Showing papers on "Pentacene published in 1992"

Optical modification of a single impurity molecule in a solid

Abstract: THE possibility of obtaining information about solids on a truly microscopic scale has stimulated several recent advances in the optical detection and spectroscopy of single impurity centres in solids. For the system composed of pentacene impurity molecules in the crystal p-terphenyl, absorption1and fluorescence excitation2 studies at liquid-helium temperatures have led to direct observations of the lifetime-limited homogeneous linewidth of a single pentacene molecule3, as well as the surprising observation of spontaneous spectral diffusion in a crystal4. Spectral diffusion—changes in the resonance frequency of an impurity molecule with time as a result of structural relaxation processes in the molecular environment—is generally expected in amorphous hosts. We report here the observation of optical spectra of single perylene impurity molecules in a polymeric (polyethylene) host. At 1.5 K, individual perylene molecules show the expected spectral diffusion; further-more, we observe light-induced changes in resonance frequency (that is, persistent spectral hole-burning5) for certain single molecules. These observations suggest the possibility of optical storage at the single-molecule level.

Structural studies on highly ordered and highly conductive thin films of pentacene

Abstract: Structural studies on highly conductive thin films of pentacene (PEN) were carried out by x‐ray and electron diffraction methods. The ultrathin film before and after doping with iodine was confirmed to consist of single crystalline domains, and the lattice parameters were determined. Drastic elongation along the c axis as a result of doping was observed, while the a‐b plane did not change during doping. The intercalation of iodine molecules between molecular layers of PEN was confirmed.

Electrical properties of highly ordered and amorphous thin films of pentacene doped with iodine

Abstract: Studies on electrical properties of highly ordered and amorphous thin films of pentacene (PEN) doped with iodine have been made. Highly ordered film heavily doped with iodine (PEN1I2.2) showed electrical conductivity of 150 Ω−1 cm−1 with a hole mobility of 0.2 to 1 cm2 V−1 s−1 at room temperature. Metallic temperature dependence of the conductivity of the film from 240 to 4 K was observed as the first metallic transport phenomenon ever noted in an acenic compound. In contrast, amorphous film of PEN doped with iodine showed a conductivity of 10−3 Ω−1 cm−1 with an estimated hole mobility of 2×10−5 cm2 V−1 s−1 and semiconductive transport. These results revealed that the electrical properties of PEN thin films are strongly correlated with the degree of molecular orientation.

Detection and Spectroscopy of Single Pentacene Molecules in a p- Terphenyl Crystal by Means of Fluorescence Excitation.

Abstract: Recent advances in fluorescence excitation spectroscopy with high efficiency have produced greatly improved optical spectra for the first electronic transition of individual single molecules of pentacene in p‐terphenyl crystals at low temperatures (1.5 to 10 K). Two classes of single molecule behavior are observed: class I molecules have time‐independent resonance frequencies, and class II molecules show a diffusive motion among several resonant frequencies with time which we term ‘‘spectral diffusion’’ by analogy with a similar effect which is common in amorphous materials. The temperature dependence of the linewidth and the power dependence of the fluorescence emission rate and of the linewidth are reported and analyzed. Various forms of the surprising class II behavior are described, including jumping among several discrete frequencies, creeping toward the center of the inhomogeneous line in many small steps, and a wandering among many possible resonance frequencies. The occurrence of class II behavior is restricted to the wings of the inhomogeneous line suggesting that the effect is correlated with some form of local disorder. The spectral diffusion rate increases with increasing temperature, suggesting that the effect may be due to phonon‐assisted transitions of local degrees of freedom around the pentacene defect whose source remains to be identified conclusively.

Deuteration of pentacene in benzoic acid : monitoring the reaction kinetics via low-temperature optical spectroscopy

Abstract: For pentacene dissolved in molten deuterated benzoic acid a proton-deuterium exchange between the solvent and solute molecules is observed. The reaction is monitored by recording at low temperature the visible absorption spectra of pentacene in the crystallized benzoic acid. The rate of exchange at 125°C is 6×10 -6 s -1 for six of the 14 protons of pentacene and is larger by more than 2 orders of magnitude than the exchange rate of the remaining eight protons

Dynamics of the photoexcited triplet state of pentacene in an asymmetric double-well potential of p-terphenyl crystals

Abstract: The electron paramagnetic resonance spectrum of the photoexcited triplet state of pentacene-d 14 in p-terphenyl aystals exhibits a doubling at temperatures below the phase transition temperature of p-terphenyl. The relative intensities and the separation of the two members of the doublets vary with temperature. We ascribe the spectral changes to the accessibility of each pentacene molecule to two conformations with unequal energies. The data are fitted to a two-conformation jumping model. The energy difference between these two conformations (ΔE) is calculated to be 53±4 cm -1

Intermolecular and Intramolecular Radiationless Processes in p-Terphenyl and Benzoic-Acid Single Crystals Doped with Tetra-Cene or Pentacene

Abstract: Singlet excitation energy transfer processes and inter-system crossing in the mixed crystalline systems, p-terphenyl: :tetracene, p-terphenyl:pentacene and benzoic acid:pentacene were investigated in the temperature range 2 - 300 K using stationary fluorescence spectroscopy.

Thin film gas sensor

Abstract: PURPOSE:To contrive the improvement of detection sensitivity by composing an organic thin film of a condensation polycyclic aromatic compound in which the number of condensed benzene rings is the specific one and using it in which electron acceptance molecules are doped. CONSTITUTION:An electron giving gas detection organic thin film gas sensor is formed of an organic thin film in which a condensation polycyclic aromatic compound in which the number of condensed benzene rings is 4 or more and 13 or less is doped by electron acceptance molecules. The condensation polycyclic aromatic compounds indicate a hydrocarbon compound such as naphthacene (n=4) and pentacene (n=5) and a derivative in which a part of carbon such as triphenodioxazine (n=5) and triphenodithiadine (n=5) is displaced by N, S, O and the like. Amines such as ammonia and trimethylamine, aromatic such as pyridine and pyrrole and a sulfur-contained compound such as amine and thiophene can be detected by the use of the gas sensor.