A central issue in molecular electronics in order to build functional devices is to assess whether changes in the electronic structure of isolated compounds by chemical derivatization are retained once the molecules are inserted into molecular junctions. Recent theoretical studies have suggested that this is not always the case due to the occurrence of pinning effects making the alignment of the transporting levels insensitive to the changes in the electronic structure of the isolated systems. We explore here this phenomenon by investigating at both the experimental and theoretical levels the I/ V characteristics of molecular junctions incorporating three different three-ring phenylene ethynylene derivatives designed to exhibit a significant variation of the HOMO level in the isolated state. At the theoretical level, our NEGF/DFT calculations performed on junctions including the three compounds show that, whereas the HOMO of the molecules varies by 0.61 eV in the isolated state, their alignment with respect to the Fermi level of the gold electrodes in the junction is very similar (within 0.1 eV). At the experimental level, the SAMs made of the three compounds have been contacted by a conducting AFM probe to measure their I/ V characteristics. The alignment of the HOMO with respect to the Fermi level of the gold electrodes has been deduced by fitting the I/ V curves, using a model based on a single-level description (Newns-Anderson model). The extracted values are found to be very similar for the three derivatives, in full consistency with the theoretical predictions, thus providing clear evidence for a HOMO level pinning effect.

We herein propose a new type of efficient neutral photoacid generator. A photoinduced 6π-electrocyclization reaction of photochromic triangle terarylenes triggers subsequent release of a Brønsted acid, which took place from the photocyclized form. A H-atom and its conjugate base were introduced at both sides of a 6π-system to form the self-contained photoacid generator. UV irradiation to the 6π-system produces a cyclohexa-1,3-diene part with a H-atom and a conjugate base on the sp(3) C-atoms at 5- and 6-positions, respectively, which spontaneously release an acid molecule quantitatively forming a polyaromatic compound. A net quantum yield of photoacid generation as high as 0.52 under ambient conditions and a photoinitiated cationic polymerization of an epoxy monomer are demonstrated.

New dyes based on BODIPY and tetrazine fluorophores connected through a phenyl spacer have been synthesized and their absorption, emission and electrochemical properties characterized. BODIPY can be reversibly oxidized into a stable cation radical whereas tetrazine can be reduced to a stable anion radical. The electrochemical and absorption studies demonstrate that both fluorophores behave independently. The bichromophoric compounds show an expected

A new series of distyryl-BODIPY has been rationally designed and synthesised from a novel fluorinated platform, 8-pentafluorophenylBODIPY, which has enhanced reactivity in the presence of both electron rich, and for the first time, electron deficient aldehydes. The pentafluorobenzene leads to larger red shifts of absorption and emission compared to previously reported analogues. The reactivity and spectroscopic results have been rationalised with quantum mechanics calculation. The fluorescence sensitivity of one derivative to acidity is also presented.

A very sensitive technique where an electrochemical cell is coupled to a total internal reflection fluorescence microscopy setup is described and applied for the first time to the electrochemical monitoring of the fluorescence of organic dyes in solution. It is shown that this setup basically allows both spatial and time resolution for the recorded fluorescence signal as a function of the electrode potential: indeed the variations of the emission intensity are recorded within the diffusion layer for a classical cyclic voltammetry or chronoamperometry experiment inducing the redox conversion of an emissive form into a non emissive one (and conversely). Simultaneously, the variations of the emissive state lifetime are measured to discriminate between a mechanism involving only the conversion into a non emissive form from one involving a quenching between the emitter and the electrogenerated species. The results concerning the investigation of the electrochemical monitoring of the fluorescence properties for two types of original dyes are presented, demonstrating the possibility to switch on and off the emission in a fully reversible way and to investigate in depth the mechanisms associated to this switch.

The high reactivity of 6π-electrocyclization in polar solvents has remained one of the important challenges for diarylethenes because of the emergence of a twisted intramolecular charge transfer (TICT) state at the excited state in such polar media, which usually quenches the photocyclization reaction. Herein we report on the preparation and highly efficient photocyclization of 2,3-diarylbenzo[b]thiophenes with nonsymmetric side-aryl units in a polar solvent. While the dithiazolylbenzo[b]thiophene showed a suppressed quantum yield of 6π-electrocyclization of 54 % in methanol, the replacement of a thiazole unit with a thiophene ring led to a photon-quantitative 6π-cyclization reaction. The nonsymmetrical modification into the side-aryl units was considered to enhance the CH/π interactions between side-aryl units to support a photoreactive conformation in methanol. The stabilization of the photochromic reactive conformation is expected to suppress the formation of the TICT state at the excited state, leading to highly efficient photoreactivity.

A new boron dipyrromethene-ferrocene (BODIPY-Fc) conjugate with pentafluorophenyl as the meso substituent and two Fc termini was synthesized and its spectroscopic and electrochemical features were analysed. An intramolecular charge transfer from the donor Fc to the acceptor BODIPY has been predicted by theory and confirmed experimentally, leading to efficient fluorescence quenching when the dyad is in the neutral state. Fluorescence can be triggered by oxidizing both ferrocenyl units either chemically or electrochemically. Eventually, a fully reversible fluorescence switch is evidenced by coupling TIRF microscopy with electrolysis in an electrochemical cell.

Metal complexes associated with photochromic molecules are attractive platforms to achieve smart light-switching materials with advanced properties and to draw exciting perspectives that will boost the field of photoswitchable materials.