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Zawartość zarchiwizowana w dniu 2022-12-23

Experimental and theoretical studies of excited state properties of newly synthesised porphyrin systems in solution, solid-state layers and biopolymers. Effects of macrocycle nonplanarity and intramolecular charge transfer

Cel

Study of the mechanisms involved in dramatic perturbations of the photophysical properties observed for nonplanar highly substituted porphyrins. Relationships between degrees of distortion and photophysical properties. Synthesis of series of asymmetrically substituted nonplanar tetraphenylporphyrins with progressive degrees of b-ethyl substitutions and of series of porphyrins with near-constant structural perturbations in the porphyrin core (due to full protonation) and different peripheral substituents is planned. A theoretical structural analysis of these nonplanar porphyrins by molecular mechanics and quantum chemistry will be done: information concerning different accessible conformers is expected. Ground and excited state conformations of these porphyrins in solution will be studied by steady state and time-resolved resonance Raman spectroscopy. Picosecond and nanosecond transient absorption, time-resolved fluorescence measurements will provide the deactivation rates of the singlet and triplet excited states. Measurements at different temperatures should inform about the energy barriers to the "quenching" molecular conformations. ODMR will provide independent information about the porphyrins structure and symmetry. These studies are important for understanding how the nonplanarity of native porphyrins, induced by the protein surrounding, may govern physicochemical properties of this type of molecules.

Effects of porphyrin core nonplanarity in thin spincoated porphyrin layers. Layers of initally planar (in solution) porphyrins will be prepared and studied as for the distorting influence of constraining environment on the porphyrin macrocycle. Then layers of initially nonplanar porphyrins will be prepared. Resonance Raman, electronic absorption, fluorescence and ODMR spectroscopies will be applied. This information may be helpful for a creation of solar photovoltaic cells and molecular electronic devices based on tetrapyrrolic structures.

Effects of intramolecular charge transfers on excited state properties of b-nitro-substituted porphyrins and analogs in solution. Synthesis of series of porphyrins with electron-withdrawing b-substituents of various strength will be carried out. The origin of unusual fluorescent state of b-nitro-substituted porphyrins and their analogs will be studied by time-resolved transient absorption, fluorescence and resonance Raman spectroscopies.

A theoretical structural analysis of the porphyrins will be made: information concerning the dependence of the porphyrin electronic structure and electronic state energies on angles between the porphyrin and substituent planes is expected. The influence of electron-withdrawing substitution on the porphyrin triplet state structure will be monitored by ODMR. This should improve the knowledge about the donor-acceptor orientation effects in electron transfer processes.

Study of the interaction of b-nitro-substituted porphyrins with DNA and polynucleotides. Synthesis of water-soluble cationic b-nitro-substituted porphyrins will be made and their ground and excited state interactions with DNA and polynucletides will be studied by different spectroscopic methods. Evidences for electron-transfer reactions between DNA components and excited porphyrin are expected.

These porphyrins are considered to be a perspective for photosensitised nucleic acid damage which has recently been widely used for the photodestruction of viral nucleic acids in blood.

Effects of intramolecular charge transfers in thin spincoated layers of b-nitro-substituted porphyrins. Preparation of spincoated thin layers of b-nitro-substituted porphyrins and study of their ground and excited state conformations by resonance Raman, electronic absorption, fluorescence and ODMR spectroscopies will be carried out. Study of the photovoltaic properties of these layers will be performed. These layers are considered as to be a perspective for electron-accepting layers in photovoltaic cells.

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Koordynator

Universite Pierre et Marie Curie
Wkład UE
Brak danych
Adres
4 Place Jussieu
75252 Paris Cedex 05
Francja

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