Over the last three decades, the performance of OLEDs has been improved rapidly, however, as an important assessment for OLED, the EQE data are still quite low. As outlined in the theoretical background, the EQE is the product of out-coupling efficiency and internal quantum efficiency (IQE). Therefore, this thesis focuses on designing two types of polymers with different optical functionalities, to increase the EQE addressing the two aforementioned determining factors. Thus, the first part of the thesis addresses the light out-coupling efficiency in OLED devices. Here high refractive index (HRI) polymers are aimed for as potential material for the out-coupling layer, which are so far scarily reported for application in OLED devices, due to existing limitations, such as limited transparency, extra fluorescence, tedious synthesis, poor thermal stability and low solubility. However, if suitable polymers are becoming easily available, they will offer the unique advantage, compared to low molar mass HRI compounds, of being able to using cost-effective solution based technology for large area film preparation. In addition, polymeric materials will allow to introducing fully new concepts for increasing the light-out-coupling efficiency, like patterning allowing micro-lens preparation, or the incorporation of light scattering particles into the out-coupling layer. The approach described in this thesis is based on a previous work where HRI polymers were prepared via metal-free thiol-yne “A2+B3” polyaddition reaction, which led in an easy one-pot synthesis to hyperbranched polyvinylsulfides of high solubility and already reasonable high RI. For further increasing RI, in this work B3 as well as finally A2 monomers with high naphthalene content were chosen which should, in addition to the positive effect of the sulfur-containing units, render polymers with even higher RI, and hopefully also of high solubility due to the branching. A challenging aspect of this work was to find reaction conditions which allow the preparation of high molar mass as well as highly soluble, highly aromatic polymers by that A2+B3 approach, even so very sterically demanding monomers are used. In addition, the material properties should be fine-tuned by careful selection of the monomer ratio. It was expected that these new, easily available HRI polymers will be of high potential in OLED application. Thus, the work in this part of the thesis comprises on the one hand monomer and polymer synthesis as well as detailed characterization of the structure and the solution and thermal properties of the new materials. But on the other hand, the elucidation of the thin film preparation and the quality and optical properties of the resulting polymer films are major objectives. Finally, evaluation of the performance of the polymer films in an OLED device compared to conventionally low molar mass our-coupling layers was aimed for, which could be realized with the help of partners from the Institute of Applied Photophysics at TU Dresden. For increasing the IQE in OLEDs, this thesis focuses on the development of a new type of polymeric thermally activated delayed fluorescence (TADF) material. TADF materials have the potential of theoretical 100% IQE and are considered as key materials for the next generation of OLEDs. So far, a significant amount of low molar mass TADF molecules has been developed, however, only a limited number of design rules are reported so far for polymers, even though polymers would offer, as already outlined above, significant advantages with regard to processing cost-effectively more efficient OLEDs for large area application. The new concept described in this thesis for TADF polymers is based on a new monomer which exhibits individual promising structural units for achieving TAFD properties but does not emit TADF itself due to its large ΔEST (the energy gap between singlet S1 and triple T1 state). However, it has to be expected that once the monomer is polymerized, the resulting polymeric product will have reduced ΔEST due to the increased conjugation length and thus can be expected to emit TADF. This new concept has the potential to significantly increase the scope of polymeric materials with TADF properties. Thus the second part on the thesis focuses on the design of a new monomer based on carbazole units with a pendant benzophenone moiety and its polymerization and full structural elucidation with the help of model compounds involving intensive NMR and MALDI-TOF analysis. In addition to the expect TADF properties, the benzophenone unit will also provide the possibility for film stabilization and even photopatterning due to photo-crosslinking. Thus the study of film formation and photo-crosslinking of the new TADF polymers was a further objective of this thesis. Finally, first theoretical as well as experimental studies of the photo physical properties of the monomer, a low molar mass model compound and the polymer, again together with the partners from the Institute of Applied Photophysics, should provide evidence on the suitability of the new polymer design principle.

Over the last three decades, the performance of OLEDs has been improved rapidly, however, as an important assessment for OLED, the EQE data are still quite low. As outlined in the theoretical background, the EQE is the product of out-coupling efficiency and internal quantum efficiency (IQE). Therefore, this thesis focuses on designing two types of polymers with different optical functionalities, to increase the EQE addressing the two aforementioned determining factors. Thus, the first part of the thesis addresses the light out-coupling efficiency in OLED devices. Here high refractive index (HRI) polymers are aimed for as potential material for the out-coupling layer, which are so far scarily reported for application in OLED devices, due to existing limitations, such as limited transparency, extra fluorescence, tedious synthesis, poor thermal stability and low solubility. However, if suitable polymers are becoming easily available, they will offer the unique advantage, compared to low molar mass HRI compounds, of being able to using cost-effective solution based technology for large area film preparation. In addition, polymeric materials will allow to introducing fully new concepts for increasing the light-out-coupling efficiency, like patterning allowing micro-lens preparation, or the incorporation of light scattering particles into the out-coupling layer. The approach described in this thesis is based on a previous work where HRI polymers were prepared via metal-free thiol-yne “A2+B3” polyaddition reaction, which led in an easy one-pot synthesis to hyperbranched polyvinylsulfides of high solubility and already reasonable high RI. For further increasing RI, in this work B3 as well as finally A2 monomers with high naphthalene content were chosen which should, in addition to the positive effect of the sulfur-containing units, render polymers with even higher RI, and hopefully also of high solubility due to the branching. A challenging aspect of this work was to find reaction conditions which allow the preparation of high molar mass as well as highly soluble, highly aromatic polymers by that A2+B3 approach, even so very sterically demanding monomers are used. In addition, the material properties should be fine-tuned by careful selection of the monomer ratio. It was expected that these new, easily available HRI polymers will be of high potential in OLED application. Thus, the work in this part of the thesis comprises on the one hand monomer and polymer synthesis as well as detailed characterization of the structure and the solution and thermal properties of the new materials. But on the other hand, the elucidation of the thin film preparation and the quality and optical properties of the resulting polymer films are major objectives. Finally, evaluation of the performance of the polymer films in an OLED device compared to conventionally low molar mass our-coupling layers was aimed for, which could be realized with the help of partners from the Institute of Applied Photophysics at TU Dresden. For increasing the IQE in OLEDs, this thesis focuses on the development of a new type of polymeric thermally activated delayed fluorescence (TADF) material. TADF materials have the potential of theoretical 100% IQE and are considered as key materials for the next generation of OLEDs. So far, a significant amount of low molar mass TADF molecules has been developed, however, only a limited number of design rules are reported so far for polymers, even though polymers would offer, as already outlined above, significant advantages with regard to processing cost-effectively more efficient OLEDs for large area application. The new concept described in this thesis for TADF polymers is based on a new monomer which exhibits individual promising structural units for achieving TAFD properties but does not emit TADF itself due to its large ΔEST (the energy gap between singlet S1 and triple T1 state). However, it has to be expected that once the monomer is polymerized, the resulting polymeric product will have reduced ΔEST due to the increased conjugation length and thus can be expected to emit TADF. This new concept has the potential to significantly increase the scope of polymeric materials with TADF properties. Thus the second part on the thesis focuses on the design of a new monomer based on carbazole units with a pendant benzophenone moiety and its polymerization and full structural elucidation with the help of model compounds involving intensive NMR and MALDI-TOF analysis. In addition to the expect TADF properties, the benzophenone unit will also provide the possibility for film stabilization and even photopatterning due to photo-crosslinking. Thus the study of film formation and photo-crosslinking of the new TADF polymers was a further objective of this thesis. Finally, first theoretical as well as experimental studies of the photo physical properties of the monomer, a low molar mass model compound and the polymer, again together with the partners from the Institute of Applied Photophysics, should provide evidence on the suitability of the new polymer design principle.

As the third generation of luminescent materials, thermally activated delayed fluorescence (TADF)-type compounds have great potential as emitter molecules in OLEDs allowing for electro-fluorescence with 100 % internal quantum efficiency. For organic electronics, the general wide range of applications from OLEDs, bio-fluorescence imaging to sensor technologies and photonic energy storages roots on the enormous variety of organic materials. Especially in the field of metal- free aromatic designs, the range of possible materials showing diverse triplet harvesting effects is immense, making material development a highly complex task. Firstly, initial efforts in the understanding of the basic concepts behind TADF will be highlighted. A rational design strategy for TADF materials will be illustrated on an innovative material series based on phenylcarbazoles. A reasonable branch of isomers are theoretically constructed and slight stoichiometric modifications are performed to understand how molecular structure and intramolecular steric hindrance affects reverse intersystem crossing (RISC), while simultaneously revealing the strategy for deep blue TADF. The rational design of a bluish green TADF material called 5CzCF3Ph providing CIEy ≤ 0.4 is demonstrated, enabling peak EQE values of 12.1 % with a promising LT50 of 2 hrs at 500 cd∙m-2. Subsequently, the photophysics of five newly designed trimeric donor (D)-acceptor (A)-donor (D) type material compounds, analogue concepts to archetypical TADF designs, highlight the importance of intramolecular electronic couplings between adjacent triplet states for adiabatically-driven TADF, revealing the mechanism of local type triplet state perturbations on 3CT states. The most promising candidate (DMAC-PTO-DMAC) is disclosed and in turn optimized to meet required conditions for deep blue TADF emission. Ultimately, a deep blue luminescent material called isoDMAC-PTO is developed, featuring CIE coordinates of (0.16, 0.14) with an overall quantum yield of (86.4 ± 0.5) %. The focus switches to the fundamental understanding of the underlying mechanism giving rise to TADF in small molecules, leaving the scope of deep blue emission. While investigating the photophysical properties of a synthesized donor (D)-acceptor (A) type thermally activated delayed fluorescence (TADF) emitter named methyl 2-(9,9-dimethylacridin-10-yl)benzoate (DMAC-MB), it is possible to identify the excited state dynamics mediating the spin-flip process and hence the reutilization of non-radiative triplet states allowing for an internal quantum efficiency approaching unity. As experimentally observed by detailed temperature- and time-dependent transient photoluminescence (PL) measurements and consolidated by comprehensive quantum-chemical considerations, excited state configuration interaction by non-adiabatic couplings are anticipated as key property behind triplet up-conversion in the vicinity of conical intersections, contributing to recent research facing the exciton management within the auspicious field of TADF. For the first time, this thesis reports that even a TADF-silent molecule can be converted into efficient TADF systems by increasing the donor π- conjugation length through polymerization of the building block itself. With a total photoluminescence quantum yield up to 71 %, comprehensible research illustrates an efficient thermally activated delayed fluorescence polymer P1, based solely on non-TADF chromophores represented by a model compound 2 (PLQY of 3 % at RT). Finally, as predicted by TDDFT calculations and shown for the first time in the aspiring field of TADF, a thermally activated delayed fluorescence polymer based on a merely radiative, solely phosphorescent repeating unit is demonstrated. Intramolecular π-conjugation is exploited to trigger the charge-transfer excited state energy, revealing a general design tool to provoke TADF, reserved in particular for polymers. While the introduced twisted methyl 2-(9,9-dimethylacridin-10-yl) benzoate (DMAC-MB) reveals efficient thermally activated delayed fluorescence (TADF), a modified analogue 9,9-Dimethyl-5H,9H-quinolino[3,2,1-de]acridin-5-one (DMAC-ACR) shows emerging room temperature phosphorescence (RTP). As for TADF, intramolecular non-adiabatic couplings are unlocked as key feature actuating persistent RTP, linking photophysical analogies between TADF and RTP to structural self-similarities. Last but not least, degradation processes in TADF materials will be addressed. A correlation between theoretically calculated bond-dissociation energies (BDEs) and phenomenological observations reveals that low BDEs, in particular along pronounced charge-transfer bonds, ultimately lead to irreversible TADF material degradation induced by bi-molecular processes comprising TPQ as well as TTA. Finally, this thesis reveals the photophysics of 24 newly designed, synthesized and characterized TADF materials and demonstrates a fundamentally new approach for RTP, based on structural analogues to TADF. Far reaching design principles as conjugation induced TADF in polymers, as well as new design strategies selectively incorporating virbonic couplings yield device performances comprising LT50 of 2 hrs at 500 cd∙m-2 and targeted deep blue emission with CIE (0.16, 0.14). While lighting the way for TADF as future luminescent OLED materials, intrinsic material instabilities due to low bond-dissociation energies are disclosed as key-issues for tomorrows research.

No description available.

High performance optoelectronic applications require simultaneously high mobility ($\mu$) and high quantum efficiency of fluorescence ($\Phi$). While this has been realised for organic small molecule semiconductors, applications such as high efficiency organic photovoltaics and bright organic light-emitting diodes towards electrically driven lasing are hampered by an apparent trade-off between $\mu$ and $\Phi$ in disordered systems. Recent reports of state-of-the-art device performance often optimise $\mu$ and $\Phi$ in disordered organic materials separately, and employ multi-layer architectures. In this work, we investigate materials in a class of donor-acceptor polymer materials; the indacenodithiophene-$\textit{alt}$-benzothiadiazole family, which demonstrate high $\mu$ in spite of a low long-range structural order, to understand the interplay between these two important device figures-of-merit. In the first section, we evaluate the effect of various tuneable parameters on $\mu$ and device performance in organic field-effect transistors. Using chemical modifications to the solubilising side chains, we observe that the substitution of bulky groups leads to a reduction of the hole mobility $\mu_h$ > 2 cm$^{2}$/Vs to ~ 0.5 cm$^{2}$/Vs in the benchmark polymer of this family, indacenodithiophene-$\textit{alt}$-benzothiadiazole. Crystallographic and exciton-quenching based experiments confirm this observation is closely related to the degree of polymer backbone aggregation, and this leads to a different temperature evolution of the transport behaviour. In order to reliably improve $\mu$ in these systems, an elongation of the donor subunit is required. This increases the $\pi$-electron density on the donor, and can lead to an improvement in $\mu$ where the side chain density is decreasing. This chemical design, leading to a more highly aggregated structural motif is much more potent in determining $\mu$, it seems, than design strategies to further improve the energetic disorder in the joint density of states and the potential barrier to torsion, which may be near optimised in these low-disorder systems. In the second section, we unpick the precise relationship between the degree of aggregation apparently linking high $\mu$ to low $\Phi$. With a prototype system, we compare the photophysics of two indacenodithiophene-$\textit{alt}$-benzothiadiazole polymers differing by side chain bulkiness. Despite the aforementioned suppression of $\mu$, we observe an improvement to $\Phi$ of $< 0.02$ to $\sim 0.18$ upon backbone separation. This derivative has the highest $\Phi$ reported for any polymer with $\mu$ exceeding that of amorphous-Si. However, the $\Phi$ in the more aggregated derivative is not limited by the formation of non-emissive excitons, but rather by an additional internal conversion pathway which is strongly temperature dependent, and mediated by Raman-active vibrations and close chain coupling. Extending this study, we analyse additional materials in this family with the highest $\Phi \cdot \mu$ values reported for conjugated polymers. We find that increasing the energy gap leads to an increase in $\Phi$, and secondary emission pathways via weakly luminescent inter-chain charge transfer species. By solving the rate equations for exciton recombination, we use the radiative rate of inter-chain luminescence as a probe to show strong wavefunction mixing at close-contact points for some polymers, and suggest this as the origin for a superior $\mu$ in dithiopheneindenofluorene-$\textit{alt}$-benzothiadiazole compared to indacenodithiophene-$\textit{alt}$-benzothiadiazole. We demonstrate how low $\mu$ can be decoupled from the energy gap ($E_g$), and propose backbone elongation leading to increased inter-chain wavefunction overlap and a higher $E_g$ as a design rule to increase $\Phi$ and $\mu$ together. Finally, we assess the role of low-frequency vibrations in organic semiconductors displaying thermally activated delayed fluorescence (TADF). In the low-aggregation limit where $\Phi$ is maximised, we show that non-radiative triplet recombination is strongly related to low frequency torsional motion, and both are reduced in the presence of a rigid polymer host matrix for various TADF materials across different classes. However, we also explore the importance of rotational freedom in determining the oscillator strength, exchange energy, and spin-orbit coupling matrix elements which mediate luminescence in the absence of a rigid host. We demonstrate that suppressing dynamic motion is a powerful tool to modulate the photophysical properties of these emitters, and can lead to improved $\Phi$ particularly for low $E_g$ emitters.

La nouvelle technologie innovatrice OLEDs (diodes organiques électroluminescentes) ne cesse de susciter l'engouement des scientifiques ainsi que les recherches à leurs égards. Ces dispositifs à base de matériaux organiques s'appliquent dans quasiment tous les domaines tels que l'éclairage, l'affichage...Une découverte récente vient d'apporter sa pierre à l'édifice en mettant au point une nouvelle troisième génération d'OLEDs. Cette révélation consiste en la réduction du coût des matériaux des OLEDs en utilisant des matériaux peu onéreux dits à fluorescence retardée. C'est dans cette optique que s'inscrit ce travail de thèse qui porte sur l'étude de ce type de matériaux pour les applications dans les OLEDs. Cette thèse est décomposée en deux principales parties. Dans un premier temps, nous avons étudié et synthétisé des matériaux pour cette nouvelle génération d'OLED en se basant sur un modèle de molécules existant. Ce dernier représente des dérivés de triazine-carbazole connus pour leurs propriétés adéquates aux OLEDs. Cette étude a démontré pour la première fois le caractère de fluorescence retardée de ces molécules. Nous avons par la suite caractérisé ces molécules au sein des OLEDs. Les résultats montrent l'efficacité de ces molécules. Dans un deuxième temps nous nous sommes intéressés à l'étude de molécules innovantes. Ainsi, des molécules dotées de fluorescences retardées et innovantes ont été synthétisées. Cette synthèse a été effectuée par une méthode très avantageuse. Par ailleurs, la structure et propriétés de ces molécules indiquent qu'elles sont dotées de fluorescences retardées. Ainsi, il est important de poursuivre ce travail, en évaluant les propriétés de ces molécules synthétisées, ainsi que de les caractériser au sein des OLEDs. / Recently, the synthesis of free metal materials for organic LEDs by Uoyama et al adds a third kind of luminescence, named thermally activated delayed fluorescence (TADF). The added value of this discovery is to lower significantly OLED cost thanks to the metal-free structure of these so-called hyper-fluorescent molecules. This work reports on this recent discovery in OLED's. We first studied the thermally activated delayed fluorescence from an existing molecular model. The latter, fulfil the condition of the delayed fluorescence and are based from triazine-carbazole derivatives. The results revealed for thefirst time the exhibition of the delayed fluorescence from this existing model. In a second part, a novel hyperfluorescent molecule have been synthesized following the design rules for the delayed fluorescence molecules. The synthesis was done by a method based on an attractive process. Furthermore, the structure and properties of these new materials indicate that these molecules are expected to exhibit delayed fluorescent. Thus, it is important to continue this work by evaluating the properties of these molecules and the OLEDs made from these materials.

Thermally activated delayed fluorescence (TADF) has been proposed as a pathway to achieve high efficiency organic light-emitting diodes (OLEDs) without the use of heavy metal atoms in molecular structures. Many different factors can be decisive for efficient light emission from TADF emitters. However, a complete picture of the working mechanisms behind TADF is still missing and further research exploring novel material and device ideas is required. This thesis aims to extend the understanding of TADF emitter and OLED design considerations by investigating photophysical properties of novel materials as well as fabricating, optimizing and characterizing devices. TADF emitters have great potential of being used in OLEDs because they allow for high quantum efficiencies by utilizing triplet states via reverse intersystem crossing (RISC). In small molecules this is done by spatially separating the frontier orbitals, forming an intramolecular charge-transfer state (iCT) and leading to a small energy difference between lowest excited singlet and triplet states (Δ𝐸ST). In polymer emitters, sufficient frontier orbital separation is harder to achieve, and typical strategies usually include adding known TADF units as sidechains onto a polymer backbone. In this thesis, a novel pathway of TADF polymer design is explored. A shift from a non-TADF monomer to TADF oligomers is explored. The monomer shows non-TADF emission and the delayed emission is shown to be of triplet-triplet annihilation (TTA) origin. An iCT state is formed already in the dimer, leading to a much more efficient TADF emission. This is confirmed by an almost two-fold increase of photoluminescence quantum yield (PLQY), a decrease in the delayed luminescence lifetime and the respective spectral line shapes of the molecules. Recently, intermolecular effects between small-molecule TADF emitters have been given more attention, revealing strong solid-state solvation or aggregation induced changes of sample performance. Implications of this on device performance are not yet fully covered. A thorough investigation of a novel TADF emitter 5CzCO2Me is conducted. Steady-state emission spectra reveal a luminescence redshift with increasing emitter concentration in a small molecule host. In all investigated concentrations, the emission profile remains the same, thus the redshift is attributed to the solid-state solvation effect. The highest photoluminescence quantum yield (PLQY) is achieved in the 20 wt% sample, reaching 66 %. The best OLED in terms of current-voltage-luminance and external quantum efficiency parameters is the device with 60 wt% emitter concentration, reaching maximal EQE values of 7.5 %. It is shown that the emitter transports holes and that charge carrier recombination does not take place on the bandgap of the host, but rather, a mixed host-guest concentration dependent recombination is seen. The hole transporting properties of 5CzCO2Me allows for a new dimension in tuning the device performance by controlling the emitter concentration.

No description available.

No description available.

L'objet de cette thèse est la définition et l'étude, au moyen d'une maquette, du concept de Traduction Automatisée Fondée sur le Dialogue pour auteur monolingue. Nous situons d'abord l'objet de cette étude dans une perspective historique en montrant pourquoi les travaux précédents en TAFD n'ont pas (encore) conduit à des systèmes utilisés en pratique. Nous proposons alors le concept de TAFD pour auteur monoligue qui offre de nouvelles perspectives concrètes et permet de poser des questions scientifiques intéressantes. Le but est de permettre à un auteur monolingue de documentation technique de traduire les documents qu'il rédige. Dans ce cadre, l'auteur aide le système à traduire dans une ou plusieurs langues cibles, via une standardisation et une clarification interactives effectuées une seule fois quel que soit l'ensemble des langues cibles visées. Afin que la station de rédaction de l'auteur soit un ordinateur personnel de milieu de gamme, le système est distribué. Les traitements linguistiques couteux (analyse, transfert et génération) - écrits en Ariane-G5 par les linguistes du GETA - sont donc effectués sur un serveur de traduction distribué en mode asynchrone. La maquette LIDIA-1 permet d'étudier les contraintes informatiques, ergonomiques et linguistiques d'un tel système, et de proposer des solutions. Elle permet de traduire une pile de démonstration qui explique certaines ambiguités du français, vers l'allemand, l'anglais et le russe. Pour vérifier les traductions produites, l'auteur peut demander des rétrotraductions. Nous avons utilisé une architecture distribuée dans laquelle trois serveurs communiquent au moyen de messages et de boîtes aux lettres. Le processus de clarification est basé sur un mécanisme de reconnaissance de patrons à chacun desquels est associée une méthode de production du dialogue en langue naturelle.