Showing papers on "Pentacene published in 1991"
TL;DR: In this paper, 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 is termed "spectral diffusion" by analogy with a similar effect which is common in amorphous materials.
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.
327 citations
TL;DR: In this article, the authors demonstrated the iodine doping of vacuum-deposited pentacene (PEN) film which showed characteristic changes in structure and electrical conductivity, and the iodine-doped film exhibited a high electrical conductivities of 110 Ω−1 1/cm−1, which was 11 orders of magnitude larger than that of as- deposited film, and high electrical anisotropy of 108.
Abstract: We have demonstrated the iodine doping of vacuum‐deposited pentacene (PEN) film which showed characteristic changes in structure and electrical conductivity. The iodine‐doped film exhibited a high electrical conductivity of 110 Ω−1 cm−1, which was 11 orders of magnitude larger than that of as‐deposited film, and a high electrical anisotropy of 108. The structural changes by the iodine doping were studied by means of x‐ray diffraction method, ultraviolet‐VIS absorption spectroscopy, and FT‐infrared spectroscopy. These results revealed that iodine molecules were intercalated between the layers of PEN molecules to form charge transfer complex of PEN‐iodine with highly ordered structure.
119 citations
TL;DR: In this paper, the authors reported unambiguous optical detection of single molecules of pentacene in p-terphenyl crystal, showing that the relative shift of the molecular resonance frequencies with temperature changes demonstrates the phenomenon of activated spectral diffusion.
Abstract: We report unambiguous optical detection of single molecules of pentacene in p-terphenyl crystal. The relative shift of the molecular resonance frequencies with temperature changes demonstrates the phenomenon of activated spectral diffusion. These results show the feasibility of the optical study of a single molecule and its local environment.
48 citations
Patent•
22 Aug 1991
TL;DR: In this article, the electron donative molecule is used to create a thin film of a condensed polycyclic aromatic compound with high anisotropy of conductivity and high electrical conductivity.
Abstract: PURPOSE:To provide an easily producible thin film of a condensed polycyclic aromatic compound having high anisotropy of conductivity and high electrical conductivity. CONSTITUTION:The objective organic thin film having conductivity anisotropy of 10 to 10 is produced by doping an electron donative molecule (e.g. halogen, Lewis acid, protonic acid or organic acid) to a thin film of a condensed polycyclic aromatic compound having 4-13 condensed benzene rings and preferably having straight-chain structure free from branch (e.g. naphthacene, pentacene or terrylene). The thin film of the compound can be formed by a dry film-forming process such as vacuum deposition, MBE process, CVD process or sputtering or by a spray-coating method, spin-coating method, blade-coating method, etc., using a solution or molten liquid of the compound. The doping of the electron donative molecule is performed e.g. by doping in a thin film prepared beforehand or introducing the electron donative molecule in the formation of the thin film.
12 citations
TL;DR: In this paper, a laser-induced reaction leading to a rearrangement of the acid protons in benzoic acid crystals at very low temperature was studied, where the authors showed that the induced changes were very long-lived (10 orders of magnitude longer than in the tautomerization case), and that the energy difference between the two two states was at least 30 times larger than the one reported in the literature for a tautomated BA crystal.
Abstract: We study here a laser induced reaction leading to a rearrangement of the acid protons in benzoic acid crystals at very low temperature. This hydrogen motion results from the electronic excitation of pentacene molecules substitutionally included into a benzoic acid host matrix, protonated or deuterated. The growth of a deuterated benzoic acid crystal doped with pentacene leads to a partial deuteration of pentacene molecules, resulting in several origin bands in the absorption spectrum. The dynamics of the system following non selective and selective laser irradiations of the differently deuterated pentacene molecules is analyzed in terms of hydrogen Introduction. Hydrogen motion in solids at low temperature is intensively studied with a wide variety of methods. Among them, optical spectroscopy is a very sensitive one, specially when performed on crystals giving narrow spectral lines. Carboxylic acid crystals represent a class of model systems commonly used for studies on proton transfer 11-51, In such a system where two molecules associate to form a dimer bound by two hydrogen bonds, the hydrogen motion consists in a double exchange of the acid protons along the two hydrogen bonds giving rise to a tautomer form. For an isolated dimer the two tautomer forms are identical and the potential energy may be represented by a symmetrical double well. In the crystal the two forms are no longer equivalent and the double well becomes asymmetric, modifying the protons dynamics. An optical way of monitoring the proton movement is to replace a dimer by a dye impurity: any change in the dye environment, a tautomerization in the neighboring dimer for example, is reflected in its absorption spectrum. A particularly interesting feature of such a system is that the optical excitation of the dye molecule induces the desired environmental change which is then probed using the same dye molecule. By such a method, it was possible to study the protons tunneling mechanism in mixed thioindigolbenzoic acid crystals at very low temperature 161. In the system studied here, composed of benzoic acid (BA) as the matrix and pentacene (PC) as the impurity, it has been proved that the induced modification of the neighborhood was not a double proton exchange but a more severe rearrangement 171. This conclusion was drawn from the fact that the induced changes were very long-lived (10 orders of magnitude longer than in the tautomerization case), and that the energy difference between the two states was at least 30 times larger than the one reported in the literature for a tautomerization in a BA crystal 181. A proposed mechanism was an