Exciplex luminescence of difluoroboron meta- and para-Nitrodibenzoylmethanates in solutions and polymer matrix.

Molecular systems with intense exciplex luminescence are promising for the creation of OLEDs and light-transforming materials. The luminescent properties of difluoroboron meta- and para-nitrodibenzoylmethanates (1 and 2) were studied by the steady-state and time-resolved luminescence spectroscopy methods and quantum chemistry simulation. The influence of the position of the nitro group on the spectral properties of the complexes was revealed. The nitro group withdraws the electron density upon photoexcitation in the para-isomer in contrast to the meta-isomer. The bond order of the CC bond between the phenyl and chelate rings decreases in the excited relaxed state of 2, which leads to rotation of the substituent and a low quantum yield. Formation of exciplexes of 1 and 2 in benzene, toluene and polystyrene was found. The formation of the ground and excited-state electron donor-acceptor complexes based on difluoroboron nitrodibenzoylmethanates and benzene was revealed. The TDDFT method showed that the complexes are characterized by the presence of short contacts between the fluorine atom of the dye molecule and the hydrogen atoms of the aromatic hydrocarbon molecule. These contacts shorten during the transition from the ground state to the excited state. Polymeric compositions based on polystyrene (PS) and poly(methyl methacrylate) (PMMA) doped with 1 and 2 were obtained. The luminescence intensity of dyes 1 and 2 increases during the transition from PMMA to PS. A significant bathochromic shift of the luminescence maximum of 1 is observed, which is associated with the formation of exciplexes and triplexes. The obtained polymeric materials are promising for the development of optical smart materials.

Fluorescent boron difluoride curcuminoides as perspective materials for bio-visualization.

Curcuminoids of boron difluoride, 1-aryl(hetaryl)-5-phenylpenta-2,4-dien-1-onates of boron difluoride, have been synthesized. A comparative study of the electronic structure, luminescent properties and their potential for applications in bio-imaging has been carried out. The influence of the electronic structure of α-substituents on the luminescence of compounds was studied by the methods of stationary and time-resolved luminescence spectroscopy and DFT modeling. The introduction of π-donor substituents leads to a noticeable bathochromic shift and an increase in the Stokes shift in the luminescence spectra. On going from σ-donor substituents in the phenyl ring to π-donor substituents, the luminescence quantum yield increases from 0.03 to 0.22. The maximum Stokes shift and high quantum yield of luminescence is exhibited by the complex with a stilbene substituent, which has the longest π-system and the maximum efficiency of charge transfer. Dyes are able to penetrate into the cells of the model cell line and accumulate, moreover, accumulation occurs mainly in the cytoplasm of cells. The compounds penetrate into the cells by 12 h of incubation without damaging it's structure and without causing rapid cell death. The submicromolar range of non-toxic concentrations during long-term incubation for a model cell line was determined, which is a characteristic of fluorescent imaging. Due to uniform distribution in the cytoplasm of cells dye with naphtyl substituent is promising for visualization of the cell cytoplasm. This leader compound has the lowest cytotoxicity for cells from the synthesized series of dyes, which makes it promising for further studies as a fluorescent imaging agent. The leader compound has the lowest cytotoxicity for cells from the synthesized series of dyes, which makes it promising for further studies as a fluorescent imaging agent.

Thermoluminescent Tb(III) and Dy(III) complexes with redox-active ligands: experimental and theoretical study.

Thermoluminescence and persistent luminescent materials with unique delayed emission have attracted much attention and exhibit great promise in optical information storage. In this manuscript, to reveal the thermoluminescence mechanism, a combined experimental and theoretical study of ternary Ln(NO3 )2 Acac(Phen)2 complexes, where Ln is Tb(III), Dy(III), Eu(III), Acac is acetylacetonate anion, and Phen is 1,10-phenanthroline, was carried out. The terbium and dysprosium complexes had thermoluminescence properties, while the europium complex did not. A thermoluminescence mechanism is proposed: the powerful double π-conjugate phenanthroline system appearance upon photoexcitation, the peculiarities of frontier orbitals, the abnormally small highest occupied molecular orbital-lowest unoccupied molecular orbital gap, and the geometrical changes in the terbium and dysprosium complexes led us to suggest that phenanthroline molecules serve as 'chemical' electron traps. Therefore, we succeeded in 'freezing' and storing the excited state of complexes I and II indefinitely. The obtained thermoluminescent materials with 'chemical' traps of electrons are capable of storing the energy from incident photons and exhibit a great opportunity in optical information storage and anticounterfeiting applications.

Polymer films doped with boron difluoride ortho-hydroxydibenzoylmethanates: Solvatochromism and solvent-induced exciplex formation.

The spectral properties and solvatochromic behavior of boron difluoride ortho-hydroxydibenzoylmethanates in polymer matrices with different polarity (polystyrene, polyvinyl chloride, polycarbonate, poly(methyl methacrylate)) were investigated. The specific interaction of polystyrene, polycarbonate and poly(methyl methacrylate) with the investigated fluorophores was revealed. It was shown that the dyes are capable to form exciplexes with phenyl rings of polystyrene. The spectral properties of polystyrene films doped with boron difluoride ortho-hydroxydibenzoylmethanates, which were obtained by the pouring method, significantly depend on the solvent from which they were formed. This makes it possible to control the luminescence color of the films at the manufacturing stage.

o-Hydroxydibenzoylmethanate of boron difluoride: A complex with multi-stimuli-responsive emission effects.

The structural, luminescence and chemosensor properties of boron difluoride o-hydroxydibenzoylmethanate (1) have been investigated. In the concentrated solution, PE (polyethylene) matrix, and crystals of 1, one observes the formation of J-aggregates. The crystal structure of 1 is in compliance with that of J-aggregates of the "brickwork type" consisting of dimers that comprise excimer traps. In time-resolved luminescence spectra of 1 in PE films and crystals, one observes luminescence bands corresponding to the luminescence of excimer J-aggregates. At application of external stimuli on the crystals of 1 (heating, grinding), one observes changes in the luminescence spectrum caused by redistribution of intensities of excimer and J-aggregate bands. 1 could act as an optic chemosensor for probing amines vapors with different response rates and different sensitivities controlled by their morphologies.

Spectroscopic and quantum chemical study of difluoroboron ß-diketonate luminophores: Isomeric acetylnaphtholate chelates.

The electronic structure and optical properties of the isomeric difluoroboron ß-diketonates, 2,2-difluoro-4-methylnaphtho-[2,1-e]-1,3,2-dioxaborin (I) and 2,2-difluoro-4-methylnaphtho-[1,2-e]-1,3,2-dioxaborin (II), were studied by means of X-ray photoelectron, absorption and luminescence spectroscopies. The experimental results were interpreted using high-level ab initio quantum chemical computations, including the algebraic-diagrammatic construction method for the polarization propagator of the second and third orders (ADC(2) and ADC(3)), the outer-valence Green's function (OVGF) method, and the time-dependent density functional (TDDFT) approach. The X-ray photoelectron measurements were assigned in the entire energy range using the results of the Kohn-Sham orbital calculations which employed the B3LYP functional. Pronounced hypsochromic shift of crystal-state fluorescence was observed in I upon the lowering of temperature, which can be explained by the deterioration of the conditions for excimers formation. According to our results, remarkable feature of II, absent in I, is its phosphorescence at room temperature. Basing on our calculations, a decay mechanism for the S1 state was proposed, explaining the observed differences in the phosphorescence of I and II.

Luminescent amine sensor based on europium(III) chelate.

The effect of methylamine vapor on luminescence of Eu(III) tris-benzoylacetonate (I) immobilized in thin-layer chromatography plates has been investigated. It has been revealed that interaction of I with analyte vapor results in increase of the intensity of Eu(III) luminescence. The mechanism of the effect of methylamine vapors on intensification of the Eu(III) luminescence has been suggested using the data of IR spectroscopy and quantum chemistry calculations. The mechanism of luminescence sensitization consists in bonding of an analyte molecule with a water molecule into the coordination sphere of Eu(III). As a result, the bond of a water molecule with the luminescence centre weakens, rigid structural fragment including europium ion, water and methylamine molecules forms. The presence of such fragment must naturally promote decrease of influence of OH-vibrations on luminescence of the complex I.

Design, Synthesis, and Crystallization-Induced Emission of Boron Difluorides ß-Ketoiminates.

A series of new nitrogen-containing analogues of boron difluoride benzoylacetonates with hydrogen and methyl substituents at the nitrogen atom have been synthesized. A comparative study of boron difluoride ß-ketoiminates and their oxygen-containing analogues by means of luminescence and IR spectroscopic methods as well as quantum chemistry simulations was also performed.

Nitrogen-Containing Analog of Dibenzoylmethanate of Boron Difluoride: Luminescence, Structure, Quantum Chemical Modeling, and Delay Fluorescence.

Boron difluoride of 3-amino-1,3-diphenyl-2-propene-1-onate (1) has been synthesized and its crystal structure has been determined. The comparative studies of 1 and its oxygen analog 1,3-diphenyl-1,3-dionate (dibenzoylmethanate) of boron difluoride (2) have been performed using the methods of stationary and time-resolved spectroscopy and quantum chemical modeling. It was established that at the transition from solutions to crystals, a bathochromic shift of the spectra and a significant increase of luminescence intensity of 1 take place. The luminescent properties of solutions of 1 and 2 are similar. The peculiarities of crystal packings of 1 and 2 are responsible for differences in crystals luminescent properties. For crystals of 2, one observes the luminescence of J-aggregates and excimers, while for 1, in which a dimer is an elementary structural fragment, only the excimer luminescence is registered. A delayed excimer fluorescence of the P-type was observed for crystals of 1 and 2 at room temperature. The intensity of the delayed fluorescence of 1 is 300-fold higher than that of 2. Graphical Abstract Luminescence of J-aggregates and the formation of excimers in crystals of 1 and 2.

Europium(III) tris-dibenzoylmethanate as an efficient chemosensor for detection of ammonia.

The effect of ammonia vapor on luminescence of Eu(III) tris-dibenzoylmethanate immobilized in various matrices has been investigated. It has been revealed that interaction of Eu(III) tris-dibenzoylmethanate with analyte vapor results in increase of the intensity of Eu(III) luminescence. The mechanism of the effect of ammonia vapors on intensification of the Eu(III) luminescence has been suggested using the data of IR spectroscopy, X-ray diffraction analysis and quantum chemistry calculations. The mechanism of luminescence sensitization consists in bonding of an analyte molecule with a water molecule into the coordination sphere of Eu(III). As a result, the bond of a water molecule with the luminescence centre weakens and the blockage of the quenching of luminescence on OH-vibrations takes place.