A sample-drying technique for room-temperature phosphorescence

The sample-drying procedure described improves the precision, decreases the time needed and reduces the expense of the solid-surface room-temperature phosphorescence technique. Samples are dried in a glovebg apparatus interfaced to the sample compartment of the spectrophotophosphorimeter. The samples are treated with sodium citrate to prevent moisture quenching the phosphorescence emission The relative standard deviations of measurements are reduced to less than 2% for large sets of samples. The total time required for 37 samples is only 5.5 h compared to 20 h by a conventional technique.     

Liquid chromatographic separation of electrochemical oxidation products of biologically important purines

A liquid Chromatographie method utilizing a dual column system (Sephadex G-10 gel permeation and Sephadex QAE A-25 anion exchange) has been developed for the quantitative separation of mixtures of compounds found as products of electrochemical oxidation of biologically important purines. Milligram quantities of such product mixtures may be separated and quantitative analysis is also possible in some cases.     

Determination of naproxen in pharmaceutical preparations by room-temperature phosphorescence. A comparative study of several organized media.

Different methods for the determination of naproxen by room-temperature phosphorescence (RTP) using organized media such as cyclodextrins (beta-CD and gamma-CD) and micelles (Triton X-100 and sodium dodecyl sulfate) are reported. The inclusion complexes formed between both beta- and gamma-cyclodextrins and naproxen were previously investigated at both acid and basic pH by spectrofluorimetry. In both cases, 1:1 guest-host stoichiometries were established and the corresponding association constants were calculated. Different systems were examined with the purpose of obtaining phosphorescent emission from naproxen solutions, and the best signals were obtained when naproxen was in the presence of beta-CD-cyclohexane-Tl(I), gamma-CD-1,3-dibromopropane, Triton X-100-Tl(I) and SDS-Tl(I), respectively. In all cases, sodium sulfite was used as deoxygenator. The use of an inorganic compound (thallium nitrate) as a heavy-atom source in a cyclodextrin system represents a novel finding. Surface response optimization approaches were carried out to optimize the chemical variables which have an influence on the RTP emission of naproxen. Based on the results obtained, univariate RTP calibration methods for the determination of the analyte in pharmaceutical preparations were satisfactorily developed. In one case, the standard additions method was applied to a mixture of naproxen and the antibiotic tetracycline.     

Oxidation chemistry and biochemistry of some biologically important purines and indoleamines

The electrochemical oxidation of 7-methyluric acid and 5,6-dihydroxytryptamine (5,6-DHT) in aqueous solutions has been studied. The oxidation products have been separated and characterized using melting point, mass, ¹H nuclear magnetic resonance and spectral studies, and tentative mechanisms for the oxidation have been suggested. One of the oxidation products of 5,6-DHT, i.e. 2,7′-bi(5,6-DHT), has been found to produce a substantial neurotoxic effect in mice brain.     

Studies of cyclodextrin-enhanced room-temperature phosphorescence

The enhancement of room-temperature phosphorescence by α-, β- and γ-cyclodextrins in the presence of heavy atoms is described for p-aminobenzoic acid, anthracene and six of its derivatives, dibenzofuran and some other compounds. The sensitivity can be improved by treating the filter paper substrate with the cyclodextrin (preferably β-cyclodextrin) or by mixing the analyte with β-cyclodextrin prior to sample spotting on the substrate.     

Relativistic heavy-atom effects on heavy-atom nuclear shieldings

The principal relativistic heavy-atom effects on the nuclear magnetic resonance (NMR) shielding tensor of the heavy atom itself (HAHA effects) are calculated using ab initio methods at the level of the Breit-Pauli Hamiltonian. This is the first systematic study of the main HAHA effects on nuclear shielding and chemical shift by perturbational relativistic approach. The dependence of the HAHA effects on the chemical environment of the heavy atom is investigated for the closed-shell X(2+), X(4+), XH(2), and XH(3) (-) (X=Si-Pb) as well as X(3+), XH(3), and XF(3) (X=P-Bi) systems. Fully relativistic Dirac-Hartree-Fock calculations are carried out for comparison. It is necessary in the Breit-Pauli approach to include the second-order magnetic-field-dependent spin-orbit (SO) shielding contribution as it is the larger SO term in XH(3) (-), XH(3), and XF(3), and is equally large in XH(2) as the conventional, third-order field-independent spin-orbit contribution. Considering the chemical shift, the third-order SO mechanism contributes two-thirds of the difference of approximately 1500 ppm between BiH(3) and BiF(3). The second-order SO mechanism and the numerically largest relativistic effect, which arises from the cross-term contribution of the Fermi contact hyperfine interaction and the relativistically modified spin-Zeeman interaction (FC/SZ-KE), are isotropic and practically independent of electron correlation effects as well as the chemical environment of the heavy atom. The third-order SO terms depend on these factors and contribute both to heavy-atom shielding anisotropy and NMR chemical shifts. While a qualitative picture of heavy-atom chemical shifts is already obtained at the nonrelativistic level of theory, reliable shifts may be expected after including the third-order SO contributions only, especially when calculations are carried out at correlated level. The FC/SZ-KE contribution to shielding is almost completely produced in the s orbitals of the heavy atom, with values diminishing with the principal quantum number. The relative contributions converge to universal fractions for the core and subvalence ns shells. The valence shell contribution is negligible, which explains the HAHA characteristics of the FC/SZ-KE term. Although the nonrelativistic theory gives correct chemical shift trends in present systems, the third-order SO-I terms are necessary for more reliable predictions. All of the presently considered relativistic corrections provide significant HAHA contributions to absolute shielding in heavy atoms.     

Effects of polyacrylic acid on the room-temperature phosphorescence of selected compounds

Polyacrylic acid solutions of 4-phenylphenol, p-aminobenzoic acid, 1,2-benzocarbazole, and 5,6-benzoquinoline were spotted on filter paper and the results obtained by room-temperature phosphorescence were compared with similar samples spotted on filter paper without polyacrylic acid. Improvements in sensitivity ranged from 26 times to 1.1 times and limits of detection from 100 times to 1.1 times for the samples on filter paper with polyacrylic acid. The relative standard deviations for the samples with polyacrylic acid added were also improved.     

A comparative study of solvation dynamics in room-temperature ionic liquids

The solvation dynamics of ionic liquids have been the subject of many experimental and theoretical studies but remain poorly understood. We analyze these dynamics by modeling the time-resolved fluorescence response of coumarin 153 in two room-temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bromide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. Our results demonstrate that phenomena such as electrostatic screening operate significantly differently in the two liquids, and the relative importance of translational and rovibrational components of the ionic response depends significantly on the character of the ions involved. However, collective motion dominates the response of both ionic liquids, and the qualitative features of this collective behavior are strikingly similar in both cases.     

Some aspects of room-temperature phosphorescence in liquid solutions

Experimental requirements for room-temperature phosphorescence measurements in liquids (RTPL) are discussed. Phosphorescence quantum yields and triplet lifetimes of some brominated naphthalenes and halogenated biphenyls at 77 K in 2-methyltetrahydrofuran and at room temperature in hexane are reported and compared. Surprisingly the naphthalenes show only little loss in quantum yields in going from 77 K to room temperature. Sensitized phosphorescence is discussed as a means of expanding the analytical potential of RTPL. Results with a model system of benzophenone as a donor (analyte) and 1,4-dibromonaphthalene as an acceptor are presented.     

Photo-controllable room-temperature phosphorescence of organic photochromic polymers based on hexaarylbiimidazole

Pure organic room-temperature phosphorescent(RTP) materials have been attracting widespread attention due to the unique properties and broad applications. However, RTP materials with the adjustable photochromic property are still a challenge.Based on this, two polymers containing hexaarylbiimidazole are strategically designed with dual emission of both fluorescence and phosphorescence. Furthermore, both polymers show sensitive photochromic responses from faint yellow to brown upon exposure to ultraviolet light. This study can enrich pure organic luminescent systems and provide new ideas for functional RTP materials.     

The effects of ion-exchange filter papers and of heavy atoms on room-temperature phosphorescence of several indoles

Room-temperature phosphorescence (r.t.p.) of twelve indoles on different ion-exchange filter papers is examined. Anion-exchange filter paper Whatman DE-81 gives the largest r.t.p. signals in the presence of iodide; S & S 903 paper treated with diethylenetriamine-pentaacetic acid or supported carboxymethylcellulose resin are less useful. The heavy atom effect is necessary to observe analytically useful r.t.p. signals of indoles, with the trend iodide > thallium(I). Lifetimes of the r.t.p. of indoles are very short, in the millisecond range, and show two components. Absolute limits of detection between 0.2 and 14 ng show r.t.p. to be sensitive and simple analytical technique for these compounds.     

The applicability of the second-derivative method to room-temperature phosphorescence analysis

The use of the second-derivative (d²) technique to overcome some of the problems encountered in room-temperature phosphorescence analysis is investigated. Despite some reduction in the signal-to-noise values, the d²-technique was shown to be particularly suited to improving the selectivity of the assay. The utility of this method for applications in multicomponent mixture analysis is discussed. The two most significant figures of merit for room-temperature phosphorescence are the reduction of spectral overlap and the decrease of background interference.     

Organic room-temperature phosphorescence from halogen-bonded organic frameworks: hidden electronic effects in rigidified chromophores

Development of purely organic materials displaying room-temperature phosphorescence (RTP) will expand the toolbox of inorganic phosphors for imaging, sensing or display applications. While molecular solids were found to suppress non-radiative energy dissipation and make the RTP process kinetically favourable, such an effect should be enhanced by the presence of multivalent directional non-covalent interactions. Here we report phosphorescence of a series of fast triplet-forming tetraethyl naphthalene-1,4,5,8-tetracarboxylates. Various numbers of bromo substituents were introduced to modulate intermolecular halogen-bonding interactions. Bright RTP with quantum yields up to 20% was observed when the molecule is surrounded by a Br⋯O halogen-bonded network. Spectroscopic and computational analyses revealed that judicious heavy-atom positioning suppresses non-radiative relaxation and enhances intersystem crossing at the same time. The latter effect was found to be facilitated by the orbital angular momentum change, in addition to the conventional heavy-atom effect. Our results suggest the potential of multivalent non-covalent interactions for excited-state conformation and electronic control.

The number and position of halogen substituents in purely organic π–π* chromophores critically affect the efficiency of phosphorescence.     

Nature of the room-temperature phosphorescence of cyclodextrin-aromatic compound complexes in water

The lifetime of the room-temperature phosphorescence (RTP) of ß-cyclodextrinphenanthrene-chloroform complexes in water at 274 K increases from 1.7 to 2.3 s as the concentration of chloroform increases from 2.5 · 10^–3 to 0.125 mol L^–1. This dependence is explained by the formation of insoluble aggregates possessing RTP.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1014–1015, April, 1996.     

A new sample cell design for studying solid-matrix room-temperature phosphorescence moisture quenching

A new sample chamber was developed that can be used in the measurement of the effects of moisture on the room-temperature solid-matrix phosphorescence of phosphors adsorbed onto filter paper. The sample chamber consists of a sealed quartz cell that contains a special teflon sample holder. Sulfuric acid solutions in the quartz cell determine the percentage relative humidity in the cell and also determine the amount of moisture adsorbed onto the filter paper. The new sample chamber is much easier to use than a flowing nitrogen gas system. Results from both systems are compared with respect to ease of use and the amount of moisture adsorbed onto the filter paper.     

Fluorescence and liquid room-temperature phosphorescence of the aluminium-ferron chelate in vesicles

In order to evaluate the analytical potential of vesicles for enhancing the room-temperature luminescence of metal chelates, the photoluminescence emission of the aluminium-ferron complex in vesicular solutions was examined. The presence of vesicles of didodecyldimethylammonium bromide produced a six-fold enhancement in the fluorescence intensity of the metal chelate. Vesicles also proved to be efficient stabilizers to obtain analytically useful liquid room-temperature phosphorescence for aluminium. Optimum experimental conditions and luminescence characteristics of the aluminium complex in the presence of vesicles are described and compared with those obtained for the same chelate in micellar media. As a result, a vesicle-enhanced fluorimetric procedure is proposed which has been successfully applied to the determination of low levels of aluminium in milk powders.     

Influence of the alkyl side chain length on the room-temperature phosphorescence of organic copolymers

Pure organic room-temperature phosphorescence(RTP) materials have attracted wide attention owing to their excellent luminescent properties and great potential in various applications. In this work, iminostilbene and its analogues are applied to realize RTP emission by copolymerizing with acrylamide. It can be concluded that the growth of alkane chain in monomers can enhance the lifetime and photoluminescence quantum yield of RTP emission, and polymers with the larger conjugated structure of the ...     

pH-Responsive amorphous room-temperature phosphorescence polymer featuring delayed fluorescence based on fluorescein

Numerous researchers have paid attention to achieve metal-free phosphorescence by exploring new structures or new mechanisms. Herein, a facile way is introduced to endow a common fluorescence dye, tetrabromofluorescein (4Br-Flu), some fabulous optical characteristics such as dual emission including thermally activated delayed fluorescence, room-temperature phosphorescence (RTP), and the excellent pH-sensitivity. Shortly, 4Br-Flu with good light-emitting properties is composed into the polymer system. The multiple bromine atoms promote the spin-orbit coupling effect and facilitate triplet excitation. Especially, the hydrogen bonding network of the polymer restricts the molecular motion of 4Br-Flu so that the system can emit long-wavelength RTP when 4Br-Flu is doped into polyvinyl alcohol or co-polymerized with acrylamide. Due to the reversible transformation of protonation and deprotonation, the 4Br-Flu based polymer responded to acid and alkali like a phosphorescent switch which makes it an excellent hydrogen chloride/ammonia gas leak detector in dry environment.     

The effect of sample environment on the room-temperature phosphorescence of several polynuclear aromatic hydrocarbons

Room-temperature phosphorescence (r.t.p.) of numerous molecules has been studied with emphasis on several polynuclear aromatic hydrocarbons (PAH). The heavy atom effect has led to a significant enhancement of r.t.p. signals for the PAH studied with the trend being Tl⁺ > Ag⁺ > Pb²⁺ > Hg²⁺. The Tl⁺ also resulted in enhanced spectral features of emission bands. R.t.p. could be induced from PAH on a sodium acetate sample support as well as on filter paper. A study of the effect of different gaseous environments provided anomalous results.