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.     

σ<Superscript>H</Superscript>-Adducts of <Emphasis Type="Italic">N</Emphasis>-alkylpyrazinium and quinoxalinium salts with nucleophiles. The <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectra and the crystal structures of P-adducts

The previously unknown addition products of P-nucleophiles to 5-aryl- and 5-hetaryl- 2,3-dicyano-1-ethylpyrazinium salts and to 5-aryl- and 5-hetaryl-14nethylquinoxalinium salts were synthesized. The three-dimensional structures of the P- σ^H-adducts of the 1,4-diazine series were established by X-ray diffraction.     

Neutrino disintegration of deuteron and electromagnetic form factos of neutrinos

We consider disintegration of deuteron by low energy neutrinos or antineutrinos due to their electromagnetic form factors. Effects of magnetic or electric dipole moments, electric charge radii and anapole moments of neutrinos are taken into account.     

On stability of rapid granular shear flows

We study stability properties of rapid granular flows that are described by the balance laws of mass, momentum and fluctuation energy with phenomenological relationships based upon dimensional arguments [12, 13]. Small disturbances propagating perpendicular to the shear plane are only studied. Calculations show that such flows are stable at small free path lengths of the granules but unstable if free path lengths are large. Received June 17, 1997     

Vibrational Spectra and Structural-Dynamic Models of Phenyldichlorarsine and Phenyldichlorophosphine

Vibrational spectra of phenyldichlorarsine and phenyldichlorophosphine are analyzed for free molecules and in water solutions within the framework of the ab initio methods. Characteristic spectral parameters of compounds are determined for their subsequent use in ecological monitoring.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 58–61, March, 2005.     

Specific features of the synthesis and the physicochemical properties of nanocomposite polymer electrolytes based on poly(ethylene glycol) diacrylate with the introduction of SiO<Subscript>2</Subscript>

The specific features of the synthesis and the physicochemical properties of new nanocomposite polymer electrolytes (NPE) based on poly(ethylene glycol) diacrylate, a liquid electrolyte, and silicon dioxide were studied. The kinetics of polymerization of the system in question were studied by isothermal calorimetry and the optimal conditions for the hardening of the NPE were selected. The dependence of the conductivity of the electrolyte samples on the amount of SiO₂ nanopowder introduced, the presence of preliminary ultrasonic treatment of the nanocomposite mixture before the synthesis, and the storage duration of the samples was studied using the electrochemical impedance method. The maximum conductivity (4.3?10^–3 S cm^–1 at 20 °C) was observed for samples without preliminary treatment with the introduction of 6 wt.% of SiO₂ and for the samples after ultrasonic treatment with 8 wt.% of SiO₂. The electrolyte films with the optimal SiO₂ content of 4 wt.% maintained their properties for 24 months.     

Synthesis,spectral-luminescent properties of B(III) and Zn(II) complexes with alkyl- and aryl-substituted dipyrrins and azadipyrrins

Effect of complexing atom, molecular structure of dipyrrolylmethene and its aza analog on spectral-luminescent properties of heteroleptic boron(III) and homoleptic zinc(II) complexes with 3,3′,5,5′-tetramethyl-2,2′-dipyrrolylmethene, 3,3′,5,5′-tetraphenyl-2,2′-dipyrrolylmethene, and 3,3′,5,5′-tetraphenyl-ms-aza-2,2′-dipyrrolylmethene in organic solvent solutions was studied. The complexes were found to exhibit strong chromophore (λ = 350–690 nm, ? ～ 10⁵ L/mol cm) and fluorescent properties. Quantum yield (γ^fl) for fluoroborate complexes reaches 100% and is weakly dependent on medium nature. The value of γ^fl for phenyl- and alkyl-substituted zinc(II) dipyrrolylmethenates in nonpolar solvents is not higher 0.3 and 0.03, respectively; complete fluorescence quenching is observed in electron-donating solvents. Aza-substitution at the meso spacer causes considerable shift of electronic absorption and fluorescence spectra to the red region but completely quenches fluorescence of zinc(II) chelates and decreases γ^fl of boron(III) complex to 0.04.     

Thermochemistry of ethyl acetate solvation in the 1-octanol-N,N-dimethylformamide system

The thermal effects of ethyl acetate (EtOAc), 1-octanol (OctOH), and N,N-dimethylformamide (DMF) solution in a OctOH-DMF model system were measured using a calorimeter of variable temperature with an isothermal shell at 298 K. The standard enthalpies of solution and ester transfer from an alcohol to a binary mixture, and partial mole enthalpies of mixed solvent components were determined. The state of non-electrolyte molecules in OctOH-DMF and OctOH-DMF-EtOAc systems were studied using extended coordination model. It was found that the binary solvent is subjected to microclusterization, since the fraction of the single-type molecules in the solvation sphere of both components of a mixture is significantly higher than in the liquid phase volume. The conclusion was drawn that in the triple system, the ethyl acetate solvation sphere in the whole range of compositions is significantly enriched with amide owing to stronger esteramide dipole-dipole interaction.     

Thermal stability of porphyrins with chemicaly active NH bond and their associates with electron-donor solvents

The composition and stability of the crystalline H associates of NH active tetrapyrroles with electron-donor solvents were investigated by thermogravimetry. It was found that common porphyrins and their analogs can form 1: 1 and 1: 2 macrocycle solvent H associates whose energy of formation depends on their composition and ranges from 20 to 115 kJ/mol. Based on the results from an analysis of the Stokes shifts, we concluded that the formation of H associates in a solution is accompanied by variations in the degree of macrocycle nonplanarity. The stability of a series of tetrapyrroles with regard to thermal destruction in argon atmosphere and in the presence of atmospheric oxygen was shown to drastically vary.