Synthesis and Fluorescence Properties of Donor-Acceptor-Substituted Novel Dipyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>:3′,4′-<Emphasis Type="Italic">d</Emphasis>]Pyridines (DPP)

A rapid and efficient method for the synthesis of novel dipyrazolo[3,4-b:3′,4′-d]pyridines (DPP) from pyrazolo[3,4-b]pyridine was successfully developed. The DPP derivative was further N-alkylated (6, 8) as well as N-linked with amino acids (13) and their photophysical properties were studied along with N-aryl DPP 4 and observed that the chromophores at C₄ position in the aryl ring changed the absorption and emission λ_max.     

Two-photon absorption-induced optical properties of a new lasing dye in two solvents

Pumped by an infrared lasing and its frequency-doubling source, the fluorescence and superradiance emission properties of a new lasing dye trans-4-[4^′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated DEASPS), have been studied in benzyl alcohol and chloroform. The two-photon absorption (TPA) and emission properties of DEASPSare influenced by the solvents used. The emission wavelength of the dye in benzyl alcohol is redshifted relative to that in chloroform. The lifetime of two-photon absorption-induced fluorescence is about 529 ps in benzyl alcohol, whereas it is 340 ps in chloroform. Correspondingly, the one-photon-excited fluorescence lifetimes in the two solvents are also given. The upconversion efficiency of DEASPS in chloroform is higher than in benzyl alcohol. Finally, the effective molecular two-photon absorption cross-sections were measured by the nonlinear transmittance method. It is found that the optical limiting effect of the dye in benzyl alcohol is stronger than that in chloroform. Received: 3 May 2001 / Revised version: 6 July 2001 / Published online: 19 September 2001     

Spectrophotometric Characteristics of New Pyridylindolizine Derivatives Solutions

Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence.     

Oriental behaviour of some homologues of 4-n-pentyl-phenylthio-4′-n-alkoxybenzoate doped with dichroic dye

The long-range orientational order of three members of 4-n-pentylphenylthio-4′-n-alkoxybenzoate series doped with a dichroic dye was studied by means of electronic absorption and fluorescence measurements. The order parameters <P₂> and <P₄> as well as the orientational distribution function were determined on the basis of absorption and emission spectra of linearly polarized light recorded as a function of temperature in the nematic, smectic A, and smectic C phases. An influence of the dye molecular structure on the orientational order of the dye/liquid crystal mixture was observed. Moreover, the dependence of the order parameter values on the length of the alkoxy chain in liquid crystal molecules was found. It was shown that the order parameter <P₄>, obtained from fluorescence measurements, can be helpful in recognizing the second-order or weakly first-order transitions between various liquid crystalline phases.     

A Simple and Neutral Receptor Acting as a Sensitive and Switch-on Fluorescent Chemosensor for H<Subscript>2</Subscript>PO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack>

A novel artificial anion chemosensor 1 based on 2, 2′-di (4-nitrophenylurea-β-N-yl) -1, 1′-binaphthyl is designed and synthesized for sensing anions including halide ions and oxoanions. The fluorescent emission of the binaphthyl of receptor 1, forming the hydrogen bonding with anions as the sensing mechanism, is monitored in DMSO for detecting anions. In brief, while most of the anion chemosensors are switch-off fluorescent chemosensor, or non-fluorescent sensor, receptor 1 exhibits obviously the switch-on emission during the complexation with H₂PO₄⁻.     

New one-pot synthesis of spiro[furo[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidine-6,5′-pyrimidine]pentaones and their sulfur analogues

Reaction of barbituric acid (BA), 1,3-dimethyl barbituric acid (DMBA) and 2-thiobarbituric acid (TBA) with cyanogen bromide and various aldehydes in presence of triethylamine afforded a new class of heterocyclic stable 5-alkyl and/or 5-aryl-1H, 1′H-spiro[furo[2,3-d]pyrimidine-6,5′-pyrimidine]2,2′,4,4′,6′(3H,3′H,5H)-pentaones which are dimeric forms of barbiturate (uracil and thiouracil derivatives) at 0 °C to ambient temperatures. Structure elucidation is proved by X-ray crystallography, ¹H NMR, ¹³C NMR, FT-IR, CHN and mass analyses techniques. Mechanisms of the formations are discussed.     

Solvent Effects in Optical Spectra of ortho-Aminobenzoic Acid Derivatives

We investigated three amino derivatives of ortho-aminobenzoic or anthranilic acid (o-Abz): a) 2-Amino-benzamide (AbzNH₂); b) 2-Amino-N-methyl-benzamide (AbzNHCH₃) and c) 2-Amino-N-N′-dimethyl-bezamide (AbzNH(CH₃)₂), see Scheme 1. We describe the results of ab-initio calculations on the structural characteristics of the compounds and experimental studies about solvent effects in their absorption and steady-state and time-resolved emission properties. Ab-initio calculations showed higher stability for the rotameric conformation in which the oxygen of carbonyl is near to the nitrogen of ortho-amino group. The derivatives present decrease in the delocalization of π electron, and absorption bands are blue shifted compared to the parent compound absorption, the extent of the effect increasing from to Abz-NH₂ to Abz-NHCH₃ Abz-NH(CH₃)₂. Measurements performed in several solvents have shown that the the dependence of Stokes shift of the derivatives with the orientational polarizability follows the Onsager-Lippert model for general effects of solvent. However deviation occurred in solvents with properties of Bronsted acids, or electron acceptor characteristics, so that hydrogen bonds formed with protic solvents predominates over intramolecular hydrogen bond. In most solvents the fluorescence decay of AbzNH₂ and AbzNHCH₃ was fitted to a single exponential with lifetimes around 7.0 ns and no correlation with polarity of the solvent was observed. The fluorescence decay of AbzN(CH₃)₂ showed lifetimes around 2.0 ns, consistent with low quantum yield of the compound. The spectroscopic properties of the monoamino derivative AbzNHCH₃ are representative of the properties presented by Abz labelled peptides and fatty acids previously studied.     

Two-Photon Optical Properties of Novel Branched Conjugated Derivatives Carrying Benzophenone Moiety with Various Electron Donor-Acceptor Substituent Groups

This paper presents a range of novel new branched conjugated dyes containing benzophenone moiety. As compared with those of 4-(p-benzoyl-styrene)yl-4'-(styrene)yl-triphenylamine (C1) and 4-(p-benzoyl-styrene)yl-4'-3,4,5-trimethoxyl-styrene)yl-triphenylamine (C2), the maximal linear absorption and emission wavelength of 4-(p-benzoyl-styrene)yl-4'-(p'-nitro-styrene)yl-triphenylamine (C3) displays red-shifted remarkably, While the fluorescence quantum yields of C3 are lower than those of C1 and C2 in various solvents. The fluorescence lifetimes of the derivatives were measured, and radiative and non-radiative transition constants of the derivatives were calculated. Two-photon absorption (TPA) optical data of the derivatives were measured by Ti:sapphire femtosecond laser tuning from 720 to 880 nm at intervals of 20 nm. TPA induced fluorescence emission of C3 is red-shifted with respected to that of C1 and C2. TPA cross sections of C3 are larger than those of C1 and C2 in various excited laser frequencies. TPA cross section of C2 and C3 are much larger than those of 3,4,5-(trimethoxylstyrene)yl-triphenylamine (C4) and 4-(p-nitrostyrene)yl-triphenylamine (C5) respectively under various near-IR Ti:sapphire femtosecond laser wavelength. C1 and C2 show similar one- and two- photon optical nature. Geometry optimization with ab initio method confirms that C3 has different electron density distribution, the energy levels in frontier orbitals, the dipole moment changes, the absorption and emission spectroscopy from those of C1 and C2. The cyclic voltammograms of the derivatives were detected in methylene chloride at various scan rates, and the energy of frontier orbials were estimated further from the redox potentials.     

A new polymeric material for optical switching

′ -(2^′′,4^′′,6^′′-trichlorophenazoamino)-phenazo-4-nitrobenzene, was studied. Large nonresonant optical nonlinearity (χ⁽³⁾≥10^-28 C⁴m/J³ or 10^-9 esu) and fast response time (t<20 ps) were measured by forward degenerate four-wave mixing experiment. Optical bistable behavior in a quasi-waveguide interferometer with the thin film of the material was observed. The potential of the material for optical switching was evaluated. Received: 20 July 1998/Revised version: 11 September 1998     

Fluorescence Studies on Potential Antitumoral Heteroaryl and Heteroannulated Indoles in Solution and in Lipid Membranes

Fluorescence properties of three potential antitumoral compounds, a 3-(dibenzothien-4-yl)indole 1, a phenylbenzothienoindole 2 and a 3-(dibenzofur-4-yl)indole 3, were studied in solution and in lipid aggregates of dipalmitoyl phosphatidylcholine (DPPC), dioleoyl phosphatidylethanolamine (DOPE) and egg yolk phosphatidylcholine (Egg-PC). The 3-(dibenzofur-4-yl)indole 3 exhibits the higher fluorescence quantum yields in all solvents studied (0.32 ≤ Φ_F ≤ 0.51). All the compounds present a solvent sensitive emission, with significant red shifts in alcohols. The results point to an ICT character of the excited state, more pronounced for compound 1. Fluorescence (steady-state) anisotropy measurements of the compounds incorporated in lipid aggregates of DPPC, DOPE and Egg-PC indicate that the three compounds are deeply located in the lipid bilayer, feeling the difference between the rigid gel phase and fluid phases.     

Preparation and Time-Resolved Luminescence Bioassay Application of Multicolor Luminescent Lanthanide Nanoparticles

Because highly luminescent lanthanide compounds are limited to Eu³⁺ and Tb³⁺ compounds with red (Eu, ~615 nm) and green (Tb, ~545 nm) emission colors, the development and application of time-resolved luminescence bioassay technique using lanthanide-based multicolor luminescent biolabels have rarely been investigated. In this work, a series of lanthanide complexes covalently bound silica nanoparticles with an excitation maximum wavelength at 335 nm and red, orange, yellow and green emission colors has been prepared by co-binding different molar ratios of luminescent Eu³⁺–Tb³⁺ complexes with a ligand N,N,N¹,N¹-(4′-phenyl-2,2′:6′,2′′-terpyridine-6,6′′-diyl)bis(methylenenitrilo) tetrakis (acetic acid) inside the silica nanoparticles. The nanoparticles characterized by transmission electron microscopy and luminescence spectroscopy methods were used for streptavidin labeling, and time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) as well as time-resolved luminescence imaging detection of an environmental pathogen, Giardia lamblia. The results demonstrated the utility of the new multicolor luminescent lanthanide nanoparticles for time-resolved luminescence bioassays.     

Resonant two-photon absorption in a tetragonal CdP2

Kinetic, spectral, intensity, angular, and polarization of resonant two-photon absorption (TPA) in β-CdP₂ has been investigated. Resonant TPA was observed for which the total energy of the two photons was 2.60 eV. It is shown that resonant TPA takes place via a real intermediate level d ₃ in the band gap at the depth E _c-0.86 eV. The electron transverse relaxation time for resonant TPA, the cross section for absorption of laser photons in d ₃→C transitions, the equilibrium population of d ₃ centers in a doped n-type sample, and the resonant TPA constant were determined as 4.3×10⁻¹⁴ s, 1.25×10⁻¹⁷ cm², 0.95, and 0.028 cm/MW, respectively. Fiz. Tverd. Tela (St. Petersburg) 40, 1252–1256 (July 1998)     

Quantum Gravitational Corrections to the Real Klein-Gordon Field in the Presence of a Minimal Length

The (D+1)-dimensional (β,β′)-two-parameter Lorentz-covariant deformed algebra introduced by Quesne and Tkachuk (J. Phys., A Math. Gen. 39, 10909, 2006), leads to a nonzero minimal uncertainty in position (minimal length). The Klein-Gordon equation in a (3+1)-dimensional space-time described by Quesne-Tkachuk Lorentz-covariant deformed algebra is studied in the case where β′=2β up to first order over deformation parameter β. It is shown that the modified Klein-Gordon equation which contains fourth-order derivative of the wave function describes two massive particles with different masses. We have shown that physically acceptable mass states can only exist for b < \frac18m²c²\beta<\frac{1}{8m^{2}c^{2}} which leads to an isotropic minimal length in the interval 10⁻¹⁷ m<(ΔX ⁱ )₀<10⁻¹⁵ m. Finally, we have shown that the above estimation of minimal length is in good agreement with the results obtained in previous investigations.     

Tuning of the emission color of organic electroluminescent devices by exciplex formation at the organic solid interface

′ ,4^′′-tris(3-methylphenylphenylamino)triphenylamine, 1,3,5-tris[(4-diphenylaminophenyl)phenylamino]benzene, N, N^′-bis(3-methylphenyl)-N, N^′-diphenyl-[1,1^′-biphenyl]-4,4^′-diamine, and 4,4^′,4^′′-tri(N-carbazolyl)triphenylamine, emitted bright light resulting from the exciplex formed at the solid interface between TPOB and the hole-transporting material. The exciplex formation was evidenced by the measurements of the photoluminescence spectra and lifetimes of the mixture of an equimolar amount of TPOB and each of the hole-transporting materials. Tuning of the emission color from greenish blue to orange was attained by varying the ionization potential of the hole-transporting material for the fixed electron-transporting material of TPOB. Received: 27 July 1998/Accepted: 28 July 1998     

Solvent effect profiles of absorbance and fluorescence spectra of some indole based chalcones

The photophysical properties of a series of 3-(1′H-Indol-3′-yl)-1-phenylprop-2-en-1-one and its derivatives (indole chalcones) were studied in different solvents. Solvent effects on the absorption and fluorescence spectra were quantified using Reichardt’s and bulk solvent polarity parameters and were complemented by the results of the Kamlet-Taft treatment. The observed excited state dipole moment was found to be larger than the ground state dipole moment of these chalcones. The correlation of the solvatochromic Stokes-shifts with the microscopic solvent polarity parameter (E_T^N E_T^N ) was found to be superior to that obtained using bulk solvent polarity functions.     

Nonlinear optical properties of a new two-photon-absorption organic dye: HEASPS

Trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) is a two-photon-absorption (TPA) dye newly synthesized by our research group. It possesses a much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dyes (such as rhodamine) when excited with near-infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPS solution at different wavelengths have been measured. The largest molecular TPA cross-section σ₂ ^′ is measured to be 2.06×10^-47 cm⁴ s/photon at 930 nm. At 1064 nm, σ₂ ^′ is 2.71×10^-48 cm⁴ s/photon, which is only one-ninth of that at 930 nm. The upconverted lasing efficiency spectrum has been measured at different wavelengths. The highest efficiency is 5.1% at 1020 nm, whereas it is 3.5% at 1064 nm. Its optical-power-limiting properties at 930 nm have also been illustrated. Received: 30 November 2000 / Published online: 27 April 2001     

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.     

Structure and Luminescence Properties of Monomeric and Dimeric Re(I) Complexes with Dicarboxylic Acid-2,2′-Bipyridine Ligands

The luminescence properties of Re(I) complexes incorporating the dcbpy ligand (dcbpy = n,n′-dicarboxylic acid-2,2′-bipyridine; n = 3, 4) were investigated as well as their utility as Pb²⁺ sensors. An unusual binuclear complex of the 3,3′- species was isolated. The emission intensity and lifetime for all complexes were found to be highly temperature-dependent, with quantum yields and lifetimes dramatically greater at 77 K than at room temperature. The monomeric 3,3′-dcbpy Re(I) complex demonstrates nearly 1:1 binding with Pb²⁺. The effect of this lead binding on the emission intensity is great, but the low quantum yields allow only for detection of the metal at the micromolar level. The binding of Pb²⁺ to the 4,4′-dcbpy complex is modeled and the interaction is demonstrated to involve two binding sites.     

Steady-State and Time Resolved Fluorescence Analysis on Tyrosine–Histidine Model Compounds

Four model compounds, for a tyrosine–histidine covalent bonding, 2-(5-imidazolyl)-4-methylphenol (C–C bonding in ortho-position at the phenyl group); 2′-(1-imidazolyl)-4-methylphenol (C–N bonding in ortho′-position at the phenyl group); 2-(5-imidazolyl)-4-H-phenol and 2-(5-imidazolyl)-4-H-phenol, at physiological pH have been studied by UV-Vis absorption, steady-state and time resolved fluorescence spectroscopy. Their absorption and emission properties are presented and discussed. The photophysical properties depend on the para-substituted phenyl group as well as on C–C/C–N bonding in the Phenol–Imidazole linkage. The N position, N1–N3/N1–N4, in the imidazole group was found to be relevant. The results are discussed with relevance to the redox processes of tyrosine and to better understand the role of a tyrosine–histidine covalent linkage as found in cytochrome c oxidase.     

On the maximum in the differential cross sections of the F + H2 reaction in the region of small scattering angles

By means of quantum mechanical simulation of the reaction F + H₂(v = 0; j = 0, 1, 2) → H + HF(v′, j′) on the Stark-Werner ground state potential energy surface at collision energies of 1.84, 2.74, and 3.42 kcal/mol, we have analyzed interference of the “partial waves” corresponding to different values of the total angular momentum J. As the vibrational quantum number v′ of the HF(v′, j′) product increases, the interference for the HF forward scattering becomes noticeably more constructive. This is probably the reason for the maximum in the angular distributions of the HF(v′= 3) molecules at small scattering angles that was discovered experimentally by D.M. Neumark, A.M. Wodtke, G.N. Robinson, C.C. Hayden, and Y.T. Lee, J. Chem. Phys. 82 (7), 3045 (1985) at the same collision energies. We have also determined the intervals of J values most effective for forward scattering of the HF(v′, j′) molecules.