Electronic states of pyrene single crystal and of its single molecule inserted in a molecular vessel of cyclodextrin

Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The absorption spectra of the single crystal have been transformed from the reflection spectra between 2.5 and at 2, and room temperature. The dry powder of β-cyclodextrin including pyrene single molecule were prepared in vacuum to investigate the electronic states of the isolated molecule. The absorption spectra of the single molecule show similar spectra to those of the single crystal. The pyrene molecule keeps its electronic character even in the single crystal.     

Vibronic spectra of charge transfer excitons and of mixed charge transfer and Frenkel excitons

The linear absorption spectra in the excitonic and vibronic regions in the case of mixing of Frenkel excitons (FEs) and charge-transfer excitons (CTEs) have been theoretically studied for the exciton parameters of the crystals of MePTCDI and PTCDA. Two coupling parameters for the exciton–phonon coupling are introduced: the FE–phonon coupling and the CTE–phonon coupling. The main features of the vibronics in the absorption spectra are the following: (a) the existence of a doublet structure in the vibronic spectra of CTEs; (b) the vibronic levels of the FE at intermediate values of both coupling parameters are located in the continuum of the many-particle exciton–phonon states which makes its absorption line wide and flat; (c) in the case of strong coupling (coupling constants larger than 1) a doublet of bound states appears above this continuum; (d) in the case of vanishing CTE–phonon coupling the vibronics of the charge transfer excitons practically disappear in the absorption spectra.     

Raman spectra of single H2O molecules isolated in cavities of crystals

The vibrational (Raman) spectra of H₂O molecules isolated in cavities of beryl, cordierite, bikitaite, natrolite, scolecite, lawsonite, and hemimorphite have been measured in the temperature range of 4–295 K. The influence of van der Waals and hydrogen bonds on the values of frequency, intensity, and half-width of stretching and bending modes of H₂O is considered. The spectra of translational vibrations of H₂O molecules in crystal cavities are discussed. For the firsts time, the ratio between the frequencies of translation and stretching vibrations of H₂O and the dependence of frequencies of bending vibrations on the angle H-O-H in H₂O molecule are presented.     

Palladium catalyzed synthesis of Ca indicators with aryl bithiophene and terthiophene fluorophores

Five new fluorescent indicators for Ca²⁺ were synthesized using the Stille reaction. They all consist of the tricarboxylate chelator APTRA (o-aminophenol-N,N,O-triacetic acid) linked to a (substituted) bithiophene or terthiophene fluorophore. The dissociation constants K_d measured via fluorimetric titrations at 21 °C in 100 mM KCl buffered solution, pH 7.05, for the Ca²⁺ complexes with the new probes are in the range between 10 and 40 μM.     

Diazaisoindigo bithiophene and terthiophene copolymers for application in field‐effect transistors and solar cells

Two donor–acceptor conjugated polymers with azaisoindigo as acceptor units and bithiophene and terthiophene as donor units have been synthesized by Stille polymerization. These two polymers have been successfully applied in field‐effect transistors and polymer solar cells. By changing the donor component of the conjugated polymer backbone from bithiophene to terthiophene, the density of thiophene in the backbone is increased, manifesting as a decrease in both ionization potential and in electron affinity. Therefore, the charge transport in field‐effect transistors switches from ambipolar to predominantly hole transport behavior. PAIIDTT exhibits hole mobility up to 0.40 cm²/Vs and electron mobility of 0.02 cm²/Vs, whereas PAIIDTTT exhibits hole mobility of 0.62 cm²/Vs. Polymer solar cells were fabricated based on these two polymers as donors with PC₆₁BM and PC₇₁BM as acceptor where PAIIDTT shows a modest efficiency of 2.57% with a very low energy loss of 0.55 eV, while PAIIDTTT shows a higher efficiency of 6.16% with a higher energy loss of 0.74 eV. Our results suggest that azaisoindgo is a useful building block for the development of efficient polymer solar cells with further improvement possibility by tuning the alternative units on the polymer backbone. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2691–2699     

Orientation of anthracene molecules in naphthalene single crystals

The orientation of anthracene in naphthalene matrix has been determined by EPR of the triplet state of the guest molecule. It differs from the host molecule orientation mainly by a rotation of 25° about the z axis.     

Orientation of anthracene molecules in naphthalene and tetracene molecules in anthracene single crystals

The orientation of isolated anthracene and tetracene molecules in naphthalene and anthracene single crystals, respectively, was determined using electron spin resonance. The result indicates only small deviations of less than 60° from that of a molecule in a substitutional position.     

Nanoscale calorimetry of isolated polyethylene single crystals

We used thin‐film differential scanning calorimetry to investigate the melting of isolated polyethylene single crystals with lamellar thicknesses of 12 ± 1 nm. We observed the melting of as few as 25 crystals. Over a wide number of crystals (25–2000 crystals), the heat of fusion was 40% larger than the bulk value. The melting temperature of the isolated single crystals was 123 ± 2 °C, 9 °C lower than that of the bulk material. We also measured the heat of fusion of quenched crystals (±15%) over a wide range of heating rates (20,000–100,000 K/s). Annealing the quenched crystals resulted in shifts in the endotherm peak by as much as 15 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1237–1245, 2001     

Ring rotation of ferrocene in interlocked molecules in single crystals

This work describes unique molecular motions of ferrocene-containing interlocked molecules observed by single-crystal X-ray crystallography. The rotational flexibility of ferrocene is achieved using combinations of ferrocene-tethered ammonium and 30-membered ring dibenzo-crown ether. By contrast, ferrocene was locked in the complex with an 18-membered ring dibenzo-crown ether and CH₂Cl₂. When the complex was heated at 358 K, CH₂Cl₂ was removed from the complex, which led to drastic structural changes, including a semieclipsed-to-disordered transition of ferrocene and flipping of the dibenzo-crown ether.

Unique molecular motions, reversible internal rotation of ferrocene and flipping of crown ether are observed in DB30C10 and DB18C6-containing interlocked molecules, respectively.     

Single dibenzoterrylene molecules in naphthalene and 2,3-dimethylnaphthalene crystals: vibronic spectra

Fluorescence excitation spectra of single dibenzoterrylene (DBT) molecules embedded in naphthalene (N) and 2,3-dimethylnaphthalene (2,3-DMN) crystals were studied at 5 K. The frequencies characterizing the vibronic structure of single DBT molecules in an N crystal agree with the theoretical prediction for the isolated DBT molecule. The 'dipolar' disorder encountered in 2,3-DMN crystals leads to a broad distribution of frequencies of the (0,0) lines of single DBT molecules. Moreover, the observed vibronic frequencies and intensities in the spectrum of DBT in 2,3-DMN crystals are slightly different to those in an N crystal. We conclude that the structure of DBT molecules in a 2,3-DMN crystal is disturbed in comparison with isolated DBT and the main change concerns its central tetracene moiety.     

Orientational effects on atomic photoelectric cross sections and their relevance to photoelectron spectra from single crystals

We have examined the dependence of the photoelectric cross section from individual atomic orbitals and from groups of orbitals adapted to crystal symmetries in order to ascertain the relevance of this effect to the photoelectron spectra arising from single crystals.     

Vibrational spectra of anhydrous and monohydrated caffeine and theophylline molecules and crystals

Density functional theory and classical molecular dynamics simulations are used to investigate the vibrational spectra of caffeine and theophylline anhydrous and monohydrate molecules and those of their crystalline anhydrous and monohydrated states, with emphasis in the terahertz region of the spectra. To better understand the influence of water in the monohydrate crystal spectra, we analyze the vibrational spectra of water monomer, dimer, tetramer, and pentamer, and also those of liquid water at two different temperatures. In small water clusters, we observe the progressive addition of translational and librational modes to the terahertz region of the spectra. The water spectra predicted by rigid and flexible water models is examined with classical molecular dynamics, and the respective peaks, especially in the terahertz region, are compared with those found in the small clusters. Similar analysis done for caffeine and theophylline monohydrate molecules using density functional theory clearly shows the presence of water modes in the librational states and in the water stretching region. Molecular dynamics of caffeine and theophylline anhydrous and monohydrate crystals reveal the influence of vibrations from the molecule-molecule (caffeine or theophylline) crystal stacks and those from the water-molecule interactions found in the monohydrate molecules and new modes from molecule-molecule, water-molecule, and water-water hydrogen bonding interactions arising from collective effects in the crystal structure. Findings illustrate challenges of terahertz technology for the detection of specific substances in condensed phases.     

Chemical bonding in isolated molecules and crystals of zwitterionic pentacoordinate silicon chelates

The electronic structures of a number of zwitterionic pentacoordinate silicon chelates were investigated using the results of X-ray diffraction studies and quantum-chemical calculatoins by the MPW1PW91/6-311G(d) method. The topological analysis of the electron density distribution function and the study in the framework of the natural bond orbital partitioning scheme showed that the character of chemical bonding in the axial fragments of the molecules under consideration changes from dative to three-center, four-electron as the silicon atom assumes a trigonal-bipyramidal coordination.     

Calculation of the spectral distribution of absorption coefficients in vibrational spectra of complicated molecules,polymers and molecular crystals

The interpretation of vibrational spectra of complicated systems is necessary for the subsequent use of these spectra in the analysis of the structure and physical properties of complicated molecules, polymers and molecular crystals.This interpretation is accomplished with the aid of various methods including calculations of frequencies and in certain cases use of the intensities of absorption bands.     

Electronic spectra of metal cluster molecules

The electronic absorption spectra (UV-visible-NIR) of a range of molecular metal cluster compounds, including new spectra of Pt₃₀₉(phen*)₃₆O₂₈ in solution and Au₅₅(PPh₃)₁₂Cl₆ in the solid state, are discussed and compared with the spectra of colloidal particles of the corresponding metals. We consider frontier orbital separations, the development of interband absorptions, the possible appearance of molecular plasma resonances, and charge-transfer in the solid state.     

Infrared spectra of some uranium oxyfluoride molecules isolated in solid argon

Reaction of laser-ablated uranium with oxygen/fluorine mixtures or laser-ablated uranium dioxide ceramic with fluorine produces the uranium oxyfluorides molecules UO₂F₂, UO₂F and UOF₄, which have been isolated in solid argon and identified by virtue of the effects of oxygen isotopic substitution on their infrared spectra.     

Raman spectra of lanthanide sesquioxide single crystals: Correlation between A and B-type structures

Structures and Raman spectra of lanthanide sesquioxide single crystals with A-type trigonal structure (La₂O₃, Pr₂O₃, Nd₂O₃, Sm₂O₃) and B-type monoclinic structure (Sm₂O₃, Eu₂O₃, Gd₂O₃) are compared. The B form (C³_2h or $\text{C2}\text{m}\text{, Z = 6}$) derives from the A form (D³_3d or $\text{P}\text{3}\text{m1, Z = 1}$) by a slight lattice deformation, implying a splitting of D_3d and C_3v atomic positions into less symmetrical C_2h and C_s sites. This close structural relationship allows one to relate the Raman active modes of the B-type crystals to vibrations of the A-type crystals and to deduce an interpretation of the complex B-type spectra from those of the simpler A-type spectra. Furthermore, it is shown that the frequency of the modes which mainly involve metal-oxygen stretching motion increases with the lanthanide atomic number in the A and B series. This evolution is interpreted in terms of increasing compactness of the structure.     

Fluorescence detection of single guest molecules in ultrasmall droplets of nonpolar solvent

We have investigated emissive behaviours of individual perylenebisimide derivatives, N,N'-dipropyl-1,6,7,12-tetrakis(4-tert-butylphenoxy)-3,4,9,10-perylenetetra-carboxydiimide (BP-PDI), in single ultrasmall droplets of n-octane at room temperature by using confocal and wide-field microscopic techniques. Single BP-PDIs in the small droplets show no distinguishable blinking in the time courses of fluorescence intensity. This is attributed to small probabilities of the formation of the long-lived ionized state leading to the off-state of the fluorescence. Temporal change in the degree of polarization of fluorescence and wide-field fluorescence images indicated short-time adsorption of the fluorescent molecules at the interfaces between n-octane and watery environments. Fluorescence correlation spectroscopy revealed that the adsorption/desorption processes took place at least in two different time scales, probably due to the difference in the adsorption geometry and/or in the interaction, such as van der Waals interaction and hydrogen bonding, between the dye and the interface.     

13C Nuclear magnetic resonance spectra of cyclodextrin monomers,derivatives and their complexes with methyl orange

Low molecular mass fractions of water soluble -, -, and -cyclodextrin epichlorohydrin polymer products (cdx-Ep) were characterized by¹³C nuclear magnetic resonance. The derivatives proved not to be polymers, but substituted cdx having one or two glyceryl groups per one glucose at the C-2, C-3 and C-6 positions. Spectra of analogous hydroxy-propyl -cdx indicate that the degree of substitution is rather higher at the C-6 position. Methyl orange (MO) was included into nine kinds of cdx having different inner diameters and hydrophobic torus heights; -, -, and -cdx monomers, 2, 6-dimethyl and 2, 3, 6-trimethyl -cdx, water soluble -, -, and -cdx-Ep and ethyleneglycol-bis(epoxy-propyl) ether products. The inclusion shifts were compared with each other and with the dioxane-induced solvent shift of MO. TheN, N-dimethyl-aniline side of MO shifted to a higher field site with the increase of the inner diameter in cdx. By substituting cdx with ether groups of different length, the mechanism of inclusion formation remains substantially the same, but by lengthening the hydrophobic cavity, the hydrophobic interaction becomes stronger, as a better resemblance of inclusion shifts and solvent shifts can be observed.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.