Influence of ligand donor-acceptor properties on the structure,optical, and electrochemical characteristics of Ir(III) complexes with cyclometallated 2-phenylbenzotiazole

The cis-C,C-structure of a series of cyclometallated Ir(III) complexes with 2-phenylbenzotiazole was determined by the methods of X-ray diffraction (XRD) analysis, ¹H, ¹³C, ³¹P NMR, and IR spectroscopy. Long-wave absorption bands, phosphorescence, and processes of electrochemical oxidation and reduction of the complexes were assigned to the transfer of electrons presumably located on d _π and π* orbitals of cyclometallated 2-phenylbenzotiazole. The decrease in donor and acceptor properties of the ligands leads to the blue shift of absorption spectra and phosphorescence and to the anodic shift of oxidation and reduction potentials of the complexes.     

Phosphorescence and its characteristics in pyridine vapor

The phosphorescence emission of pyridine-d₀ and -d₅ has been observed in the vapor phase by means of time-resolved spectroscopy. The results of the experiments, which are described in full detail in this paper, on the phosphorescence spectrum, the excitation spectrum, the phosphorescence decay and sensitization of biacetyl phosphorescence indicate that the emission concerned is the genuine phosphorescence of the pyridines. For pyridine-d₀ (-d₅), the wavelength of the phosphorescence maximum is 450 nm (440 nm), the phosphorescence quantum yield 1.5 × 10^?6) (1.7 × 10^?6) and the phosphorescence lifetime is 1.2 μs (2.1 μs), the values for pyridine-d₅ being given in parentheses. The phosphorescence characteristics of pyridine are compared with those of other related molecules. The nature of the phosphorescent triplet state of pyridine is discussed with particular regard to the exceptionally fast non-radiative decay from that state.     

Phosphorescence sensitization via heavy-atom effects in d10 complexes

Heavy atom-induced phosphorescence of organic chromophores that originates from spin?Corbit coupling (SOC) is always accompanied by fluorescence quenching concomitant with a reduction of the triplet excited state lifetime. However, such changes are typically manifest by fluorescence quenching at room temperature and phosphorescence sensitization at cryogenic temperatures. Herein we overview our efforts over the past decade in which both internal and external heavy-atom effects (HAEs) can trigger room temperature phosphorescence (RTP) with dramatic shortening of the phosphorescence radiative lifetime by several orders of magnitude. Such spectral properties render new classes of phosphorescent materials for potential use in organic light-emitting diodes (OLEDs). The molecular systems described in this paper are organic fluorophores that are ??-complexed or ??-bonded to a multinuclear d¹⁰ transition metal center, the presence of which leads to phosphorescence sensitization because of the significant SOC in such materials.     

A new analytical application of nylon-induced room-temperature phosphorescence: determination of thiabendazole in water samples

This paper discusses the first analytical determination of the widely used fungicide thiabendazole by nylon-induced phosphorimetry. Nylon was investigated as a novel solid-matrix for inducing room-temperature phosphorescence of thiabendazole, which was enhanced under the effect of external heavy-atom salts. Among the investigated salts, lead(II) acetate was the most effective in yielding a high phosphorescence signal. An additional enhancement of the phosphorescence emission was attained when the measurements were carried out under a nitrogen atmosphere. There was only a moderate increase in the presence of cyclodextrins. The room-temperature phosphorescence lifetimes of the adsorbed thiabendazole were measured under different working conditions and, in all cases, two decaying components were detected. On the basis of the obtained results, a very simple and sensitive phosphorimetric method for the determination of thiabendazole was established. The analytical figures of merit obtained under the best experimental conditions were: linear calibration range from 0.031 to 0.26 μg ml⁻¹ (the lowest value corresponds to the quantitation limit), relative standard deviation, 2.4% (n = 5) at a level of 0.096 μg ml⁻¹, and limit of detection calculated according to 1995 IUPAC Recommendations equal to 0.010 μg ml⁻¹ (0.03 ng/spot). The potential interference from common agrochemicals was also studied. The feasibility of determining thiabendazole in real samples was successfully evaluated through the analysis of spiked river, tap and mineral water samples.     

Structures and optical and electrochemical properties of the Pt(II) and Pd(II) complexes with cyclometallated 2-phenylbenzothiazole and 1,4,7-trithiocyclononane

The distorted square pyramidal structures of the Pt(II) and Pd(II) complexes with cyclometallated 2-phenylbenzothiazole and flexible 1,4,7-trithiocyclononane are shown by X-ray diffraction analysis, IR spectroscopy, and ¹Н, ¹³С{¹H{, and ¹⁹⁵Pt NMR spectroscopy. The axial interaction of the d _Z2 orbital of Pt(II) and Pd(II) with the S atom of 1,4,7-trithiocyclononane results in the temperature quenching of the intraligand phosphorescence of the cyclometallated complexes in a solution and the one-electron ligand- and metal-centered reduction and oxidation of the complexes with the formation of the relatively stable Pd(III) complex (CIF file CCDC no. 1483011).     

The Effects of Salts on the Room-Temperature Fluorescence and Room-Temperature Phosphorescence of Tetrols on Filter Paper and Filter Paper with Silicone

Abstract

Several salts were investigated to enhance the room-temperature solid-matrix phosphorescence of the four stereoisomeric tetrols on filter paper. Thallium acetate was found to enhance the phosphorescence to the greatest extent, but it was necessary to prepare the thallium acetate in an acetic acid solution to achieve the maximum phosphorescence from the solid matrix. Also, thallium acetate essentially quenched the solid-matrix fluorescence of the tetrols. Without thallium acetate adsorbed on filter paper, strong room-temperature fluorescence signals were observed from the tetrols adsorbed on filter paper. With a new solid matrix, filter paper which contained silicone, no heavy-atom was needed to obtain strong phosphorescence from the adsorbed tetrols. In fact, the room-temperature fluorescence from the tetrols adsorbed on this type of filter paper was very strong. The room-temperature fluorescence gave a limit of detection in the sub-picogram range for one of the tetrols with the silicone treated filter paper.     

Sensitive and simple determination of the vasodilator agent dipyridamole in pharmaceutical preparations by phosphorimetry

The applicability of heavy atom-induced room-temperature phosphorescence to pharmaceutical samples is demonstrated in this work. Thus a new, simple, rapid, and selective phosphorimetric method for dipyridamole determination is proposed. The phosphorescence signals are a consequence of intermolecular protection when analytes are exclusively in the presence of heavy atom salts and sodium sulfite as an oxygen scavenger to minimize RTP quenching. The determination was performed in 0.1 mol L^–1 thallium(I) nitrate and 8 mmol L^–1 sodium sulfite at a measurement temperature of 20 °C. The phosphorescence intensity was measured at 635 nm, with excitation at 305 nm. Phosphorescence was easily developed; a linear concentration range was obtained between 0 and 100 ng mL^–1 with a detection limit of 940 ng L^–1, an analytical sensitivity of 2.5 ng mL^–1, and a standard deviation of 2.7% at 60 ng mL^–1 concentration. The method has been successfully applied to the analysis of dipyridamole in a unique Spanish commercial formulation containing 100 ng mL^–1 per capsule. The recovery was 101.6% with 6.5% standard deviation of analytical measurement. The method using the standard addition methodology has been validated.     

Direct determination of 1-naphthoxylactic acid in biological fluids by non-protected fluid room temperature phosphorimetry

A selective and sensitive room-temperature phosphorimetric method for the direct determination of 1-naphthoxylactic acid (NA) in biological fluids is described. It is based on obtaining a phosphorescence signal from NA using TlNO₃ as a heavy atom perturber and Na₂SO₃ as a deoxygenator without a protective medium. This technique is named non-protected room-temperature phosphorescence (NP-RTP), which allows to determine analytes in complex matrices without the need for tedious prior separation. Optimization of the operational conditions resulted in a detection limit for NA of 9.6 ng/mL according to the error propagation theory. The repeatability and standard deviation were also determined. This method was successfully applied to the determination of NA in urine and human serum.     

Complexes of Ir(III) and Pt(II) with cyclometallated 2-phenylbenzothiazole and chelating diethyldithiocarbamate and O-ethyldithiocarbonate ions: Structures and optical and electrochemical properties

It is shown by X-ray diffraction analysis, IR spectroscopy, and ¹Н, ¹³С{1H}, and ¹⁹⁵Pt NMR spectroscopy that the Pt(II) and octahedral Ir(III) complexes with metallated 2-phenylbenzothiazole and chelating diethyldithiocarbamate and O-ethyldithiocarbonate ions have the square and cis-C,C structure, respectively. The highest occupied and lowest unoccupied molecular orbitals of the complexes determining their long-wavelength absorption, phosphorescence, and one-electron oxidation and reduction are assigned to those predominantly localized on the mixed p(S)/d(M) and π* orbitals of the metallated ligand. The cathodic shift of the oxidation voltammogram and the bathochromic phosphorescence shift of the Pt(II) complex with the О-ethyldithiocarbonate ion are attributed to the enhanced donor–acceptor interaction of the donor S atoms of the ligand with Pt(II). The structural data are deposited with the Cambridge Crystallographic Data Centre (CIF files CCDC nos. 1058768 (Ia) and 1058767 (IIb)).     

Flexibility in Proteins: Tuning the Sensitivity to O2 Diffusion by Varying the Lifetime of a Phosphorescent Sensor in Horseradish Peroxidase¶

The heme in horseradish peroxidase (HRP) was replaced by phosphorescent Pt‐mesoporphyrin IX (PtMP), which acted as a phosphorescent marker of oxygen quenching and allowed comparison with another probe, Pd‐mesoporphyrin IX (Khajehpour et al. (2003) Proteins 53, 656–666). Benzohydroxamic acid (BHA), a competitive inhibitor of the enzyme, was also used to monitor its effects on phosphorescence quenching. With the addition of BHA, in the presence of oxygen, the phosphorescence intensity of the protein increased. In contrast, the addition of BHA, in the absence of oxygen, reduced the phosphorescence intensity of the protein. K_d= 18 μM when BHA binds to PtMP‐HRP. The effect of BHA can be explained by two factors: ( 1 ) BHA reduces the accessibility of O₂ to the protein interior and ( 2 ) BHA itself quenches the phosphorescence. Consistent with this, the oxygen quenching of the phosphorescence of PtMP‐HRP gave a quenching constant of k_q= 234 mm Hg^?1 s^?1 in the absence of BHA and k_q= 28.7 mm Hg^?1 s^?1 in the presence of BHA. The quenching rate of BHA is 4000 s^?1. The relative quantum yield of the phosphorescence of the Pt derivative is about six times that of the Pd derivative, whereas the phosphorescence lifetime is approximately eight times shorter. The high quantum yield and suitable lifetime make Pt‐porphyrins appropriate as sensors of O₂ diffusion and flexibility in heme proteins.     

New Wine in Old Bottles: Prolonging Room-Temperature Phosphorescence of Crown Ethers by Supramolecular Interactions

Supramolecular macrocyclic hosts have long been used in smart materials. However, their triplet emission and regulation at crystal level is rarely studied. Herein, ultralong and universal room-temperature phosphorescence (RTP) is reported for traditional crown ethers. A supramolecular strategy involving chain length adjustment and morphological locking through complexation with K⁺ was explored as a general method to tune the phosphorescence lifetime in the solid state. A maximum 10-fold increase of lifetime after complex formation accompanied with by invisible to visible phosphorescence was achieved. A deep encryption based on this activated RTP strategy was also facilely fabricated. This work thus opens a new world for supramolecular macrocycles and their intrinsic guest responsiveness offers a new avenue for versatile smart luminescent materials.     

Comparison of the Solution Luminescence Properties and Solid-Matrix Luminescence Properties of 2-Amino-1-Methyl-6-Phenylimidazo[4,5-B]Pyridine

Abstract

The solution fluorescence properties of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were compared with the solid-matrix luminescence properties of PhIP. The fluorescence properties were obtained in ethanol and several binary solutions of ethanol:water. An ethanol solution of PhIP gave a very strong fluorescence signal and the ethanol:water solutions only showed a small increase in the fluorescence signal. Acidic solutions of PhIP in ethanol:water (7:3) showed a major decrease in fluorescence intensity with at HCl of 10^?4 M and greater, but NaOH solutions of PhIP did not affect the fluorescence intensity to any great extent. Both acidic and basic solutions gave fluorescence emission spectra that were shifted to longer wavelengths. Solid-matrix room-temperature fluorescence (SMRTF) and solid-matrix room-temperature phosphorescence (SMRTP) were readily obtained on filter paper. SMRTP showed some distinct advantages over SMRTF and gave a limit of detection of 0.2 ng on filter paper. Several aspects of both solution luminescence and solid-matrix luminescence of PhIP are discussed.     

Thermally Activated Long Persistent Luminescence of Organic Inorganic Metal Halides

Long persistent luminescence (LPL) materials of SrAl₂O₄ doped with Eu²⁺ or Dy³⁺ can maintain emission over hours after ceasing the excitation but suffer from insolubility, high cost, and harsh preparation. Recently, organic LPL of guest-host exciplex systems has been demonstrated via an intermediate charge-separated state with flexible design but poor air-stability. Here, we synthesized a nontoxic two-dimensional organic–inorganic metal hybrid halides (OIMHs), called PBA₂[ZnX₄] with X=Br or Cl and PBA=4-phenylbenzylamine. These materials exhibit stable LPL emission over minutes at room-temperature, which is two orders of magnitude longer than those of previously reported OIMHs. The mechanism study shows that the LPL emission comes from thermally activated charge separation state rather than room-temperature phosphorescence. Moreover, the LPL of PBA₂[ZnX₄] can be excited by low power sources, representing an effective strategy for developing low-cost and high-stability LPL systems.     

Micellar-stabilized room-temperature phosphorimetric determination of the fungicide thiabendazole in canned pineapple samples

A method for the determination of the fungicide thiabendazole (TBZ) by micellar-stabilized room-temperature phosphorescence is described. It does not require any separation step and allows the direct determination of the fungicide in canned pineapple samples. The effect of various experimental conditions is discussed in detail. The analytical curve of thiabendazole gives a linear dynamic range of 23.8–500.0 ng mL^–1 and a detection limit of 23.8 ng mL^–1. Recoveries of 103.9 and 89.2% for syrup and canned pineapple pulp, respectively, were obtained for 250 ng mL^–1 thiabendazole.     

3nπ* spectra of benzaldehyde. I. Vapor phosphorescence

Vibrational analysis of the vapor ³nπ* phosphorescence for three isotopic benzaldehydes (B-h₆, B-1d₁, B-Rd₅) shows that the out-of-plane aldehyde hydrogen wagging vibration (ν₂₆) is the most active non-totally symmetric mode in the spectrum. Since the intensity of 26₂⁰ ? 26₁⁰ the mechanism of ν₂₆ activity is primarily as a Franck—Condon mode. The only other out-of-plane mode definitely attributed to the vapor phosphorescence is the weakly active CHO torsional vibration (ν₃₆) with I (36₁⁰) > I (26₁⁰). Other Franck—Condon modes are ν₇, ν₂₅, ν₂₀, ν₁₇ and ν₈.     

Manganese-Doped Zinc Sulfide Quantum Dots for Determination of Bisphenol A by Room Temperature Phosphorescence

Manganese-doped ZnS quantum dots were synthesized through a facile process in aqueous solution using L-cysteine as a surface modifying agent. The quantum dots were characterized by transmission electron microscopy and X-ray diffraction spectroscopy, and had a favorable room-temperature phosphorescence property, with a longer emission time and a narrower emission profile than fluorescence. The phosphorescence was quenched by bisphenol A. Based on these findings, a room temperature phosphorescence quenching method was developed for the sensitive and selective detection of bisphenol A. Under the optimized conditions, the detection limit was 0.2 ng · mL^?1, and the relative standard deviation was 1.14% (C = 10 ng · mL^?1, n = 11). The proposed method was successfully applied to plastic products with satisfactory results. The recovery of the method was in the range of 96% to 106%.     

Analysis of vibronic intensities in the phosphorescence spectrum of dimethylbenzaldehydes in durene

An attempt is reported to explain the main intensity patterns in the phosphorescence spectra of 2,4-, 2,5- and 3,4-dimethyl-benzaldehyde-1h₁ and -1d₁, observed previously. The analysis is based on CNDO and MINDO calculations of (transition) dipole moments, spin-orbit couplings, vibronic couplings, state energies, normal coordinates and vibrational frequencies. Where possible these quantities are empirically checked and corrected. Additional information, especially about the separation of the closely spaced T₁(³ππ^*) and T₂(³nπ^*) states, is obtained from phosphorescence excitation spectra reported here for all six isomers. The phosphorescence spectra consist of two components, an “allowed” component of ³ππ^* and a “forbidden” component of ³nπ^* symmetry. It is concluded that the allowed component is partly induced by the crystal field. The forbidden component is vibronically induced by out-of-plane vibrations among which the aldehydic CH(CD)-wag mode is the most active. The observed intensity patterns for this component are ascribed to interference between two mechanisms, one involving vibronic coupling between S₀ and S₁(¹nπ^*) and spin-orbit coupling between S₁ and T₁, the other involving vibronic coupling between T₁ and T₂ and spin-orbit coupling between S₀ and T₂. Within the groups of either 1h₁ or 1d₁ isomers, the main changes in the spectrum are shown to be due to the change in T₁–T₂ energy separation. The changes observed upon deuterium substitution in the aldehyde group involve, in addition to changes in the T₁–T₂ gap, changes in vibronic coupling due to normal-coordinate mixing. All these spectral changes are reproduced by calculations based on a mixture of theoretical and empirical input parameters, derived from, or at least consistent with, other observations, including excitation spectra, dipole moments and zero-field splittings. It is concluded that the mechanisms underlying these calculations offer a satisfactory explanation of the observed intensity patterns in the phosphorescence spectra of dimethylbenzaldehydes.     

Spectroscopic effects of vibronic coupling between nearby 3nπ* and 3ππ* states of dimethylbenzaldehydes in a durene matrix

A vibrational analysis is presented of high resolution ππ* phosphorescence spectra of the 2,4-, 2,5- and 3,4-dimethylbenzaldehyde-1h₁ and ?1d₁, guests in durene host. As previously reported for the fully hydrogenated molecules, the energy gaps between the zero-point levels of the ³ngp*, and ³ππ* states of the guests deuterated on the aldehydic group are determined from the temperature dependence of their phosphorescence spectra and lifetimes. These vibronic energy gaps tend to be larger in the deuterated species.The existence of the vibronic coupling between ³nπ* and ³ππ* states of dimethylbenzaldehydes is suggested by the important activity, in the ππ* phosphorescence spectra, of nontotally symmetric modes involving the aldehydic group and the aromatic ring. Among these vibrations, the most active are the aldehydic CH and CD wagging modes which also show overtone activity. The intensities of the induced bands show a strong deuterium effect which in the 2,4 and 2,5 compounds is anomalous in that the deuterated species shows the higher induced intensity. The observation of phosphorescence spectra from each molecule in two different sites allows an assessment of the crystal field effect which is found to be moderately strong. These observations can be understood qualitatively on the basis of weak pseudo Jahn-Teller-like coupling between the ³ππ* and ³nπ* states which is subject to interference from Herzberg-Teller coupling involving at least one additional state. No convincing evidence is found for nonplanar distortions of the guest molecules.     

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.     

Determination of traces of bismuth by quenching of solid-substrate room-temperature phosphorescence from morin-labeled silicon dioxide nano-particles

Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO₂) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO₂ solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (I_p) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot^–1 (sample volume 0.40 L spot^–1, corresponding to the concentration range 0.40–36.0 fg mL^–1). The regression equation of the working curve is I_p=14.86+5.279×[Bi³⁺] (ag spot^–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot^–1 (corresponding to a concentration of 6.5×10^–17 g mL^–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples.