Charge-transfer states in triazole linked donor-acceptor materials: Strong effects of chemical modification and solvation

© the Owner Societies 2017. A series of 1,2,3-triazole linked donor-acceptor chromophores are prepared by Click Chemistry from ene-yne starting materials. The effects of three distinct chemical variations are investigated: enhancing the acceptor strength through oxidation of the sulphur atom, alteration of the double bond configuration, and variation of the triazole substitution pattern. A detailed photophysical characterization shows that these alterations have a negligible effect on the absorption while dramatically altering the emission wavelengths. In addition, strong solvatochromism is found leading to significant red shifts in the case of polar solvents. The experimental findings are rationalized and related to the electronic structure properties of the chromophores by time-dependent density functional theory as well as the ab initio algebraic diagrammatic construction method for the polarization propagator in connection with a new formalism allowing to model the influence of solvation onto long-lived excited states and their emission energies. These calculations highlight the varying degree of intramolecular charge transfer character present for the different molecules and show that the amount of charge transfer is strongly modulated by the conducted chemical modifications, by the solvation of the chromophores, and by the structural relaxation in the excited state. It is, furthermore, shown that enhanced charge separation, as induced by chemical modification or solvation, reduces the singlet-triplet gaps and that two of the investigated molecules possess sufficiently low gaps to be considered as candidates for thermally activated delayed fluorescence

Development of an immunofluorescence assay module for determination of the mycotoxin zearalenone in water

Project Aquafluosense is designed to develop prototypes for a fluorescence-based instrumentation setup for in situ measurements of several characteristic parameters of water quality. In the scope of the project an enzyme-linked fluorescent immunoassay (ELFIA) method has been developed for the detection of several environmental xenobiotics, including mycotoxin zearalenone (ZON). ZON, produced by several plant pathogenic Fusarium species, has recently been identified as an emerging pollutant in surface water, presenting a hazard to aquatic ecosystems. Due to its physico-chemical properties, detection of ZON at low concentrations in surface water is a challenging task. The 96-well microplate-based fluorescence instrument is capable of detecting ZON in the concentration range of 0.09–400 ng/mL. The sensitivity and accuracy of the analytical method has been demonstrated by a comparative assessment with detection by high-performance liquid chromatography and by total internal reflection ellipsometry. The limit of detection of the method, 0.09 ng/mL, falls in the low range compared to the other reported immunoassays, but the main advantage of this ELFIA method is its efficacy in combined in situ applications for determination of various important water quality parameters detectable by induced fluorimerty—e.g., total organic carbon content, algal density or the level of other organic micropollutants detectable by immunofluorimetry. In addition, the immunofluorescence module can readily be expanded to other target analytes if proper antibodies are available for detection

Control of intramolecular charge transfer phenomena in functional organic materials

Zusammenfassung in deutscher SpracheAbweichender Titel nach Übersetzung der Verfasserin/des VerfassersIn den letzten Jahren wurden funktionelle organische Moleküle hinsichtlich ihrer Verwendung in vielfältigen technologischen Anwendungen ausgiebig erforscht. Aromatische push-pull Moleküle, die aus einer elektronenreichen Donor- und einer elektronenarmen Akzeptor-Untereinheit aufgebaut sind, die durch ein konjugierte π-System miteinander verbunden werden, haben sich hierfür als besonders geeignet erwiesen. Im Speziellen deren Einsatz in Organischen Leuchtdioden, in der Organischen Photovoltaik, als Farbstoffe, oder als nichtlineare optische Materialien sind bereits weit entwickelt. Die molekularen Eigenschaften dieser organischen Moleküle werden durch deren elektronische Struktur bestimmt, die wiederum durch die Wechselwirkung zwischen der Donor- und der Akzeptor-Einheit geprägt wird. Daher ist es von enormer Bedeutung diese Wechselwirkung zu kontrollieren, um neue maßgeschneiderte Materialien zu entwerfen. In dieser Arbeit werden neue Strategien entwickelt, um die Wechselwirkung zwischen den elektronenziehenden und den elektronenschiebenden molekularen Untereinheiten zu kontrollieren. Dabei werden drei unterschiedliche Ansätze verfolgt: i) Modifizierung der Stärke der Elektronendonoren durch die Planarisierung von Triarylaminen und die Unterbrechung des konjugierten π-Systems durch das Einführen sterisch anspruchsvoller Gruppen; ii) Anwendung von 1,2,3-Triazolen als funktioneller Verbindung zwischen Donor- und Akzeptoreinheit, um die elektronische Interaktion der beiden Gruppen zu kontrollieren; iii) Untersuchung von En-In Verbindungen, die sich durch Ringfragmentierung aus Thiophenen herstellen lassen, hinsichtlich ihrer Einsetzbarkeit als molekularer Baustein und der Möglichkeit durch gezielte chemische Modifizierung dieses Bausteins die π-Konjugation zu beeinflussen.Organic push-pull materials consisting of an electron donating and an electron withdrawing subunit within one π-conjugated molecule have been investigated extensively during the last decades due to a wide range of technologically relevant applications. Among those the most important are organic light emitting diodes, imaging, organic photovoltaics, dyes and nonlinear optical materials for two-photon absorption or second harmonic generation to name a few. The molecular properties of these materials are determined by their electronic structure, which is in turn dominated by the donor-acceptor interaction by means of intramolecular charge transfer (ICT). Therefore, controlling ICT is among the most important challenges in the development of new functional bipolar materials. In this thesis new strategies to control the delicate interaction between electron donating and electron withdrawing groups in bipolar organic materials are developed. In particular three different approaches are pursued: i) modification of the donor unit to modulate the donor strength by planarization of triarylamines and disruption of the conjugated system by introduction of strategic sterically demanding groups; ii) application of a Click-derived 1,2,3-triazole bridge, as functional linker between the donor and acceptor unit in order to control the electronic interaction of both groups; iii) investigation of ene-yne compounds, derived from thiophene ring fragmentation, as tunable building blocks to realize conjugation control by chemical modification of the methylthio-substituted ene-yne fragment.48