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The present study describes the development of heterogeneous photoredox catalysts based on ruthenium complexes anchored onto a glass surface (glass wool). These easy-to-handle, inexpensive and reusable fiber-like materials allow Ru-based photoredox catalysis in the heterogeneous phase. Here we report the synthesis and characterization of these new materials, and evaluate their remarkable photocatalytic activity to engage in aerobic photooxidative reactions. In particular, the oxidative hydroxylation of arylboronic acids and the singlet oxygen-mediated photooxidation of 9,10-dimethylanthracene (DMA) and 2-ethylfuran are achieved with excellent yields (>95%) within 6 h of irradiation using blue LEDs (λ ∼ 450 nm). Further, the materials can be reused at least 6 times without any significant loss of activity, thus revealing their high stability and recyclability. The strategy takes advantage of the broad knowledge on Ru-based photocatalysis while adding the recovery and reuse benefits of heterogeneous catalysis. Additionally, these materials are promising alternatives for flow photochemistry. This approach that allows attachment of Ru complexes onto glass wool can be extended for use to other transition-metal complexes as photoredox catalysts.

4-quinolones derivatives can present fluorescent properties, depending on their substituents and on the chemical environment (e.g., acidic medium), allowing their application as ion sensors. We theoretically evaluated the photophysical properties of previously synthesized 3-acyl-4-quinolones to verify how different substituents (R1=H, NH2 and R2 = OEt, OH, NHPh) affect their absorption profiles and the emission profile of a reference compound, PB3. All DFT and TD-DFT calculations were performed at B3LYP-D3/6-311++G(d,p) level and continuum polarization model for simulated acetonitrile as solvent. For PB2 (R1 = H, R2 = OEt), we observed hypsochromic shift compared to PB3 due to the increase of the gap between HOMO/LUMO (absence of electron-donating group), in accordance with experimental data. For R1=NH2 and R2=OH, NHPh (PB6 and PB10, respectively), the gap between HOMO/LUMO increases, resulting in a soft bathochromic shift for the simulated absorption spectra. In addition, we evaluated the effect of acid addition on the absorption and emission profile of PB3 and the results were compared with experimental data. Our thermodynamic results suggest that protonation occurs on the endocyclic carbonyl of the quinolone moiety, probably due to an increased aromatic character, as suggested by our NICS calculations. Finally, we associate the increase of the fluorescence in the acidic medium to the establishment of an intramolecular hydrogen bond and, thus, increased rigidity.

The present study details the experimental and theoretical characterization of the photophysical properties of 14 examples of 2-(phenylamino)-1,10-phenanthrolines (1). The absorption spectra of 1 are substituent-dependent but in a general manner present absorption bands at wavelengths of ~230; ~300; ~335 and a shoulder at ~380 nm. Electron-donating groups (EDG) and electron-withdrawing groups (EWG), respectively, result in bathochromic and hypsochromic shifts. Compounds 1 are highly luminescent, in contrast to phenanthroline, and emit in the region between 350 and 500 nm with substituent-dependent λmax emission. The emission spectra show a redshift for EDG (4-OMe 62 nm; 4-Me 19 nm) and a blueshift for EWG (4-CN 41 nm; 4-CF3 38 nm) relative to the emission of the unsubstituted parent compound 1a. Plotting the λ max EM against Hammett σ+ constants gave an excellent linear correlation demonstrating the electron-deficient nature of the excited state and how the substituents (de)stabilize S1 . Theoretical calculations revealed a HOMO-LUMO π-π* electronic transition to S1 which in combination with difference (S1 -S0 ) in electron density maps revealed charge-transfer character. Strongly electron-withdrawing substituents switch off the charge transfer to give rise to a local excitation.

Made available in DSpace on 2020-12-12T01:51:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01. Added 1 bitstream(s) on 2021-07-15T15:07:22Z : No. of bitstreams: 1 S0103-50532020000100201.pdf: 802994 bytes, checksum: 3466162bdcdee7f288db8220b1b96ce2 (MD5) This study shows a preparation and evaluation of a new non-expensive TiO2 based photocatalyst built over sand grains surfaces as an alternative green technology for water treatment. The semiconductor covalently bonded to the silica sand grains (sand@TiO2) prepared by hydrolysis of isopropoxide orthotitane over sand grains, showed a high surface area 296 m2 g-1 and a high reaction rate for methylene blue (MB) photodegradation (0.064 min-1), on steady state condition by using 3 g of sand@TiO2 and an MB solution (20 mL, 3 × 10-5 mol L-1) or ciprofloxacin hydrochloride (CIP) solution (20 mL, 1.9 × 10-3 mol L-1). Under UV irradiation with a medium pressure Hg lamp, the total MB removal reached 70% after 7 min and 45% for CIP in 60 min. Further, the photocatalyst showed to be a promising reusable material for removal of ciprofloxacin hydrochloride antibiotic (CIP) on wastewater. This new material appears as a new promising low cost and low impact reusable catalyst for water treatment. Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez de Mello (CENPES) Petróleo Brasileiro S.A. (PETROBRAS) Instituto de Química Universidade Federal do Rio de Janeiro (UFRJ) Instituto Nacional de Tecnologias Alternativas para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química Universidade Estadual Paulista (Unesp), CP 355 Instituto Nacional de Tecnologias Alternativas para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química Universidade Estadual Paulista (Unesp), CP 355

The present study details a metal- and solvent-free synthesis of 11H-pyrido[2,1-b]quinazolin-11-one (1) and its photophysical properties as an acid or base-sensitive sensor. The absorption spectra in organic solvents revealed a small blue shift on passing from nonpolar to polar solvents, but when measured in buffered aqueous solutions the spectra were observed to be pH-dependent. Additionally, the emission spectra recorded in different organic solvents revealed only minor differences between the solvents and a moderate fluorescence quantum yield. However, the emission spectrum of 1 revealed a pH-dependent behavior. At pH 7 the emission spectrum was similar to that in acetonitrile, whereas at pH 1 the emission intensity skyrocketed, whilst at pH 14 fluorescence was switched off. The emission from 1 was reversibly switched on and off by control of the pH. The adsorption of 1 on silica disks provided a simple means for sensing gas-phase acids or basic amines. Exposure of the disks to AcOH, HCl, or TFA vapors revealed an acid-dependent increase of the emission spectrum intensity area. Disks exposed to acid vapors (switch on fluorescence) were readily recycled by exposure to ammonia or other volatile amines (switch off fluorescence). The modified silica disks could be cyclically switched on and off multiple times without significant change to the signal efficiency. NMR spectroscopy and TD-DFT calculations were used to investigate the dramatic changes to the photophysical properties of 1 as a consequence of the pH-dependent behavior.

In the present study a series of N-phenyl-1,10-phenanthroline-2-amine derivatives were obtained by heating 2-chlorophenanthroline with aniline derivatives under solvent free conditions in good to excellent yields. The N-phenyl-1,10-phenanthroline-2-amines were employed as substrates in a copper(ii)-catalyzed C-H amination reaction to give derivatives of the novel heterocyclic system benzo[4,5]imidazo[1,2-a][1,10]phenanthroline. The structure of these compounds was predicted to be helical by DFT calculations and single crystal X-ray diffraction of an example of this system confirmed the non-planar helical structure. The luminescence properties of the parent heterocyclic system were characterized.

The photochemical reactivity of the triplet state of pyrano- and furano-1,4-naphthoquinone derivatives (1 and 2) has been examined employing nanosecond laser flash photolysis. The quinone triplets were efficiently quenched by l-tryptophan methyl ester hydrochloride, l-tyrosine methyl ester hydrochloride, N-acetyl-l-tryptophan methyl ester and N-acetyl-l-tyrosine methyl ester, substituted phenols and indole (k ∼10 L mol s ). For all these quenchers new transients were formed in the quenching process. These were assigned to the corresponding radical pairs that resulted from a coupled electron/proton transfer from the phenols, indole, amino acids, or their esters, to the excited state of the quinone. The proton coupled electron transfer (PCET) mechanism is supported by experimental rate constants, isotopic effects and theoretical calculations. The calculations revealed differences between the hydrogen abstraction reactions of phenol and indole substrates. For the latter, the calculations indicate that electron transfer and proton transfer occur as discrete steps., The authors thank the following Brazilian agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for financial assistance. The authors also thank the Generalitat Valenciana (Prometeo Program).

The present study details the use of nanosecond laser transient absorption spectroscopy to investigate the reactivity of the triplet excited states of pyrene-4,5-dione and pyrene-4,5,9,10-tetrone and the respective 2,7-di-t-butyl derivatives. The quinone triplet excited states were quenched by 2-propanol and 1,4-cyclohexadiene with quenching rate constants (kq) of the order 107 L mol−1 s−1, as well as by phenols, amines, and N-acetyl tryptophan methyl ester (model biological compounds) with near diffusion limit experimental rate constants (kq > 109 L mol−1 s−1) and very small kinetic isotopic effects for phenolic H/D abstraction. Hydrogen abstraction from the quenchers gave rise to the corresponding radical pairs. The intermediates were spectroscopically characterized. The quinones can also act as type II photosensitizers as they can generate singlet oxygen with quantum yields of up to 0.90. Finally, steady-state photolysis of the compounds demonstrated that pyrene-4,5-diones undergo a one-step reduction whilst pyrene-4,5,9,10-tetrones are reduced in two sequential stages. Both the diones and the tetrones are reduced to the respective aromatic catechols. Notably, the changes are reversible indicating that the compounds can act as photo-redox catalysts for reactions involving hydrogen atom abstraction (HAT).

The development of long-lived luminescent nanoparticles for lifetime imaging is of wide interest as luminescence lifetime is environmentally sensitive detection independent of probe concentration. We report novel iridium-coated gold nanoparticles as probes for multiphoton lifetime imaging with characteristic long luminescent lifetimes based on iridium luminescence in the range of hundreds of nanoseconds and a short signal on the scale of picoseconds based on gold allowing multichannel detection. The tailor-made IrC

Chemical investigation of nonindigenous Tubastraea coccinea and T. tagusensis by Raman spectroscopy resulted in the identification of carotenoids and indolic alkaloids. Comparison of Raman data obtained for the in situ and crude extracts has shown the potential of the technique for characterizing samples which are metabolic fingerprints, by means of band analysis. Raman bands at ca. 1520, 1160, and 1005 cm(-1) assigned to ν1(C═C), ν2(C-C), and ρ3(C-CH3) modes were attributed to astaxanthin, and the band at 1665 cm(-1) could be assigned to the ν(C-N), ν(C-O), and ν(C-C) coupled mode of the iminoimidazolinone from aplysinopsin. The antioxidant activity of the crude extracts has also been demonstrated, suggesting a possible role of these classes of compounds in the studied corals.

The absorption spectra for both families of naphthoquinones reveal a solvatochromic red shift in polar solvents which is consistent with the π,π* character of the S 0 → S 1 electronic transition in all cases. The photochemical reactivity of a series of substituted furano- and pyrano-1,2-naphthoquinones has been examined by laser flash photolysis. Excitation ( λ = 355 nm or 266 nm) of degassed solutions of the quinones 1a – f and 2a – f , in acetonitrile, resulted in the formation of their corresponding triplet excited state. Addition of hydrogen donors, such as 2-propanol, toluene and methylcyclohexane led to the formation of new transients, which were assigned to the corresponding ketyl radicals derived from the hydrogen abstraction reaction by the corresponding triplets. The low values ( k q ∼ 10 5 L mol −1 s −1 ) observed for the hydrogen abstraction rate constants for the naphthoquinones using 2-propanol as the quencher led us to conclude that the triplet excited state has ππ* character. The triplet excited state of these naphthoquinones was efficiently quenched by 4-methoxyphenol and N -acetyl l -tryptophan methyl ester ( k q ∼ 10 9 L mol −1 s −1 ). In all cases a new transient was formed in the quenching process, which was assigned to the corresponding radical pair resulting from an initial electron transfer from the quencher to the excited quinone, followed by a fast proton transfer. The quantum efficiency of singlet oxygen ( 1 O 2 ) formation from the naphthoquinones was determined by employing time-resolved near-IR emission studies upon laser excitation and revealed large values in all cases, which are fully in accord with the ππ* character of these triplets in acetonitrile. Theoretical calculations (TD) DFT were used to calculate UV–vis spectra and to investigate the nature of the transition of λ max as well as to investigate the structure and reactivity of the first triplet state. The calculated triplet energies are compatible with the experimental findings and the calculated hydrogen abstraction from phenol by T 1 quinones indicates a PCET mechanism.