Thermal cyclotrimerization was first discovered in 1866 by Bertholet, then, in 1948, Reppe and Schweckendiek reported the first transition metal catalyzed [2+2+2] cyclotrimerization of alkynes using Ni complexes. In the following 70 years of research, transition metal catalyzed [2+2+2] cyclotrimerization have become a powerful method for the synthesis of variously decorated aromatic rings and new catalytic systems as well as reaction conditions have been successfully applied. Herein, I would like to show the use of this reaction for the synthesis of the important class of fluorene-based compounds. In particular, a regioselective cyclotrimerization of 2,4-disubstituted fluorenols was achieved by Ru-catalyzed partially intermolecular [2+2+2] cyclotrimerization of diynes with terminal alkynes. Rh-based complex proved to be a straightforward transition metal catalyst for the construction of selectively fluorinated [5] and [6]helical dispiroindenofluorenes using intramolecular [2+2+2] cycloaddition of triynediols as the key synthetic step. Moreover, Ni complexes demonstrated to be a valid choice for the selective synthesis of unsymmetrical [7]helical indenofluorenones, while other catalytic systems based on Rh, Ru, Pd and Co gave mixture of the desired cyclotrimerization compound together with the...

This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are promising candidates for 2PA applications because their material properties can be tailored through molecular engineering thereby facilitating optimization of their nonlinear optical properties. Fluorene derivatives are particularly interesting since they possess high photochemical stability for organic molecules and are generally strongly fluorescent. By systematically altering the structural properties in a series of fluorenyl molecules, we have determined how these changes affect their two-photon absorbing capabilities. This was accomplished through characterization of both the strength and location of their 2PA spectra. In order to ensure the validity of these results, three separate nonlinear characterization techniques were employed: two-photon fluorescence spectroscopy, white-light continuum pump-probe spectroscopy, and the Z-scan technique. In addition, full linear spectroscopic characterization was performed on these molecules along with supplementary quantum chemical calculations to obtain certain molecular properties that might impact the nonlinearity. Different designs in chemical architecture allowed investigation of the effects of symmetry, solvism, donor-acceptor strengths, conjugation length, and multi-branched geometries on the two-photon absorbing properties of these molecules. In addition, the means to enhance 2PA via intermediate state resonances was investigated. To provide plausible explanations for the experimentally observed trends, a conceptually simple three level model was employed. The subsequent correlations found between chemical structure and the linear and nonlinear optical properties of these molecules provided definitive conclusions on how to properly optimize their two-photon absorbing capabilities. The resulting large nonlinearities found in these molecules have already shown promise in a variety of the aforementioned applications.