Showing papers by "S. Roth published in 1993"
TL;DR: A review of industrial applications of synthetic metals is given in this paper, where the authors are confident that the evidence presented convincingly supports the assertion that the promise of the 1970's is reality in 1992.
159 citations
TL;DR: In this article, a clear dependence of electroluminescence and electrical transport properties on chain length is found, and the supramolecular assembly of functionalized (oligo)thiophenes is achieved by oriented adsorption on single crystal surfaces and self-organization in highly ordered LB films.
38 citations
TL;DR: In this article, a time-resolved photoluminescence study in powders and single crystals of C60 is reported, which is consistent with those reported for steady state conditions which may be associated with an intramolecular process and the observed luminescence decay times are of the order of 1 ns.
Abstract: Time-resolved photoluminescence studies in powders and single crystals of C60 are reported. The observed emission spectra, resulting from excitation above the HOMO-LUMO transition energy, are consistent with those reported for steady state conditions which may be associated with an intramolecular process and the observed luminescence decay times are of the order of 1 ns. No long lived decay from the triplet is observed at low intensities. A dramatic increase in the lifetime as well as a redshift and broadening of the spectrum is observed at high excitation densities. The luminescence intensity is seen to increase with the cube of the input intensity. The phenomenon is interpreted as an abrupt onset of emission from the highly populated excited state resulting from an interaction of the intramolecular states, a process which is dependent on a critical excited state density. Furthermore, the phenomenon may be photoexcited at photon energies which lie below the HOMO-LUMO transition energy, under which conditions an intensity dependence of the output luminescence on input to the sixth power is observed. Under “off-resonant” conditions the process is interpreted as two-photon assisted nonlinear emission.
36 citations
TL;DR: In this paper, time-resolved photoluminescence studies in films, powders and single crystals of C60 are reported, and the observed spectra in all forms are consistent with those reported for steady state conditions and may be associated with an intramolecular process.
33 citations
TL;DR: In this article, the authors measured the infrared of C60 films sublimed on gold from 25 to 300 K in the frequency range 15-5000 cm−1 and observed several new lines emerging below 250 K which they assigned to the infrared active modes of C 60 in the Pa 3 phase, based on the temperature dependence of these modes around the orientational phase transition.
22 citations
TL;DR: A fast temperature-independent photocurrent, which decays within a few picoseconds and reflects the intrinsic motion of charge carriers along the chains, is observed on highly oriented trans-polyacetylene.
Abstract: We present the results of transient photoconductivity measurements on highly oriented trans-polyacetylene. Using a photoconductive switching method utilizing picosecond optical pulses we have improved the temporal resolution of the photoresponse by one order of magnitude. We observe a fast temperature-independent photocurrent, which decays within a few picoseconds and reflects the intrinsic motion of charge carriers along the chains. Estimation of the mobility yields values of the order 1 cm 2 /V s, in good agreement with theoretical calculations. By comparison of the data to that obtained from recent transient photoinduced midgap absorption experiments, we conclude that the fast photocurrent is mainly due to polarons
14 citations
TL;DR: Using gold and aluminium electrodes as contacts, a broad band emission spectrum, extending from 400 nm to 1100 nm, was observed in this article, with a primary maximum at 920 nm and a weaker feature centered on 420 nm.
Abstract: The observation of electroluminescence from crystalline fullerenes is described and discussed for the first time Using gold and aluminium electrodes as contacts, a broad band emission spectrum, extending from 400 nm to 1100 nm is observed The spectrum has a primary maximum at 920 nm and a weaker feature centered on 420 nm The spectral characteristics are independent of the applied field and the longer wavelength region is identical to that measured in the high excitation density photoluminescence spectrum In addition, the electroluminescent output intensity increases with the cube of the injection current, strengthening the association to the nonlinear phenomena observed in the highly excited state of fullerenes
13 citations
TL;DR: In this paper, the authors investigated Langmuir-Blodgett (LB) films of the molecule 3-thienylpentadecanoic acid (3TC15), and the results indicated that the molecules are oriented with their long axis upright on the substrate with a weak tilt of 10°.
10 citations
TL;DR: In this paper, it is suggested that the high anisotropy of the internal kinetic parameters, which is required for the explanation of these data, could be additionally produced by the electron scattering by dopants.
8 citations
TL;DR: In this paper, a transition between intramolecular and banded intermolecular behavior at high excited state densities is discussed in terms of a transition in luminescence, which is dependent on micro-crystallite size.
8 citations
TL;DR: In this paper, the electron acceptor molecule bianthrone covalently linked to the electron donor molecule 2,3-dimethyl-6-alkyl-l,4-dithiafulven are prensented.
Abstract: Ab initio and semi-empirical calculations on a supramolecular structure consisting of the electron acceptor molecule bianthrone covalently linked to the electron donor molecule 2,3-dimethyl-6-alkyl-l,4-dithiafulven are prensented. The molecule may act as a molecular switch and calculations show that a charge transfer state is involved in the initial stage of the switch process. The charge recombination process is calculated to occur early in the switching process. Experimental data supports this interpretation and calculations are used as a guideline for synthetic strategies leading to molecules with improved switching properties.
TL;DR: In this paper, a picosecond time resolved excited state absorption spectroscopy was employed to determine the evolution and lifetime of photochromic states in anthracene based molecular systems and the contribution of conformational changes.
TL;DR: In this article, photochromic states in anthracene based molecular systems and the contribution of conformational changes were determined using rime resolved excited state absorption spectroscopy, and the metastable nature of the state was confirmed by rime delay measurements.
Abstract: In this study, picosecond rime resolved excited state absorption spectroscopy is employed to determine the evolution and lifetime of the photochromic states in anthracene based molecular systems and the contribution of conformational changes. The unsubstituted bianthrone shows a broad transient absorption which peaks in the region of 600 nm. Equivalent measurements on anthracene give similar results indicating that this transition originates from a locally excited state on the anthrone ring system. Upon substitution of the bianthrone, an additional transient absorption at 700 nm evolves within 10 ps after excitation. This is assigned to a twisted state in which the excited state is stabilised by a sarong conformational change. The metastable nature of the state is confirmed by rime delay measurements
TL;DR: In this paper, surface-plasmon-resonance (SPR) investigations on Langmuir-Blodgett films of two different types of donor-acceptor substituted polyenes are presented.
TL;DR: In this article, the reduced state of the fullerene was stabilized using two organic cations of a different size: N-methyl-N-ethylmorpholine+ and acridizine+.
01 Jan 1993
TL;DR: In this paper, the variance in the fabrication of C60 films to increase crystallinity and grain size within the polycrystalline film structure in sublimed and solution cast films was investigated.
Abstract: We investigate the variance in the fabrication of C60 films to increase crystallinity and grain size within the polycrystalline film structure in sublimed and solution cast films. Ultra Violet/Visible absorption spectroscopy is seen to be strongly dependent on morphology in sublimed films. Strong solvent and post-heat treatment effects on morphology in solution cast films are observed. Further evidence of varying film crystallinity is provided by scanning electron microscopy. Production of large crystalline structures is shown to be most promising in solution cast films.
TL;DR: In this paper, the influence of donor substitution on the bianthrone system was investigated through the solvatochromism of the absorption and fluorescence spectra as well as time resolved fluorescence measurements.
TL;DR: In this article, the authors considered the problem of high field photoconduction in undoped trans-Polyacetylene and showed that polarons can be field ionised into the continuum and that evidence for this effect already exists in the photoconductivity work of Tubino et al.
TL;DR: In this paper, the degree of stretching of polyacetylene was determined from the angle dependence of the ESR linewidth of stretched polyacetylacetylene, and the orientation was preserved during isomerization.
01 Mar 1993
TL;DR: In this article, a review of molecular electronics, discussing shift registers and cellular automata as examples of long-term goals, is presented as steps towards the Langmuir-Blodgett films of functionalised polyenes.
Abstract: This paper gives an introductory review into molecular electronics, discussing shift registers and cellular automata as examples of long-term goals. Langmuir-Blodgett films of functionalised polyenes are presented as steps towards such final goals. The switching behaviour of some prototype molecules (in particular of substituted bianthrone) is investigated by transient spectroscopy in the picosecond regime.
01 Jan 1993
TL;DR: In this article, a broad band emission spectrum was observed from crystalline fullerenes, extending from 400nm to 1100nm, with a primary maximum at 920nm and a weaker feature centered on 420nm.
Abstract: The observation of electroluminescence from crystalline fullerenes is described. A broad band emission spectrum, extending from 400nm to 1100nm is observed. The spectrum has a primary maximum at 920nm and a weaker feature centered on 420nm. The spectral characteristics are independent of the applied field and the longer wavelength region is identical to that measured in the high excitation density photoluminescence spectrum. In addition, the electroluminescence intensity increases with the cube of the injection current, strengthening the association to the nonlinear phenomena observed in the highly excited state of fullerenes.