Showing papers by "Jean Roncali published in 2003"
197 citations
TL;DR: Three layered compounds designed for their incorporation in organic-inorganic materials based on iodometalates have been synthesized as crystals from slowly cooled aqueous solution containing metal halide and bithiophene derivative salts, revealing a semiconductive behavior and molecular interactions.
Abstract: 2,2'-bithiophene derivatives, 5-ammoniumethylsulfanyl-2,2'-bithiophene (AESBT) and 5,5'-bis(ammoniumethylsulfanyl)-2,2'-bithiophene (BAESBT), have been designed for their incorporation in organic-inorganic materials based on iodometalates. Three layered compounds, (BAESBT)PbI(4), (AESBT)(4)Pb(3)I(10), and (AESBT)(3)Bi(2)I(9), have been synthesized as crystals from slowly cooled aqueous solution containing metal halide and bithiophene derivative salts. When starting from the diammonium cation, (BAESBT)PbI(4) hybrid perovskite is obtained. (BAESBT)PbI(4) adopts a triclinic cell (P1) with the lattice parameters a = 8.4741(5) A, b = 8.9255(6) A, c = 16.876(1) A, alpha = 88.328(5) degrees, beta = 81.806(4) degrees, gamma = 88.864(5) degrees, Z = 2. In the structure, PbI(4)(2)(-) perovskite sheets and diammonium cation layers alternate along c. The incorporation of the corresponding monoammonium cation (AESBT) leads to a head to tail arrangement of the molecules in the (AESBT)(4)Pb(3)I(10) hybrid, precluding the formation of the perovskite layers. (AESBT)(4)Pb(3)I(10) is orthorhombic, Pna2(1), with a = 38.333(4) A, b = 22.239(3) A, c = 8.448(2) A, Z = 4. The structure consists of corrugated layers of Pb(3)I(10)(4)(-) separated by organic layers of monoammonium cations. A similar relative situation of molecules in organic layers is observed in (AESBT)(3)Bi(2)I(9), with the inorganic sheets being built up from Bi(2)I(9)(3)(-) entities. (AESBT)(3)Bi(2)I(9) crystallizes in an orthorhombic cell (P2(1)2(1)2(1)) with a = 8.4564(6) A, b = 21.368(2) A, c = 30.747(2) A, Z = 4. In the three compounds, the molecular packings appear different, underlining the interplay between both organic and inorganic components. New packings are stabilized, as illustrated by an original mixed kappa-alpha type arrangement of the bithiophene units in (AESBT)(3)Bi(2)I(9). Furthermore, molecular interactions, especially of S.S type, appear stronger in the hybrids based on the monoammonium cations. The electrical conductivity of a (BAESBT)PbI(4) single crystal has also been investigated, revealing a semiconductive behavior with a characteristic energy of E(g) = 2.535 eV.
151 citations
TL;DR: Optical and electrochemical results indicate that the synergy between the direct electron-releasing effects of the ethylenedioxy groups and the self-rigidification resulting from intramolecular interactions controls to a large extent the HOMO-LUMO gap.
Abstract: The synthesis of a new series of stable and soluble EDOT oligomers end-capped with n-hexyl groups is described. Optical and electrochemical results indicate that the synergy between the direct electron-releasing effects of the ethylenedioxy groups and the self-rigidification resulting from intramolecular interactions controls to a large extent the HOMO-LUMO gap.
134 citations
91 citations
TL;DR: In this paper, a series of C60-derivatized bithiophenic precursors with low oxidation potential have been synthesized using the thiolate deprotection chemistry.
Abstract: New series of C60-derivatized bithiophenic precursors with low oxidation potential have been synthesized using the thiolate deprotection chemistry. The analysis of the electropolymerization of these compounds shows that the use of two-site precursors leads to polymers combining enhanced conjugation length, faster switching time, and improved stability under redox cycling. The unsuccessful attempts to identify the optical signature of the reduced forms of the attached C60 by spectroelectrochemistry suggest that the PT backbone is unstable in the presence of the C60 anion radical. Preliminary photoelectrochemical experiments on films deposited on platinum electrode reveal a significant enhancement of the photocurrent for the C60-derivatized polymer when compared to a nonsubstituted reference polymer, indicating that these new materials are potentially useful for photovoltaic energy conversion.
75 citations
TL;DR: Results are provided showing that incorporation of ethylenic linkages in an oligothiophene structure leads to a faster decrease of the HOMO-LUMO gap with chain extension due to the combined effects of enhanced planarity and lower overall aromatic character of the system.
Abstract: Three series of thiophene-based π-conjugated oligomers built with different combinations of thiophene cycles and double bonds have been synthesized and characterized. The analysis of the chain length dependence of the electronic, electrochemical, and vibrational properties of the three series of oligomers has been carried out using cyclic voltammetry, UV−vis, IR, and Raman spectroscopies. These various investigations provide consistent results showing that incorporation of ethylenic linkages in an oligothiophene structure leads to a faster decrease of the HOMO−LUMO gap with chain extension due to the combined effects of enhanced planarity and lower overall aromatic character of the system. Although the incorporation of two consecutive double bonds in the system leads to a stabilization of the dicationic state, this structural modification does not produce the expected further decrease of the HOMO−LUMO gap at large chain extension. This phenomenon is discussed on the basis of an interplay between aromatici...
75 citations
TL;DR: Analysis of the cation-binding properties of the macrocycles by (1)H NMR and UV-vis spectroscopy reveals the formation of a 1:1 complex with Ba(2+), Sr(2-), or Pb(2+) and shows that cation complexation results in a conformational transition in the pi-conjugated system.
Abstract: Crown-annelated quater- (4T) and sexithiophenes (6T) with oligooxyethylene chains of various lengths attached at the 3-positions of the terminal thiophene rings have been synthesized. Analysis of the cation-binding properties of the macrocycles by 1H NMR and UV−vis spectroscopy reveals the formation of a 1:1 complex with Ba2+, Sr2+, or Pb2+ and shows that cation complexation results in a conformational transition in the π-conjugated system. Theoretical analysis of this process by density functional methods predicts that this conformational transition results in a narrowing of the highest occupied−lowest unoccupied molecular orbital gap of the conjugated system with a decrease of the redox potentials (E01 and E02) associated with the formation of the 4T cation radical and dication. Cyclic voltammetry shows that, depending on the binding constant, the presence of metal cation produces a negative or a positive shift of E01 while E02 always shifts negatively. This unusual behavior is discussed in terms of int...
69 citations
TL;DR: In this paper, a series of linearly extended tetrathiafulvalene analogues with thienothiophene and dithienothio-thiophene π-conjugating spacers has been synthesized.
Abstract: A new series of linearly extended tetrathiafulvalene analogues with thienothiophene and dithienothiophene π-conjugating spacers has been synthesized. Electronic absorption spectra present a vibronic fine structure typical for rigid conjugated systems. Investigation of the electrochemical behaviour of the new donors by cyclic voltammetry reveals the successive generation of stable radical cation and dication species. The crystallographic structure of a single crystal of a dication salt of TT-TTF(ClO4)2 has been analysed by X-ray diffraction. The dication presents a syn conformation stabilised by S⋯S intramolecular interactions. The quinoid structure expected for the spacer for the +2 oxidation state is clearly revealed by the bond lengths.
63 citations
TL;DR: A photodynamic molecular architecture synthesized by covalent fixation of a photoisomerizable azobenzene group at two fixed points of a conformationally flexible pi-conjugated quaterthiophene chain is synthesized, providing a first example of photomechanical control of the electronic properties of the pi- Conjugated system.
Abstract: A photodynamic molecular architecture has been synthesized by covalent fixation of a photoisomerizable azobenzene group at two fixed points of a conformationally flexible π-conjugated quaterthiophene chain. The crystallographic structure shows that the two systems lie in parallel planes with a short interplane distance. Theoretical modelization and experimental analysis by 1H NMR and cyclic voltammetry unequivocally show that trans to cis photoisomerization of the azobenzene group induces dimensional and conformational changes in the underlying π-conjugated system. These geometrical changes produce, in turn, an increase of the HOMO level and a narrowing of the HOMO−LUMO gap, thus providing a first example of photomechanical control of the electronic properties of the π-conjugated system.
51 citations
TL;DR: Comparison of the Raman features of NLO-phores based on a covalently rigidified dithienylene (DTE) spacer with those of their open chain DTE analogues shows that the bridging of the central double bond of DTE with the nearest beta-positions of the thienyl units through two ethylene bridges significantly improves the intramolecular charge transfer.
Abstract: Two types of push ± pull chro- mophores built around thiophene-based -conjugating spacers rigidified by ei- ther covalent bonds or noncovalent intramolecular interactions have been analysed by means of IR and Raman spectroscopical measurements in the solid state as well as in a variety of solvents. Comparison of the Raman features of NLO-phores based on a covalently rigidified dithienylene (DTE) spacer with those of their open chain DTE analogues shows that the bridging of the central double bond of DTE with the nearest -positions of the thienyl units through two ethylene bridges significantly improves the intra- molecular charge transfer. This also occurs for NLO-phores based on a 2,2- bi(3,4-ethylenedioxythiophene) (BED- OT) spacer as compared with their corresponding parent compounds based on an unsubstituted bithiophene (BT) spacer. For NLO-phores based on a BEDOT spacer, noncovalent intramo- lecular interactions between sulfur and oxygen atoms are responsible for the rigidification of the spacer. The Raman spectra of these NLO-phores obtained in the form of solutes in dilute solutions reveal two different behaviours: i) chro- mophores based on covalently bridged or open chain DTE spacers display Raman spectral profiles in solution quite similar to those of the corresponding solids, with a very little dependence on the polarity of the solvent, while ii) - larger spectral changes are noticed for NLO-phores built around BEDOT or BT spacers on going from solids to solutions. In the second case, spectral changes must be ascribed not solely to conformational distortions of the donor and acceptor end groups with respect to the -conjugated backbone mean- square-plane (as for the DTE-based NLO-phores) but also to distortions of the thienyl units of the -conjugating spacer from coplanarity. The insertion of vinylenic bridges between the thienyl units of the -conjugating spacer and between the spacer and the donor and acceptor end groups is a suitable strat- egy to reach a fairly large intramolecular charge transfer both in polar and non- polar solvents. Density functional theory (DFT) calculations have been carried out to assign the relevant electronic and vibrational features and to derive useful information about the molecular struc- ture of these NLO-phores.
51 citations
TL;DR: In this article, strong π-donors based on the association of TTF and 2,2′-bi(3,4-ethylenedioxy)thiophene conjugating unit have been synthesized; optical and an X-ray data show that intramolecular interactions lead to full rigidification of the conjugated system.
TL;DR: In this article, the solid-state infrared absorption and Raman scattering spectra of 5-(2,2-dicyanoethenyl)-5′-[(E)- N, N ′-dimethylaminobenzylidene)methyl] bithiophene are reported.
TL;DR: Experimental results unequivocally show that the photochemically induced geometrical changes produce in turn an increase in the HOMO level and a narrowing of theHOMO-LUMO gap, providing the first evidence of photomechanical control of the electronic properties of linear pi-conjugated systems.
Abstract: Photodynamic molecular ar- chitectures have been synthesized by covalent fixation of a photoisomerizable dimethylazobenzene group at two fixed points of conformationally flexible - conjugated quater- and sexithiophene chains. Theoretical geometry optimiza- tion shows, in excellent agreement with crystallographic structures, that the mode of fixation of the azo group plays a determining role in the geometry of the final molecular architecture and on its ability to perform the expected pho- toinduced molecular motion. Thus, co- valent fixation of meta-dimethylazoben- zene on a quaterthiophene chain results in a conformationally locked system in which photoisomerization of the azo group is hindered. However, the exper- imental results of optical, 1 HNMR spec- troscopic, and electrochemical investi- gations show that when an azobenzene group is connected at the para positions of the phenyl rings, trans-to-cis photo- isomerization of the azo group induces a conformational transition and dimen- sional changes in the underlying -con- jugated oligothiophene chain. These ex- perimental results unequivocally show that the photochemically induced geo- metrical changes produce in turn an increase in the HOMO level and a narrowing of the HOMO ± LUMO gap. This therefore provides the first evi- dence of photomechanical control of the electronic properties of linear -conju- gated systems.
TL;DR: A π-conjugated {C} 3 h -oligomer was synthesized and deposited either on the Si(100) surface or on the highly oriented pyrolytic graphite (HOPG) surface as discussed by the authors.
Abstract: A π-conjugated {C} 3 h -oligomerinvolving three dithienylethylene branches bridged at the meta positions of a central benzenic core has been synthesized and deposited either on the Si(100) surface or on the highly orientedpyrolytic graphite (HOPG) surface. On the silicon surface, scanning tunneling microscopy allows the observation of isolated molecules. Conversely, when the thiophene rings of the oligomers are substituted with alkyl chains, a spontaneous ordered film is observed on the HOPG surface. As the interaction of the oligomers is different with both surfaces, the utility of the Si(100) surface to characterize individual oligomers prior to their use into a two-dimensional layer is discussed.