Structure-properties Relationships In Small Pi-conjugated Molecules: Electrochromism, Photovoltaic Conversion And Mechano-fluorochromism

This work deals with the design, synthesis and evaluation of molecular pi-conjugated systems as active materials for(opto)electronics devices. A short first chapter describes three X-shaped oligothiophenes, the characterization of their structure and properties and a first evaluation of their performances in electrochromic devices. The second chapter describes the synthesis of molecular acceptors based on a benzodithiophene and the analysis of their potentialities when combined with molecular donors in organic solar cells.The major part of the work is focused on the analysis of structure-properties relationships of a series of small push-pull molecules involving di- or tri-arylamine donor blocks linked to an acceptor group by a thienyl bridge. In a first step, a phenyl ring of triphenylamine(TPA) is replaced by p-fluorophenyl, anthryl and naphtyl groups. Optical and electrochemical results show that substitution has little effect at the molecular level but can markedly affect solid-state properties with in particular an improvement of charge-transport and short-circuit current density of solar cells based on these donor materials.In a second step, a phenyl ring of TPA is replaced by alkyl, perfluoroalkyl and oligo(oxyethylene) chains. Results of X-ray diffraction, absorption and photoluminescence spectroscopies, second harmonic generation, and electrochemistry demonstrate that some of these molecules undergo aggregation-controlled photoluminescence emission wavelength while the corresponding materials spontaneously reorganize in the solid-state to form either H or J aggregates with enhanced charge mobility, photovoltaic conversion efficiency and mechanically-induced chromism, fluorochromism and NLO-chromism.