@phdthesis{Huegel2018,
  author    = {H{\"u}gel, Markus},
  title     = {The control of nanomorphology in star-shaped mesogens},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-165321},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Stilbene-based star-shaped mesogens have been synthesized with and without fullerene guests. Thermotropic properties and the mechanism of space-filling in the mesophases of these systems have been examined.},
  subject      = {Fl{\"u}ssigkristall},
  language  = {en}
}
@phdthesis{Roos2021,
  author    = {Roos, Markus},
  title     = {Synthesis, Photophysics and Photocatalysis of [FeFe] Complex Containing Dyads and Bimolecular Systems},
  doi       = {10.25972/OPUS-23453},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-234537},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {In the course of this work, a total of three photocatalytically active dyads for proton reduction could be synthesized together with the associated individual components. Two of them, D1 and D2, comprised a [Ru(bpy)3]2+ photosensitizer and D3 an [Ir(ppy)2bpy]+ photosensitizer. A Ppyr3-substituted propyldithiolate [FeFe] complex was used as catalyst in all systems. The absorption spectroscopic and electrochemical investigations showed that an inner-dyadic electronic coupling is effectively prevented in the dyads due to conjugation blockers within the bridging units used. The photocatalytic investigations exhibited that all dyad containing two-component systems (2CS) showed a significantly worse performance than the corresponding bimolecular three-component systems (3CS). Transient absorption spectroscopy showed that the 2CS behave very similarly to the associated multicomponent systems during photocatalysis. The electron that was intended for the intramolecular transfer from the photosensitizer unit to the catalyst unit within the dyads remains at the photosensitizer for a relatively long time, analogous to the 3CS and despite the covalently bound catalyst. It is therefore assumed that this intramolecular electron transfer is likely to be hindered as a result of the weak electronic coupling caused by the bridge units used. Instead, the system bypasses this through an intermolecular transfer to other dyad molecules in the immediate vicinity. In addition, with the help of emission quenching experiments and electrochemical investigations, it could be clearly concluded that all investigated systems proceed via the reductive quenching mechanism during photocatalysis.},
  subject      = {Fotokatalyse},
  language  = {en}
}
@phdthesis{Sieck2018,
  author    = {Sieck, Carolin},
  title     = {Synthesis and Photophysical Properties of Luminescent Rhodacyclopentadienes and Rhodium 2,2'-Biphenyl Complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154844},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {The photochemistry and photophysics of transition metal complexes are of great interest, since such materials can be exploited for a wide range of applications such as in photocatalysis, sensing and imaging, multiphoton-absorption materials and the fabrication of OLEDs. A full understanding of the excited state behavior of transition metal compounds is therefore important for the design of new materials for the applications mentioned above. In principle, the luminescence properties of this class of compounds can be tuned by changing the metal or subtle changes in the ligand environment. Furthermore, transition-metal complexes continue to play a major role in modern synthetic chemistry. In particular, they can realize selective transformations that would either be difficult or impossible by conventional organic chemistry. For example, they enable the efficient and selective formation of carbon-carbon bonds. One famous example of these types of transformations are metal-catalyzed cyclization reactions. Herein, metallacyclopentadiene complexes are considered as key intermediates in a number of metal-mediated or -catalyzed cyclization reactions, i.e. the [2+2+2] cyclotrimerization of alkynes. Recent research has focused on the synthesis and characterization of these metallacyclic intermediates such as MC4 ring systems. Metallacyclopentadienes are structurally related to main group EC4 systems such as boroles, siloles, thiophenes and phospholes. Overall, this group of compounds (EC4 analogues) is well known and has attracted significant attention due to their electron-transport and optical properties. Unlike transition metal analogues, however, these EC4 systems show no phosphorescence, which is due to inefficient SOC compared to 2nd and 3rd row transition metals, which promoted us to explore the phosphorescence potential of metallacyclopentadienes. In 2001, Marder et al. developed a one-pot high-yield synthesis of luminescent 2,5 bis(arylethynyl)rhodacyclopentadienes by reductive coupling of 1,4-diarylbuta-1,3-diynes at a suitable rhodium(I) precursor. Over the past years, a variety of ligands (e.g. TMSA, S,S' diethyldithiocarbamate, etc.) and 1,4-bis(p-R-phenyl)-1,3-butadiynes or linked , bis(p-R-arylethynyl)alkanes (R = electron withdrawing or donating groups) were investigated and always provided a selective formation of 2,5 bis(arylethynyl)rhodacyclopentadienes, which were reported to be fluorescent despite presence of the heavy atom. To examine the influence of the ligand sphere around the rhodium center on the intersystem-crossing (ISC) processes in the above-mentioned fluorescent rhodacyclopentadienes and to increase the metal character in the frontier orbitals by destabilizing the Rh filled d-orbitals, a -electron donating group was introduced, namely acetylacetonato (acac). Interestingly, in 2010 Tay reacted [Rh(κ2-O,O-acac)(PMe3)2] with ,-bis(p-R-arylbutadiynyl)alkanes and observed not only the fluorescent 2,5 bis(arylethynyl)rhodacyclopentadienes, but also rhodium 2,2'-bph complexes as products, which were reported to be phosphorescent in preliminary photophysical studies. In this work, the reaction behavior of [Rh(κ2-O,O-acac)(L)2] (L = PMe3, P(p-tolyl)3) with different ,-bis(p-R-arylbutadiynyl)alkanes was established. Furthermore, the separation of the two isomers 2,5-bis(arylethynyl)rhodacyclopentadienes (A) and rhodium 2,2'-bph complexes (B), and the photophysical properties of those were explored in order to clarify their fundamentally different excited state behaviors. Reactions of [Rh(κ2-O,O-acac)(P(p-tolyl3)2)] with ,-bis(arylbutadiynyl)alkanes gives exclusively weakly fluorescent 2,5-bis(arylethynyl)rhodacyclopentadienes. Changing the phosphine ligands to PMe3, reactions of [Rh(κ2-O,O-acac)(PMe3)2] and , bis(arylbutadiynyl)alkanes afford two isomeric types of MC4 metallacycles with very different photophysical properties, as mentioned before. As a result of a normal [2+2] reductive coupling at rhodium, 2,5 bis(arylethynyl)rhodacyclopentadienes (A) are formed, which display intense fluorescence. Rhodium 2,2'-bph complexes (B), which show phosphorescence, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent -H-shift. Control of the isomer distribution, of 2,5-bis(arylethynyl)rhodacyclopentadienes (A) and rhodium biphenyl complexes (B), is achieved by modification of the linked , bis(arylbutadiynyl)alkane. Changing the linker length from four CH2 to three CH2 groups, dramatically favors the formation of the rhodium biphenyl isomer B, providing a fundamentally new route to access photoactive metal biphenyl compounds in good yields. This is very exciting as the photophysical properties of only a limited number of bph complexes of Ir, Pd and Pt had been explored. The lack of photophysical reports in the literature is presumably due to the limited synthetic access to various substituted 2,2'-bph transition metal complexes. On the other hand, as the reaction of [Rh(κ2-O,O-acac)(P(p-tolyl)3)2] with , bis(arylbutadiynyl)alkanes provides a selective reaction to give weakly fluorescent 2,5 bis(arylethynyl)rhodacyclopentadiene complexes with P(p-tolyl)3 as phosphine ligands, a different synthetic access to 2,5-bis(arylethynyl)rhodacyclopentadiene complexes with PMe3 as phosphine ligands was developed, preventing the time-consuming separation of the isomers. The weak rhodium-phosphorus bonds of 2,5-bis(arylethynyl)rhodacyclopentadiene complexes bearing P(p tolyl)3 as phosphine ligands, relative to those of related PMe3 complexes, allowed for facile ligand exchange reactions. In the presence of an excess of PMe3, a stepwise reaction was observed, giving first the mono-substituted, mixed-phosphine rhodacyclopentadiene intermediates and, subsequently, full conversion to the highly fluorescent 2,5 bis(arylethynyl)-rhodacyclopentadienes bearing only PMe3 ligands (by increasing the reaction temperature). With spectroscopically pure 2,5-bis(arylethynyl)rhodacyclopentadiene complexes A (bearing PMe3 as phosphine ligands) and rhodium 2,2-bph complexes B in hand, photophysical studies were conducted. The 2,5-bis(arylethynyl)rhodacyclopentadienes (A) are highly fluorescent with high quantum yields up to 54\% and very short lifetimes (τ = 0.2 - 2.5 ns) in solution at room temperature. Even at 77 K in glass matrices, no additional phosphorescence is observed which is in line with previous observations made by Steffen et al., who showed that SOC mediated by the heavy metal atom in 2,5-bis(arylethynyl)rhodacyclopentadienes and 2,5 bis(arylethynyl)iridacyclopentadienes is negligible. The origin of this fluorescence lies in the pure intra-ligand (IL) nature of the excited states S1 and T1. The HOMO and the LUMO are nearly pure  and * ligand orbitals, respectively, and the HOMO is energetically well separated from the filled rhodium d orbitals. The absence of phosphorescence in transition metal complexes due to mainly IL character of the excited states is not unusual, even for heavier homologues than rhodium with greater SOC, resulting in residual S1 emission (fluorescence) despite ISC S1→Tn being sufficiently fast for population of T1 states. However, there are very few complexes that exhibit fluorescence with the efficiency displayed by our rhodacyclopentadienes, which involves exceptionally slow S1→Tn ISC on the timescale of nanoseconds rather than a few picoseconds or faster. In stark contrast, the 2,2'-bph rhodium complexes B are exclusively phosphorescent, as expected for 2nd-row transition metal complexes, and show long-lived (hundreds of s) phosphorescence (Ф = 0.01 - 0.33) at room temperature in solution. As no fluorescence is detected even at low temperature, it can be assumed that S1→Tn ISC must be faster than both fluorescence and non-radiative decay from the S1 state. This contrasts with the behavior of the isomeric 2,5-bis(arylethynyl)rhodacyclopentadienes for which unusually slow ISC occurs on a timescale that is competitive with fluorescence (vide supra). The very small values for the radiative rate constants, however, indicate that the nature of the T1 state is purely 3IL with weak SOC mediated by the Rh atom. The phosphorescence efficiency of these complexes in solution at room temperature is even more impressive, as non-radiative coupling of the excited state with the ground state typically inhibits phosphorescence. Instead, the rigidity of the organic -system allows the ligand-based excited triplet state to exist in solution for up to 646 s and to emit with high quantum yields for biphenyl complexes. The exceptionally long lifetimes and small radiative rate constants of the rhodium biphenyl complexes are presumably a result of the large conjugated -system of the organic ligand. According to TD DFT studies, the T1 state involves charge-transfer from the biphenyl ligand into the arylethynyl moiety away from the rhodium atom. This reduces the SOC of the metal center that would be necessary for fast phosphorescence. These results show that the π-chromophoric ligand can gain control over the photophysical excited state behavior to such an extent that even heavy transition metal atoms like rhodium participate in increasing the fluorescence such as main-group analogues do. Furthermore, in the 2,2'-bph rhodium complexes, the rigidity of the organic -system allows the ligand-based excited triplet state to exist in solution for up to hundreds of s and to emit with exceptional quantum yields. Therefore, investigations of the influence of the ligand sphere around the rhodium center have been made to modify the photophysical properties and furthermore to explore the reaction behavior of these rhodium complexes. Bearing in mind that the P(p-tolyl)3 ligands can easily be replaced by the stronger -donating PMe3 ligands, ligand exchange reactions with N heterocyclic carbenes (NHCs) as even stronger -donors was investigated. Addition of two equivalents of NHCs at room temperature led to the release of one equivalent of P(p-tolyl3) and formation of the mono-substituted NHC rhodium complex. The reaction of isolated mono-NHC complex with another equivalent of NHC at room temperature did not result in the exchange of the second phosphine ligand. Moderate heating of the reaction to 60 °C, however, resulted in the formation of tetra-substituted NHC rhodium complex [Rh(nPr2Im)4]+[acac]-. To circumvent the loss of the other ligands in the experiments described above, a different approach was investigated to access rhodacyclopentadienes with NHC instead of phosphine ligands. Reaction of the bis-NHC complex [Rh(κ2-O,O-acac)(nPr2Im)2] with , bis(arylbutadiynyl)alkanes at room temperature resulted 2,5-bis(arylethynyl)-rhodacyclopentadienes with the NHC ligands being cis or trans to each other as indicated by NMR spectroscopic measurements and single-crystal X-ray diffraction analysis. Isolation of clean material and a fundamental photophysical study could not be finished for reasons of time within the scope of this work. Furthermore, shortening of the well conjugated -system of the chromophoric ligand (changing from tetraynes to diynes) was another strategy to examine the reaction behavior of theses ligands with rhodium(I) complexes and to modify the excited state behavior of the formed rhodacyclopentadienes. The reaction of [Rh(κ2-O,O-acac)(PMe3)2] with 1,7 diaryl 1,6-heptadiynes (diynes) leads to the selective formation of 2,5 bis(aryl)rhodacyclopentadienes. These compounds, however, are very weakly fluorescent with quantum yields ФPL < 1, and very short emission lifetimes in toluene at room temperature. Presumably, vibrational modes of the bis(phenyl)butadiene backbone leads to a higher rate constant for non-radiative decay and is thus responsible for the low quantum yields compared to their corresponding PMe3 complexes with the bis(phenylethynyl)butadiene backbone at room temperature. No additional phosphorescence, even at 77 K in the glass matrix is observed. Chancing the phosphine ligands to P(p-tolyl)3, reactions of [Rh(κ2-O,O-acac)(P(p-tolyl3)2)] with 1,7-diaryl-1,6-heptadiynes, however, resulted in a metal-mediated or -catalyzed cycloaddition reaction of alkynes and leads to full conversion to dimerization and trimerization products and recovery of the rhodium(I) starting material. This is intuitive, considering that P(Ar)3 (Ar = aryl) ligands are considered weaker -donor ligands and therefore have a higher tendency to dissociate. Therefore, rhodium(I) complexes with aryl phosphines as ligands have an increasing tendency to promote catalytic reactions, while the stronger -donating ligands (PMe3 or NHCs) promote the formation of stable rhodium complexes. Finally, in Chapter 4, the findings of the work conducted on N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) is presented. These compounds have unique electronic and steric properties and are therefore of great interest as ligands and organo-catalysts. In this work, studies of substitution reactions involving novel carbonyl complexes of rhodium and nickel are reported. For characterization and comparison of CAACmethyl with the large amount of data available for NHC and sterically more demanding CAAC ligands, an overview on physicochemical data (electronics, sterics and bond strength) is provided. The reaction of [Rh(-Cl)(CO)2]2 with 2 equivalents of CAACmethyl at low temperature afforded the mononuclear complex cis-[(RhCl(CO)2(CAACmethyl)]. However, reacting [Rh( Cl)(CO)2]2 with CAACmethyl at room temperature afforded a mixture of complexes. The mononuclear complex [(RhCl(CO)(CAACmethyl)2], the chloro-bridged complexes [(Rh2( Cl)2(CO)3(CAACmethyl)], [Rh(-Cl)(CO)(CAACmethyl)]2 and a carbon monoxide activation product were formed. The carbon monoxide activation product is presumably formed via the reaction of two equivalents of the CAAC with CO to give the bis-carbene adduct of CO, and subsequent rearrangement via migration of the Dipp moiety. While classical N-heterocyclic carbenes are not electrophilic enough to react with CO, related diamidocarbenes and alkyl(amino)carbenes undergo addition reactions with CO to give the corresponding ketenes. Consequently, to obtain the CAAC-disubstituted mononuclear complex selectively, 8 equivalents of CAACmethyl were reacted with 1 equivalent of [Rh(-Cl)(CO)2]2. For the evaluation of TEP values, [Ni(CO)3(CAAC)] was synthesized in collaboration with the group of Radius. With the complexes [(RhCl(CO)(CAACmethyl)2] and [Ni(CO)3(CAAC)] in hand, it was furthermore possible to examine the electronic and steric parameters of CAACmethyl. Like its bulkier congeners CAACmenthyl and CAACcy, the methyl-substituted CAAC is proposed to be a notably stronger -donor than common NHCs. While it has a very similar TEP value of 2046 cm-1, it additionally possess superior -acceptor properties (P = 67.2 ppm of phosphinidene adduct). CAACs appear to be very effective in the isolation of a variety of otherwise unstable main group and transition metal diamagnetic and paramagnetic species. This is due to their low-lying LUMO and the small singlet-triplet gap. These electronic properties also allow free CAACs to activate small molecules with strong bonds. They also bind strongly to transition metal centers, which enables their use under harsh conditions. One recent development is the use of CAACs as ligands in transition metal complexes, which previously were only postulated as short-lived catalytic intermediates.[292,345] The availability of these reactive species allows for a better understanding of known catalytic reactions and the design of new catalysts and, moreover, new applications. For example Radius et al.[320] prepared a CAAC complex of cobalt as a precursor for thin-film deposition and Steffen et al.[346] reported a CAAC complex of copper with very high photoluminescent properties, which could be used in LED devices. With the development of cheap and facile synthetic methods for the preparation of CAACs and their corresponding transition metals complexes, as well as the knowledge of their electronic properties, it is safe to predict that applications in and around this field of chemistry will continue to increase.},
  subject      = {{\"U}bergangsmetallkomplexe},
  language  = {en}
}
@phdthesis{Ceymann2016,
  author    = {Ceymann, Harald},
  title     = {Synthesis and Optical Spectroscopic Properties of Squaraine Superchromophores},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-136850},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2016},
  abstract  = {In this work the successful synthesis, the linear and nonlinear spectroscopic properties as well as the electrochemical behaviour of some linear and star-shaped squaraine superchromophores that are based on indolenine derivatives were presented. The attempt to synthesise similar chromophores which contained only benzothiazole squaraines failed unfortunately. However, one trimer that contained mixed benzothiazole indolenine squaraines could be synthesised and investigated as well. The linear spectroscopic properties, like red-shift and broadening of the absorption, of all superchromophores could be explained by exciton coupling theory. The heterochromophores (SQA)2(SQB)-N, (SQA)(SQB)2-N and (SQA)(SQB)-NH displayed additional to the typical squaraine fluorescence from the lowest excited state some properties that could be assigned to localised states. While the chromophores with N-core showed very small emission quantum yields, the chromophores with the other cores and the linear oligomers display an enhancement compared to the monomers. Transient absorption spectroscopy experiments of the star-shaped superchromophores showed, that their formally degenerated S1 states are split due to a deviation of the ideal C3 symmetry. This is also the reason for the observation of an absorption band for the highest exciton state, which is derived from the S1-state of the monomers, as its transition-dipole moment would be zero in the symmetrical case. The linear oligomers and the star-shaped superchromophores with a benzene or triarylamine core showed at least additive, sometimes even weak cooperative, behaviour in the two-photon absorption experiments. Additional to higher two-photon absorption cross sections the chromophores showed a pronounced broadening of the nonlinear absorption, due to symmetry breaking and a higher density of states. Unfortunately it was not possible to solve the problem of the equilibrium of the cisoid and the transoid structure of donor substituted azulene squaraines, due to either instability of the squaraines or steric hindrance.},
  subject      = {Squaraine},
  language  = {en}
}
@phdthesis{Maisch2018,
  author    = {Maisch, Stefan},
  title     = {Synthese von V- und brettf{\"o}rmigen Nematogenen und die Untersuchung ihrer biaxialen Ordnung in Mesophasen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-155409},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Die vorliegende Arbeit befasst sich mit der Synthese und Untersuchung V- und brettf{\"o}rmiger Fl{\"u}ssigkristalle zur Realisierung einer biaxialen nematischen Mesophase. Es wurde erfolgreich eine Serie neuer Mesogene mit hockeyschl{\"a}gerf{\"o}rmiger und V-f{\"o}rmiger Struktur synthetisiert. Zus{\"a}tzlich wurden Dimere aus einem dieser hockeyschl{\"a}gerf{\"o}rmigen Verbindungen dargestellt. Als Kernbaustein wurde Benzo[1,2-b:4,3-b']dithiophen verwendet, dessen lokales Kerndipolmoment von 1.0 Debye sich nach theoretischen Vorgaben zus{\"a}tzlich zum Bindungswinkel (108.9 °) positiv auf die Bildung einer Nb-Phase auswirken soll. {\"U}berraschenderweise bilden nur die hockeyschl{\"a}gerf{\"o}rmigen Molek{\"u}le eine uniaxiale, optisch positive nematische Mesophase aus. Alle anderen V-f{\"o}rmigen Verbindungen und sogar die Dimere sind ausschließlich kristallin und keine Fl{\"u}ssigkristalle. Die Einkristallstrukturanalyse eines hockeyschl{\"a}gerf{\"o}rmigen Mesogens sowie eines V-f{\"o}rmigen Molek{\"u}ls zeigt bemerkenswerte {\"A}hnlichkeiten auf. Ein Modell des Phasen{\"u}bergangs wird pr{\"a}sentiert, welches die Abwesenheit der nematischen Mesophase in der Familie der V-f{\"o}rmigen, formstabilen Mesogene mit terminalen aliphatischen Ketten erkl{\"a}rt. Zudem befasst sich die Arbeit mit der Synthese und der Untersuchung brettf{\"o}rmiger Molek{\"u}le, welche dem optimalen Seitenverh{\"a}ltnis von 15 : 5 : 3 mit L > B > T zur Bildung biaxialer Mesophasen, relativ nahekommen. Ein Anthrachinon-Kernbaustein wurde dabei mit Armen bestehend aus einem Oligo(phenylenethinylen)-Grundger{\"u}st entsprechender L{\"a}nge verkn{\"u}pft. Es konnten verschiedene dachf{\"o}rmige Mesogene dargestellt werden, bei denen die Art und Anzahl der Seitenketten sowie der terminalen Ketten variiert wurde. Thermische sowie mikroskopische Untersuchungen zeigen bei allen Verbindungen eine breite nematische Mesophase. Mittels spezieller R{\"o}ntgenstreuung im magnetischen Feld kann die Bildung nematischer Dom{\"a}nen mit SmC-artigen biaxialen Aggregaten best{\"a}tigt werden.},
  subject      = {Thermotroper Fl{\"u}ssigkristall},
  language  = {de}
}
@phdthesis{Dechant2022,
  author    = {Dechant, Moritz Thomas},
  title     = {Synthese und Struktur-Eigenschaftsbeziehungen neuer Phthalocyanin-Sternmesogene - Ein neues Design f{\"u}r organische, fl{\"u}ssigkristalline Photovoltaikmaterialien},
  doi       = {10.25972/OPUS-23888},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-238888},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Es wurde eine Vielzahl neuer, fl{\"u}ssigkristalliner Phthalocyanin-Sternmesogene synthetisiert. Die Struktur-Eigenschaftsbeziehungen und die thermotropen Eigenschaften neuer Phthalocyanin-Sternmesogene mit Freiraum sowie von sterisch {\"u}berfrachteten Verbindungen wurden insbesondere hinsichtlich der Freiraumf{\"u}llung untersucht. Diesbez{\"u}glich wurde ein neuer supramolekularer, freiraumf{\"u}llender "Klick-Prozess" zwischen einem Molek{\"u}l mit Freiraum und einem sterisch {\"u}berfrachteten Molek{\"u}l mit vier Fullerenen beobachtet. Die photophysikalischen Eigenschaften wurden zudem insbesondere im Hinblick auf die Anwendung f{\"u}r die Organische Photovoltaik untersucht.},
  subject      = {Phthalocyanin},
  language  = {de}
}
@phdthesis{Maier2020,
  author    = {Maier, Philipp},
  title     = {Synthese und Struktur-Eigenschafts-Beziehungen sterisch {\"u}berfrachteter Sternmesogene mit hexasubstituiertem Benzolkern und ihrer Wirt-Gast-Mesogene},
  doi       = {10.25972/OPUS-18527},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-185274},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {Die vorliegende Dissertation befasst sich mit den Struktur-Eigenschafts-Beziehungen von sternf{\"o}rmigen Mesogenen mit kontrollierbaren Konformationen in den LC-Phasen. Zun{\"a}chst sollte mithilfe verschiedener Molek{\"u}ldesigns gekl{\"a}rt werden, wie eine Faltung der Arme verhindert werden kann, und somit, ob sternf{\"o}rmige Konformationen in den kolumnaren Packungen realisiert werden k{\"o}nnen. Hierzu wurde erfolgreich eine Bibliothek von dreiarmigen Amidsternen, semiflexiblen Oligoestersternen mit hexasubstituiertem Benzolkern und formtreuen hexasubstituierten Benzolen synthetisiert. Die besondere Herausforderung bei der Darstellung letzterer lag in der C3-Symmetrie der Verbindungen und konnte durch Optimierung der Synthesestrategie mittels aufeinander folgender Wittig-Horner- und Suzuki-Reaktionen in einem divergenten Ansatz gemeistert werden. Ein herausragendes Ergebnis ist die Fl{\"u}ssigkristallinit{\"a}t dieser formtreuen hexasubstituierten Strukturen, wenn sie mindestens neun bzw. zw{\"o}lf periphere Ketten besitzen. Die detaillierte Auswertung der Kolumnendurchmesser mithilfe von {\"a}quatorialen Reflexen sowie der Dichte und der meridionalen Beugungsmuster zeigen, dass lediglich f{\"u}r die formtreuen hexasubstituierten Benzolderivate eine Faltung verhindert werden kann. Intrinsische Freir{\"a}ume (K{\"a}vit{\"a}ten) zwischen den Oligo(phenylenvinylen)-Armen werden durch außergew{\"o}hnliche Dimerenbildung und helikale Packung der Molek{\"u}le kompensiert. In die Kavit{\"a}ten der Trispyridylverbindungen k{\"o}nnen Carbons{\"a}ure-funktionalisierte G{\"a}ste unter Ausbildung von Wasserstoffbr{\"u}cken eingelagert werden. Mit zunehmender Gastkonzentration wird die helikale Dimerphase des Wirts kontinuierlich in eine neue kolumnare Phase von monomeren Supermesogenen ohne helikale Struktur umgewandelt. Da die G{\"a}ste in den Supermesogenen vollst{\"a}ndig von den Oligo(phenylenvinylen)-Armen und den aliphatischen Ketten umschlossen sind, handelt es sich bei der Wirtverbindung erstmals um einen fl{\"u}ssigkristallinen Endorezeptor mit drei Bindungsstellen. Das Sternmesogen mit gr{\"o}ßeren intrinsischen Freir{\"a}umen erm{\"o}glicht die Einlagerung von funktionalen Bausteinen wie z.B. Anthracenchromophoren. Aus Untersuchungen mittels Festk{\"o}rper-NMR- und Fluoreszenzspektroskopie geht hervor, dass sich die Mesophase mit drei Anthraceng{\"a}sten langsam in eine doppelt nanosegregierte Struktur umwandelt, in der intrakolumnar Oligo(phenylenvinylen)-Arme und Anthracene Seite an Seite segregiert stapeln und so segmentierte Kolumnen bilden. Diese Art von doppelter Nanosegregation offenbart das Potential des verwendeten Molek{\"u}ldesigns im Bezug auf die Entwicklung mesomorpher Multikabelstrukturen. Im Vergleich zu den Supermesogenen weisen die analogen Sternverbindungen mit kovalent gebundenen Pseudog{\"a}sten um {\"u}ber 100 °C h{\"o}here Kl{\"a}rpunkte auf, was unter Ber{\"u}cksichtigung der strukturellen {\"A}hnlichkeit der kolumnaren Phasen und der {\"a}hnlichen Mischungsenthalpien in unterschiedlichen Werten der Mischungsentropie begr{\"u}ndet liegen muss. Der Vergleich mit einer 1:3-Mischung ohne spezifische Wirt-Gast-Wechselwirkung best{\"a}tigt in diesem Zusammenhang den Einfluss der Bindungsart der G{\"a}ste auf die Mesophasenstabilit{\"a}t. Die Kl{\"a}rtemperaturen der Sternmesogene lassen sich folglich {\"u}ber die Art der Bindung der Gastmolek{\"u}le kontrollieren. Dies ist vor allem f{\"u}r die Orientierung kolumnarer Phasen in d{\"u}nnen Filmen großer funktionaler Mesogene, die h{\"a}ufig erst bei sehr hohen Temperaturen unter Zersetzung in die isotrope Phase {\"u}bergehen, interessant.},
  subject      = {Thermotroper Fl{\"u}ssigkristall},
  language  = {de}
}
@phdthesis{Wachtler2020,
  author    = {Wachtler, Stefan},
  title     = {Synthese und Charakterisierung von funktionalisierten Nanodiamantmaterialien f{\"u}r biomedizinische Anwendungen},
  doi       = {10.25972/OPUS-21075},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-210757},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {In dieser Arbeit ist die Synthese von funktionalisiertem Nanodiamant mit bioaktiven Substanzen, welche vor allem als Wirkstofftransporter eingesetzt werden sollen, beschrieben. Dazu werden zum einen bereits bekannte Anbindungsm{\"o}glichkeiten an Nanodiamant, wie zum Beispiel die Klick-Reaktion, sowie die Ausbildung von Amidbr{\"u}cken verwendet. Zum anderen werden neuartige Funktionalisierungsm{\"o}glichkeiten wie Protein Ligation und Thioharnstoffbr{\"u}cken verwendet und somit das Repertoire an bekannten Anbindungsreaktion erweitert. Des weiteren wurde ein multifunktionales Nanodiamantsystem synthetisiert. Dieses ist in der Lage, zwei verschiedene Molek{\"u}le auf einem Partikel zu immobilisieren. Die verwendeten Methoden erm{\"o}glichen die Anbindung verschiedener Substanzen aus unterschiedlichen Molek{\"u}lgruppen an Nanodiamanten und sind somit universell einsetzbar.},
  subject      = {Synthesediamant},
  language  = {de}
}
@phdthesis{Gloza2014,
  author    = {Gloza, Steffi},
  title     = {Synthese und Charakterisierung von Anthracen- und Anthrachinon-substituierten sternf{\"o}rmigen Mesogenen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-110595},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Im Rahmen der vorliegenden Arbeit wurden promesogene Arme sowie eine Bibliothek von Sternmesogenen mit Anthracen als Donor- und Anthrachinon als Akzeptorbaustein synthetisiert und untersucht. Ein Schwerpunkt der Arbeit lag auf der Synthese, dem Upscaling, der selektiven Sch{\"u}tzung und weiteren Umsetzung der 2,6-substituierten Anthracen- und Anthrachinon-Chromophore zu den Armbausteinen. Besondere Herausforderungen ergaben sich nicht nur in der Entwicklung einer effizienten Synthesestrategie zur Gewinnung der Chromophore, sondern auch in der Wahl geeigneter Schutzgruppen. Die sternf{\"o}rmigen Verbindungen, die im Rahmen der vorliegenden Arbeit pr{\"a}pariert wurden, enthalten 1,3,5-Trihydroxybenzen (Phloroglucin) als Kerneinheit und sind Multiarmmesogene mit der kleinstm{\"o}glichen Zahl an Armen. Durch geeignete Schutzgruppenstrategien gelang neben den C3-symmetrischen Verbindungen die gezielte Darstellung der C2-symmetrischen und unsymmetrischen Verbindungen. Die Gesamtausbeuten der semiperfluorierten Verbindungen fallen deutlich geringer aus als die der ausschließlich mit Alkylketten dekorierten Derivate, da ihre Isolierung sehr anspruchsvoll ist. Alle Verbindungen bilden ausnahmslos kolumnare Phasen. Semiperfluorierte Ketten wurden eingef{\"u}hrt, um eine Trennung des Donors Anthracen und des Akzeptors Anthrachinon zu erreichen. Die Kolumnendurchmesser sind bei allen kolumnaren Mesophasen wesentlich kleiner als die Durchmesser der sternf{\"o}rmigen Konformere der Mesogene. Angelehnt an die fr{\"u}her untersuchten Oligobenzoatsterne werden Modelle mit gefalteten, E-f{\"o}rmigen Konformeren aufgestellt. So ist es m{\"o}glich, die erforderliche Anzahl an Molek{\"u}len pro Elementarzelle in einer dichten, nanosegregierten Packung anzuordnen. Mit Absorptions- und Emissionsmessungen konnte dieses Modell best{\"a}tigt werden. In allen Donor- und Akzeptor-substituierten Verbindungen wird die Fluoreszenz durch Energietransferprozesse nach F{\"o}rster und Dexter fast vollst{\"a}ndig gel{\"o}scht. Restfluoreszenz wird in dem Bereich beobachtet, der nur noch den Transfer nach Dexter zul{\"a}sst und ist f{\"u}r die Derivate am h{\"o}chsten, die in den E-f{\"o}rmigen Konformeren Donor und Akzeptor am besten trennen k{\"o}nnen. Die Ergebnisse dieser Arbeit zeigen, dass Anthracen- und Anthrachinonderivate eine Vielzahl komplexer zwei- und dreidimensional hochgeordneter kolumnarer Strukturen ausbilden und damit hochinteressant sind als fl{\"u}ssigkristalline organische Halbleitermaterialien.},
  subject      = {Fl{\"u}ssigkristall},
  language  = {de}
}
@phdthesis{Bahndorf2022,
  author    = {Bahndorf, Katrin},
  title     = {Synthese und Charakterisierung von Aminos{\"a}ure-basierten Amphiphilen und deren Umsetzung zu C\(_3\)-symmetrischen Sternmesogenen - Strukturkontrolle in weicher Materie {\"u}ber Oligopeptidaggregation},
  doi       = {10.25972/OPUS-25275},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-252753},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Synthese einer Bibliothek von Aminos{\"a}ure-basierten Oligopeptid-Amphiphilen mittels Festphasensynthese, deren kovalente Kn{\"u}pfung an einen nukleophilen Kern zu C3-symmetrischen Sternmesogenen und die Analyse der Einfl{\"u}sse der verwendeten Aminos{\"a}uren auf die Sekund{\"a}rstruktur des synthetisierten Molek{\"u}ls.},
  language  = {de}
}