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Organic molecules have been intensively studied during the last few decades because of their photonics and biological applications.

The search for optical materials, particularly organic compounds, is still an attractive and essential field for developing several photonic devices and applications. For example, some applications are based on light scattering with twice the energy of the incoming photon for selected compounds, that is, the nonlinear optical effect related to the second-order susceptibility term from the electronic polarization expression. The microscopic interpretation of this phenomenon is called the first-order molecular hyperpolarizability or incoherent second harmonic generation of light. Understanding such phenomena as a function of the incoming wavelength is crucial to improving the optical response of future materials. Still, the experimental apparatus, hyper-Rayleigh scattering, apparently simple, is indeed a challenging task. Therefore, we proposed a proper alternative to obtain the dispersion of the first-order hyperpolarizability using the well-known one- and two-photon absorption techniques. By the spectral analysis of both the spectra, we gathered spectroscopic parameters and applied them for predicting the first-order hyperpolarizability dispersion. This prediction is based on an

We determine the two-photon absorption (2PA) cross section spectra branched polyfluorenes distinguished by the number of fluorenes and chemical architecture. Moreover, the optical properties were determined in function of the effective electrons number of each compound.

We determine the incoherent molecular second-order scattering dispersion β(λ) applying the semi-classical time-dependent perturbation theory on experimentally observable electronic transition whose properties were measured with one- and two-photon absorption techniques. The β dispersion obtained showed to be accurate with well-established direct theoretical and experimental measurements.

Incoherent second-harmonic generation is quantified by the first-order molecular hyperpolarizability, which could be estimated through a fast and reliable method using homemade software to post-process the output files from the Gaussian software package.

The luminescence of skim milk samples with distinct protein content doped with rhodamine B was investigated. The samples were excited by a nanosecond laser tuned at 532 nm, and the emission was characterized as a random laser. Its features were analyzed as a function of the protein aggregate content. The results showed a linear correlation between the random laser peak intensity and the protein content. This paper proposes a rapid detection photonic method to evaluate the protein content in skim milk based on the intensity of the random laser emission.

Fluorene-based molecules exhibit significant nonlinear optical responses and multiphoton absorption in the visible region, which, combined with the high fluorescence quantum yield in organic solvents, could make this class of materials potentially engaging in diverse photonics applications. Thus, herein, we have determined the two-photon absorption (2PA) of oligofluorenes containing three, five, and seven repetitive units by employing the wavelength-tunable femtosecond Z-scan technique. Our outcomes have shown that the 2PA cross-section in oligofluorenes presents an enhanced value of around 18 GM per Neff, in which Neff is the effective number of π-electrons, for the pure 2PA allowed transition (11Ag-like → 21Ag-like). Furthermore, a weak 2PA transition was observed in the same spectral region strongly allowed by one-photon absorption (11Ag-like → 11Bu-like). This last result suggests a molecular symmetry perturbation, probably induced by the molecular disorder triggered by the increase of moieties in the oligofluorene structure. We have calculated the permanent dipole moment difference related to the lowest-energy transition using the Lippert-Matagaformalism and the 2PA sum-over-states approach to confirm this assumption. Moreover, we have estimated the fundamental limits for the 2PA cross-section in oligofluorenes.

In this work, we report the experimental and theoretical first molecular electronic hyperpolarizability (βHRS) of eleven π-conjugated oxazoles compounds in toluene medium. The Hyper-Rayleigh Scattering (HRS) technique allowed the determination of the experimental dynamic βHRS values, by exciting the compounds with a picosecond pulse trains from a Q-switched and mode-locked Nd:YAG laser tuned at 1064 nm. Theoretical predictions based on time-dependent density functional theory level using the Gaussian 09 program package were performed with three different functionals (B3LYP, CAM-B3LYP, and M06-2X), to calculate both static and dynamic theoretical βHRS values. Good accordance was found between the experimental and theoretical values, in particular for the CAM-B3LYP and M06-2X functionals.

Made available in DSpace on 2021-06-25T10:55:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 Mesoporous silica, known as SBA-15, possesses a hexagonal pore structure, with 8-nm-diameter pores and high surface area (∼700m2/g). The mesoporosity of SBA-15 is excellent to be filled with luminescent chromophores aiming at optical and photonic applications. SBA-15 powder infiltrated with Rhodamine B (RB) was prepared with different RB loads. Using the second harmonic of a pulsed Nd:yttrium aluminum garnet (YAG) laser (8 ns, 10 Hz) as the excitation source, the light emission spectra of the samples were investigated. Typical incoherent feedback random laser behavior was observed. Tunable random laser emissions from 579 to 585 nm were obtained depending on the excitation laser spot diameter and the RB load. The results indicate that mesoporous SBA-15 infiltrated with RB is a promising material for the development of solid-state random lasers. Universidade Estadual Paulista (UNESP) IGCE Departamento de Fisica Universidade Federal de Sergipe (UFS) Departamento de Fisica Universidade Federal de Sergipe (UFS) Laboratorio de Corrosao e Nanotecnologia (LCNT) Universidade de Sao Paulo (USP) Instituto de Fisica de Sao Carlos Instituto de Fisica Universidade Federal de Goias Universidade Estadual Paulista (UNESP) IGCE Departamento de Fisica

The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications field. Organic compounds have emerged as promising candidates for raw materials to develop nonlinear optical devices, such as optical converters, due to their intrinsic ultra-fast electronic responses. Also, the easy tailoring of organic molecular structures makes organic materials much more appealing than the inorganic ones. In this work, we have performed a linear and nonlinear optical characterization of a set of dibenzylideneacetone derivatives. The nonlinear optical responses investigated correspond to second- and third-order nonlinear processes, namely, first electronic molecular hyperpolarizability and two-photon absorption cross-section, respectively. The value of the first electronic molecular hyperpolarizability, up to 52 cm4&middot, statvolt&minus, 1, could be considered a robust value when compared to the short-sized &pi, electron backbone length of the studied compounds. Such results suggest that these compounds exhibit the potential to be used as optical frequency converters. Quantum chemical calculations were used to predict the theoretical value of the first molecular hyperpolarizability, as well as to simulate the one- and two-photon absorption spectra for all compounds.

In this work, we investigate theoretically and experimentally second harmonic generation (SHG) in three pyrazoline compounds, being two derivatives of dibenzylideneacetone (DBA) (C23H20N2 and C25H24N2O2) and one derivative of chalcone (C21H18N2). The compounds were synthesized after two steps employing a Claisen-Schmidt condensation followed by an addition-elimination reaction with phenylhydrazine. All compounds were characterized using NMR, FT-IR, UV-Vis, and XRD. We calculated the first-order hyperpolarizabilities of these molecules using program packages based on the time-dependent Hartree-Fock (TDHF) and density functional theory (DFT). SHG was characterized by Kurtz and Perry’s powder method. We observed that these organic crystals present SHG efficiencies up to 5 times larger than the KDP, and we associated these values to their molecular structure and crystalline arrangements. The values obtained experimentally and theoretically evidence that these compounds have good potential for application in electronic devices based on second-order nonlinear responses.

Fluorescent organic molecules have received great attention due to their largest applications, for example, in DNA and RNA spectroscopies studies, development of new photoluminescence bioprobes, an...

This work investigates the influence of different electron-withdrawing groups (Cl, Br, fluorobenzonitrile), on the two-photon absorption cross-section of six imidazo[4,5-b]pyridine derivatives. The two-photon absorption cross-section spectra were obtained by ultra-fast Z-scan technique from 470 nm up to 700 nm. The Sum-Over-States approach was applied to model the two-photon absorption spectra, using a three-level energy system. Photophysical properties, such as transition dipole moment, the difference of permanent dipole moments, and anisotropy coefficient were determined through the analysis of one-photon absorption spectra, solvatochromism, and fluorescence anisotropy, respectively. Besides, the excited state absorption spectra were measured through ultra-fast transient absorption, allowing the excited state lifetime and spectral position determination. Two-photon absorption cross-sections of about 160 GM were observed when two electron-withdrawing groups are linked to the imidazo[4,5-b]pyridine core, elucidating a path to achieve high optical nonlinearities in imidazopyridine derivatives. Furthermore, a increase in the two-photon cross-section was observed when chloride is linked at the C-6 position (90 GM) instead of the C-5 position (50 GM), which is related to the proximity of a higher excited state.

This work reports the study of the second- and third-order nonlinear optical properties of two dibenzylideneacetone derivatives: (1E,4E)-1,5-bis(4-bromophenyl)penta-1,4-dien-3-one (4-DBDBA) and (1E,4E)-1,5-bis(4-chlorophenyl)penta-1,4-dien-3-one (4-DCDBA) in dichloromethane solution. The nonlinear optical properties investigated were the first molecular hyperpolarizability and the two-photon absorption (2PA) cross-section by using the hyper-Rayleigh scattering (HRS) and Z-scan techniques respectively. The values of the first molecular hyperpolarizability obtained by HRS ( β H R S ) were 25 × 10 - 30 c m 4 s t a t v o l t - 1 for 4-DBDBA whereas for 4-DCDBA was 27 × 10 - 30 c m 4 s t a t v o l t - 1 . The peak value for 2PA cross-section by the spectral measurement was around 24 G M for 4-DBDBA and 17 G M for 4-DCDBA. In addition, quantum chemical calculations were performed to support the interpretation from experimental results.

The brightness study of emissive compounds is one of the fundamental spectroscopic characterizations. In this work, we assessed the brightness values of eight 2,5-disubstituted oxazole dyes derivatives by combining linear and nonlinear spectroscopic parameters. The range of the brightness values obtained is from 0.26 GM to 15.15 GM. The highest value belongs to compound 14 m, which, compared to previously investigated compounds of similar π-conjugation length, is at least two times higher. Brightness values were determined in the spectral region between 700 nm–720 nm, revealing this class of dyes' potential to be used as photoluminescence bioprobes excited by two-photons.

This work describes the second and third orders of nonlinear optics properties of unsubstituted chalcone (C15H12O) and mono-substituted chalcone (C16H14O2) in solution, using hyper-Rayleigh scattering and Z-Scan techniques to determine the first molecular hyperpolarizability (β) and the two-photon absorption (2PA) cross section respectively. β Values of 25.4 × 10−30 esu and 31.6 × 10−30 esu, for unsubstituted and mono-substituted chalcone, respectively, dissolved in methanol have been obtained. The highest values of 2PA cross-sections obtained were 9 GM and 14 GM for unsubstituted and mono-substituted chalcone, respectively. The experimental 2PA cross sections obtained for each chalcone are in good agreement with theoretical results.

The development of electrospun polymer fiber networks embedded with metal oxide nanoparticles in organic dye media favors the photons waveguiding and multiple scattering, providing the adequate environment for random laser action. The use of water-soluble polymer solution as support for electrospun matrix introduces relevant application in biomedical applications. Herein, it is explored the use of block copolymers (Eudragit L100) as support for electrospinning of polymer fiber doped with titanium dioxide (scatter centers) and rhodamine B (gain media). The resulting fiber net presented random laser behavior that depends on aggregation degree of gain media (rhodamine B) due to the combination of reabsorption/reemission processes with tunable response (emission peak position). These results open new possibilities for use of low-cost and water soluble electrospun-based random lasers based on organic dyes and random network of polymer matrix.

Five chalcone-based molecules denominated by C-3 ((E)-1-(4-methoxyphenyl)-3-phenylprop-2-en-1-one), C-4 ((E)-1,3-bis(4-methoxyphenyl)prop-2-en-1-one), C-5 ((E)-1-(benzo[d][1,3]dioxol-5-yl)-3-(4-methoxyphenyl)prop-2-en-1-one), C-6 ((E)-3-(naphthalen-1-yl)-1-phenylprop-2-en-1-one) and C-7 ((E)-1-(4-methoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one) were synthesized by Claisen-Schmidt reaction in solution of NaOH in water/ethanol 2:1. The aldehydes used were benzaldehyde, anisaldehyde, and β-naphthaldehyde, while the used ketones were acetophenone, p-methoxyacetophenone, and 3,4-methylenedioxyacetophenone. Z-scan and hyper-Rayleigh scattering techniques were used to study the nonlinear optical properties of these compounds in dichloromethane medium. By using Z-scan technique with femtosecond pulses, two-photon absorption cross-sections (σTPA) were determined, while the first molecular electronic hyperpolarizabilities (βHRS) were evaluated by the hyper-Rayleigh scattering technique, with picosecond pulses. From the recorded two-photon absorption spectra, it was identified that compound C-7 presented the highest σTPA, regarding the HOMO-LUMO transition, with a value of 40 GM, while C-6 achieved the lowest value for the same transition with 13 GM. Concerning the values of the first molecular hyperpolarizability, compound C-4 presented the highest value, 38 × 10−30 cm4 statvolt−1, while C-3 presented the lowest βHRS value of about 16 × 10−30 cm4 statvolt−1. Time-dependent density functional theory calculations were used to simulate the one- and two-photon absorption spectra, as well to predict the theoretical value of βHRS in dichloromethane and vacuum medium.

Two π-conjugated oxazoles compounds dissolved in toluene were characterized by the hyper-Rayleigh scattering technique in order to determine the value of the first molecular hyperpolarizability (βHRS). Quantum-chemical calculations using time-dependent density functional theory level were performed to calculate the static and dynamic βHRS theoretical values. Experimental βHRS have shown values of about 42 × 10 −30 cm 4 statvolt −1 and 31 × 10 −30 cm 4 statvolt −1 for both organic compounds, which are in a satisfactory accordance with the calculated results. Dos compuestos oxazoles conjugados con π disueltos en tolueno se caracterizaron por la técnica de dispersión Hyper-Rayleigh para determinar el valor de la primera hiperpolarizabilidad molecular (βHRS). Para calcular los valores teóricos estáticos y dinámicos de βHRS se realizaron cálculos cuántico-químicos utilizando el nivel de teoría funcional de la densidad dependiente del tiempo. Los βHRS experimentales han mostrado valores de aproximadamente 42 × 10 −30 cm 4 statvolt −1 y 31 × 10 −30 cm 4 statvolt −1 para ambos compuestos orgánicos, que están en una conformidad satisfactoria con los resultados calculados.

Strapped acceptor–π–donor–π–acceptor type fluorophores exhibit intense near infrared emission, together with near infrared two-photon absorption., Fluorophores that can undergo excited-state intramolecular proton transfer (ESIPT) represent promising scaffolds for the design of compounds that show red-shifted fluorescence. Herein, we disclose new near infrared-emissive materials based on a dialkylamine-strapped 2,5-dithienylpyrrole as an ESIPT scaffold. The introduction of electron-accepting units to the terminal positions of this scaffold generates acceptor–π–donor–π–acceptor (A–π–D–π–A) type π-conjugated compounds. Following the ESIPT, the electron-donating ability of the core scaffold increases, which results in a substantially red-shifted emission in the NIR region, while increasing the oscillator strength. The electron-accepting units play a vital role to achieve intense and red-shifted emission from the ESIPT state. The strapped dialkylamine chain that forms an intramolecular hydrogen bond is also essential to induce the ESIPT. Moreover, an extended A–π–D–π–A skeleton enables two-photon excitation with the NIR light. One of the derivatives that satisfy these features, i.e., borylethenyl-substituted 5, exhibited an intense NIR emission in polar solvents such as acetone (λem = 708 nm, ΦF = 0.55) with a strong two-photon-absorption band in the NIR region.

In this work, six π-conjugated oxazole compounds dissolved in dichloromethane were characterized with linear and nonlinear optical measurements. Z-scan with femtosecond laser pulses was employed to determine the two-photon absorption (TPA) spectra. Other photophysical parameters, such as absorbance, solvatochromism, lifetime fluorescence, and fluorescence anisotropy, were evaluated with linear optical techniques. The experimental TPA cross section spectra were adjusted by the sum-over-states (SOS) model, by which important parameters such as transition dipole moments and broadening parameters were determined. To better understand the TPA spectra of the oxazole compounds, quantum-chemical calculations using the response function formalism and the density functional theory level of theory were performed. Using the results provided by the quantum-chemical calculations and the broadening parameters estimated through the application of the SOS model, the TPA spectra were simulated by the superposition (summation) of individual homogeneous Lorentzian absorption profiles.

This work reports a novel deltamethrin (DM) sensor able to detect nano-molar concentrations in ethanol solutions. The sensing layer consists of a thin film, obtained via a layer-by-layer technique, from alternate adsorption of poly(allylamine chloride) (PAH) and poly[1-[4-(3-carboxy-4-hydroxyphenylazo)-benzenesulfonamide)-1,2-ethanediyl]sodium salt] (PAZO) onto a solid support with interdigitaded gold electrodes. The sensor response, obtained from impedance spectroscopy measurements, was revealed to be linear with respect to the real part of impedance, taken at 100 Hz, when plotted as a function of the logarithm of deltamethrin molar concentrations in the micro- to nano-molar range. Sensor sensitivity was of 41.1 ± 0.7 kΩ per decade of concentration for an immersion time above 2 min and the reproducibility is approximately 2% in a binary solution of ethanol and deltamethrin. The main insight of this work concerns to DM detection limits as the sensor revealed to be able to detect concentrations below 0.1 nM, a value which is significantly lower than any reported in the literature and close what is appropriate for in situ environmental contaminant detection.

Roughness of a positively charged poly(allylamine hydrochloride) (PAH) polyelectrolyte surface was shown to strongly influence the adsorption of 1.2-dipalmitoyl-sn-3-glycero-[phosphorrac-(1-glycerol)] (DPPG) liposomes on it. The adsorption kinetic curves of DPPG liposomes onto a low-roughness PAH layer reveal an adsorbed amount of 5 mg/m2, pointing to liposome rupture, whereas a high-roughness surface leads to adsorbed amounts of 51 mg/m2, signifying adsorption of intact liposomes. The adsorption kinetic parameters calculated from adsorption kinetic curves allow us to conclude that the adsorption process is due to electrostatic interactions and also depends on processes such as diffusion and reorganization of lipids on the surface. Analysis of the roughness kinetics enabled us to calculate a growth exponent of 0.19 ± 0.07 and a roughness exponent of around 0.84, revealing that DPPG liposomes adsorbed onto rough surfaces follow the Villain self-affine model. By relating self-affine surfaces with hydrophobicity, the liposome integrity was explained by the reduction in the number of water molecules on the PAH surface, contributing to counterion anchorage near PAH ionic groups, reducing the liposome/PAH layer electrostatic forces and, consequently, avoiding liposome rupture.

The luminescence spectra of milk containing rhodamine 6G are shown to exhibit typical signatures of random lasing when excited with 532 nm laser pulses. Experiments carried out on whole and skim forms of two commercial brands of UHT milk, with fat volume concentrations ranging from 0 to 4%, presented lasing threshold values dependent on the fat concentration, suggesting that a random laser technique can be developed to monitor such important parameter.

Made available in DSpace on 2018-12-11T16:47:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-06-01 A Rhodamine B-doped 3-glycidoxypropyltrimethoxysilane (GPTS)/tetraethyl orthosilicate (TEOS)-derived organic/silica monolithic xerogel with excellent optical properties was prepared and its potential as a random laser host investigated. This hybrid material has a non-porous organic/inorganic morphology with silica-rich nanoparticles of less than 10 nm in diameter homogeneously dispersed within the matrix. Random laser emission with incoherent feedback, centered at 618 nm, was observed from Rhodamine B incorporated into the monolithic xerogel when excited by a 532 nm pulsed laser. This hybrid system is shown to be very promising for the development of a new class of random laser-based integrated devices, with applications ranging from optical bio-imaging to sensing. Departamento de Física Universidade Federal de Sergipe Departamento de Física Unesp - Universidade Estadual Paulista Departamento de Física Universidade Federal de São Carlos Instituto de Física de São Carlos Universidade de São Paulo, CP 369 Departamento de Física Unesp - Universidade Estadual Paulista

Here we report the aqueous synthesis of CdTe nanocrystals capped with 3-mercaptopropionic acid (MPA) and the evaluation of the effect of mixing different thiols with MPA on the spectroscopic and electrochemical properties. Additional ligands were cysteine (CYS) and glutathione (GSH). CYS and GSH produce opposite effects on the photoluminescence quantum yield (QY) with a decrease and increase in QY in comparison to MPA, respectively. All samples exhibited monoexponential photoluminescence decays indicating the presence of high-quality nanocrystals. Electrochemical measurements evidenced the presence of several redox peaks and allowed the calculation of the electrochemical band gaps, which were in agreement with the values estimated from absorption spectra and reflected differences in nanocrystal size.

Quartz Crystal Microbalance (QCM) is a widely used technique to characterize adsorption/desorption phenomena at the solid/liquid interface. However, the obtained adsorption/desorption kinetics curves are often not reproducible and present some noise and long term fluctuations. In this work, the accuracy of a commercial QCM to measure the adsorbed amount of polyelectrolytes and biological molecules was evaluated in terms of experimental QCM configurations with respect to quality, stability, and reproducibility of the measured data. Evaluation consisted in comparing the adsorption kinetics curves of the cationic polyelectrolyte poly(ethyleneimine) and the anionic 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) liposomes, when setting the quartz crystal surface in stationary horizontal open, stationary horizontal closed, stationary vertical open, continuous vertical closed, and stationary vertical closed measuring configuration. For this last configuration, a new cell was designed and implemented. The analysis of the kinetics curves revealed that horizontal modes are more unstable when subjected to fostering noise due to the mechanical vibrations and lead to resonance frequency shift. This shift is caused by the measurement of non-adsorbed molecules which are deposited on the quartz crystal due to gravity force. The vertical modes proved to be more reproducible and reliable.