Abstract in English:Despite the preponderance of literature pertaining to photosensitisers based on the porphyrin system, many other chemical classes are available with similar or improved characteristics and potential for use in photodynamic medicine. Several of these classes are based on small, tricyclic, heteroaromatic chromophores, often originally developed from textile dyes or biological stains. The latter classification is useful in providing a basis for biological uptake and antimicrobial activity. The current review covers the chemistry and photoantimicrobial applications of established and novel cationic bisamino derivatives of the acridine, phenazine, phenoxazine, phenothiazine and xanthene systems and related compounds. The range covered is considerable and demonstrates photodynamic performance to rival the porphyrin class. In addition, the chemical synthesis of new analogues of lead compounds such as methylene blue or acridine orange is relatively straightforward and inexpensive, and compound series with varying physicochemical profiles have been produced for structure-activity studies in order to furnish improved photosensitisers for clinical trialling.
Abstract in English:We present a review of recent works on optically investigated thermal effects in crystalline and amorphous materials doped with trivalent rare-earth (RE) ions. The paper describes how the frequency upconversion (UC) photoluminescence (PL) technique is used to investigate the thermal behavior of samples and how to perform optical measurements of temperature. The UC technique is based on the sequential multiphoton absorption phenomenon that leads to anti-Stokes type emission. By measuring the relative intensity between UC emissions from thermally coupled RE energy levels, the absolute temperature of a sample can be determined. Research in this area is motivated by the possible uses of UC for basic characterization of materials and for noncontact thermometry using nanoscale devices as well as for biological and medical studies. Examples based on the application of bulk materials and nanopowders doped with several RE ions are presented.
Abstract in English:Materials specially designed for photonics have been at the vanguard of chemistry, physics and materials science, driven by the development of new technologies. One particular class of materials investigated in this context are glasses, that in principle should exhibit high third order optical nonlinearities and fast response time, whose optical properties can be tailored by compositional changes, such as, for instance, the incorporation of metallic nanoparticles to explore plasmon resonances. Simultaneously to the development of novel materials, and motivated by the need of device miniaturization, direct laser writing by femtosecond pulses has been used to advanced processing of glasses. Such method allows fabricating high resolution three-dimensional optical devices, as well as to produce spatially localized metal nanoparticles. This review paper initially presents results on the nonlinear optical characterization of special glasses, in addition to progresses on the use of femtosecond laser micromachining for producing waveguides and spatially confined metal nanoparticles.
Abstract in English:In the early seventies, Giuseppe Cilento (São Paulo University), Emil White (Johns Hopkins University) and Angelo Lamola (AT&T Bell Laboratories) postulated that typical photochemical reactions could occur in dark parts of living organisms if coupled to enzymatic sources of electronically excited products. Their paradoxical hypothesis of "photochemistry without light" was chemically anchored on the synthesis and weak chemiluminescence of several 1,2-dioxetanes, unstable cyclic peroxides whose thermal cleavage produces long-lived and reactive triplet carbonyls. Collisional reactions or energy transfer of triplet species to cellular targets could eventually result in "photo" products that potentially trigger normal or pathological responses. These ideas flourished in the labs of various researchers who attempted to explain the presence and biological roles of "dark" secondary metabolites, including plant hormones, pyrimidine dimers, alkaloid lumi-isomers, protein adducts, and mitochondrial permeators, thereby broadening the field of photobiology.
Abstract in English:Photodynamic therapy (PDT) is a minimally invasive and effective procedure for treatment of cancer, based on the combination of a drug (photosensitizer, PS), light (visible or near-infrared, NIR) and induced local formation of reactive oxygen species (ROS) and radicals. Despite its less significant side effects as compared with conventional therapies, many efforts still are been focused on enhancing the selectivity and efficiency of PSs and thus, of commercial drugs. Nanotechnology is providing many interesting possibilities and tools to develop drug delivery systems (DDS) and multifunctional platforms for therapy, diagnosis and theranostics. More recently, their effectiveness against tumor cells and tissues is being improved by combining the synergic effects of chemotherapeutic agents and other therapies, making them more interesting therapeutic alternatives. Accordingly, this review is focused on the recent contributions of nanotechnology on PDT, converging to the development of DDSs and multifunctional systems and their application for cancer therapy.
Abstract in English:Light and rare earths (RE) have a long lived relationship that dates from the discoveries of these elements in the nineteenth century. Since then, the increasing comprehension of their spectroscopic properties conducted to a wide and alluring literature about light absorption and emission by this particular and fascinating group. For more than 50 years, RE-containing solid-state optical materials have undoubtfully been an important subject for the development of more efficient lighting, visualization, communication and health everyday applications. Therefore, this review introduces the spectroscopic properties of rare earth materials and their applications, with a brief discussion of the main mechanisms of light absorption and emission from a 4f elements inorganic physical chemistry perspective. Special attention is devoted to the use of these elements in systems concerning photoprotection and to the fundamentals of visible light generation for lighting and visualization.
Abstract in English:In this work, the synthesis, characterization and photophysical study of new derivatives of triazinyl-benzazoles with fluorescence by excited-state intramolecular proton transfer (ESIPT) are presented. It regards the synthesis of cyanuric chloride with different 2-(2’-hydroxyphenyl) benzazoles, two quite attractive groups from the synthetic and technological point of view. These new compounds have several potential applications such as biological markers and new photoluminescent materials. The derivatives were characterized by 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), high-resolution mass spectrometry (HRMS), UV-Vis absorption and fluorescence emission. The dyes are fluorescent by an excited-state ESIPT in the blue-orange region, with a large Stokes’ shift.
Abstract in English:Two novel compounds, 4-(pyren-1-ylimino)methylphenol and 4-[(triisopropylsilyl)oxy]phenylmethylenepyren-1-amine) were synthesized. Solutions of 4-(pyren-1-ylimino)methylphenol in dimethyl sulfoxide (DMSO) are colorless, but on addition of cyanide and fluoride they become colored due to the deprotonation of the chemosensor. The system is highly selective toward cyanide with the addition of water. This compound can be solubilized in water with addition of cetyltrimethylammonium bromide above its critical micellar concentration. The pKa of the compound in water was determined as 10.49 ± 0.02 and this value is lowered in micellar medium to 7.49 ± 0.02, which means that only cyanide is sufficiently basic to achieve the deprotonation of the compound. Solutions of 4-[(triisopropylsilyl)oxy]phenylmethylenepyren-1-amine) in DMSO are colorless, but they are colored in the presence of cyanide and fluoride and only cyanide could be detected in DMSO-water mixture. The nucleophilic attack of the anions on the silicon center of the compound releases colored 4-(pyren-1-ylimino)methylphenolate, enabling the detection of nucleophilic analytes.
Abstract in English:The influence of silver nanoparticles (Ag-NPs) on the optical properties of Bi2O3-GeO2 glasses was investigated aiming the characterization of their potential for applications in photonic devices. The samples were prepared by the melt-quenching technique starting from high purity oxides (GeO2, Bi2O3 and AgNO3). Heat-treatment during different times was performed to nucleate Ag-NPs. A transmission electron microscope was used to confirm the presence of Ag-NPs and to determine their sizes and composition. The glass network was studied by spontaneous Raman scattering. The optical absorption spectra showed an absorption band at ca. 500 nm associated to the bismuth ions, and a 7-fold enhancement of absorption was observed in the samples with Ag-NPs. Photoluminescence (PL) spectra were obtained by exciting the samples with a 808 nm laser. Maximum enhancements of ca. 100% of the PL band centered at 1300 nm and ca. 70% of the Raman spectrum were observed due to the nucleation of the Ag-NPs. The enhanced optical response of the samples with Ag-NPs is attributed to the growth of the local field on the isolated bismuth ions and clusters that are located in the vicinity of the nanoparticles. The results illustrate the large potential of Bi2O3-GeO2 with Ag-NPs to be used in photonic devices.
Abstract in English:Energy conversion, involving UV and Vis absorption to generate near infrared (NIR) emission at 1000 nm from nanostructured Pr3+/Yb3+ co-doped SiO2-Nb2O5 for solar cell application was the main focus of this work. The synthesis, structural and optical characterization of Pr3+/Yb3+ co-doped 70SiO2-30Nb2O5 nanocomposites and planar waveguides prepared by the sol gel method are reported. The influence of the rare earth content and thermal annealing on the crystallization process and the luminescence properties was studied. The excitation spectra revealed the energy transfer between the Pr3+ and Yb3+, involving mainly the 3P2 level of Pr3+ ions. Multiphonon decay and cross relaxation processes take place at higher rare earth concentration and annealing temperature, which increases the 1D2 level population and consequently the NIR emission from the Pr3+ ions. The nanostructured Pr3+/Yb3+ co-doped SiO2-Nb2O5 nanocomposites and waveguides show interesting NIR emission and optical properties for photonic applications.
Abstract in English:New luminescent organic-inorganic hybrid particles based on Tb-doped aluminates and asparagine (Asn) surface modifiers were investigated. The Tb3+ doped inorganic core was obtained by spray pyrolysis, at 200 ºC γ-AlOOH (BOE:Tbx%) or at 700 ºC γ-Al2O3 (γTA:Tbx%). The reaction of Asn with boehmite in water disaggregated the sub-micronic boehmite particles to give stable dispersion of surface modified nanoparticles Asn:BOE:Tbx% (x = 1 or 5). Concerning the Asn:γTA:Tbx% system, an Asn film wrapping alumina particles was observed. Photoluminescence spectra exhibited the bands assigned to Tb3+5D4 → 7FJ = 6-3 transitions. A broad absorption band (240 nm) was assigned to the host (aluminate) to ion (Tb3+) energy transfer. Efficient energy transfer was observed when active ions are incorporated in the defect-spinel structure of γTA, whereas it was relatively weak for BOE:Tb where Tb3+ are bonded to the hydroxyls groups at nanocrystals surface. It is noticeable that Asn strengthens the linkage of Tb3+ with the aluminate matrix, enhancing the host to dopant energy transfer.
Abstract in English:Samples of (1 – x)SiO2:xGeO2 compositions, containing x = 10 and 20, and doped with Er3+, were prepared by a simple sol-gel route. Homogeneous and transparent gels were synthesized and xerogels were obtained by gel annealing from 700 ºC to 1100 ºC. Films exhibiting high transmittance in the visible and near infrared were deposited by spin-coating technique using the colloidal precursors. The materials were characterized structurally and microstructurally by some techniques. Spherical completely amorphous and tetragonal GeO2 nanocrystals from 3.7 nm to 25.0 nm in diameter embedded in silica-rich amorphous phase materials were obtained. The optical properties were studied by transmission spectra from ultraviolet to near infrared region, photoluminescence measurements in the infrared region, and the average lifetime of the metastable state 4I13/2 of Er3+ ions were determined. The 1 mol% Er3+ doped host with x = 20 have an infrared emission 4.9 times higher than the compound containing x = 10, and the Er3+4I13/2 level present lifetime between 15.0 ms and 7.5 ms. The optical band gap and refractive index values were determined, as well as the Sellmeier parameters. Finally, rib channel waveguides using femtosecond laser etching technique on silica substrates were obtained with width of 15 mm. The 1 mol% Er3+ doped 80SiO2:20GeO2 compounds can be applicable in integrated optical systems.
Abstract in English:The phosphor-converted light-emitting diode technique is an important solid-state illumination strategy. Sulfide-based materials are the most often employed red phosphors, but they are chemically unstable and present lower efficiency in comparison to the blue and green phosphors. Therefore, it is important to find a new red phosphor source that can emit intense red light while absorbing light in the near ultraviolet (UV) spectral region. This paper describes the photoluminescence properties of Nb2O5:La3+,Eu3+ obtained by the non-hydrolytic sol-gel process. The X-ray results indicated that the thermal treatment allowed to obtain the different crystalline structures such as, the orthorhombic and monoclinic phases for the Nb2O5 and the orthorhombic phase for the La2Nb10O28. This polymorphism was also confirmed by the Raman spectroscopy. The luminescence spectra revealed the existence of the Eu3+ ions in both crystalline phases for the samples annealed at higher temperature, depending of the excitation wavelength. The emission spectrum showed that increasing the annealing temperature promotes the narrowing of all intraconfigurational f-f transitions for the Eu3+ ions, due to the structural changes. In addition, all samples present good CIE (International Illumination Committee) chromaticity coordinates when excited in the UV (275 and 394 nm), blue (465 nm) and green (525 nm) radiation.
Abstract in English:This work evaluated the influence of ionizing and non-ionizing irradiations on the chemical structure of hard tissues using the mid-infrared spectroscopy. Enamel, dentin and bone slabs were submitted to gamma irradiation, as well as to Nd:YAG (λ = 1064 nm) and Er,Cr:YSGG (λ = 2078 nm) laser irradiations. The composition of slabs were evaluated by the Fourier transformed infrared spectroscopy (FTIR), considering the content of organic matrix (amides I, II and III), and inorganic matrix (phosphate and carbonate). Data were statistically analyzed (α = 5%). All irradiations altered the organic and inorganic content of enamel, dentin and bone, and the changes are dependent on the doses applied, as well as on the wavelength used considering the infrared lasers. In conclusion, the attenuated total reflection (ATR)-FTIR technique is an efficient tool to monitor the chemical changes on hard tissues due to ionizing and non-ionizing irradiations, which is important in order to choose safe parameters for a future clinical application.
Abstract in English:Our goal was to build, characterize and test a red light-emitting diode (LED) device suitable for wound healing and disinfection of biomedical appliances. We designed and built a unique irradiator metallic box, for which irradiation distribution and spectral irradiance were calculated. In addition, we explored the device’s potential in photobiology comparing the healing of irradiated third degree burns with lesions that were left to heal spontaneously in mice. We also compared photodynamic microbial reduction with LED-irradiator and methylene blue vs. disinfection with a standard chemical solution, for photochemical applications. Our results showed that the LED-irradiator was able to accelerate the wound healing process compared to control group. In addition, a statistically significant microbial reduction was obtained with photodynamic inactivation compared to chemical decontamination. Thus, the prototype design is suitable for phototherapy studies since it is advantageous for low-level light therapy as well as for antimicrobial photodynamic therapy. In our perspective, this device can potentiate the dissemination of phototherapy studies to determine its suitable application in health sciences.
Abstract in English:Biopolymer-based materials have been of particular interest as alternatives to synthetic polymers due to their low toxicity, biodegradability and biocompatibility. Among them, chitosan is one of the most studied ones and has recently been investigated for the application as solid state polymer electrolytes. Furthermore, it can serve as a host for luminescent species such as rare earth ions, opening up the possibility of combined electro-optical functionality, of particular interest for electroluminescent devices. In this study, we perform a fundamental, initial, investigation of chitosan based luminescent materials doped with EuIII and LiI triflate salts, from the structural, photophysical and conducting points of view. Because the host presents a broad emission band in the blue to green, while EuIII emits in the red, fine-tuning of emission colour and/or generation of white light is proven possible, by proper combination of optimized composition and excitation scheme. Europium lifetimes (5D0) are in the range 270-350 µs and quantum yields are up to 2%. Although LiI does not interfere with the luminescent properties, it grants ion-conducting properties to the material suggesting that a combination of both properties could be useful in the development of electro-luminescent devices.
Abstract in English:In this study, polyoxometallate based hybrid photochromic materials were prepared by incorporating phosphotungstate anion, PW12O403−, (PW) in hybrid tetraethyl orthosilicate and (3-glycidyloxypropyl)trimethoxysilane TEOS-GPTMS derived organomodified silicates (Ormosil) matrices by sol-gel method and the resulting materials were used to prepare multilayer films by dip-coating method. The effect of alkaline earth metal cations doping and matrix composition (%GPTMS) on the photochromic response of the hybrid films was studied in details. GPTMS, after undergoing ring opening reaction, leads to the formation of chelating sites (diol and ether functionalities) which helps in anchoring of cations, which in turn interacts with phosphotungstate anions and favors their incorporation in the hybrid films. For a fixed concentration of GPTMS, the cation-phosphotungstate electrostatic interaction and hence the photochromic response of the films follow the order Mg2+ < Ca2+ < Sr2+ < Ba2+, thereby, indicating that larger cations interact more strongly with the heteropolyanions. The presence of these cations and GPTMS concomitantly leads to increased incorporation of phosphotungstic acid hydrate (HPW) in the films, resulting in a significant enhancement of the photochromic response.
Abstract in English:New glass compositions in the system 1-x(SbPO4-ZnO-PbO)-xMnO (with 0 ≤ x ≤ 20 in mol%) were prepared by melt-quenching methodology. Thermal, structural and optical properties of the new glasses were systematically studied by means of differential scanning calorimetry (DSC), UV-Vis and Raman spectroscopy, fluorescence and electronic paramagnetic resonance (EPR). The addition of MnO increases the thermal stability of the glasses with Tx – Tg close to 140 ºC for higher Mn contents. EPR measurements show that Mn2+ ions are in octahedral arrangement which is in agreement with UV-Vis and luminescence results. Samples present red luminescence when excited with 408 nm source.
Abstract in English:Two new photosensitizers (PSs) derived from copper-chlorophyllin were designed to have excitation wavelengths appropriate for the use in photodynamic therapy (PDT) and to have amphiphilic character with positive charge, which favors binding to cell membranes and walls and the intracellular localization in mitochondria. Herein we describe the synthesis and characterization of several properties of these two new PS, i.e., photophysical (absorption, fluorescence and singlet oxygen emission quantum yields, Φf and ΦΔ, respectively), physical-chemical (aggregation) and photobiological (binding, incorporation and cell killing). As expected, the aggregation affected not only the absorption spectra but also lowered considerably the values of Φf and ΦΔ, which could be controlled by the interaction of the PS with aqueous micelles. In vitro studies were performed in cells, mitochondria, and vesicles to determine uptake, membrane binding, cytotoxicity, phototoxicity, and intracellular localization. The positively charged derivatives showed to be considerably more efficient for cell killing than methylene blue.
Abstract in English:Simple synthetic procedures have been applied to obtain luminescent carbon quantum dots, also referred as C-dots, from an abundant carbon source, that is, from the brewing industry waste. The synthetic procedures have been conducted aiming to investigate the effects of the oxidation stage on the properties of the nanomaterial. C-dots down- and up-conversion properties, as well as their potential for cellular imaging experiments in live (and adhered) cells, are disclosed herein.
Abstract in English:[RE(TLA)·(H2O)n:Eu3+] (RE3+: Y, Gd and Lu; TLA: trimellitic acid) precursor complexes were synthesized by an one step aqueous co-precipitation method. After annealing for 1 h, RE2O3:Eu3+ nanophosphors were formed through the benzenetricarboxylate low temperature thermolysis method (500-1000 ºC). The compounds were characterized by using different techniques [elemental analysis (CHN), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG/DTG), X-ray powder diffraction (XPD) and scanning electron microscope (SEM)]. The XPD data indicated that the Y2O3:Eu3+ materials have crystallite size range from 11 to 62 nm. The SEM and transmission electron microscopy (TEM) images show that the annealed materials keep morphological similarities with the precursor complexes. The photoluminescence properties were studied based on the excitation and emission spectra, and luminescence decay lifetimes of the 5D0 emitting level of the Eu3+ ion. The experimental intensity parameters (Ωλ), lifetimes (τ), as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed. The RE2O3:Eu3+ phosphors (RE: Y3+ and Lu3+) annealed at 500 to 1000 ºC have emission quantum efficiency (intrinsic quantum yield) values from 60 to 82%, indicating that this material can be potentially used for optical markers applications.