Novel Radical Peroxyester Photoinitiators: Decomposition Mechanisms and Potential Applications
Date of Award
Doctor of Philosophy (Ph.D.)
The present thesis describes transient studies of the photodecomposition of organic peroxyesters. The successful implementation of transient techniques over wide temporal (picosecond to microsecond) and spectral (UV-Vis to mid-IR) windows allows characterization of the transient species involved in the decomposition. The first part of the thesis illustrates a model approach for transient studies of coumarin based peroxyesters. Direct observation of transient species yielded the rates of decays of singlet and triplet excited states of the coumarin chromophore as well as provided spectra of the radical intermediates. Particularly, to the best of our knowledge, this is the first observation of an aroyloxyl radical by time-resolved infrared spectroscopy. Transient studies of a series of peroxyesters containing the 1,4-bis(phenylethynyl)benzene chromophore elucidated the photodecomposition mechanism together with providing information about the electronic structure of radical intermediates involved therein. The fission of the peroxy bond leads to formation of an aroyloxyl radical possessing 2B1 molecular orbital symmetry with the unpaired electron delocalized through the entire phenylene-ethynylene chormophore. This delocalization causes a decrease in the acetylene bond order that can be observed experimentally as a red shift of IR vibration conveying cumulene-like character to the structure of the radical. Studies of two-photon absorption (TPA) properties of phenylene-ethynylene peroxyesters reveal them promising candidates for two photon microfabrication. The compounds possess relatively high TPA cross-sections (110 GM) and are capable of initiating the polymerization of acrylic monomers. Model structures with 10 micrometers resolution were fabricated in two-photon process using phenylene-ethynylene peroxyesters as photoinitiators.
Polyansky, Dmitry, "Novel Radical Peroxyester Photoinitiators: Decomposition Mechanisms and Potential Applications" (2005). Photochemical Sciences Ph.D. Dissertations. 3.