Search results for "LUMO"
showing 10 items of 164 documents
Polythiophene S,S dioxides: an investigation on electrochemical doping
2000
Abstract A new strategy for functionalizing oligothiophenes is the transformation of the thienyl sulphurs into the corresponding S,S dioxides, with the effect of lowering the LUMO energy without significantly affecting the HOMO one. From a quinquethiophene S,S dioxide derivative, a polymer (pQTDO) which can be reversibly n-doped at not very negative potentials still maintaining the property of being p-doped at moderate potential values was electrosynthesized. There is, however, a great difference in the ability to store charge of the polymer’s p- and n-doped forms: a great amount of injected negative charge irreversibly modifies the structure of pQTDO.
Controlling the electronic properties of polythiophene through the insertion of nonaromatic thienyl S,S-dioxide units
1999
A new class of thiophene-based polymers characterized by the presence of one nonaromatic thienyl S,S-dioxide moiety (O) to every two, four, and six aromatic thienyl units (T) was prepared from the newly synthesized precursors TOT, TTOTT, and TTTOTTT, and electrochemically characterized. The polymers displayed remarkably greater electron affinities than that of polythiophene and could be reversibly n-doped at moderate potentials, while still maintaining the property of also being p-doped at moderate potential values. All polymers were characterized by good p-doping/undoping cyclability, while at least four aromatic units to every nonaromatic one were needed to ensure good n-doping/undoping c…
The Role of Emission Layer Morphology on the Enhanced Performance of Light-Emitting Diodes Based on Quantum Dot-Semiconducting Polymer Hybrids
2016
The influence of the morphology of quantum dot (QD)-semiconducting polymer hybrid emission layers on the performance of quantum dot-based light emitting diodes (QLEDs) is systematically investigated. Chemically grafted QD-semiconducting polymer hybrids are fabricated by the ligand exchange procedure between CdSe/CdxZn1−xS QDs and a new block copolymer consisting of a carbazole-based electroactive block with a low highest occupied molecular orbital level and a disulfide-based anchor block. The performance of QLEDs with hybrid emission layers is compared with QLEDs utilizing QD-only and physically mixed QD/polymer emission layers. It is shown that only in the emission layers formed by chemica…
The first spiroconjugated TTF- and TCNQ-type molecules: a new class of electroactive systems?
2005
[Structure: see text] Spiroconjugated TTF-type electron donors (13a-c) and TCNQ-type electron acceptors (10, 11) have been prepared from spiroquinone 9. Cyclic voltammetry reveals a relatively weak accepting ability for 10 and 11, and a strong electron-donor character for 13a-c. Whereas the spiroconjugation introduces a destabilization of the LUMO for compounds 9-11, the opposite is observed for compound 13, thus justifying the redox potential values.
Synthesis and photophysical properties of hyperbranhced polyfluorenes containing 2,4,6-tris(tiophen-2-yl)-1,3,5-triazine as the core
2011
A series of new hyperbranched polymers containing a 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine core unit and polyfluorene chain arms have been synthesized via Suzuki coupling, and characterized by NMR, IR and GPC. All the polymers exhibit good thermal stability with a high decomposition temperature. By changing the 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine/fluorene ratio the UV-vis absorption and emission spectra can be partially tuned. It has been found that the polymers containing a low ratio of 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine units (P1-P3) have an absorption maximum around 385 nm, localized in the polyfluorene chain, and a shoulder around 425 nm ascribable to a charge transfer stat…
Experimental and theoretical investigations of the redox behavior of the heterodichalcogenido ligands [(EP(i)Pr2)(TeP(i)Pr2)N](-) (E = S, Se): cyclic…
2008
The two-electron oxidation of the lithium salts of the heterodichalcogenidoimidodiphosphinate anions [(EP (i)Pr 2)(TeP (i)Pr 2)N] (-) ( 1a, E = S; 1b, E = Se) with iodine yields cyclic cations [(EP (i)Pr 2)(TeP (i)Pr 2)N] (+) as their iodide salts [(SP (i)Pr 2)(TeP (i)Pr 2)N]I ( 2a) and [(SeP (i)Pr 2)(TeP (i)Pr 2)N]I ( 2b). The five-membered rings in 2a and 2b both display an elongated E-Te bond as a consequence of an interaction between tellurium and the iodide anion. One-electron reduction of 2a and 2b with cobaltocene produces the neutral dimers (EP (i)Pr 2NP (i)Pr 2Te-) 2 ( 3a, E = S; 3b, E = Se), which are connected exclusively through a Te-Te bond. Two-electron reduction of 2a and 2b …
New n-dopable thiophene based polymers
1999
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.
Solution processable 2-(trityloxy)ethyl and tert-butyl group containing amorphous molecular glasses of pyranylidene derivatives with light-emitting a…
2015
Abstract Small organic molecules with incorporated 4 H -pyran-4-ylidene (pyranylidene) fragment as the π-conjugation system which bonds the electron acceptor fragment (A) with electron donor part (D) in the molecule – also well known as derivatives of 4-(dicyano-methylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran ( DCM ) laser dye-have attracted considerable attention of scientists as potential new generation materials for organic photonics and molecular electronics due to their low-cost fabrication possibility, flexibility and low-weight. Six glassy derivatives of 4 H -pyran-4-ylidene (pyranylidene) with attached bulky 2-(trityloxy)ethyl and tert -butyl groups are described in this re…
Stilbenoid phosphors with increased electron affinity: sulfones as electron accepting groups
2001
Stilbenoid compounds are one of the preferred classes of luminescent materials for the use in light emitting diodes (LEDs). A problem connected with the use of poly(phenylenevinylene) (PPV) in LEDs is the unbalanced charge carrier transport, electron injection from aluminium and electron transport properties are only poor. The substitution with electron accepting groups like nitriles is a suitable way to lower the LUMO level of the chromophore. The electron withdrawing strength of sulfones is comparable to cyanides and the second binding site is useful to attach solubilising side chains. A two-step synthesis of model compounds and polymers from ethene and sulfonyl dibromobenzene and bromo a…
Soluble Complexes of Cobalt Oxide Fragments Bring the Unique CO2 Photoreduction Activity of a Bulk Material into the Flexible Domain of Molecular Sci…
2021
The deposition of metal oxides is essential to the fabrication of numerous multicomponent solid-state devices and catalysts. However, the reproducible formation of homogeneous metal oxide films or of nanoparticle dispersions at solid interfaces remains an ongoing challenge. Here we report that molecular hexaniobate cluster anion complexes of structurally and electronically distinct fragments of cubic-spinel and monoclinic Co3O4 can serve as tractable yet well-defined functional analogues of bulk cobalt oxide. Notably, the energies of the highest-occupied and lowest-unoccupied molecular orbitals (HOMO and LUMO) of the molecular complexes, 1, closely match the valence- and conduction-band (VB…