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Fluorescence microscopy is a powerful method to examine cellular structures and biological processes with high spatial and temporal resolution. The development of novel microscopy techniques and labeling systems has expanded the limits of cellular imaging. However, this progress also relies on the availability of suitable fluorescent probes, thereby creating a need for new synthetic strategies that enable systematic modification of fluorophores. Rhodamine derivatives are widely used fluorophores, which exist in an equilibrium between a non-fluorescent, cell-permeable spirocyclic form and a fluorescent zwitterion. This spirocyclization equilibrium affects crucial properties of rhodamines regarding their applicability in cellular imaging, including fluorogenicity, cell-permeability and blinking behavior. Strategies that provide control over this equilibrium therefore hold the potential to generate suitable fluorescent probes for different microscopy techniques and labeling systems. This thesis describes the development and application of a synthetic strategy, which allows systematic tuning of the spirocyclization equilibrium of rhodamines. To this end, the ortho-carboxy group of various rhodamine derivatives was transformed into amides with different substituents. Introduction of substituted acyl benzenesulfonamides enables to control the spirocyclization equilibrium with unprecedented precision and to specifically optimize the fluorogenicity for HaloTag and SNAP-tag labeling. The resulting probes show suitable properties for live-cell, no-wash confocal and stimulated emission depletion (STED) microscopy. Replacing the ortho-carboxy group with more electron-rich amides strongly shifts the position of the equilibrium toward the spirocyclic state and results in spontaneous blinking. This led to the development of fluorophores for single molecule localization microscopy (SMLM). The generality of this synthetic strategy allowed conversion of various rhodamine-based scaffolds into highly fluorogenic HaloTag and SNAP-tag probes as well as spontaneously blinking dyes. In addition to HaloTag and SNAP-tag labeling, fluorogenic probes for Escherichia coli dihydrofolate reductase (eDHFR), tubulin and human immunodeficiency virus-1 (HIV-1) protease were generated. The ortho-carboxy group was also used as a handle for further functionalization of rhodamines, thereby introducing a zinc ligand to form a localizable and fluorogenic zinc indicator. Altogether, differently colored fluorescent probes optimized for various microscopy techniques and labeling systems were developed. These results demonstrate the value of systematic modification of rhodamines for expanding the fluorophore palette in cellular imaging.

In the presented work, five bio-based and bio-degradable cyclic esters, i.e. lactones, have been investigated as possible phase change materials for applications in latent heat storage systems. Commercial natural lactones such as &epsilon, caprolactone and &gamma, valerolactone were easily purchased through chemical suppliers, while 1,2-campholide, oxa-adamantanone and dibenzochromen-6-one were synthesized through Baeyer-Villiger oxidation. The compounds were characterized with respect to attenuated total reflectance spectroscopy and gas chromatography coupled with mass spectroscopy, in order to confirm their chemical structures and identity. Subsequently, thermogravimetric analysis and differential scanning calorimetry were used to measure the phase change temperatures, enthalpies of fusion, degradation temperatures, as well to estimate the degree of supercooling. The lactones showed a wide range of phase change temperatures from &minus, 40 &deg, C to 290 &deg, C, making them a high interest for both low and high temperature latent heat storage applications, given the lack of organic phase change materials covering phase change temperature ranges below 0 &deg, C and above 80 &deg, C. However, low enthalpies of fusion, high degrees of supercooling and thermal degradations at low temperatures were registered for all samples, rendering them unsuitable as phase change materials.