Molecular switches based on Dihydroazulene/Vinylheptafulvene photochromism

Item type:	Thesis of the University of Regensburg (PhD)
Date:	21 August 2005
Referee:	Jörg (Prof. Dr.) Daub
Date of exam:	26 July 2005
Institutions:	Chemistry and Pharmacy > Institut für Organische Chemie
Keywords:	Photochromie , Dihydroazulene , Vinylheptafulvenderivate , Molekularer Schalter , Blaulicht , Photorezeptor , Photochromie , Dihydroazulen , Vinylheptafulven , molekulare Schaltung , Blaulichtphotoreceptor , Photochromism , Dihydroazulene , Vinylheptafulvene , molecular Switches , blue light receptor
Dewey Decimal Classification:	500 Science > 540 Chemistry & allied sciences
Status:	Published
Refereed:	Yes, this version has been refereed
Created at the University of Regensburg:	Yes
Item ID:	10333

Abstract (English)

This work reports on the synthesis of new dihydroazulene/vinylheptafulvene systems and on the study of their photochromic and physical properties. Main emphasis is given to multiple addressable systems in order to control of different properties of the molecules such as emission, absorption and the rate of thermal reaction as a response on blue light irradiation, protonation, ...

Abstract (English)

This work reports on the synthesis of new dihydroazulene/vinylheptafulvene systems and on the study of their photochromic and physical properties. Main emphasis is given to multiple addressable systems in order to control of different properties of the molecules such as emission, absorption and the rate of thermal reaction as a response on blue light irradiation, protonation, and
complexation.
Sterically constrained dihydroazulene systems:
The phenyl-dihydroazulene A2a have been modified to prevent s-cis-s-trans isomerisation. Have been found that six-ring annulation as shown in A1a leads to an increase of the rate of the thermal back reaction (VHF/DHA) and as a consequence the photochromism cannot be observed at room temperature under the normal experimental conditions. Lowering the temperature the colouring
occurs on irradiating the DHA form.
Receptor functionalized chromophores:
The photochromic behaviour of B1a and B2a has been investigated. The protonation changes significantly their chemical and photophysical properties, such as the rate of the photochemical and thermal back reactions, the absorption and emission, the appearance of the photochromism at room temperature, and the quantum yield of photoreaction. It has been shown that the multi functionality of the pyridine substituted DHAs B1a and B2a as are photochromism, receptor properties, emission and absorption changes makes them to interesting
�two-mode input/multi-output� systems, which are important for using molecular switches for digital processing and communication. The multi-mode switching may be further extended via transition metal complexation which expands the potential of application towards molecular sensing and supramolecular architecture.
Porphyrin conjugates:
It has been shown that the pyridine substituted dihydroazulene B1a and Zn-porphyrin C2 form a complex of the stoichiometry 1:1. This follows from 1H-NMR titration studies and data analysis by the Benesi-Hildebrand approach.
The interaction of the pyridine nitrogen with the Zn-porphyrin depends on the state of the DHA/VHF equilibrium. The electron attracting VHF form decreases the electron density at the pyridine nitrogen and presumably reduces the strength of complexation. The thermal back reaction VHF/DHA is slower in the coordination complex. Preliminary studies on the synthesis of a wire-type DHA-Porphyrin-DHA triad are reported. It is hypothesised that this triad may be used as a gated molecular switch. Furthermore by using the molecular subunits described in this work a supramolecular and multiadressible molecular switch is designed. These molecular units are of interest for molecular information processing.Extension of this work might be the synthesis of annulated cyano-phenyl-DHA A4 to compare with well-studied A4 by the time-resolved laser spectroscopy. The receptor topic could be extended to a photochromic system with two coordination sites. Porphyrin conjugates might be extended towards two-dimensional photosensitive systems containing two covalently bound photochromic units bridged by a metal porphyrin. The interaction between the chromophores would be mediated by the photochromic switch coordinated to the metalporphyrin.

Translation of the abstract (German)

In der vorliegenden Arbeit werden multifunktionelle Dihydroazulene synthetisiert und bezüglich der Photochromie und ihres molekularen Schaltvermögens untersucht. Drei Schwerpunkte werden bearbeitet: 1. Rotationseingeschränkte Dihydroazulene und Vinylheptafulvene Durch die geometrische Fixierung der photochemisch aktiven pi-Teilstruktur wird die Kinetik sowohl der photochemischen Hin- als auch ...

Translation of the abstract (German)

In der vorliegenden Arbeit werden multifunktionelle Dihydroazulene synthetisiert und bezüglich der Photochromie und ihres molekularen Schaltvermögens untersucht.
Drei Schwerpunkte werden bearbeitet:
1. Rotationseingeschränkte Dihydroazulene und Vinylheptafulvene
Durch die geometrische Fixierung der photochemisch aktiven pi-Teilstruktur wird die Kinetik sowohl der photochemischen Hin- als auch der thermischen Rückreaktion signifikant beeinflusst. Das in der Arbeit beschriebene Dihydronaphthalinderivat zeigt eine beschleunigte thermische Rückreaktion. Die ultraschnelle Kinetik im angeregten Zustand wird derzeit noch bearbeitet ( vgl. J. Am. Chem. Soc. 2002, 124, 2438-2439).
2. Protonensensitive Dihydroazulen/Vinylheptafulven Systeme
Pyridinfunktionalisierte Dihydroazulene wurden erstmals synthetisiert. Das Photochromieverhalten der 3- und 4-Pyridinylsysteme wird sensitiv durch Protonierung beeinflusst. Dies betrifft sowohl die photochemische Hin- als auch die thermische Rückreaktion. Das molekulare Schalten dieser Verbindungen wird somit bestimmt durch zweifachen �input� und variabler �output� Funktion. Die Verbindungen sind daher aus der Sicht der molekularen Logik und der molekularen Informationsverarbeitung von Interesse.
3. .Porphyrin funktionalisierte Dihydroazulen/Vinylheptafulven Systeme
Die kovalente und nichtkovalente Verknüpfung des photochromen Dihydroazulen/Vinylheptafulven Schalters mit Porphyrinsubstrukturen führt in das Gebiet der multifunktionellen supramolekularen Schalter. Das Konzept für diese Forschungsrichtung wird vorgestellt und orientierende Syntheseversuche werden beschrieben.

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