Synthesis and characterization of 2-aryl-imidazo[4,5-c]carbazoles, which are made by reaction between 3-amino-4-(carbazol-3'-ylamino)-9,9'dialkyl-carbazoles (semidines) and arylaldehydes, is reported in this dissertation. The compounds are characterized by their fluorescence properties (spectral properties and quantum efficiency), which are dependent on substituents and solvents. Several aromatic and heteroaromatic carbaldehydes were chosen for the synthesis of the imidazocarbazoles to obtain a large series of the imidazocarbazole chromophore. Reactive functional groups , i.e. NCS ore NH2, open the possibility to form a chemical bond between the imidazo[4,5-c]carbazoles and biological subtrates. Therefore the products can be used as fluorescence markers in in-vitro diagnostics. The imidazo[4,5-c]carbazoles can be grouped as effective fluorescent heterocycles (quantum yield between 10 and 90%). The appereance of two emission maxima is a significant feature of these products. The emission band with the higher energy is spectrally positioned at 350-400 nm and is comparable with fluorescence of carbazolyl compound substituted in 3-position. The second band, which is assigned to the lower energy band, appears bathochromic and shows solvatochromism by changing the environment of the fluorophore. The emission depends on the imidazocarbazole segment. From the solvatochromism of the fluorescence are drawn conclusions about the based photophysical processes. The results are compared with quantum chemical calculations, by using the AM1 Hamiltonian for calculation of ground state geometry and ZINDO/S for calculation of excited state transitions. These solvent dependent emissions are caused by an intramolecular charge transfer (ICT) and an excited state intramolecular proton transfer (ESIPT) in the case of hydroxy substituted compounds. Furthermore, the oxidation of hydrophilic substituted semidines results in water soluble diindolophenacines. Their uv/vis and fluorescence spectroscopical properties are discussed as function of the solvents used.