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The fundamental influence of the structure and substitution of radical photoinitiators was investigated via a trifold combination of pulsed-laser polymerization with subsequent electrospray-ionization mass spectrometry (PLP-ESI-MS), femtosecond transient absorption (fs-TA) spectroscopy, and quantum chemistry. For the first time, a library of benzoin-derived photoinitiators with varied substitution patterns was synthesized. In the PLP-ESI-MS study, different photoinitiators were compared pairwise in so-called cocktail experiments, enabling the direct comparison of their initiation efficiency. In the fs-TA experiments, the transient response was observed after UV excitation in the visible spectral region, allowing for a description of excited state dynamics, which was analyzed with the aid of TD-DFT calculations. Ab initio calculations were undertaken to determine the reactivity of the radical fragments generated from these photoinitiators and to quantify the influence of various substituents on the rate of addition to monomer. In summary, the influence of the substituent on the initiation efficiency, intersystem crossing (ISC) behavior, excited state dynamics, and the extinction coefficients were analyzed. Hence, relaxation pathways and reaction mechanisms were optimized to explain disparate initiation efficiencies of a wide range of newly designed photoinitiators with varying substitution patterns. The strongly divergent absorptivities of the different photoinitiators and their corresponding initiation efficiencies underline that the absorptivity of a molecule is by no means an unequivocal measure for its reactivity when excited at a specific wavelength. In fact, the most efficient initiators are governed by one nπ* singlet state with a very low extinction coefficient at the excitation wavelength and one or two triplet states with nπ* character.

By comparing the phosphorescence spectra of Gd(acac) 3 (acac~acetylacetone), Gd(TFacac) 3 ( TFacac1,1,1-trifluoroacetylacetone), the effects of fluorine replacement of hydrogen on the triplet state energy of the ligands were revealed. Fluorine can lower the triplet state energy of Hacac and make it more suitable for energy transfer towards the 5 D 4 state of terbium. Organic electroluminescent devices (OELDs) with the corresponding trivalent terbium complexes as emissive layers were fabricated. Triple-layer-type devices with a structure of glass substrate/ITO (indium tin oxide)/PVK [poly(N-vinylcarbazole)]/PVK : Tb complex: PBD [2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]/PBD/Al exhibit bright green luminescence upon applying a dc voltage. The luminance of a device with Tb(TFacac) 3 phen (1,10-phenanthroline) and Tb(TFacac) 3 as emissive layer is higher than that of the corresponding devices with Tb(acac) 3 (phen) and Tb(acac) 3 as emissive layers. The EL device with Tb(TFacac) 3 (phen) as emitter exhibits characteristic emission of Tb 3z ions with a maximum luminance of 58 cd m 22 at 25 V.