Quasi-line benzaldehyde phosphorescence spectra from toluene solutions

Low temperature phosphorescence spectra have been measured for benzaldehyde, acetophenone and benzophenone in toluene glasses. The emission is typical of an nπ1 triplet. On slow cooling the spectra sharpen and appear to originate from two different crystal sites for which there is a considerable energy difference, ≈350 cm^-1 for benzaldehyde.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

The Schiff Base Probe With J-aggregation Induced Emission for Selective Detection of Cu2+

Here, three Schiff bases 3a-c, differing by the substitutions (–H, –Cl, and –N(CH₃)₂) on the phenyl ring, have been designed and synthesized via the reaction of ortho-aminophenol with benzaldehyde, 2,4-dichlorobenzaldehyde and para-dimethylamine benzaldehyde in 1:1 molar ratio with favourable yields of 89–92%, respectively. Their structural characterizations were studied by FT-IR, NMR, MALDI-MS and elemental analysis. The fluorescence behaviours of compounds 3a and 3b exhibited a severe aggregation caused quenching (ACQ) effect in EtOH/water system. On the contrary, compound 3c had an obvious J-aggregation induced emission (AIE) feature in EtOH/water mixture (v/v?=?1:1), and exhibited excellent sensitivity and anti-interference towards Cu²⁺ with the limit of detection (LOD) of 1.35?×?10^–8 M. Job’s plot analysis and MS spectroscopic study revealed the 2:1 complexation of probe 3c and Cu²⁺. In addition, probe 3c was successfully applied to the determination of Cu²⁺ in real aqueous samples.

     

Photophysics and Electrochemistry of some Thione Far-Red/Near-IR Triplet Emitters

The photophysics and cyclic voltammetry of two novel phosphorescent thiones, 2,2-dimethyl-indan-1-one-3-thione (DMIKT) and 2,2-dimethyl-indan-1,3-dithione (DMIDT), and three known phosphorescent thiones, 4H-pyran-4-thione (PT), 4H-1-benzopyran-4-thione (BPT) and 2,2-dimethylindan-1-thione (DMIT), have been characterised and compared. The phosphorescence emission of DMIT, DMIKT and DMIDT extends from the red into the near-IR spectral region. The additional carbonyl or thione group of DMIKT and DMIDT causes a significant shift in the emission maxima to 680 nm compared to that of DMIT, at 637 nm, in perfluorinated hydrocarbons. In acetonitrile the emission maxima of DMIKT and DMIDT are at 696 and 706 nm, respectively, and the spectra show vibronic bands which extend out beyond 850 nm. There is a significant reduction in triplet lifetime along this series (from 44 (±2) μs (DMIT) to 10 ((±0.8) μs (DMIKT) in perfluorinated solvents, and 8.6 (±0.5) (DMIT), 1.3 (±0.5) (DMIKT) and 0.35 (±0.07) μs (DMIDT) in acetonitrile), as well as a reduction in the rate constant for ground-state quenching of the triplet, (from 9.8 ((±0.9) to 3.5 ((±0.6) and 1.3 ((±0.2) × 10⁹ mol⁻¹ dm³ s⁻¹ for the same compounds). The addition of the C=O or C=S groups also causes a decrease in phosphorescence quantum yield with the highest emission quantum yield obtained for DMIT (Φ _P = 0.149 (±0.015)). Electrochemical studies show that while PT and BPT exhibit irreversible redox behaviour, DMIT, DMIKT and DMIDT all show at least one reversible reduction wave attributed to a one-electron process centred on the C=S moiety. The suitability of these lumophores for use in OLEDs is discussed.     

Luminescence Study of Singlet Oxygen Production by Meso-Tetraphenylporphine

The research in the field of the photodynamic therapy of cancer (PDT) is focused on a development of photosensitizers exhibiting high quantum yield of singlet oxygen production. Direct time-resolved spectroscopic observation of singlet oxygen phosphorescence can provide time constants of its population and depopulation as well as photosensitizer phosphorescence lifetime and relative quantum yields. In our contribution, a study of time and spectral resolved phosphorescence of singlet oxygen photosensitized by meso-tetraphenylporphine in acetone together with the photosensitizer phosphorescence is presented. Time constants of singlet oxygen population and depopulation were determined at wide range of photosensitizer concentrations. The time constant of singlet oxygen generation (0.28 ± 0.01) s is slightly shorter then the lifetime of photosensitizer's triplet state (0.32 ± 0.01) s. It is caused by lower ability of TPP aggregates to transfer excitation energy to oxygen. The lifetime of singlet oxygen (50 s) decreases with increasing photosensitizer concentration. Therefore, the photosensitizer acts also as a quencher of oxygen singlet state, similarly to the effects observed in [A. A. Krasnovsky, P. Cheng, R. E. Blankenship, T. A. Moore, and D. Gust (1993). Photochem. Photobiol. 57, 324–330; H. Küpper, R. Ddic, A. Svoboda, J. Hála, and P. M. H. Kroneck (2002). Biochim. Biophys. Acta Gen. Subj. 1572, 107–113]. Moreover, the increasing concentraion of the photosensitizer causes a slight hypsochromic shift of the singlet oxygen luminescence maximum.     

Pulsed Laser Ablation for Tin Dioxide: Nucleation,Growth, and Microstructures

Pulsed-laser ablation approaches are being developed for the growth of oxide thin films as versatile platform for advanced applications. Semiconducting SnO ₂ thin film is of fundamental importance in the advancement of microdevices. In this review, SnO ₂ thin films of various microstructures have been made using the pulsed-laser deposition method. The microstructural aspects include tetragonal, porous, and orthorhombic structure characteristics. The quantum-dots and dynamic simulations of SnO ₂ nanocrystals have blossomed into a submonolayer regime devoted to the nucleation and growth for these functional films. SnO ₂ thin films with some of the microstructural features may have great implications for the development of novel prototype gas sensors and transparent conduction electrodes.     

Luminescence of biologically active 24-epicastasterone and a model compound

Biologically active brassinosteroid 24-epicastasterone, ring B of which contains a C=O group and has the nπ*-configuration for a low-lying electronic excited state, exhibits rapid fluorescence. The wavelengths of the fluorescence maxima of the steroid dissolved in hexane and acetonitrile are equal to 332 and 394 nm, respectively. The fluorescence lifetime of the steroid dissolved in acetonitrile is τ = 9.9 nsec. Solutions of 24-epibrassinolide do not luminesce. The long-wavelength electronic absorption band λ_max^abs = 340 nm in the absorption spectrum of an ethanol solution of model compound 2, ring D of which contains a C=O group π*-conjugated with the C=C double bond of ring C, like in the spectrum of the steroid, has a low extinction coefficient. An ethanol solution of 2 does not fluoresce. 24-Epicastasterone at 77 K in ethanol solution exhibits phosphorescence with λ_max^phos = 447 nm. The phosphorescence decay is exponential with τ = 0.79 msec. Compound 2 also phosphoresces. The phosphorescence spectrum of its ethanol solution has a maximum at 490 nm. The phosphorescence decay is nonexponential in the early stage. The phosphorescence lifetime is 25 msec in the exponential decay region. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 182–186, March–April, 2008.     

Characteristic features of the phosphorescence of the complex “naphthalene-d8-β-cyclodextrin” at 77 K

It is found that the phosphorescence of naphthalene-d8 in an inclusion complex in crystalline β-cyclodextrin at 77 K differs substantially from that of frozen homogeneous solutions: The vibrational structure of the spectrum is better-resolved, the Stokes shift in the spectrum is smaller, and the lifetime is longer than the values known previously. Similar effects are observed for naphthalene-h8 and phenanthrene. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 507–510 (10 April 1997)     

The Influence of Human Serum Albumin on The Photogeneration of Singlet Oxygen by meso-Tetra(4-Sulfonatophenyl)Porphyrin. An Infrared Phosphorescence Study

meso-Tetra(4-sulfonatophenyl)porphyrin (TPPS₄) is a water soluble photosensitizer, which is currently clinically tested as a PDT drug. In our contribution, we present IR spectral- and time-resolved phosphorescence data reflecting the influence of human serum albumin (HSA) on singlet oxygen photogeneration by TPPS₄. IR emission of TPPS₄ was studied in samples containing various concentrations of HSA in phosphate buffer. The observed changes in spectral and temporal behaviour of TPPS₄ and singlet oxygen phosphorescence caused by the addition of HSA are equivalent to the effect of nitrogen purging of HSA-free solutions of TPPS₄. The main feature induced by addition of HSA appears to be the occurrence of a long-lived (tens of microseconds) photosensitizer phosphorescence at 900 nm besides ordinary short-lived (≈2 μs) one at 820 nm. It is accompanied by presence of a long-lived component of singlet oxygen emission with lifetime roughly corresponding to that of the long photosensitizer phosphorescence component. Moreover, the quantum yield of singlet oxygen phosphorescence decreases with increasing HSA concentration, while total quantum yield of TPPS₄ phosphorescence rises. These facts are explained by a shielding effect of HSA on bound molecules of TPPS₄ against quenching by oxygen which is analogous to oxygen removal by nitrogen purging.     

Influence of successive electron and laser irradiation on the photoluminescence of porous silicon

The influence of electron irradiation on the light-emitting properties of p-and n-type porous silicon prepared by electrochemical etching is investigated. The dose and energy dependences of the electron-stimulated quenching of the photoluminescence (PL) are determined. It is shown that electron treatment of a porous silicon surface followed by prolonged storage in air can be used to stabilize the PL. The excitation of photoluminescence by a UV laser acting on sections of porous silicon samples subjected to preliminary electron treatment is discovered for the first time. The influence of the electron energy and the power of the laser beam on this process is investigated. The results presented are attributed to variation in the number of radiative recombination centers as a result of the dissociation and restoration of hydrogen-containing groups on the pore surface. Zh. Tekh. Fiz. 68, 58–63 (March 1998)     

Spectral Properties of Cyclodextrin Inclusion Complexes with Nonionic Surfactants and 1‐Bromonaphthalene

Abstract

Steady‐state fluorescence and phosphorescence of inclusion complexes of cyclodextrins (CDs) with fluorescent nonionic surfactant and 1‐bromonaphthalene (BN) are described in detail. The inclusion of the hydrophobic moiety of surfactants inside the cavity of CDs led to enhanced monomer‐like fluorescence with a bathochromic shift of λ_ex and a hypsochromic shift of λ_em. ¹H‐NMR provides additional evidence for deep inclusion of the hydrophobic moiety of surfactants. BN can squeeze into more hydrophobic cavity of β‐CD that has accommodated the hydrophobic moiety of a surfactant and show its phosphorescence and remarkable quenching effect on the fluorescence of a surfactant in aerated aqueous solution. Stern–Volmer quenching depends on the inclusion of the phenyl rings of surfactants and BN into the cavity of CDs. Comparison of molecular sizes reveals that further inclusion of BN into the cavity of β‐CD occupied by a surfactant may force the flexible octyl group of a surfactant to deform to a greater extent, and close‐packing complexes were obtained. In the case of heptakis(2,6‐di‐O‐methyl)‐β‐CD, BN only binds to its cavity opening due to the steric hindrance of methyl substituents at the rim of its cavity.     

Ag2O nanoparticle clusters coated with porous gelatin-g-PMMA copolymer

Herein a special nanoparticle cluster coated with a porous copolymer is designed and prepared. At first, Ag₂O nanoparticles (secondary particles) were fabricated in gelatin solution by a facile chemical approach. Then these nanoparticles were entrapped in a copolymerization system containing gelatin, methyl methacrylate (MMA), an initiator, and using water as a solvent. The nanoparticle clusters coated with porous gelatin-g-PMMA copolymer (Ag₂O/gelatin-g-PMMA) were prepared by grafting methyl methacrylate onto gelatin, followed by coating solidification. One significant feature for our approach is that every Ag₂O aggregated cluster has been coated with porous gelatin-g-PMMA copolymer film in a unique way, and the Ag₂O nanoparticle could penetrate and escape from the coating freely in water by ultrasonication. As a result, this study provides a new approach to prepare monodispersed nanoparticles by ordered porous copolymers with controlled releasing.     

Coulomb interaction controlled room temperature oscillation of tunnel current in porous Si

A novel phenomenon of regular oscillations is observed in I-V characteristics of porous silicon under illumination by visible light. The measurements are performed at room temperature using a scanning tunneling microscope. The heights of the oscillation peaks appear to be a linear function of the oscillation number. The experimental value of the Coulomb energy determined from the oscillation period is much smaller than k _B T. The oscillations are attributed to a Coulomb effect, i.e., to the periodic trapping of a multielectron level in a quantum well within a Si nanocrystal under the combined influence of the voltage variation at the STM tip and the Coulomb interaction among the carriers. Fiz. Tverd. Tela (St. Petersburg) 40, 1147–1150 (June 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

On the photophysics of four heteroleptic iridium(III) phenylpyridyl complexes investigated by relativistic multi-configuration methods

ABSTRACT

In this work, we present a detailed analysis of the photophysical properties of four phosphorescent iridium(III) complexes, i.e. trans-N,N- and cis-N,N-(ppy)₂Ir^III(acac) as well as their fluorinated derivatives trans-N,N- and cis-N,N-(F₂ppy)₂Ir^III(acac). These properties include absorption and emission characteristics, intersystem crossing rates from the lowest singlet excited state, phosphorescence lifetimes of the individual triplet sublevels as well as the orientations of the transition dipole vectors. To this end, we have carried out combined density functional theory and multi-reference configuration interaction studies including spin–orbit coupling by perturbational as well as variational procedures. For the experimentally known complexes, we observe excellent agreement between our computed data and literature data. Also the blueshifts of the emission maxima occurring upon fluorination of the (ppy)₂Ir(acac) compounds are well reproduced. To our surprise, we find the experimentally not yet investigated cis-N,N-(F₂ppy)₂Ir(acac) isomer to be thermodynamically more stable than the well-known blue phosphorescent emitter trans-N,N-(F₂ppy)₂Ir(acac).     

Orientational fluctuations and phase transitions in 8CB confined by cylindrical pores of the PET film

Abstract

Results of optical investigations of the isotropic-nematic and nematic-smectic A phase transitions in porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) are reported. Samples of porous films of thickness 23 µm with normally oriented cylindrical pores of a radius R ranging from 10 nm to 1000 nm were prepared using the track-etched membrane technology. The dynamic light scattering method was used to probe the nematic orientational fluctuations of confined LC samples. The corresponding relaxation time τ was measured as a function of R and temperature T at slow enough cooling rates (0.3–0.6 K/h) to locate the phase transition temperatures. Changes in τ(T) dependencies relatively sensitivity fingerprint the LC phase transformations. Experimental results are analysed using the Landau-de Gennes-Ginzburg phenomenological approach.     

Vanillin Phosphorescence as a Probe of Molecular Mobility in Amorphous Sucrose

Changes in molecular mobility are important in defining the stability and quality of amorphous solid foods, pharmaceuticals, and other solid biomaterials. Predictions of stability must consider matrix mobility below and above T_g (the glass transition temperature); measurement of molecular mobility in amorphous solids over time scales ranging from <10⁻⁹ s to >10⁸ s requires specialized methods. This research investigated how the steady-state and time-resolved emission and intensity of phosphorescence from vanillin (4-hydroxy-3-methoxy benzaldehyde), a common flavor compound, can be used to probe molecular mobility when dispersed within amorphous pure sucrose films. Phosphorescence emission spectra and time-resolved intensity decays, measured in sucrose as a function of temperature in the absence of oxygen, were strongly modulated by matrix molecular mobility. Temperature had a significant effect on vanillin phosphorescence peak frequency and bandwidth, intensity, and lifetime both in the glass and in the melt. Time-resolved phosphorescence intensity decays from vanillin were multiexponential both below and above the glass transition temperature, indicating that the pure (single component) amorphous matrix was dynamically heterogeneous on the molecular level. These data show that vanillin is a promising intrinsic probe of molecular mobility and dynamic heterogeneity in amorphous solid foods and perhaps pharmaceuticals.     

Saturation effects on phosphorescence anisotropy measurements at high laser pulse energies

Triplet spectroscopic methods such as time-resolved phosphorescence anisotropy permit successful measurement of slow rotational diffusion of membrane proteins. However, these methods are potentially subject to saturation phenomena. We present theoretical and experimental studies of how high excitation energy densities can complicate measurements of phosphorescence intensity and anisotropy. Increases in excitation laser pulse energy initially increase phosphorescence intensity. Further increases then lead to phosphorescence saturation. As a consequence, the initial phosphorescence anisotropy decreases and approaches zero at very high excitation energies. The relative standard deviation of anisotropies measured in any system reaches a minimum at some particular excitation energy density. These results allow us to define optimum experimental conditions for time-resolved phosphorescence anisotropy measurements. For example, for excitation of erythrosin chromophores at typical wavelengths by the center of a Gaussian laser beam, optimum pulse energies in microjoules are approximately 5.0R ², whereR is the beam 1/e² radius in mm.     

Backscattering of low-energy (0–8 eV) electrons by a silicon surface

An experimental apparatus and method for investigating elastic and inelastic backscattering (180°) of low-energy (0–8 eV) monoenergetic electrons by a solid surface are described and the first results are presented for the reflection of electrons by samples of pure single-crystalline silicon with a polished surface (Si), doped p-type single-crystalline silicon with a porous surface (Si-p) as well as H₂O and H₂O₂ passivated porous samples, Si-p + H₂O and Si-p + H₂O₂. A structure due to the excitation of surface plasmons has been observed for the first time in the loss spectra. Features corresponding to a resonance excited state of molecular nitrogen adsorbed on the surface of porous silicon have been observed in the constant residual energy spectra. Zh. Tekh. Fiz. 67, 103–108 (May 1997)     

Monitoring the pH-Dependent Oximation of Methyl Ethyl Ketone and Benzaldehyde by in situ Fourier Transform IR Spectroscopy in a Heterogeneous Liquid–Liquid Two-Phase System

In situ Fourier transform IR spectroscopy was a useful tool in monitoring the pH-dependent and two-step oximation of methyl ethyl ketone and benzaldehyde in a liquid–liquid two-phase system, one phase of which was water. Carrying out the oximations at pH 8, the oximation was complete within 45 min and the corresponding carbonyl compound–hydroxylamine adduct (2) could be detected as an intermediate, but at pH 10, the corresponding oxime (3) was formed faster, practically without the appearance of the intermediate. At pH ～ 2.5 using methyl ethyl ketone, the protonated form of the corresponding oxime (3'a) developed gradually without the transient appearance of the intermediate (2). pH dependence of the 3a → 3'a and 3'a → 3a interconversions were studied in separate experiments.     

Influence of spin-orbit coupling on vibronic spectra of metalocomplexes porphin: Manifestation of out-of-plane vibrations

In fine-structure phosphorescence spectra of metallocomplexes of porphin with ions of the Pd(II) and Pt(II) and their meso-deuterated derivatives additional lines have been detected which have no analogs in fluorescence and resonance Raman spectra of metalloporphyrins and in phosphorescence spectra of metallocomplexes of porphin with light ions of the Mg(II) and Zn(II). For Zn-porphin, quantum-chemical calculations of frequencies and forms of in-plane and out-of-plane vibrations have been performed. Based on experimental data and calculation results it has been found, that in vibronic phosphorescence spectra of metallocomplexes of porphin, out-of-plane gerade modes of the E _g symmetry (D _4h symmetry group) are manifested. The activity of out-of-plane vibrations increases with enhancing spin-orbital coupling upon changing to heavier chelated metal ions. Vibronic transitions with participation of out-of-plane gerade E _g vibrations manifest in the T ₁ → S ₀ transition through the vibronic intensity borrowing from the triplet-triplet ³ E _u -³ E _g transition.