Ia&ndash;d, were prepared and mesomorphically studied by differential scanning calorimetry (DSC) and their mesophases identified by polarized optical microscopy (POM). The lateral group (1-naphthyl, 2-F, 2-Br, 3-F in Ia&ndash;d, respectively) is attached to different positions of the phenyl Schiff moiety. The mixtures investigated were made from two differently shaped compounds that differ from each other in the polarity, size, orientation, and relative positions of the lateral group. The results revealed that the binary mixture Ia/Ib (bearing the naphthyl and 2-flouro substituents) exhibited the SmA phase, which covered the whole composition range. For the mixtures Ib/Id (2-F and 2-Br), the isomeric lateral F-group in compound Ib distributed the SmA arrangement of Id. In the Ic/Id mixture bearing two positionally and structurally different substituents, the addition of Ic to Id resulted in solid binary mixtures where its behavior may be attributed to the negligible steric effect of the small electronegative fluorine atom compared to the Br atom. Density functional theory (DFT) theoretical calculations were carried out to estimate the geometrical parameters of individual components and to show the effect of these parameters in the mesophase behavior of the binary system, where the higher dipole moment of Id (6 Debye) may be the reason for its high &pi;&ndash;&pi; molecular stacking, which influences its mesophase range and stability

Characterization of New H-Bonded Liquid Crystalline Complexes Based on Iminophenyl Nicotinate

Two new 1:2 supramolecular H-bonded liquid crystalline complexes (SMHBCs) were prepared through double H-bond interactions between either isophthalic acid (A) or terephthalic acid (B) and a nicotinate Schiff base (I6). The formed complexes were thermally investigated by differential scanning calorimetry (DSC), and their phases were identified by polarized optical microscopy (POM) and UV-spectroscopy. The formation of 1:2 hydrogen-bonded complexes was confirmed through their Fermi-bands observed by FT-IR spectroscopy. The first system (I6/A) was found to possess enantiotropic smectic A and nematic mesophases. Induced broad range of smectic A phase was observed in I6/A complex which is not shown by their individual components. The second complex system (I6/B) was purely nematogenic. Density functional theory (DFT) calculations were applied to predict their geometrical parameters. Theoretical studies revealed that the isophthalic complex adopted the W-shape; while the U-shape was adopted by the terephthalic acid complex (I6/B). The linear geometry of the complex based on the isophthalic acid enhanced the mesomorphic behavior observed by the terephthalic complex; I6/B. Actually; the orientation of the two carboxylic groups was shown to highly affect the softness of the derived complex. On the other hand; the mapping orientation of the charge distribution can be used to explain the mesophase behavior. The photophysical characterization of isophthalic complex (I6/A) is also discusse

Circularly polarized luminescence from helically chiral N,N,O,O-Boron-chelated dipyrromethenes

Helically chiral N,N,O,O-boron chelated dipyrromethenes showed solution-phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λem(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5-ortho-phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|glum| up to 4.7 ×10−3) and fluorescence quantum yields (ΦF up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL-based bioimaging