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A monolithic silica glass doped with Pr3+ was prepared by immersing a mesoporous SiO2–polyvinly alcohol (PVA) nanocomposite in a Pr nitrate solution and then sintering it at 1100℃ in air. The sintered glass exhibited pink emission when excited by ultraviolet irradiation. The photoluminescence intensity of the glass depended on the total concentration of Pr ions, which was adjusted by changing the concentration of the Pr nitrate solution and the immersion time. The glass with the highest photoluminescence intensity was prepared by using a 1- or 10-mM Pr solution at an immersion time of 60 min. To reveal how the immersion conditions affected the photoluminescence intensity, we analyzed and discussed the adsorption kinetics of the Pr ions onto the surface of the mesoporous nanocomposite. At immersion times below 60 min, the Pr ions diffused into pores of the nanocomposite without aggregating. To prepare Pr3+-doped silica glass with high photoluminescence, both the concentration of the Pr solution and the immersion time must be controlled. [ABSTRACT FROM AUTHOR]

Highlights: [•] The monolithic silica glass doped with Tb3+ ions was fabricated utilizing the SiO2–PVA nanocomposite. [•] To obtain the silica glass, the nanocomposite was immersed in a Tb ions solution, subsequently sintered at 1100°C in air. [•] The doped glass exhibited green fluorescence attributed to 5D4 → 7F5 main transitions by Tb3+ ions under UV excitation. [•] The Tb concentration in the glass can be adjusted by the concentration of the Tb solution and immersion time. [ABSTRACT FROM AUTHOR]

Abstract: Colorless crystals of 1,4-dicyano-2-(4′-methoxybenzyloxy)methylnaphthalene (2), which is a 1,4-dicyano-2-methylnaphthalene (DCMN)–4-methylanisole (MA) dyad linked by an ether unit, selectively form a fluorescent intermolecular DCMN–MA exciplex (greenish blue, ). In contrast, 1,4-dicyano-2-(4′-methylbenzyloxy)methylnaphthalene (3), which is a DCMN–p-xylene dyad, forms a fluorescent intermolecular DCMN–DCMN excimer in the crystalline state (blue, ). These findings demonstrate that a moderate charge transfer interaction takes place between the DCMN moiety of 2 and MA moieties of the adjacent molecules of 2, which successfully facilitates the preparation of light-emissive organic crystals. [ABSTRACT FROM AUTHOR]

The results of an investigation of the thermoluminescence (TL) and electroluminescence (EL) of arylated methylenecyclopropanes 1, systems whose photoinduced electron-transfer (PET) chemistry has been thoroughly studied, are described. In both the TL and EL experiments with 1, electronically excited triplet trimethylenemethane (TMM) biradicals ³2•• are generated by back electron transfer (charge recombination) of a TMM radical cation (hole) 2•+, formed by isomerization of the substrate radical cation (hole, 1•+). The application of this chemistry to the design of new organic light-emitting diodes (OLEDs) is described. The mechanistic features of this reaction system have the potential of overcoming significant problems (e.g., quantum efficiency, difficulty obtaining long wavelength emission, and device durability) normally associated with OLEDs that rely on the use of organic closed-shell hydrocarbons. [ABSTRACT FROM AUTHOR]

Abstract: Four kinds of N-dansyl-amino acid-modified β-cyclodextrins (β-CDs) were prepared as fluorescent chemosensors for chiral discrimination. The use of an amino acid as a spacer improved binding affinities and chiral discrimination abilities of the chemosensors. N-dansyl-l-Phe-modified β-CD showed high d-selectivity for norbornane derivatives and N-dansyl-d-Phe-modified β-CD showed high l-selectivity for menthol. Microcalorimetric titration results indicate that the chemosensors selectively accommodate the enantiomer that induces the least unfavorable entropy change on making an inclusion complex. [Copyright &y& Elsevier]

Discusses the synthesis and characterization of fluorophore-amino acid-cyclodextrin (CD) triad systems as fluorescent indicators of molecular recognition. Structural analyses of beta-CD derivatives; Difference in the enantiomeric configuration of the leucine residue; Guest-responsive variations of fluorescence intensity.

A new fluorescent chemosensor, NBDamine-appended α-cyclodextrin, was prepared and showed high selectivity for perhalogenated methanes via multisite interactions between the perhalogenated methane and the cyclodextrin molecule. [ABSTRACT FROM AUTHOR]

Boron difluoride (BF 2 ) complexes of N -(5-phenyl-2-pyrazinyl)pivalamide and its derivatives having a substituent on the phenyl group were prepared and their spectroscopic properties were investigated. It was found that the BF 2 complexes show fluorescence in solution and the solid state. The origins of the fluorescence properties are discussed on the basis of the fluorescence yields and lifetimes, crystal structures and DFT calculations. The present work would provide a guide to design BF 2 complexes of amidopyrazines exhibiting solid state fluorescence. [ABSTRACT FROM AUTHOR]

Abstract: A simple assay method for α-amylase was developed based on fluorophore-modified cyclodextrins (CDs). Four kinds of CD derivatives bearing a 4-amino-7-nitrobenz-2-oxa-1,3-diazole (NBD-amine) moiety were prepared as artificial substrates for the assay method. The fluorescence intensity of all the NBD-amine-modified CDs decreased upon addition of Aspergillus oryzae α-amylase, indicating a reduction in hydrophobicity near the NBD-amine moiety induced by hydrolysis of the CD ring. NC4γCD, having a γ-CD and an amino-tetramethylene spacer, was the most sensitive substrate for the α-amylase assay. The initial rate of hydrolysis of NC4γCD displayed a liner correlation to the concentration of the α-amylase. NC4γCD was sensitive to the α-amylase but was not sensitive to guest compounds that were accommodated by the native CDs. [Copyright &y& Elsevier]

Dyad 4, comprising a triphenylamine (TPA) electron donor and 1,4-pentadien-3-one (pentadienone) electron acceptor tethered by a nonconjugated linker, displays solvatofluorochromism (SFC) and dual fluorescence associated with intramolecular charge transfer (ICT) in the excited state. While the fluorescence arises from a locally excited state of 4 (LE-4*) in saturated hydrocarbon solvents, the fluorescence from the ICT state of 4 (ICT-4*) occurs in aprotic solvents. ICT-4* has a much greater dipole moment than its corresponding ground state. The results of theoretical calculations suggest that the conversion of LE-4* to ICT-4* involves a unique structural change like a leaning of the pentadienone moiety. Two factors are responsible for the significant SFC displayed by 4, the first being the high electron-donating and -accepting abilities of the respective locally excited TPA and pentadienone moieties in LE-4* and the other being a rigid ethano bridge that links the two moieties in ICT-4*. The former property facilitates photoinduced electron-transfer (PET) and the latter prevents full single electron transfer (SET) by prohibiting direct π-conjugation and the spatial approach of the two dyad components. Consequently, these electronic and geometrical features lead to SFC arising from a large dipole moment change caused by ICT and partial intramolecular SET. [ABSTRACT FROM AUTHOR]

The substituent effect on optical properties of 3,14-diphenyl-17,17-di( n -pentyl)tetrabenzofluorene derivatives bearing electron-withdrawing groups (NC, CH 3 OCO, CH 3 SO 2 , and OHC) at 4-position of the phenyl groups were investigated. These compounds were readily prepared by using Suzuki–Miyaura cross-coupling as a key step. The 4-cyano, 4-methoxycarbonyl, and 4-methylsulfonyl derivatives display intense blue to blue-green fluorescence in CH 2 Cl 2 and in the solid states. On the other hand, the title compound forms two polymorphs, and thus, exhibit crystallochromism in fluorescence; the prismatic crystal emits intense yellow fluorescence, and the other crystal form does blue-green fluorescence. Moreover, the compound shows large solvatofluorochromism (Δ λ EM = 67 nm). The crystallographic analysis of the prismatic crystal reveals that the tetrabenzofluorene moiety of the compound possesses a helical structure with a C 2 symmetry and the molecules form a herringbone-like structure. The density function theory calculations predict the remarkable intramolecular charge-transfer character of the compound. The prediction is in good agreement with the observed fluorescence properties. [ABSTRACT FROM AUTHOR]

The thermally backward reaction involved in the mechanofluorochromism of dibenzoylmethanatoboron difluoride (BF2DBM) derivatives, accompanied by an amorphous–crystalline phase transition, was quantitatively evaluated based on kinetics and thermodynamics. The kinetics was discussed by evaluation of the effect of temperature on the time-dependent changes of the fluorescence intensity for amorphous samples obtained by mechanical grinding. The thermodynamics was discussed based on data for the amorphous–crystalline phase transition obtained by differential scanning calorimetry. The enthalpy of activation (ΔH‡) of BF2DBM derivatives with MeO groups (2aBF2) was larger than that of derivatives with alkyl groups (2b-dBF2), whereas the entropy of activation (ΔS‡) was smaller than that of the derivatives with alkyl groups. It is proposed that the reaction dynamics of 2aBF2 will be governed by rotational motion around the C(methyl)–O bond. Interestingly, the Gibbs energies of activation (ΔG‡) were comparable for the reactions of all members of the BF2DBM series, though ΔH‡ and ΔS‡ were strongly dependent on the identity of the substituent. It is proposed that the substituent-dependent ΔS‡ term is one of the key parameters for understanding the mechanofluorochromism of BF2DBM derivatives associated with the amorphous–crystalline phase transition. These findings will also provide important insights into the process of formation of crystal nuclei in moving from the melted to the crystalline state. [ABSTRACT FROM AUTHOR]

The crystal-packing structures of seven derivatives of diaroylmethanatoboron difluoride ( 1 a- gBF2) are characterized by no overlap of the π-conjugated main units of two adjacent molecules (type I), overlap of the benzene ring π-orbitals of two adjacent molecules (type II), and overlap of the benzene and dihydrodioxaborinine rings π-orbitals of adjacent molecules (type III). The crystal-packing structures govern the fluorescence (FL) properties in the crystalline states. The FL domain that is present in type I crystals, in which intermolecular orbital interactions are absent, leads to excited monomer-like FL properties. In the case of the type II crystals, the presence of intermolecular overlap of the benzene rings π-orbitals generates new FL domains, referred to as 'excited multimers', which possess allowed S0-S1 electronic transitions and, as a result, similar FL lifetimes at longer wavelengths than the FL of the type I crystals. Finally, intermolecular overlap of the benzene and dihydrodioxaborinine ring π-orbitals in the type III crystals leads to 'excited multimer' domains with forbidden S0-S1 electronic transitions and longer FL lifetimes at similar wavelengths as that in type I crystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • A crystal of the [2.2]paracyclophane-containing organoboron complex shows PFC. • Inter- and intra-molecular π-stacking distances are reduced under high pressure. • The intermolecular π–π interaction is still the important factor leading to PFC. Piezofluorochromism (PFC) of crystals of a tert -butyl and [2.2]paracyclophane-containing diaroylmethanatoboron difluoride (p CP- t Bu), which is expected to possess both intermolecular and intra molecular π–π interactions, was investigated. p CP- t Bu crystals were found to exhibit remarkable PFC associated with an over 150-nm redshift of fluorescence (FL) wavelength occurring under increasing isotropic pressure applied by using a diamond anvil cell. X-ray crystallographic analysis showed that p CP- t Bu molecules in the crystal at atmospheric pressure exist in the form of an intermolecular π-stacking dimer through back-to-back π–π interactions. Moreover, the crystallographic data under high pressure showed that increasing isotropic pressure causes a reduction in both the intermolecular π-stacking distance of the dimer (D INTER) and the intra molecular π-stacking distance between two benzene rings in the [2.2]paracyclophane moiety (D INTRA). Density functional theory calculations, using the Cartesian coordinates obtained by X-ray analysis, suggest that the origin of PFC of p CP- t Bu crystals is the reduction of the LUMO energy of the π-stacking dimer and that the intermolecular π–π interaction is still the important factor leading to PFC of p CP- t Bu crystals. [ABSTRACT FROM AUTHOR]

Abstract: The fluorescence (FL) and structural properties of dibenzoylmethanatoboron difluoride (1aBF2 ) and its diisopropyl derivative (1bBF2 ) in the crystalline state were investigated. Both 1aBF2 and 1bBF2 in their crystalline states have FL spectra that contain similar emission in the ca. 450–600nm region, which correspond to emission of green light. However, the FL lifetimes (τ FL) of these substances in their crystalline states are markedly different. Based on the results of wave deconvolution and decay profile analyses, we tentatively supposed that the FL band of 1aBF2 with average τ FL =47.7ns is mainly comprised of FL band from an excited multimer, an emitting domain consisting of three or more molecules. In contrast, an excimer with average τ FL =5.3ns is likely the emitting species in the crystalline state of 1bBF2 . The results of X-ray crystallographic analyses support the conclusion that these contrasting properties derive from a difference in molecular overlap, especially between the benzene (B) and dioxaborinine (D) rings in the crystalline states of 1aBF2 and 1bBF2 . Specifically, molecules in crystals of 1aBF2 are aligned having B-on-B and B-on-D overlap with respective short face-to-face distances (3.50 and 3.42Å) while those in 1bBF2 are aligned in a single B-on-B overlap mode with a longer face-to-face distance (3.82Å). [Copyright &y& Elsevier]

A series of 17,17-dialkyl-3,14-diaryltetrabenzofluorenes were efficiently prepared by using Suzuki-Miyaura cross-coupling reactions of the corresponding 3,14-dibromo derivatives. Studies of the unique fluorescence properties of these compounds showed that they display intense blue to yellow fluorescence with high quantum yields in the solution state and blue to orange fluorescence with moderate quantum yields in the solid state. In addition, the fluorescence wavelength of the bis( p-nitrophenyl) derivative is remarkably solvent-dependent in a manner that correlates with the solvent polarity parameter ET(30). The results of density function theory calculations suggest that the intramolecular charge-transfer character of the HOMO-LUMO transition is responsible for the large solvent effect. Moreover, addition of water to a tetrahydrofuran (THF) solution of this compound leads to quenching of the yellow fluorescence owing to an increase in the solvent polarity. However, when the amount of water fraction exceeds 70 %, a new fluorescence band appears at the same orange-red emission wavelength as that of the solid-state fluorescence. This observation suggests the occurrence of a crystallization-induced emission (CIE) phenomenon in highly aqueous THF. [ABSTRACT FROM AUTHOR]

Abstract: Metal-ion complexation of 7-benzylimidazo[1,2-a]pyrazin-3(7H)-one derivative (2) with Li+, Mg2+, Ca2+, Ba2+, Sc3+, and La3+ in acetonitrile resulted in successive modulations of its UV/vis absorption and fluorescence spectroscopic properties. This result indicates that 2 can be used as a colorimetric and fluorometric sensor of the Lewis acidity of a metal ion in aprotic solutions. The hypothesis that the metal-ion complex has a O10(imidazopyrazinone)–metal ion bond was supported by X-ray crystallographic analysis and quantum chemical calculations for a Li+ complex of 7-methylimidazo[1,2-a]pyrazin-3(7H)-one derivative (1). [Copyright &y& Elsevier]

Abstract: Fluorescence of the phenolate anion (3(O)−) and the amide anion (5(N)−) of coelenteramide analogues in ion pairs with various counter cations was systematically investigated to elucidate the ionic structure of the light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin. The fluorescent properties of 3(O)− in an ion pair with a conjugate acid of an organic base (BASE–H+) were varied depending on the structural variation of the ion pair and the solvent polarity. In particular, the fluorescence of 3(O)− in the ion pair with the conjugate acid of n-butylamine (NBA–H+) indicates that the singlet-excited state of 3(O)− (1 3(O)−∗) and NBA–H+ make a contact ion pair in which the fluorescence emission maxima of 3(O)− is sensitive to the solvent polarity and the fluorescence quantum yields of 3(O)− increase in a less polar solvent. The results also confirm that 1 3(O)−∗ is a twisted intramolecular charge transfer state. By contrast, the fluorescence of 5(N)− in an ion pair depends little on the BASE–H+ or the solvent polarity. Based on these results, we conclude that the light emitter in aequorin and obelin bioluminescences is the singlet-excited state of coelenteramide phenolate anion 2(O)− (1 2(O)−∗) in a contact ion pair with an imidazolium side chain of a histidine residue, which is located at the less polar active sites of the photoproteins. We also propose a mechanism for the bioluminescence reaction, including the chemiexcitation process to give 1 2(O)−∗. [Copyright &y& Elsevier]

Abstract: Substituent effects on the spectroscopic properties of a solvatochromic compound, 7-methyl-2-phenylimidazo[1,2-a]pyrazin-3(7H)-one ( 1c ), using derivatives 1 with a para-substituent R on the phenyl group, were investigated systematically. In the UV/visible absorption spectra, the solvatochromic property of 1 originating from hydrogen-bonding interactions was effectively regulated by the substituent effects. In particular, the cyano derivative 1e showed significant solvatochromism with a wide color variation range and a high sensitivity toward solvents. Similarly, the fluorescence of 1 showed a redshift as the electron-withdrawing property of R increased. The substituent effects were evaluated by AM1-COSMO calculations, which also suggested that derivatives 1 are good electron donors and that the electron-donating ability is regulated by R. This was confirmed by the observation of low oxidation potentials and the formation of charge-transfer complexes with tetracyanoethylene. Absorption-spectrum changes of 1c and 1e caused by metal–ion complexation were also compared, showing that the cyano derivative 1e is a good colorimetric sensor for the Lewis acidity of the metal ions. From these observations, it was established that para-substitution of R on the phenyl group of 1c caused successive modulations of the colorimetric sensor properties. [Copyright &y& Elsevier]

The front cover artwork is provided by the group of Prof. Dr. Hiroshi Ikeda in Osaka Prefecture University (Japan). The picture represents the difference in reactivity between 1‐ and 2‐naphthyl‐substituted methylenecyclopropanes. The weak bond in the former substance can be broken even by a small samurai resulting in pink fluorescence, whereas the strong bond in the latter cannot be broken even by a big samurai (resulting in green phosphorescence). Read the full text of the Communication at10.1002/cptc.201900230. [ABSTRACT FROM AUTHOR]

The Way of Tea in the world of molecules: Sakai City, where the authors’ Osaka Prefecture University is located, is internationally famous for the Way of Tea. This cover picture displays the traditional Japanese tea ceremony using powdered green tea served with rice dumplings and sugar candies, which is specially made from molecular models of boron complexes and their fluorescent crystals, respectively. The crystal packing structure of them controls its fluorescence domain, the excited monomer, excimer, and “excited multimer”, which show a different fluorescence wavelength, lifetime, and quantum yield. For more information see the Full Paper by H. Ikeda et al. on page 18128 ff. [ABSTRACT FROM AUTHOR]