T. Fournier's research while affiliated with Tampere University and other places

We report the novel cooperative properties of a complex obtained by self-assembling in solution a tetracationic cobalt porphyrin, CoIIP4+, and a tetraanionic sulfoaluminum phthalocyanine, AlIIIPc4-. In the ground state, the complex displays a charge transfer character, CoII-δ P4+/(AlIIIPc4-)+δ, and the oxidation of the phthalocyanine moiety is catalyzed in the presence of its partner. In aerated media, the neutral complex strongly binds molecular oxygen to form a stable zwitterionic species, -O2CoIIP4+/(AlIIIPc4-)+˚. The zwitterion can revert to the neutral form CoII-δP4+/(AlIIIPc4-)+δ upon vigourous bubbling of the solution with an inert gas (N2, Ar) or under light stimuli. In the excited state, the complex photoejects the oxygen and relaxes to the ground state via a triplet excited state. The latter species can transfer its excess energy to nearby oxygen molecules. The mechanism of photoproduction of 1O2 was studied via steady-state and time-resolved absorption and fluorescence techniques over a wide time window, from nanoseconds to hundreds of femtoseconds. We also investigated the potentiality of the neutral and zwitterionic complexes as a sensitizer for the photodynamic inactivation of cancer cells.

We report the novel cooperative properties of a complex obtained by self-assembling in solution a tetracationic cobalt porphyrin, CoIIP4+, and a tetraanionic sulfoaluminum phthalocyanine, AlIIIPc4-. In the ground state, the complex displays a charge transfer character, CoII-δ P4+/(AlIIIPc4-)+δ, and the oxidation of the phthalocyanine moiety is catalyzed in the presence of its partner. In aerated media, the neutral complex strongly binds molecular oxygen to form a stable zwitterionic species, -O2CoIIP4+/(AlIIIPc4-)+. The zwitterion can revert to the neutral form CoII-δP4+/(AlIIIPc4-)+δ upon vigourous bubbling of the solution with an inert gas (N2, Ar) or under light stimuli. In the excited state, the complex photoejects the oxygen and relaxes to the ground state via a triplet excited state. The latter species can transfer its excess energy to nearby oxygen molecules. The mechanism of photoproduction of 1O2 was studied via steady-state and time-resolved absorption and fluorescence techniques over a wide time window, from nanoseconds to hundreds of femtoseconds. We also investigated the potentiality of the neutral and zwitterionic complexes as a sensitizer for the photodynamic inactivation of cancer cells.

A complete study of the ground-state and excited-state optical properties of a donor-acceptor heterocomplex , self-assembled and organized in Langmuir-Blodgett films, is reported. These properties are probed at a molecular level and their relevance to the macroscopic photoelectrical and non-linear optical properties of the materials is pointed out.

Vectorial electron transfer occurs in Langmuir-Blodgett films when semiamphiphilic porphyrin-phthalocyanine dimers are photoexcited with ultrashort laser pulses. The primary charge arriers are generated from the singlet excited states of the donor-acceptor pairs while the secondary charge carriers are issued from cascade reactions involving the triplet excited state of the dimer. Their quantum yield and lifetime are measured.

Femtosecond pump and probe experiments allow to show that the first singlet excited states of the porphyrin-phthalocyanine heterodimers decay via two competitive nonradiative pathways which are intersystem crossing from singlet to triplet and charge transfer reaction. The first decay pathway is enhanced in the presence of paramagnetic metal ions such as copper ion, while electron transfer prevails in diamagnetic dimers. In the last case, electron transfer was found to occur with a high efficiency leading to the oxidized porphyrin and reduce phthalocyanine. The same photoreactions occur in the organized solid state with the same dimers. The rate constants of electron transfer in the singlet states and those corresponding to the back reaction were determined for both liquid and solid phases. The role of the solvent and the corresponding reorganization energy around the ion pair prior to electron transfer are questioned.

Charge transfer reactions are photoinduced by exciting with UV and visible light strongly coupled donor acceptor pairs. The systems investigated are composed either of porphyrin and phthalocyanine mixed dimers. In this case, the proton transfer competes with the electron transfer process. The results obtained in sol-gel matrices are compared to the ones in solutions and organized media, and discussed in terms of the effect of the confinement of the reactants and degree of organization of the environment on the efficiency of charge transfer reactions.

Subpicosecond time-resolved absorption studies have been carried out on a cerium porphyrin-phthalocyanine sandwich mixed dimer in the liquid and solid states. Following excitation, two relaxation processes having time constants of ≈ 1 and ≈ 40 ps are observed irrespective to the nature of the environment. The first process is attributed to the relaxation of the excited state of the dimer to a low-lying charge transfer state. The second one, much slower, accounts for the relaxation of the charge transfer state back to the ground state. The comparison of the liquid and solid phase data clearly allows the role of the solvent in the relaxation processes to be eliminated.

Photoinduced charge transfer (CT) between porphyrins and phthalocyanines embedded in mixed siloxane—oxide coatings, prepared from the hydrolysis—condensation process of dimethylethyldiethoxysilane and Zr(OR)4 alkoxides, is reported for the first time. CT is photoinduced by exciting with visible light a strongly coupled, diamagnetic heterodimer of porphyrin and phthalocyanine. Replacing the diamagnetic phthalocyanine by a paramagnetic compound favours intersystem crossing, which leads to the formation of the “tridoublet-quartet” states of the dimer. This behaviour can be reproduced from the liquid phase to the solid state composed of sol—gel films, allowing us to explain the discrepancy with the organized Langmuir—Blodgett films data.