Francis Garnier

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine.

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10(-9) mol L(-1) to 1.5 x 10(-2) mol L(-1) in atrazine) and low detection threshold (10(-7) mol L(-1)).

Semiconducting conjugated oligomers for molecular electronics

Abstract Oligomers of thiophene α-5T and α-6T were synthesized and vacuum evaporated as thin solid films onto platinized glass slides. They all behave as p-type semiconductors, and good rectifying barriers were obtained at α-nT/Ag junctions. Current-voltage and capacitance-voltage measurements were made, and allowed to determine electronic parameters of the organic semiconductors, such as mobility and doping level. Their values are compared to those of a polymethylthiophene (PMeT)/Ag diode. It appears that, due to their lower concentration of structural defects, well-defined oligomers present some advantages over polymers as far as their utilization to molecular electronics is concerned.

Schottky junctions based on vacuum evaporated films of thiophene oligomers

Abstract α-sexithienyl (α-6T) was synthesized and deposited as thin films onto platinized glass slides by the technique of vacuum evaporation. Metal-semiconductor (MS) junctions were then realized by evaporating small dots of Ag and Au. On the asformed film, Au gives an ohmic contact, and Ag a rectifying barrier. It is then concluded that α-6T behaves as a p-type semiconductor. After annealing at 150°C, rectifying barriers are obtained on both Au and Ag contacts, and α-6T turns to an n-type semiconductor. Changes in the respective UV-visible absorption may help in understanding the change from p- to n-type doping. A rough estimate of the band position of α-6T was obtained from the current-voltage and capacitance-voltage measurements on the MS diodes.

Influence of Chemical and Structural Properties of Functionalized Polythiophene‐Based Layers on Electrochemical Sensing of Atrazine

Sensitive layers based on conducting homopolymer [poly(3,4-ethylenedioxythiophene), denoted PEDOT] and copolymers [molecularly imprinted and non-imprinted poly(EDOT-co-3-thiophene acetic acid), denoted MICP and NICP, respectively] are electrosynthesized on gold substrates and used for the electrochemical detection of atrazine. These layers are characterized by cyclic voltammetry, ATR-FTIR spectroscopy, optical profilemetry, and AFM microscopy in order to study the effect of the chemical functionalities and of the structural properties of these conducting polymers on the physical chemistry of the interaction with atrazine targets and with the aim to improve the sensitivity of the recognition process. In particular, due to the presence in their backbones of preshaped functionalized cavities which keep the molecular memory of the targets, MICP layers show remarkable sensitivity, a low detection limit (10(-9) mol u2009L(-1)), and a large linear range of detection (10(-8) to 10(-4) mol u2009L(-1)), as demonstrated by square-wave voltammetry.

Absorption and emission properties of α, ω-dihexyl-quaterthiophene thin films grown by organic molecular beam deposition

The optical properties of thin films of α,ω-dihexyl-quaterthiophene grown by organic molecular beam deposition on different substrates are illustrated. Vibronic transitions in both the absorption and the emission spectra are observed, which originate from the coupling between vibronic states in the solid, similarly as in unsubstituted quaterthiophene films. Nevertheless, the alkyl chains in α,ω-dihexyl-quaterthiophene are responsible for a shift in both the absorption and emission peaks with respect to unsubstituted quaterthiophene and for an increased mesoscopic disorder.