Bidirectional light-induced conductance switching in molecular wires containing a dimethyldihydropyrene unit.

Photochromic coordination polymers, based on zinc(ii) bis-terpyridine-appended dimethyldihydropyrene building blocks, have been synthesized following stepwise synthesis on a surface yielding photo-switchable molecular junctions. Under irradiation, reversible structural changes occur by the isomerization of the photosensitive units, thus inducing conductance switching of the molecular junctions with a good reproducibility.

Electrochemical control of the switching process of photochromic dimethyldihydropyrene derivatives.

The electrochemical control of the isomerization process of a photo-switchable dimethyldihydropyrene (DHP) derivative has been investigated. Spectro-electrochemical experiments clearly evidence that the substitution of the DHP core by electron-withdrawing entities can be used to control the opening/closing process.

Self-assembled dimethyldihydropyrene-pyridyl substituted ligands with zinc(ii) meso-tetraphenylporphyrin via axial coordination.

A series of dimethyldihydropyrene (DHP)-pyridyl photochromic derivatives has been synthesized and its photochemical behaviour characterized by spectroscopic and electrochemical methods. The corresponding noncovalently-linked electron donor-acceptor complexes have been isolated. They combine the DHP-pyridyl ligand as a donor and the zinc(ii) tetraphenylporphyrin as acceptor. Such association allowed to explore the efficiency of dative bonds to monitor the interactions between the two units.

Oligothiophene bipyridine alternate copolymers and their ruthenium metalated analogues: in situ ESR and UV-vis investigations of metal-chain interactions.

In situ electron spin resonance (ESR) and UV-vis spectro-electrochemical studies have been performed on two copolymers consisting of alternating subunits of regioregular head to tail (HT) coupled 3-octylthiophene tetramer and 2,2'-bipyridine subunits (P4) or 3-octylthiophene hexamer subunits of the same regioregularity and 2,2'-bipyridine subunits (P6). Both P4 and P6 have been investigated in their metal-free form as well as in the ruthenium(II) metalated form (P4-Ru and P6-Ru). P4 and P6 in the p-doped state exhibit a clear ESR signal characteristic of the presence of polarons in the oligothienylene subunits. In the case of P4, no recombination of polarons into bipolarons is observed, whereas the recombination process takes place in P6. The formation of bipolarons is well-rationalized in terms of the conjugation length, and it seems clear that the higher length of the oligothiophene subunit in P6( )()stabilizes bipolarons(.)() The same effect, is induced by the coordination of -Ru(bpy)(2)(2+) to the bipyridine unit in the metalated form of both polymers, which results in an increase of the conjugation length. Important information is gained from the analysis of the ESR spectra of both nonmetalated and metalated in the oxidized (p-doped) and reduced (n-doped) forms. In the p-doped state both nonmetalated and metalated polymers reveal the presence of a narrow ESR line characteristic of the mobile spin carriers in the polymer matrix. The oxidation of the metal center occurs at higher potentials and leads to an irreversible destruction of the system. To the contrary, in the reduced (n-doped) state the ESR lines of the nonmetalated and metalated polymers markedly differ. A significant line broadening with simultaneous change of the g-value is caused by spin-orbit coupling phenomenon induced by the presence of the coordinating metal. Finally, the observation of a clear polaronic band in the UV-vis spectrum of p-doped P4 and its strong dependence on the applied potential can be clearly correlated with the potential induced changes in the ESR spin density. The same applies to P4-Ru, where the changes in the polaronic and bipolaronic bands can also be correlated with the ESR spin density changes.