Fabiano Severo Rodembusch

Novel selenoesters fluorescent liquid crystalline exhibiting a rich phase polymorphism

A simple and efficient procedure for the synthesis of a new class of selenoesters 4a and 4b was developed. Polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction showed that the selenoester 4a with a shorter alkyl chain displayed a wide nematic range (ΔT = 110.7 °C), while 4b with a longer alkyl chain possesses a rich phase polymorphism: Cr → SmI → SmC → N → I mesophase sequence during heating cycle and I → N → SmC → SmI → SmX → Cr transition on cooling. For 4b, a large temperature range (135.7 °C) from crystal to isotropic phase can be observed. In addition, UV-Vis, steady-state fluorescence emission and excitation spectra in solution were also applied in order to characterize their photophysical behaviour. Compounds 4a and 4b are fluorescent in the blue region and present a Stokes shift at around 80 nm and 39 nm in dichloromethane and dioxane, respectively.

The first silica aerogels fluorescent by excited state intramolecular proton transfer mechanism (ESIPT)

Five silyl-functionalized benzazole dyes, fluorescent by excited state intramolecular proton transfer (ESIPT) mechanism, were synthesized by reaction of amino benzazole derivatives with 3-(triethoxysilyl)propyl isocyanate. Fluorescent silica gels were prepared and monolithic aerogels (d ≈ 0.18 g cm−3) were obtained via supercritical CO2 drying of the fluorescent gel. The photophysical behaviour of the dyes and fluorescent silica aerogels was investigated by UV–vis and steady-state fluorescence spectroscopy.

Symmetrical and Asymmetrical Cyanine Dyes. Synthesis, Spectral Properties, and BSA Association Study

New cyanines were prepared by an efficient and practical route with satisfactory overall yield from low-cost starting materials. The photophysical behavior of the cyanines was investigated using UV-vis and steady-state fluorescence in solution, as well as their association with bovine serum albumin (BSA) in phosphate buffer solution (PBS). No cyanine aggregation was observed in organic solvents or in phosphate buffer solution. The alkyl chain length in the quaternized nitrogen was shown to be fundamental for BSA detection in PBS in these dyes.

Synthesis and Characterisation of Fluorescent Carbon Nanodots Produced in Ionic Liquids by Laser Ablation

Carbon nanodots (C-dots) with an average size of 1.5 and 3.0 nm were produced by laser ablation in different imidazolium ionic liquids (ILs), namely, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4 ), 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2 ) and 1-n-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (OMI.NTf2 ). The mean size of the nanoparticles is influenced by the imidazolium alkyl side chain but not by the nature of the anion. However, by varying the anion (BF4 vs. NTf2 ) it was possible to detect a significant modification of the fluorescence properties. The C-dots are much probably stabilised by an electrostatic layer of the IL and this interaction has played an important role with regard to the formation, stabilisation and photoluminescence properties of the nanodots. A tuneable broadband fluorescence emission from the colloidal suspension was observed under ultraviolet/visible excitation with fluorescence lifetimes fitted by a multi-exponential decay with average values around 7 ns.

Effects of first-row transition metals and impregnation ratios on the physicochemical properties of microwave-assisted activated carbons from wood biomass

First-row transition metals (Co, Ni, Cu and Zn) were successfully used in the preparation of activated carbons from wood biomass via microwave-assisted irradiation. Physical-chemical properties of the produced materials (MWAC) were studied by nitrogen adsorption-desorption curves, SEM, FTIR, UV-vis DRS and synchronous fluorescence spectroscopy, CHN elemental analysis, TGA/DTG, pHzpc, hydrophobic properties, and total acidity and basicity groups. Results showed that the metals were bound successfully in different amounts with surface functional groups of the wood biomass through ion exchange and surface complexation interaction during the impregnation step. Zn2+ and Cu2+ formed the most complexes. MWAC impregnated with Zn2+ showed higher pore volumes and surface areas, followed by Cu2+, Co2+ and Ni2+, independently of the ratio used. As the metal : biomass ratio was increased from 0.5 to 2, the surface area of MWAC increased from 300 to 620m2g-1 for Co-MC, 260 to 381m2g-1 for Ni-MC, 449 to 765m2g-1 for Cu-MC and from 572 to 1780m2g-1 for Zn-MC. The samples showed high values of carbon contents and oxygen-containing groups. An adsorption experiment revealed that samples prepared using ZnCl2 showed the highest sorption capacities (qe) for the tested adsorbates, followed by CuCl2, CoCl2 and NiCl2. These results matched with the surface areas and pore volumes trends, which were found to follow atomic number and melting point trends-Ni(II)bisphenol A>hydroquinone>4-nitro phenol>2-naphtol>paracetamol>caffeine>resorcinol.

Visible and near infrared, wide-angle, anti-reflection coatings with self-cleaning on glass

In this work self-cleaning and transparent surfaces were produced on glass surface with simultaneous wide-angle and good optical transmittance on the visible region. These properties are pursued by combination of multi-scale surface topology based on silica nanoparticles (SNPs), index grading and interference coating, as well as polytetrafluoroethylene (PTFE) self-assembly, using two approaches. In the first, two-layer approach (glass/SNPs/PTFE), the resulting samples presented a water contact angle (WCA) of 169° ± 2° with very low hysteresis, as well as significant antireflection. The second, three-layer approach (glass/SNPs/silica aerogel/PTFE), produced surfaces with WCA of 158° ± 2° with also very low hysteresis (<5°), in addition to normal transmittance of 99% or higher, which decreased less than 2% at 20° incidence. These results show that proper structure-coated glass, with a combination of interference and graded-index effects, may provide simultaneous wide-angle antireflection and self-cleaning properties.

Confinement effect on the photophysics of ESIPT fluorophores

The photophysics of three benzothiazole derivatives that exhibit excited state intramolecular proton transfer (ESIPT) were investigated in a confined medium afforded by the water soluble supramolecular host octaacid (OA). The dye@(OA)2 inclusion complexes were probed by UV-Vis absorption, steady-state and time resolved fluorescence emission techniques. Comparison studies of the free dyes in solution were also conducted. All three benzothiazole derivatives free in solution and as OA complexes in water absorb in the UV region. The fluorescence maxima of the OA complexes in water are similar to those in an apolar environment. This is different from the emission behavior of the dyes dissolved alone in water. The observed Stokes shift when confined within OA is related to the intramolecular proton transfer mechanism. Within OA only neutral species are present, indicating that these compounds are shielded from the bulk water. The excited state behavior of the benzothiazole derivatives in a confined medium indicates that supramolecular effects significantly alter the nature of the fluorescence emission.

Synthesis and fluorescence properties of benzoxazole-1,4-dihydropyridine dyads achieved by a multicomponent reaction

Photoactive 2-(2′-hydroxyphenyl)benzoxazole-1,4-dihydropyridine (HBO–DHP) dyads were obtained by a multicomponent one-pot Hantzsch synthesis using a fluorescent aldehyde, a 1,3-dicarbonylic compound and ammonium acetate. The key step in this synthetic methodology was the synthesis of the formyl benzoxazole derivative through a Duff-modified functionalization protocol. UV-Vis absorption and fluorescence emission spectroscopies were also applied to better understand the photophysics of these compounds. The three novel fluorescent compounds were obtained in moderate yields as stable solids with absorption in the UV region and emission in the blue-green region. Preliminary results indicate that after excitation both HBO and DHP fluorophores behave independently in the HBO–DHP structure.

Bis-arylsulfenyl- and bis-arylselanyl-benzo-2,1,3-thiadiazoles: synthesis and photophysical characterization

Bis-arylsulfenyl- and bis-arylselanyl-benzo-2,1,3-thiadiazoles were synthesized in good yields by copper-catalysed cross-coupling reaction of arylthiols or diaryl diselenides with the commercially available 4,7-dibromobenzo[c][1,2,5]thiadiazole. The arylsulfenyl derivatives present absorptions in the visible region (∼420 nm) with molar absorptivity coefficient and radiative rate constant values ascribed to spin and symmetry allowed π–π* electronic transitions, with almost complete absence of solvatochromic effect. An emission located in the cyan green to green region (514–570 nm), with a large Stokes shift (90–146 nm) was observed, probably associated to the charge transfer character of the S1 state. Theoretical calculations were also performed in order to study the geometry, charge distribution and photophysical properties of the molecules in their ground and excited electronic states. TD-DFT calculations were performed using the PBE1PBE and CAM-B3LYP functionals with cc-pVDZ basis set for geometrical optimisations in the S0 and S1 states and jun-cc-pVTZ basis set to obtain vertical transition energies and electronic properties. Solvent effects were included by IEF-PCM formalism using solvents with different dielectric constants. The computationally predicted transition energies calculated with CAM-B3LYP are in good agreement with the experimental results. No substantial solvatochromic effect was found in the absorption maxima, but in the emission from S1 state a redshift was observed on increasing the solvent polarity. This fact, combined with higher dipole moment in the first excited state and some spatial separation of HOMO and LUMO orbitals could indicate an intramolecular charge transfer character of the S1 state.

Static Light Scattering from ESIPT Copolymers of Poly(methyl methacrylate) - Benzazole Dyes

Static Light Scattering (SLS) was used for characterization of the fluorescent ESIPT copolymers of PMMA - Benzazole dyes in solution with chloroform (CHCl 3 ) and tetrahydrofuran (THF) were studied. The results show that macromolecular parameters and copolymers architectures in solution are not changing in relation to those of PMMA. In this way, the incorporation of Benzazole dyes in PMMA does not affect the final polymer properties and conformations in the investigated dilution regime.