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451 results on '"Barbarella, G."'

152. Rigid-Core Oligothiophene-S,S-dioxides with High Photoluminescence Efficiencies Both in Solution and in the Solid State

Author

Barbarella, G., Favaretto, L., Sotgiu, G., Antolini, L., Gigli, G., Cingolani, R., and Bongini, A.

Abstract

The photoluminescence (PL) frequencies and quantum efficiencies of dithieno[3,2-b;2‘,3‘-d]thiophene-4,4-dioxide (1), its 3,5-dimethyl derivative (2), and the corresponding 4-oxide (3) are reported and discussed in relation to their single-crystal X-ray structures. The peculiar packing modalities of dioxides 1 and 2, based on dimeric units originated by short S···O contacts between molecules related by an inversion center, cause an unusually high bathocromic shift of PL frequencies from solution to solid state. This effect is accompanied by a marked decrease in solid-state PL efficiencies (12% and 16%) compared to those in solution (75% and 77%). In monoxide 3 the loss of local symmetry inherent to the change SO2 → SO deeply modifies the self-assembly and PL properties, and the PL efficiency in the solid state is close to that in solution. Ab initio calculations on the ground and excited states of compound 1 were performed and compared to those of a conformationally mobile counterpart. Oligomers containing dithienothiophene 2 as internal core were synthesized and found to be characterized by high PL efficiencies in the solid-state (up to 48%) as well as in solution (up to 85%). The current−voltage and luminance−voltage plots of an electroluminescent diode fabricated with one of these new rigid-core oligothiophene-S,S-dioxides are reported.

Published
2001

157. Ring contraction reactions of bicyclic nitronic esters

Author

Barbarella, G., Pitacco, Giuliana, Russo, C., Valentin, Ennio, Barbarella, G., Pitacco, Giuliana, Russo, C., and Valentin, Ennio

Subjects
esteri nitronici ciclici, reazione di contrazione
Published
1983

158. Efficient stimulated emission due to bimolecular annihilation reduction in oligothiophene dioxide thin films.

Author

Lattante, S., Barbarella, G., Favaretto, L., Gigli, G., Cingolani, R., and Anni, M.

Subjects
*OPTICS, *THIN films, *MOLECULES, *INDUSTRIAL lasers, *LASER ablation, *PHYSICS
Abstract

We have studied the optical properties of a thienyl-S, S-dioxide oligothiophene under strong excitation. No stimulated emission is observed in neat films due to singlet-singlet bimolecular annihilation, with a bimolecular constant of A=(4.5±0.5)×10-11 cm3 s-1. On the contrary we show that strong stimulated emission is observed if the active molecule is blended to an inert polymer [poly(bisphenol A carbonate] (PC) even for a PC content as low as one PC molecule every 500 active molecules. We suggest that small PC quantities modify the film superamolecular packing, thus reducing the bimolecular recombination efficiency. These results are expected to be quite general and could allow a considerable extension of the number of molecules showing stimulated emission for organic laser applications. [ABSTRACT FROM AUTHOR]

Published
2006
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168. Full color tunability by modified oligothiophenes blends

Author

Anni, M., Gigli, G., Paladini, V., Cingolani, R., Barbarella, G., Favaretto, L., Sotgiu, G., Massimo Zambianchi, Anni, Marco, G., Gigli, V., Paladini, R., Cingolani, G., Barbarella, L., Favaretto, G., Sotgiu, and M., Zambianchi

198. A New Way to both Oligothiophene-Spaced Bimetallic Complexes and Functionalized Oligothiophenes

Author

Bianchini, C., Meli, A., Pohl, W., Vizza, F., and Barbarella, G.

Abstract

Mono- and binuclear oligothiophene rhodium complexes are obtained by single and double C−S bond cleavage of 2,2‘:5‘,2‘‘:5‘‘,2‘‘‘-quaterthiophene, respectively. S-Methylation of the C−S insertion products, followed by carbonylation of the resulting thioether complexes give the functionalized oligothiophenes 5-[1-(methylthio)-buta-1,3-diene]-2,2‘:5‘,2‘‘-terthiophene and 5,5‘-bis[1-(methylthio)-buta-1,3-diene]-2,2‘-bithiophene. The rhodium metal is recovered as a bis(carbonyl) complex.

Published
1997

200. Interplay between stimulated emission and singlet-singlet annihilation in oligothiophene dioxide thin films.

Author

Lattante, S., De Giorgi, M., Barbarella, G., Favaretto, L., Gigli, G., Cingolani, R., and Anni, M.

Subjects
*THIN films, *SURFACES (Technology), *LIGHT emitting diodes, *SEMICONDUCTOR diodes, *FIELD-effect transistors, *PHOTOLUMINESCENCE
Abstract

We have studied the optical properties of different thienyl-S,S-dioxide oligothiophenes under strong excitation. No stimulated emission is observed in neat films due to singlet-singlet bimolecular annihilation. The bimolecular recombination constant is quantified from a rate equation model in the limit of constant annihilation rate. We demonstrate that tunable stimulated emission in the range 490–660 nm, due to optical gain with an estimated cross section of the order of σg≈10-17 cm2, can be obtained by blending the active molecule with small quantities of inert polycarbonate poly(bisphenol-A-carbonate) (PC). The presence of amplified spontaneous emission (ASE) for a PC:active molecule relative concentration as small as 1:500 suggests that the polycarbonate role is to reduce the intermolecular diffusion rate rather than to isolate the active molecules. Moreover, for higher PC content, a continuous decrease of the bimolecular quenching role is observed. These results demonstrate that the absence of stimulated emission in neat films is not necessarily due to intrinsic molecular properties, as strong ASE can be obtained by slightly modifying the molecule interaction during the deposition process. This approach could allow a considerable extension of the number of molecules showing stimulated emission for organic laser applications. [ABSTRACT FROM AUTHOR]

Published
2006
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