Fluorescence spectroscopy has hugely improved our understanding of the eukaryotic cell. Thanks to fluorescence techniques, the composition and dynamic nature of the membrane, cytosol, mitochondria, and other organelles has been elucidated. However, the more we discover the more we realize that there is still much to study. In this thesis a series of fluorescence probes were developed to further improve our understanding of key cellular features. A few synthetic strategies were developed to prepare non-symmetrically substituted BODIPY-perylene conjugates. The products obtained were characterized using spectroscopic techniques. These molecules were successfully used for two purposes: first, as triplet-triplet annihilation up-conversion sensitisers; a second, as viscosity sensors. The results indicate that the dyes are good sensitisers even in the absence of heavy atoms such as iodine, but the up-conversion process was found to be very solvent-dependent. The viscosity sensitivity experiments determined the molecules that have potential as intensity-based and lifetime-based viscosity sensors. Solid-state spectroscopic studies were conducted on crystalline samples obtained from some BODIPY-perylene conjugates. The results give us some insights into the electronic effects taking place in the crystal structure. A few different sensors were prepared as part of the LogicLab project. A BODIPY- cholesterol conjugate was designed and tested as a viscosity sensor. The results indicate that this molecule can be used an intensity-based probe. A mitochondrial Raman reporter was prepared and studied in cells. The molecule was found to be better than the commercial standard. Finally, a nitric oxide sensor was synthesized and studied in solution. The molecule reacted with nitric oxide, but the results indicate the challenges associated with sensing this gas using up-conversion systems. A total of six research articles were published from the results obtained in this work and as the results of the collaboration with other research groups of the LogicLab consortium.