Biphenyl Single Crystals Research Articles

Optical, structural, thermal and dielectric spectroscopy characterizations of seeded melt grown 2-hydroxy biphenyl single crystal

Organic single crystal of 2-hydroxy biphenyl (2-HB) was grown by top seeded melt growth method. Scanning electron microscopy studies has been carried out on the surface of the grown crystals to investigate the nature of growth and defects. The crystalline perfection and lattice parameters of 2-HB has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Fdd2. The functional groups and molecular associations were confirmed by FT-IR. The optical characteristics such as cut-off and transmittance were carried out using UV–Vis–NIR spectra. Absence of absorption in the region between 320 and 1100nm makes the grown crystal desirable to optical applications. Thermal stability of grown crystals was characterized by thermogravimetric (TGA), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) analyses. Broadband dielectric studies reveals that dielectric constant of grown crystal is low. The resistivity of grown crystal was studied by impedance analysis. The second harmonic generation intensity of 3.8mJ was studied. The grown crystal belongs to soft material studied by hardness test.

Room-temperature single-molecule fluorescence imaging for terrylene in biphenyl single crystals

The technique of room-temperature wide-field epifluorescence microscopy has been applied to visualize, on a single-molecule level, impurity-related dynamical processes in sublimation-grown flakes of biphenyl single crystals doped with terrylene molecules. For dilute samples, spatially resolved fluorescence of individual terrylene molecules can be observed using a standard microscope equipped with an EMCCD camera. The 532 nm excitation laser light induces irreversible photobleaching of single-molecule emitters; this process is inhibited in a nitrogen-enriched atmosphere, thus confirming the role of photochemical reactions between terrylene and oxygen. Although most of terrylene impurity molecules appear to stay fixed in the host crystal, some of them can be observed to move around over distances of tens of micrometers, probably diffusing along the defects of the crystalline structure.

Laser-Induced Fluorescence Spectra and Phase Transitions in Biphenyl Crystals

Fluorescence spectra of biphenyl single crystals grown from methyl-alcohol solution were studied over a wide temperature range by the 295 nm UV light from a dye laser system. A fluorescence band near 530 nm originating from photo-chemically produced impurities was found to be composed of a zero phonon line and a phonon side band manifesting some of the low frequency lattice vibrations of the host crystal and the local modes of the impurity centers as well. We found that the 186 cm -1 lattice mode is coupled with the excited state of the impurity and the temperature dependence of its intensity reflects the orderness of the structural phase transitions of the host crystal at 40 K and 17 K.

Lifetime of the impurity-induced fluorescence and zero-phonon line emission in a biphenyl crystal

Fluorescence spectrum and its lifetime in a biphenyl single crystal were measured by a picosecond UV laser pulse. It was found that in addition to an impurity induced broad band fluorescence, a zero-phonon line appears at 533 nm if the excitation energy is larger than the band gap energy, in a single crystal of biphenyl. In contrast to a temperature insensitive lifetime of the zero-phonon emission, the broad band fluorescence was shown to have a shortest lifetime at T1 reflecting the divergence of the fluctuation of atomic displacement near the phase transition at 40 K.

Thin boundary layers of the melt of a biphenyl single crystal and its premelting

Thin boundary layers of the melt of a biphenyl single crystal and its premelting

Comparison of luminescence characteristics of Doped Molecular crystals grown by various methods

AbstractThe effect of growth conditions on the line broadening in low temperature luminescence spectra of pyrene‐doped biphenyl single crystals in investigated. It has been shown that the crystals, grown by plate sublimation technique, possess the minimal linewidth. Various possible mechanisms of line broadening are discussed.

High-resolution ODMR spectroscopy of phenazine in single crystal and polycrystalline host matrices

Experiments have been performed on a model guest molecule, phenazine, in biphenyl single crystal and n-heptane polycrystalline host matrices to illustrate the two main contributions to inhomogeneous line broadening in ODMR spectroscopy. These arise from (a) inhomogeneous crystal fields experienced by the guest molecule in a host lattice and (b) unresolved hyperfine splitting. It is shown that the former may be reduced by making optical site selection during both excitation and detection. In the latter category, the most offensive group of nuclei is shown to be the guest protons and to a lesser extent the near-lying host protons. This contribution may be drastically reduced by fully deuterating both guest and host systems. Performing ODMR spectroscopy under these conditions allows the typical linewidths of 1–10 MHz to be reduced to ca. 200 kHz. The advantages of such high-resolution spectroscopy are manifold, not the least of which being that it forms a prerequisite for highly specific multiresonance experiments such as the recently developed ODNQR method.

EPR and Optical Absorption Studies of Radiation-Induced Radicals in Biphenyl Single Crystals

Abstract Biphenyl single crystals irradiated with γ rays at liquid nitrogen temperature have been investigated by electron paramagnetic resonance and optical absorption experiments. EPR spectra at room temperature exhibit a triplet characteristic separated by 39 gauss and each line of the triplet further splits to a triplet. The main triplet has been interpreted as being caused by hydrogen added biphenyl radicals. The splitting of each line of the main triplet is consistent with the calculated splittings of 2-hydro-biphenyl radicals and 4-hydro-biphenyl radicals. The presence of 3-hydro-biphenyl radicals could not be judged from the EPR spectra due to the broadness of the lines. In the optical absorption spectra at low temperature, obtained with the light polarized to the a-, b- and c'-axes of the crystals, nine bands were detected. Transition energies were calculated using SCF-C1 molecular orbital theory for the three kinds of the hydrogen added biphenyl radicals. By comparing the experimental spectra wi...

The electronic spectrum of biphenyl

The reflection spectra from two faces of biphenyl single crystals have been measured in the wavelength range 300 to 130 nm. Absorption spectra obtained by Kramers—Krönig analysis of the reflection data have been used to determine the transition moment directions of seven allowed singlet transitions. The results of exciton mixing calculations are shown to be consistent with our interpretation of the data. The assignments are compared to existing theoretical calculations of the electronic states of biphenyl.

Spin alignment in the charge transfer phosphorescent state of the tetracyanobenzene-biphenyl complex in crystalline state

Intermolecular charge-transfer phosphorescence and fluorescence were observed for a biphenyl single crystal containing 1,2,4,5-tetracyanobenzene as a guest at various temperatures between 29 and 1.47°K. The non-exponential phosphorescence decay due to the spin alignment in the charge-transfer, triplet state was first observed and the phosphorescence lifetimes of the three sublevels were determined to be 0.9, 2.5, and 7.9 see at 1.47°K.

Delayed charge-transfer fluorescence of the tetracyanobenzene-biphenyl complex in the crystalline state

Intermolecular charge-transfer phosphorescence and fluorescence were observed for the biphenyl single crystal containing 1, 2, 4, 5-tetracyanobenzene as a guest. In addition, the delayed charge-transfer fluorescence due to triplet-triplet annihilation was observed for the first time.