Complexe de transfert de charge

Un complexe de transfert de charge, complexe à transfert de charge, complexe par transfert de charge, ou encore complexe donneur-accepteur d'électron est l'association de deux ou plusieurs molécules, ou de différentes parties d'une grande molécule, dans laquelle une partie de la charge électronique est transférée entre les différentes entités moléculaires. L'attraction électrostatique résultante donne une force stabilisatrice au complexe moléculaire. La molécule source depuis laquelle la charge est transférée est appelée donneur d'électron, et l'espèce la recevant est appelée accepteur d'électron. La nature de l'attraction dans une complexe de transfert de charge n'est pas une liaison chimique stable et est donc plus faible qu'une liaison covalente. Nombreux sont de tels complexes qui peuvent subir une transition électronique vers un état excité, l'énergie d'excitation étant fréquemment de l'ordre du spectre visible, ce qui explique la couleur intense de ce genre de complexes. N

Dynamics of Electronic and Ionic Charges in Cyanine Organic Semiconductor Devices

Sandra Christina Jenatsch

Organic semiconductor materials have been widely applied in optoelectronic devices to replace their inorganic counterparts and explore new fields of applications. Due to their high extinction coefficients, chemical tunability and solubility, cyanine dyes are an interesting class of molecules to be employed in organic semiconductor devices. Their beneficial properties have been demonstrated in organic solar cells (OSC), photodetectors and recently in organic light-emitting electrochemical cells (OLEC). The focus of this thesis is to analyse different aspects regarding the dynamics of electronic and ionic charges in cyanine based devices. Models and conclusions are not restricted to cyanine based devices but can potentially be applied in various systems where combined ionic and electronic charges are present. In order to focus on electronic processes in OSCs, a combination of steady-state, transient and impedance analysis is used. It is resolved that trapped charges can be introduced at the dye/hole extracting layer interface by using specific solvents for the cyanine layer fabrication. These measurements also reveal the low hole mobility of cyanine films which in turn limits the possible upper layer thickness in OSCs. A frequently used way to enhance the conductivity of organic semiconductors is the addition of extra charges by chemical doping. This concept is employed for a near-infrared absorbing dye which is used as donor in a bilayer solar cell. The dependence of all figures of merit versus doping concentration and layer thickness is studied in detail. It is found that the performance of the optimised cell is not further improved by doping, but that it presents a good option if thicker layers are required, e.g. on rough substrates. Furthermore, the stability and degradation pathway of the p-doped species is analysed. This information is of general relevance as they also occur after charge transfer at the heterojunction interface of an OSC and during operation of OLECs. The dynamics of ionic charge carriers is separated into two contributions. In a first step, the steady-state diffusion profile of the counter ion within a cyanine/fullerene bilayer structure is scrutinised using different profiling techniques. An unexpected constant ion profile is found throughout the C60 layer. Simultaneously, the potential within the acceptor is measured by the Kelvin probe technique. A mechanism of combined electron and ion transfer from the C60 to the dye and vice versa is proposed which is in agreement with the experimental results. A prerequisite for OLEC operation is the mobility of ionic charge carriers. Their dynamics in cyanine salts under the effect of an external field is therefore studied in such devices. Several methods are developed and applied to characterise the dynamic p-i-n structure in detail, i.e. the position and width of the intrinsic region as well as the doping concentrations in p- and n-doped regions. The combination of all these methods helps to understand the transient behaviour of these cyanine devices but can also be adapted to other OLEC systems. A major drawback of cyanine dyes as emissive material is their low fluorescence quantum yield in solid films. To overcome this restriction and improve the OLEC efficiency, host-guest systems with various visibly emitting dyes are studied. The gain in fluorescence quantum yield in the film can directly be transferred to an increase in external quantum efficiency of the device.

EPFL2017

Charge transfer dynamics in Ar+ + CO

Differential cross sections for the charge transfer reaction between Ar(+)and CO have been measured using three-dimensional velocity map imaging in a crossed beam setup at the two relative collision energies 0.55 and 0.74 eV. We find dominant forward scattering with CO(+)product ions predominantly in the vibrational levels=6,7 of the electronic ground state X. This is indicative of a direct resonant mechanism for the two argon spin-orbit states. At both collision energies also an isotropic distribution with product ions exhibiting high internal excitation is observed. This is more pronounced at the higher collision energy, where the first electronically excited state Abecomes accessible. We conclude that the A-state is partially populated by the product ions at 0.74 eV collision energy and suggest that the isotropic distribution stems from the formation of a charge-transfer complex, in concurrence with previously performed studies. [GRAPHICS] .

2020

Temperature and oxygen-concentration dependence of singlet oxygen production by RuPhen as induced by quasi-continuous excitation

Veronika Huntosova, Jaroslav Varchola, Georges Wagnières

Advanced Search Home > Journals > Photochemical & Photobi... > Temperature and oxygen-... For Authors & Referees | For Librarians | For Members Journal cover: Photochemical & Photobiological Sciences Photochemical & Photobiological Sciences Issue 12, 2014 A society-owned journal publishing high quality research on all aspects of photochemistry and photobiology. Impact Factor 2.939 12 Issues per Year Indexed in Medline Journal Home Previous Article | Next Article Paper Temperature and oxygen-concentration dependence of singlet oxygen production by RuPhen as induced by quasi-continuous excitation Jaroslav Varchola,a Veronika Huntosova,b Daniel Jancura,ab Georges Wagnières,c Pavol Miskovskyab and Gregor Bánó*ab Show Affiliations Photochem. Photobiol. Sci., 2014,13, 1781-1787 DOI: 10.1039/C4PP00202D Received 06 Jun 2014, Accepted 02 Oct 2014 First published online 06 Oct 2014 | | Share on citeulike | Share on facebook | Share on twitter | | More PDF Rich HTML Send PDF to Kindle Download Citation Help Request Permissions Abstract Cited by Related Content Assessment of partial pressure of oxygen (pO2) by luminescence lifetime measurements of ruthenium coordination complexes has been studied intensively during the last few decades. RuPhen (dichlorotris(1,10-phenanthroline) ruthenium(II) hydrate) is a water soluble molecule that has been tested previously for in vivo pO2 detection. In this work we intended to shed light on the production of singlet oxygen by RuPhen. The quantum yield of singlet oxygen production by RuPhen dissolved in 0.9% aqueous NaCl solution (pH = 6) was measured at physiological temperatures (285–310 K) and various concentrations of molecular oxygen. In order to minimize the bleaching of RuPhen, the samples were excited with low power (

2014

Dynamics of Electronic and Ionic Charges in Cyanine Organic Semiconductor Devices

Sandra Christina Jenatsch

EPFL2017