Giovanna Sotgiu

Organic single-layer white light-emitting diodes by exciplex emission from spin-coated blends of blue-emitting molecules

We report on white electroluminescence (EL) emission from a single-layer light-emitting diode based on a binary blend of organic soluble blue-emitting molecules, i.e., a diamine derivative and a substituted thiophene-1,1-dioxide. Weakly voltage-dependent white color, of coordinates (0.39, 0.40) according to the standard of the Commission Internationale de l’Eclairage, is obtained from the superposition of the blue emission from the donor and a low-energy peak due to a charge-transfer complex between the two molecules (exciplex). The EL spectrum is broader and more structured than the photoluminescence one: this could be due to the activation of exciplexes with different conformations as inferred from quantum-chemistry calculations.

Color engineering by modified oligothiophene blends

Fully tunable light emission is demonstrated with combinations of binary blends of modified oligothiophenes of high efficiency, covering the entire spectrum of colors according to the standards of the Commission International de l’Eclairage. The emission spectrum of each blend is determined by the Forster transfer when the energy separation between the highest occupied molecular orbital–lowest unoccupied molecular orbital gap of the constituent molecules is smaller than 0.56 eV. For larger energy separation, the blend emission is just given by the superposition of the emission spectra of the constituent molecules.

Synthesis and optical properties of soluble sexithiophenes with one central head-to-head junction

Abstract The regioselective synthesis of three sexithiophenes characterized by the presence of one central 3,3′-dimethyl-2,2′-bithiophene subsystem is described. One of these compounds was obtained under mild conditions by microwave-mediated synthesis. All sexithiophenes were soluble in organic solvents and displayed 30–40% fluorescence quantum yields in solution. In thin films the fluorescence quantum yields dropped to 1–2%, indicating conformational changes and strong intermolecular interactions in the solid state.

Push-pull amino succinimidyl ester thiophene-based fluorescent dyes: synthesis and optical characterization.

The design and synthesis of new fluorescent dyes with emission range at 490-650 nm are described. Their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. The chromophores are donor-π-bridge-acceptor push-pull compounds with a π bridge of phenyl and thiophene rings and their combination. Compared with previous thiophene fluorophores, these dyes show significant redshift in the absorption and emission spectra and offer compact, red-emitting fluorophores. The dyes have amino succinimidyl active ester and can be readily conjugated to proteins, polymers and other amino-group-containing materials.

New n-dopable thiophene based polymers

Abstract New conjugated polymers containing variable amounts of thienyl and thienyl-S,S-dioxide units have been prepared by chemical or electrochemical polymerization of the appropriate substrates. The presence of the thienyl S,S-dioxide units leads to the decrease of the LUMO energies with respect to those of the ‘all thienyl’ counterparts. Electrochemical and spectro electrochemical data of n-doping of these materials are reported.

Conformational profile, energy barriers and optical properties of quinquethiophene-S, S-dioxides

Abstract Theoretical calculations, dynamic NMR experiments and absorption and photoluminescence data in solution are reported for a series of quinquethiophene S,S-dioxides substituted with alkyl groups of variable size and steric hindrance. Ab initio B3LYP/6-31G∗ and force field MM3 theoretical calculations show that the energy barriers for rotation around the inter-ring C–C bonds amount to a few kcal/mol even in the presence of very bulky substituents such as the cyclohexyl group. Dynamic NMR data were in agreement with the results of theoretical calculations. It was found that changing the steric hindrance of the substituents leaves the emission and photoluminesce properties unaltered. However, the photoluminesce intensities and wavelengths of all compounds were found to be very sensitive to solvent variations.

Improved Synthesis of Functionalized Sexithiophenes

Yields of functioualized sexithiophenes through the Stille reactien are greatly ameliorated using in situ generated Pd(AsPh3) 4 as the catalyst. The regic6pecific synthesis of a new head-to-head/taii-to-tail hexa(methylsulfanyl)sexithiophene is reported. All sexithiophmes were distilled under high vacuum to reach the degree of purity required for use in elec~ordc appficatio~as.

Flexible organic distributed feedback structures by soft lithography

We realised and characterised distributed feedback (DFB) lasers on flexible transparent substrates of poly(dimethylsiloxane) (PDMS). The DFB is fabricated by replica molding from master gratings realised by electron beam lithography, and subsequent spin-coating on the PDMS patterned side of a soluble substituted penta-thiophene, with high photoluminescence efficiency and optical gain, as active media. We report on the properties of DFB emission under ns-pulsed optical excitation.

Synthesis, single crystal X-ray structure and optical properties of 3,4-dimethyl-dithieno[2,3-b:3', 2'-d]thiophene-7,7-dioxide

Abstract The synthesis of the title compound ( 4 ), starting from commercial 3-bromo-4-methylthiophene, is described. The single crystal packing mode of 4 , as well as the absorption and photoluminescence properties in solution and in the solid state are reported and analyzed in relation to those of the isomeric 3,5-dimethyl-dithieno[3,2-b:2′,3′-d]thiophene-4,4-dioxide ( 7 ). The different reactivities of 4 and 7 towards bromination are analyzed in the light of the results of ab initio B3LYP/6-31G∗ calculations on both compounds.

New light-emitting functionalized oligothiophenes

We present a new class of highly photo and electroluminescent oligomers based on the presence of one inner thienyl-S,S-dioxide unit as the luminophore. The light emission frequency of the new compounds, which are characterized by greater electron affinities than the corresponding oligomers bearing an unmodified thienyl ring, was tuned over the entire visible range by changing the nature of the alkyl or aryl groups attached in the α- and/or in the β-positions of the thienyl-S,S-dioxide moiety. A few aspects of the solid state supramolecular organization of the new compounds are reported.