Mechanical Bonds and Topological Effects in Radical Dimer Stabilization

While mechanical bonding stabilizes tetrathiafulvalene (TTF) radical dimers, the question arises: what role does topology play in catenanes containing TTF units? Here, we report how topology, together with mechanical bonding, in isomeric [3]- and doubly interlocked [2]catenanes controls the formation of TTF radical dimers within their structural frameworks, including a ring-in-ring complex (formed between an organoplatinum square and a {2+2} macrocyclic polyether containing two 1,5-dioxynaphthalene (DNP) and two TTF units) that is topologically isomeric with the doubly interlocked [2]catenane. The separate TTF units in the two {1+1} macrocycles (each containing also one DNP unit) of the isomeric [3]catenane exhibit slightly different redox properties compared with those in the {2+2} macrocycle present in the [2]catenane, while comparison with its topological isomer reveals substantially different redox behavior. Although the stabilities of the mixed-valence (TTF2)^(•+) dimers are similar in the two catenanes, the radical cationic (TTF^(•+))_2 dimer in the [2]catenane occurs only fleetingly compared with its prominent existence in the [3]catenane, while both dimers are absent altogether in the ring-in-ring complex. The electrochemical behavior of these three radically configurable isomers demonstrates that a fundamental relationship exists between topology and redox properties

IN VIVO PHOTOACOUSTIC SPECTROSCOPY OF THE SKIN

Un spectromètre photoacoustique utilisant un détecteur différentiel permet de mesurer in vivo les spectres d'absorption optique de la peau humaine. Sa conception et ses caractéristiques sont décrites ; les premiers résultats expérimentaux sont présentés.We describe the conception and the characteristics of an open-ended photoacoustic detector developed for doing in vivo measurements of skin optical absorption. Preliminary results are presented

Photoacoustic and photothermal detection of photosensitized oxygenations

Study of relaxation processes of excited states of hematoporphyrin IX (HP) solutions (in ethanol and methanol) in the presence of tetramethyl ethylene chemical acceptor using both the photoacoustic (PA) - microphone - and photothermal (PT) - PZT - detection, is described. A significant difference between PA and PT signal behaviour has been observed when extremely low (down to 1.25 µM, PT measurements) and high (up to 2.5 mM, PA measurements) concentrations of sensitizer were used

A molecular light switch for DNA: Ru(bpy)_2(dppz)^(2+)

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