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Journal ArticleDOI

Neuere Untersuchungen über das Elektronengasmodell organischer Farbstoffe

07 Feb 1959-Angewandte Chemie (WILEY‐VCH Verlag GmbH)-Vol. 71, Iss: 3, pp 93-101
TL;DR: In this article, Elektronengasmodelle of Farbstoffen (Cyanine, Polyene, Polyacetylene, Acridine, Xanthene, Oxazine, Azine, Bacteriochlorophyll, Phthalocyanin, Azulen) are beschrieben.
Abstract: Die Farbe organischer Verbindungen hangt von strukturellen Einzelheiten des Molekuls ab. Es werden Elektronengasmodelle von Farbstoffen (Cyanine, Polyene, Polyacetylene, Acridine, Xanthene, Oxazine, Azine, Bacteriochlorophyll, Phthalocyanin, Azulen) beschrieben. Die Zustande von π-Elektronen werden durch eindimensionale Elektronenwellen entlang der Molekulkette (eindimensionales Modell) bzw. durch Wellenfunktionen, die sich uber die Molekulebene erstrecken, (zweidimensionales Modell) dargestellt. Energiewerte und Wellenfunktionen der Elektronen lassen sich mit Hilfe eines neu entwickelten Analogrechners ermitteln, und daraus konnen Lage, Starke und Form der Absorptionsbanden berechnet werden. Beide Modelle zeigen, das z. B. in langkettigen Polyenen ein ebenso ausgepragter Unterschied zwischen alternierend auftretenden langen und kurzen Bindungen vorhanden ist wie im Butadien.
Citations
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Journal ArticleDOI
TL;DR: It is shown here that the transition from the blue phase to the red phase is a critical phenomenon that can be quantitatively described as a second order phase transition with a critical temperature T(c) of 204 K.
Abstract: The poly(p-phenylene vinylene) derivative MEH-PPV is known to exist as two morphologically distinct species, referred to as red phase and blue phase. We show here that the transition from the blue phase to the red phase is a critical phenomenon that can be quantitatively described as a second order phase transition with a critical temperature Tc of 204 K. The criticality is associated with the trade-off between the gain in the electronic stabilization energy when the π-system of a planarized chain can delocalize and the concomitant loss of entropy. We studied this transition by measuring the absorption and fluorescence in methyltetrahydrofuran (MeTHF) in two different concentrations as a function of temperature. The spectra were analyzed based upon the Kuhn exciton model to extract effective conjugation lengths. At room temperature, the chains have effective conjugation lengths of about five repeat units in the ground state (the blue phase), consistent with a disordered defect cylinder conformation. Upon ...

131 citations

Journal ArticleDOI
TL;DR: In Farbstoffmolekulen, die zwei und mehr Polymethin-Strukturelemente, oder wenigstens ein Polymithin-and ein polyen-structurelement enthalten, treten in der Regel Kopplungseffekte auf, die das spektroskopische Verhalten und andere physikalisch-chemische Eigenschaften bestimmen as discussed by the authors.
Abstract: In Farbstoffmolekulen, die zwei und mehr Polymethin-Strukturelemente, oder wenigstens ein Polymethin- und ein Polyen-Strukturelement enthalten, treten in der Regel Kopplungseffekte auf, die das spektroskopische Verhalten und andere physikalisch-chemische Eigenschaften bestimmen. Mit Hilfe der Kopplungskonzeption konnen u.a. die Chinonfarbstoffe, die Indigoide und die Indanthrene in ein allgemeines Farbsystem der Polymethine eingeordnet und neue Farbstoffstrukturen vorhergesagt werden.

111 citations

Journal ArticleDOI
TL;DR: It is shown that the radiative lifetime of rhodamines can be correlated to the charge transfer from the phenyl toward the xanthene moiety occurring upon the S(0) ← S(1) de-excitation, and to thexanthene/phenyl relative orientation assumed in the S (1) minimum structure.
Abstract: Although lifetimes and quantum yields of widely used fluorophores are often largely characterized, a systematic approach providing a rationale of their photophysical behavior on a quantitative basis is still a challenging goal. Here we combine methods rooted in the time-dependent density functional theory and fluorescence lifetime imaging microscopy to accurately determine and analyze fluorescence signatures (lifetime, quantum yield, and band peaks) of several commonly used rhodamine and pyronin dyes. We show that the radiative lifetime of rhodamines can be correlated to the charge transfer from the phenyl toward the xanthene moiety occurring upon the S0 ← S1 de-excitation, and to the xanthene/phenyl relative orientation assumed in the S1 minimum structure, which in turn is variable upon the amino and the phenyl substituents. These findings encourage the synergy of experiment and theory as unique tool to design finely tuned fluorescent probes, such those conceived for modern optical sensors.

105 citations

Journal ArticleDOI
01 Aug 1966
TL;DR: In this article, the existence of the polymethine state is deduced from simple quantum mechanical studies; its characteristic features have been investigated more closely, including the alternation of the π-electron density in the ground state.
Abstract: Die vielfaltigen Erscheinungen im Bereiche der organischen Verbindungen mit-Elektronensystemen lassen sich unter der Annahme eines Wechselspiels von drei Grenzzustanden verstehen. Dies sind der aromatische Zustand, gekennzeichnet durch maximalen Bindungsausgleich, gleiche π-Elektronendichten an allen Atomen und durch hohe Delokalisierungsenergien, der Polyenzustand, gekennzeichnet durch alternierende Bindungsordnungen und gleiche π-Elektronendichten und der Polymethinzustand, gekennzeichnet durch gleiche Bindungsordnungen, alternierende π-Elektronendichten und durch hohe Delokalisierungsenergien. Die Existenz des energetisch ausgezeichneten Polymethinzustandes wird durch einfache quantenmechanische Studien abgeleitet; seine charakteristischen Merkmale werden naher untersucht. Ein wesentliches Kriterium fur die Tieffarbigkeit der Polymethine ist die π-Elektronendichtealternierung im Grundzustand. Various phenomena in the area of organic compounds with π-electron systems can be understood by assuming an interplay of three limiting states. These are the aromatic state, characterised by maximum bond equalisation, equal π-electron densities at all atoms and by high delocalisation energies, the polyene state, characterised by alternating bond orders and equal π-electron densities, and the polymethine state, characterised by equal bond orders, alternating π-electron densities and high delocalisation energies. The existence of the energetically outstanding polymethine state is deduced from simple quantum mechanical studies; its characteristic features have been investigated more closely. An essential criterion of the dark colour of polymethines is the alternation of the π-electron density in the ground state.

84 citations

References
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Journal ArticleDOI
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 authors considered the relationship between the nature and the lengths of links in typical organic molecules, and derived an empirical relation between them from the coefficients which occur in the linear sum of canonical structures.
Abstract: The characteristic property which some molecules have of trans­mitting influences from one part to another is an indication that the electrons constituting the bonds cannot be segregated into closed localized pairs. This feature is represented in the Pauling method by the super­ position of a number of canonical structures, each of which corresponds to a chemical picture of localized bonds. The state of the molecule has properties which are different from those of the individual canonical structures, but can be defined or interpreted in terms of a set of them. The energy of the lowest or normal state is usually lower than that of any one canonical structure, even than that which would appear from the orthodox method of drawing bonds to be the most stable. The amount by which the energy sinks as a result of the superposition has been called resonance energy by Pauling, and numerical estimates of its value have been made for a large number of organic molecules. In calculating this energy change, however, no account seems to have been taken of the change in the lengths of the links which may be caused by the interaction of the electrons. Links are regarded as single or double, and the appropriate energy content calculated as though they were isolated single or double links, whereas the interaction between adjoining links may result in a length and an energy of link, to which the description single or double is no longer appropriate. Pauling has recently discussed the relationship between the nature and the lengths of links in typical organic molecules. Taking the known lengths of links in ethylene, benzene, graphite, and ethane, and the frac­tional order of their links (as two, three-halves, four-thirds, and unity) derived from the coefficients which occur in the linear sum of canonical structures, Pauling has derived an empirical relation between them. From it he deduces in other cases the extent to which the double-bonded character enters into other links. Pauling’s method will be made more precise in a paper which follows this.

196 citations

Journal ArticleDOI
Hans Kuhn1
TL;DR: In this article, the Lage des Maximums der ersten (im Sichtbaren liebenden) Absorptionsbande von symmetrischen Cyaninfarbstoffen wird ermittelt unter Zugrundelegung eines Modells der Farbstoffmolekel, which analog ist zu dem insbesondere von Sommerfeld als Modell fur das Metall verwendeten Bild des freien Elektronengases.
Abstract: Die Lage des Maximums der ersten (im Sichtbaren liegenden) Absorptionsbande von symmetrischen Cyaninfarbstoffen wird ermittelt unter Zugrundelegung eines Modells der Farbstoffmolekel, welches analog ist zu dem insbesondere von Sommerfeld als Modell fur das Metall verwendeten Bild des freien Elektronengases. Die π-Elektronengas der Polymethinkette werden als eindimensionales, freies Elektronengas betrachtet, welches sich der Polymethinkette entlang hinzieht.

175 citations

Journal ArticleDOI
TL;DR: The first three electronic transitions of porphine and tetrahydroporphine are predicted as simple one-electron LCAO molecular orbital transitions with overlap included.
Abstract: The first three electronic transitions of porphine and the first five electronic transitions of tetrahydroporphine are predicted as simple one‐electron LCAO molecular orbital transitions (with overlap included). The electron densities and bond orders in the ground states are also computed. The observed levels are tentatively assigned to the predicted levels with the help of comparisons with spectra of other aza‐amine derivatives of conjugated hydrocarbons. Probable degeneracies and polarizations are determined. The blue shift and loss of intensity of the first electronic transition, in going from tetrahydroporphine to the larger conjugated system of porphine, is typical of the change from a ``long‐field'' to a ``round‐field'' molecule (see previous paper) and is shown to occur in several other ``long‐field'' systems when additional conjugated atoms are added at the side of the system.

171 citations