Two-photon absorption (TPA) enables the activation of photophysical and -chemical processes at high spatial resolution (100 nm) reaching below the diffraction limit associated with the wavelength of the absorbed light. Amongst other important technologies it is employed in, e.g. two-photon excitation microscopy (TPEM), its use is becoming increasingly popular in sub-micrometer stereolithography for microfabrication of photonic crystals, polymer-based optical waveguides on integrated circuit boards, rapid prototyping, high-density 3D optical data storage and parts for other industries requiring high precision. Furthermore the high transparency of biological tissues towards the fs-pulsed Titanium:Sapphire near infrared lasers offers the advantages of high penetration depth and little photo-damage, making TPA especially suitable for applications like bio-imaging and in-vivo bio-fabrication using hydrogel-based materials. Stereolithography based on two-photon induced photopolymerization (TPIP) has employed classical one-photon initiators (OPIs) as used in radical photopolymerization. However since OPIs suffer from significant limitations regarding the quality of the attainable microstructures and especially the required fabrication parameters (high laser powers, very slow writing), the development of specialized two-photon initiators (TPIs) is of major interest. In the present work several novel TPIs based on the lead structure of M2CMK, a highly efficient TPI developed by the research group in previous work, were synthesized and characterized (UV-Vis spectra, two-photon absorption cross section -TPA, TPIP processing window screening & structuring tests). The first approach to improve efficiency, enhancing energy absorption via increasing the -TPA by introducing branched and/or planarized structural elements, yielded several initiators with features superior to the reference. Y-B2CMK exhibits a broad overall structuring window and especially avoids excessive damage to polymerized objects at high power densities. For high laser powers up to 110 mW, B2Trz shows the best performance of all tested TPIs. B2Cbz produces excellent results in the low to medium power range at writing speeds up to 151 mm/s. The second approach of introducing cleavable groups producing radicals while avoiding deactivation by back electron transfer (BET) was not able to enhance initiation efficiency so far because S2CMK, SNB and PADE all suffered from low -TPA. Nevertheless, successful cleavage under TPA conditions could be proved and valuable insights for future implementation of cleavable TPIs were gained.