Molecular switches based on Dihydroazulene/Vinylheptafulvene photochromism

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