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Hans Kuhn

Other affiliations: University of Basel
Bio: Hans Kuhn is an academic researcher from Max Planck Society. The author has contributed to research in topics: Monolayer & Excited state. The author has an hindex of 42, co-authored 193 publications receiving 7187 citations. Previous affiliations of Hans Kuhn include University of Basel.


Papers
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Journal ArticleDOI
TL;DR: In this article, the decay time of a molecule S in front of a metal mirror depends markedly on its distance from the mirror, which is quantitatively explained by considering the radiation field of this dipole, given by Hertz classical equation.
Abstract: The decay time of the luminescence of a molecule S in front of a metal mirror depends markedly on its distance from the mirror. This phenomenon is quantitatively explained by considering the radiation field of this dipole, given by Hertz classical equation. This field arrives at the molecule, after being reflected at the mirror, with a retardation of the order of 10−15 sec. The decay time of the luminescence depends on the phase shift produced by this retardation, and thus on the ratio of the distance of the oscillator from the mirror, and the wavelength of the emitted light. By measuring the distance dependence of the decay time of the luminescence this retardation effect can be studied. In quantum‐mechanical terms the phenomenon can be described as being due to a stimulation or inhibition of the emission of the light quantum. In contrast to the known cases of stimulated emission, the stimulating field is the radiation field of the emitter quantum itself. The energy transfer from an excited molecule S to an acceptor A can be treated in a similar manner by considering the phenomenon as a retardation effect. In classical terms the field of S induces A to oscillate, and the induced field of A arriving at S slows down this oscillator. Simple equations are given for the energy transfer from an excited dipole or quadrupole, and for a row of many dipoles, oscillating in phase, to a weakly absorbing acceptor layer. The latter case is considered as a model for a J‐aggregating dye and by comparison with experimental data conclusions concerning the size of a J aggregate are drawn.

560 citations

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TL;DR: In this paper, it was shown that the position of the absorption maxima of symmetrical polymethines and related compounds (symmetrical cyanine and oxanole dyes; Michler's hydrol blue and derivatives; malachite green and other triphenyl methane dyes, etc.) can be calculated by adopting a model of the dye molecule which is analogous to the free-electron gas model used in particular by Sommerfeld to describe the condition of metals.
Abstract: The most important organic compounds which absorb visible light can be classified into three groups typified: (a) by symmetrical polymethines, (b) by porphyrines, (c) by polyenes.Recently it was shown that the position of the absorption maxima of symmetrical polymethines and related compounds (symmetrical cyanine and oxanole dyes; Michler's hydrol blue and derivatives; malachite green and other triphenyl methane dyes; etc.) can be calculated by adopting a model of the dye molecule which is analogous to the free‐electron gas model used in particular by Sommerfeld to describe the condition of metals. The π‐electrons of the polymethine chain are considered as a one‐dimensional free‐electron gas which extends itself along the length of the chain.In the normal state the stablest energy states of the electron gas each contain two electrons in accordance with Pauli's exclusion principle. The remaining states are empty. The existence of the first absorption band is a consequence of the jump of a π‐electron from t...

474 citations

Journal ArticleDOI
TL;DR: In this article, the electron work function from metal to dielectric is obtained and the current onvoltage dependence is predicted and it is found to be in good agreement with experiment.
Abstract: Sandwiches of monolayers of Cd salts of fatty acids CH3(CH2)n−2COOH of different chain lengths between metal electrodes show the exponential decrease of conductivity vs thickness predicted by the tunnel theory. The electron work function from metal to dielectric is obtained. The current‐on‐voltage dependence is predicted and it is found to be in good agreement with experiment. The effects of changing the electrode material are quantitatively predicted from the differences between the vacuum work functions of the metals used (Hg, Al, Pb, and Au). The good agreement between theory and experiment can be taken as an extremely sensitive test for the uniformity of the monolayers obtained by the monolayer assembling technique used in this investigation.

442 citations

Journal ArticleDOI
TL;DR: In this article, the structures of aggregates of dye molecules are investigated on the basis of quantum-mechanical calculations, and a brick stone work arrangement is obtained instead of the ladder or staircase arrangement hitherto assumed.

295 citations

Journal ArticleDOI
TL;DR: Fadenmolekeln hochpolymerer Stoffe, welche in ruhender Losung eine statistisch wahrscheinlichste Gestalt (loses Knauel) haben, erfahren in stromender Losung nicht nur Richtungsanderungen der Fadenachse; vielmehr werden durch die von der stromenden Flussigkeit ausgeubten Krafte auch Anderungens der Gestalt, insbesond
Abstract: Fadenmolekeln hochpolymerer Stoffe, welche in ruhender Losung eine statistisch wahrscheinlichste Gestalt (loses Knauel) haben, erfahren in stromender Losung nicht nur Richtungsanderungen der Fadenachse; vielmehr werden durch die von der stromenden Flussigkeit ausgeubten Krafte auch Anderungen der Gestalt, insbesondere Anderungen des Abstandes h zwischen Molekelanfangs und -endpunkt erzwungen.

248 citations


Cited by
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Journal ArticleDOI
29 Aug 1997-Science
TL;DR: In this article, a general approach for multilayers by consecutive adsorption of polyanions and polycations has been proposed and has been extended to other materials such as proteins or colloids.
Abstract: Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.

9,593 citations

Journal ArticleDOI
TL;DR: In this paper, the electron transfer reactions between ions and molecules in solution have been the subject of considerable experimental study during the past three decades, including charge transfer, photoelectric emission spectra, chemiluminescent electron transfer, and electron transfer through frozen media.

7,155 citations

Journal ArticleDOI
30 Nov 2000-Nature
TL;DR: ‘mono-molecular’ electronics, in which a single molecule will integrate the elementary functions and interconnections required for computation, is proposed.
Abstract: The semiconductor industry has seen a remarkable miniaturization trend, driven by many scientific and technological innovations. But if this trend is to continue, and provide ever faster and cheaper computers, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules—a goal that will require conceptually new device structures. The idea that a few molecules, or even a single molecule, could be embedded between electrodes and perform the basic functions of digital electronics—rectification, amplification and storage—was first put forward in the mid-1970s. The concept is now realized for individual components, but the economic fabrication of complete circuits at the molecular level remains challenging because of the difficulty of connecting molecules to one another. A possible solution to this problem is ‘mono-molecular’ electronics, in which a single molecule will integrate the elementary functions and interconnections required for computation.

2,853 citations

Journal ArticleDOI
TL;DR: In this paper, a lower critical solution temperature of poly(N-isopropyl acrylamide was found to be due to an entropy effect, which was attributed to the formation of nonpolar and intermolecular hydrogen bonds.
Abstract: Aqueous solutions of poly(N-isopropyl acrylamide) show a lower critical solution temperature. The thermodynamic properties of the system have been evaluated from the phase diagram and the heat absorbed during phase separation and the phenomenon is ascribed to be primarily due to an entropy effect. From viscosity, sedimentation, and light-scattering studies of solutions close to conditions of phase separation, it appears that aggregation due to formation of nonpolar and intermolecular hydrogen bonds is important. In addition, a weakening of the ordering effect of the water-amide hydrogen bonds as the temperature is raised contributes to the stability of the two-phase system.

2,698 citations

Journal ArticleDOI
30 May 2003-Science
TL;DR: Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes and there is still limited correspondence between experimental and theoretical studies of these systems.
Abstract: Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes. In such junctions, the connection between the molecule and the electrodes greatly affects the current-voltage characteristics. Despite several experimental and theoretical advances, including the understanding of simple systems, there is still limited correspondence between experimental and theoretical studies of these systems.

2,195 citations