PHOTOCHEMISTRY ON SURFACES: TRIPLET-TRIPLET ENERGY TRANSFER ON MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE REFLECTANCE TRANSIENT ABSORPTION and EMISSION SPECTROSCOPY*

Triplet-triplet energy transfer has been studied between benzophenone and an oxazine dye (2,7-bis(diethyl-amino)-phenazoxonium chloride) co-adsorbed on the surface of microcrystalline cellulose. Ground state absorption and fluorescence measurements provide evidence for dimer formation of the oxazine dye when adsorbed on cellulose in contrast to the behaviour in ethanol solution where no dimerization is observed. The equilibrium constant for dimerization, which is found to be (1.0 × 0.1) × 10⁶ mol^?1 g (2560 × 250 dm³ mol^?1) for oxazine alone on cellulose decreases in the presence of co-adsorbed benzophenone. Fluorescence is detected from excited monomeric but not from excited dimeric oxazine. The absorption spectrum of the triplet state of oxazine adsorbed on cellulose was obtained and its extinction coefficient evaluated relative to that of triplet benzophenone which was used as a sensitizer. The lifetime of adsorbed triplet oxazine is 4.3 ms which is 300 times longer than that in acetonitrile solution. The efficiency of energy transfer from triplet benzophenone to oxazine on cellulose was studied using both time resolved sensitized absorption and phosphorescence intensity measurements as a function of oxazine concentration. Lifetime measurements show that the energy transfer process involves static quenching since the benzophenone lifetime is independent of oxazine loading at the surface. A mechanism is proposed to explain the results in which one oxazine molecule is suggested as being able to quench phosphorescence from a “pool” consisting of 2 to 3 benzophenone molecules.     

Energy transfer from chemically attached rhodamine 101 to adsorbed methylene blue on microcrystalline cellulose particles

Rhodamine 101 (R101) was chemically attached onto microcrystalline cellulose and methylene blue (MB) was adsorbed to a sample bearing nearby 6 × 10^?7 mol R101 (g cellulose)^?1. The system was studied by reflectance and emission spectroscopy in the solid state. R101 shows no aggregation in these conditions and, while pure MB builds up dimers on cellulose even at 2 × 10^?8 mol g^?1, in the presence of R101 no evidence on selfaggregation or heteroaggregation is found up to around 10^?6 mol g^?1. No exciplex formation is found as well. The overall fluorescence quantum yield measured on thick layers, once re‐absorption effects are accounted for, amounts to 0.80 ± 0.07 for pure R101 and decreases steadily on increasing the concentration of MB. Results demonstrate the occurrence of radiative and nonradiative singlet energy transfer from R101 to MB. For thick layers of particles, the combined effect of both kinds of energy transfer amounts to nearly 80% at the highest acceptor concentration, while nonradiative transfer reaches 60% both for thin and optically thick layers. The dependence of nonradiative energy transfer efficiencies on the acceptor concentration is analyzed and the origin of departures from Förster behavior at low acceptor concentration is discussed.     

吖啶橙染料在表面活性剂存在时溶液状态的光谱研究

应用紫外－可见吸收光谱和荧光光谱，研究了激光染料吖淀橙（ＡＯ）的溶液状态以及添加表面活性剂时吖啶橙染料的溶液状态变化，并应用Ｋａｓｈａ理论推算出二聚体时的状态，结果表明：在吖啶橙溶液中，ＡＯ二聚体的α＝４９°，ｒ＝１．３９ｎｍ。     

Characterization of rhodamine 6G aggregates intercalated in solid thin films of laponite clay. 2 Fluorescence spectroscopy

The photoluminescence response of Rhodamine 6G (R6G) laser dye intercalated into solid thin films of Laponite (Lap) clay is studied as a function of dye loading. Fluorescence spectroscopy (steady-state and time-resolved techniques) was used to characterize the R6G species adsorbed into the solid films. For very diluted R6G loadings (40% CEC), with a reminiscent fluorescence band at around 600 nm.     

A Carbocationic Triarylmethane-Based Porous Covalent Organic Network

A thermally stable carbocationic covalent organic network (CON), named RIO-70 was prepared from pararosaniline hydrochloride, an inexpensive dye, and triformylphloroglucinol in solvothermal conditions. This nanoporous organic material has shown a specific surface area of 990 m² g⁻¹ and pore size of 10.3 Å. The material has CO₂ uptake of 2.14 mmol g⁻¹ (0.5 bar), 2.7 mmol g⁻¹ (1 bar), and 6.8 mmol g⁻¹ (20 bar), the latter corresponding to 3 CO₂ molecules adsorbed per pore per sheet. It is shown to be a semiconductor, with electrical conductivity (σ) of 3.17×10⁻⁷ S cm⁻¹, which increases to 5.26×10⁻⁴ S cm⁻¹ upon exposure to I₂ vapor. DFT calculations using periodic conditions support the findings.     

DNA binding behaviour of mixed ligand vanadium(V) complex based on novel tridentate hydrazone and benzhydroxamic acid ligand systems

Novel tridentate ONO hydrazone ligand (HL) and the corresponding vanadium(V) complex, [VO(HL)(Benz)], based on the ligand and benzhydroxamic acid, were synthesized and characterized using UV–visible, Fourier transform infrared, NMR and mass spectral studies. In order to assess the binding efficacy of the synthesized complex with DNA, UV absorption spectral titrations, fluorescence displacement assays using ethidium bromide and acridine orange dyes, circular dichroism, viscosity and molecular docking studies were carried out. Based on the results obtained, it is evident that the complex shows significant intercalating ability almost comparable to that of the standard intercalator drug cisplatin. The binding affinity values for the [VO(HL)(Benz)] complex and cisplatin were found to be (3.84 ± 0.08) × 10⁴ M⁻¹ and (4.27 ± 0.012) × 10⁴ M⁻¹. In addition, the cytotoxicity of [VO(HL)(Benz)] was also assessed by MTT assay against the MCF‐7 cell line.     

FLUORESCENCE LIFETIME OF ACRIDINE ORANGE IN SODIUM DODECYL SULFATE PREMICELLAR SOLUTIONS

Abstract— The absorption and fluorescence spectra, and the fluorescence lifetime of acridine orange (AO) were measured in a wide range of the sodium dodecyl sulfate (SDS) concentration below and above the critical micelle concentration (cmc). The fluorescence consisted of two components with different lifetimes; short (<3 ns) and long (>3 ns). The short and long lifetime components are attributed to the AO monomer and dimer associated with detergent, respectively. The lifetime of the dimer increased with increasing the SDS concentration just below the cmc. It decreased suddenly to a constant value just above the cmc. The lifetime of the monomer showed only a slight increase in the concentration range of SDS employed.     

ZnO and TiO2 clusters as catalyst in the addition and abstraction reaction of acrylic acid with the OH radical

The present work displays the theoretical analysis on the role of metal oxide clusters as an effective catalyst in the reaction between acrylic acid and OH radical, which has an energy barrier of 12.4 kcal/mol. The formation of metal oxide cluster such as ZnO and TiO₂ with varying size from monomer to hexamer is analyzed using cohesive energy, which increases with cluster size. Adsorption of acrylic acid on clusters reveals that dimer ZnO and tetramer TiO₂ are good adsorbed entities. The dimer ZnO and tetramer TiO₂ clusters have reduced the barrier height. However, from the thermodynamical analysis of H-abstraction and OH addition reaction, the dimer ZnO cluster is found to be a good catalyst than a tetramer TiO₂ cluster. The favorable H abstraction and OH addition reactions are feasible at the active methylene group (–CH). OH addition reactions dominate over the H abstraction reaction. Further, the presence of metal oxide clusters enhances the rate of the reaction between acrylic acid and OH radical. The kinetics of the favorable reaction with a dimer ZnO cluster has a rate constant of 7.80 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, which is higher than the literature report (1.75 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹). Overall, ZnO and TiO₂ metal oxide clusters can be effectively utilized as catalyst.     

Determination of Paraquat by Cucurbit[7]uril Sensitized Fluorescence Quenching Method

A method for the determination of paraquat by cucurbit[7]uril (CB[7]) fluorescence quenching was developed. The assay was based on the reaction of the CB[7] with acridine orange. The fluorescence intensity of acridine orange regularly increased with the addition of CB[7]. However, while an appropriate amount of paraquat was added to the CB[7]- acridine orange system, the fluorescence intensity of the system was quenched which was employed to determine paraquat. Under the optimum conditions, a linear range of 3.0–800 nmol L^?1 and a detection limit of 1.61 nmol L^?1 for paraquat were obtained. The simple strategy reported here offers great practical potential for the determination of pesticide residues in agricultural products.     

Hybrid porous polymers based on double-decker and cage-ype silsesquioxanes for the high-efficiency removal of neonicotinoid insecticides and dyes

Different ratios of octavinylsilsesquioxane (OVS) reacted with phenyl-substituted double-decker silsesquioxane (Ph-DDSQ) via the simple Friedel-Crafts reaction provides several innovative silsesquioxane-based porous polymers (PCS-ODs). The hybrid polymers show adjustable porosity (specific surface areas of 1235 m² g⁻¹ and large pore volumes >1.07 cm³ g⁻¹). FTIR, SEM, BET, TGA, solid-state ¹³C and ²⁹Si MAS NMR spectra were employed to fully characterize these hybrid materials. They display good adsorption capacities for neonicotinoid insecticides (imidacloprid [IMI], acetamidine [ACE] and thiamethoxam [THI]), with capacities up to 117 ± 2, 70 ± 1 and 61 ± 4 mg g⁻¹, respectively. Dyes (Congo red [CR] and rhodamine B [RB]) can also be sufficiently removed, the adsorption capacities are 1822 ± 4 and 912 ± 3 mg g⁻¹. In addition, PCS-ODs can be cycled at least five times.     

High-performance Flexible Symmetric Supercapacitor Based on Heterostructured PANI@MoS2 Nanocomposite Electrode

Three-dimensional (3D) heterostructured molybdenum disulfide (MoS₂) is used as base materials for aniline monomer in situ polymerization on its surface. It is found that the aniline addition has a remarkable effect on the energy storage of the final compounds due to the improvement of the conductivity and structure stability combined with the synergistic effect between the two types of species. The optimal compound of PANI@MoS₂-150 not only shows a high capacitance value of 801.4 F ⋅ g⁻¹ at a current density of 0.5 A ⋅ g⁻¹ but also provides a high retention rate of 77.4 % after 10,000 cycles. The capacitance fading may be due to the increase of the internal resistance analyzed by EIS. Furthermore, a flexible symmetric supercapacitor based on PANI@MoS₂-150 has also been fabricated and the specific capacitance reaches 105 F ⋅ g⁻¹ at a current density of 1 A ⋅ g⁻¹. Impressively, the capacitance retention is larger than 100 % undergoing 10,000 cycles. Besides, the highest energy density of 21 Wh ⋅ kg⁻¹ was obtained. Additionally, the fabricated symmetric supercapacitor demonstrates excellent flexibility.     

Poly(hydroxyethyl methacrylate) membranes: as a hydrogel support for use in immobilized metal affinity chromatography

Lysozyme adsorption onto a dye ligand (Procion Red HE-3B) immobilized and Cu(II) incorporated poly(2-hydroxyethylmethacrylate) (pHEMA) membrane, were investigated. The membranes were prepared by UV initiated photopolymerization of HEMA in the presence of an initiator (α-α′-azoisobutyronitrile; AIBN). The amount of immobilized dye on the membrane was 112.2 μmol g⁻¹. Lysozyme adsorption on to these membranes from aqueous solutions containing different amounts of lysozyme at different pH was investigated in batch system. Lysozyme adsorption capacity of the dye-ligand immobilized membrane was 45.6 mg g⁻¹. Lysozyme adsorption capacity of the Cu(II) incorporated membranes (112.3 mg g⁻¹) was greater than that of the Procion Red HE-3B immobilized membranes. The non-specific adsorption of lysozyme on the pHEMA membranes was 0.14 mg g⁻¹. More than 97% of the adsorbed lysozyme were desorbed in 60 in the desorption medium containing 1.0 M KSCN at pH 8.0.     

Two-step anti-cooperative self-assembly process into defined π-stacked dye oligomers: insights into aggregation-induced enhanced emission

Aggregation-induced emission enhancement (AIEE) phenomena received great popularity during the last decade but in most cases insights into the packing structure – fluorescence properties remained scarce. Here, an almost non-fluorescent merocyanine dye was equipped with large solubilizing substituents, which allowed the investigation of it''s aggregation behaviour in unpolar solvents over a large concentration range (10⁻² to 10⁻⁷ M). In depth analysis of the self-assembly process by concentration-dependent UV/Vis spectroscopy at different temperatures revealed a two-step anti-cooperative aggregation mechanism. In the first step a co-facially stacked dimer is formed driven by dipole–dipole interactions. In a second step these dimers self-assemble to give an oligomer stack consisting of about ten dyes. Concentration- and temperature-dependent UV/Vis spectroscopy provided insight into the thermodynamic parameters and allowed to identify conditions where either the monomer, the dimer or the decamer prevails. The centrosymmetric dimer structure could be proven by 2D NMR spectroscopy. For the larger decamer atomic force microscopy (AFM), diffusion ordered spectroscopy (DOSY) and vapour pressure osmometric (VPO) measurements consistently indicated that it is of small and defined size. Fluorescence, circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy provided insights into the photofunctional properties of the dye aggregates. Starting from an essentially non-fluorescent monomer (Φ_Fl = 0.23%) a strong AIEE effect with excimer-type fluorescence (large Stokes shift, increased fluorescence lifetime) is observed upon formation of the dimer (Φ_Fl = 2.3%) and decamer (Φ_Fl = 4.5%) stack. This increase in fluorescence is accompanied for both aggregates by an aggregation-induced CPL enhancement with a strong increase of the g_lum from ∼0.001 for the dimer up to ∼0.011 for the higher aggregate. Analysis of the radiative and non-radiative decay rates corroborates the interpretation that the AIEE effect originates from a pronounced decrease of the non-radiative rate due to π–π-stacking induced rigidification that outmatches the effect of the reduced radiative rate that originates from the H-type exciton coupling in the co-facially stacked dyes.

The self-assembly of a dipolar merocyanine into preferred dimers and small-sized chiral aggregates leads to enhanced emission due to a reduced non-radiative rate as well as amplified circular polarized luminescence.     

Adsorption and spectral studies of 3,6-diaminoacridine adsorbed on montmorillonite clay and cellulose

Montmorillonite-and cellulose-adsorbed 3,6-diaminoacridine are prepared. The adsorption isotherm studies show that while 3,6-diaminoacridine molecules are adsorbed in the interlayer spaces of the montmorillonite clay, the dye molecules are adsorbed on the surface of cellulose. Quenching studies reveal that the Al³⁺ ions of the aluminosilicate layers of the clay also quench the excited state emission of the adsorbed 3,6-diaminoacridine.     

Influence of self-assembly of amphiphilic imidazolium ionic liquids on their host–guest complexes with cucurbit[n]urils

Two symmetric amphiphilic imidazolium ionic liquids having ω-undecenyl chains form supramolecular complexes with CB[7] and CB[8] in water as revealed by ¹H NMR spectroscopy and MALDI-MS. Binding constants in the range 10⁴ to 10⁵ M^?1 were estimated from the conductivity measurements for the 1:1 complexes of these imidazolium ionic liquids with CB[7] and CB[8]. Radical initiated polymerization of these host–guest complexes at concentrations above the critical self-assembly concentration of imidazolium ionic liquids to form liposomes, destroys completely (CB[7]) or partially (CB[8]) the host–guest ionic liquid@CB[n] complex; this behaviour was proved by titration with acridine orange tricyclic dye, of CB[n]s in the colloidal solutions of the liposomes before and after performing dialysis to remove free CB[n]s. Thus, the increase in the fluorescence emission of acridine orange by CB[7] is not observed if the polymerized ionic liquid@CB[7] complex is submitted to dialysis to remove uncomplexed CB[7]. Analogous study by titration of absorbance change of acridine orange solutions caused by CB[8], reveals only a partial destruction of the host–guest complex by self-assembly of amphiphilic ionic liquid above the critical self-assembly concentration. The results obtained have been rationalized considering that the driving force for the formation of supramolecular ionic liquid@CB[n] complexes is a hydrophobic interaction between the apolar alkenyl chain and the cucurbituril interior cavity and that these hydrophobic interactions are disturbed when self-assembly leading to liposomes occurs.     

The effect of preferential solvation on the kinetic order of alkyl methacrylate polymerization in benzene

The kinetic order of the polymerization of n-alkylmethacrylates with respect to monomer in benzene (fractional and greater than one) has been interpreted as due to concentration changes of a monomer at the site of reaction caused by preferential solvation of the growing macromolecule by benzene. Correlation of the rates of polymerization at 30° with determined monomer concentrations in the close vicinity of the polymer chain gives kinetic orders of 1±0.05 for both n-butyl- and n-dodecyl-methacrylates. The coefficient of preferential solvation at 30° for the polymers investigated is between 0.1 and 0.4 [cm³ g^?1] depending on the composition of the mixture of benzene and monomer. The coordination numbers 3 and 4 needed for calculation of the composition of the solvent in the solvating layer correspond to theoretical views on polymer solutions.     

The electronic structures and spectra of proflavine,acridine orange,and their DNA complexes

The electronic structure of the proflavine cation is studied by the SCF –ASMO –CI method using the Pariser–Parr–Pople approximations. It is shown that the band at 445 mμ may be assigned to the ¹A₁ → ¹B₁, transition polarized along the long axis of the molecule. The bands in the neighbourhood of 260 mμ, which are composed of three absorption bands, are tentatively assigned to the ¹A₁ → ¹B₁, ¹A₁ → ¹B₁, and ¹A₁ → ¹A₁ transitions, respectively, in order of decreasing wavelength. The spectrum of the acridine orange cation may be understood to have the same assignment as that of the proflavine cation. The acridine dye cations are well known for their dimerization with concentration. The intermolecular distances in these dimers are estimated from the band shifts due to the formation of dimers, using the exciton theory. The main contribution to the molecular interaction is shown to be the electrostatic dipole–dipole interaction. Since the first excitation band of the dye molecule which exhibits a remarkable change due to the formation of the DNA–acridine dye complex, is suggested to be polarized along the long axis, preference of the outside stacking or the intercalation model is qualitatively discussed from the spectral shift of the acridine dye bound to the DNA, assuming simple models.     

Understanding Photophysical Effects of Cucurbituril Encapsulation: A Model Study with Acridine Orange in the Gas Phase

Encapsulation of dyes by cucurbituril macrocycles has proven profitable as a strategy to alter fluorescence characteristics in useful ways. Encapsulation generally results in longer fluorescence lifetimes, enhanced brightness, and solvatochromic effects not normally seen in the condensed phase. These effects have been attributed variously to both the removal of interactions with solvent molecules and to the confined environment of extremely low polarizability provided by the cucurbituril interior. It is difficult to disentangle these effects in solution. Here, we present results from gas‐phase experiments designed to separate these effects, using cucurbit[7]uril (CB7), and the cationic dye acridine orange (AOH⁺) as a probe. Fluorescence properties of gaseous AOH⁺ are compared with those of the gaseous AOH⁺‐CB7 complex and with the properties of the dye and complex in aqueous solution. The dependence on the local environment of several spectroscopic properties is discussed, including the fluorescence excitation and emission maxima, the size of the Stokes shift, fluorescence lifetime and relative brightness. An understanding of the modulation of fluorescence properties by the local environment, such as that promoted by this work, will aid in the rational design of improved fluorophores and fluorescent sensors.     

Formation of superoxide ions upon oxygen adsorption on magnesium-doped magnesium oxide: An EPR investigation

Oxygen adsorption on the surface of MgO, previously submitted to magnesium metal vapour, gives rise to the formation of at least five distinct species of adsorbed superoxide (O₂⁻) characterized by different g_zz values. Besides species previously observed on MgO, where O₂⁻ is generated by other methods, two new species are observed, having g_zz = 2.091 and g_zz = 2.064 respectively. The latter species is tightly bound to the surface and is assigned to O₂⁻ adsorbed on top of an array of five Mg²⁺ ions exposed because of the presence of an anion vacancy. The former is assigned to O₂⁻ weakly adsorbed on top of a five-coordinated Mg²⁺ ion at the (100) planar face of the oxide. This species differs from the other species present at the surface in that it is mobile and, as the temperature is raised from 77 to 298 K, exhibits rotation around the axis perpendicular to the surface. Spectra obtained by employing ¹⁷O-enriched O₂ indicate that both superoxide species are symmetrically adsorbed on the surface.     

Cathodic Stripping Voltammetric Behavior of Cytosine in Presence of Acridine Orange at the Static Mercury Drop Electrode

Abstract

Cathodic adsorptive electrochemical behavior of cytosine in the presence of acridine orange (DNA‐intercalating dye) at the static mercury drop electrode was investigated. A 0.001 M NaOH solution containing 2 ppm of acridine orange was found to be the optimal supporting electrolyte. Other optimum experimental conditions were found to be as follows: the initial potential at 0.00 V, linear n, and the potential scan rate at 50 mV s^?1. The analytical response was found to be linear in a range of cystosine concentrations from 0.30 ppm to 1.1 ppm. For a direct response, the detection limit was 1.2 ppb. The presence of ssDNA and the interference of some trace metals were also investigated.