|Ph.D Student||Vestfrid Evgenya|
|Subject||Rational Design of Corroles with Superior Photophysical|
and Chemical Properties for a Variety of
|Department||Department of Chemistry||Supervisor||Professor Zeev Gross|
|Full Thesis text|
Room-temperature phosphorescent materials that emit light in the near-infrared (NIR) region is emerging as a new challenging research field with potential applications toward OLEDs and in vivo imaging. With respect to material design, the natural choice is coordination complexes, however the best performing ones are based on rare metals. The discovery of facile methodologies for the synthesis of triarylcorroles and modifications allowing tunability of their chemical and photophysical properties, gave access to a variety of metal complexes, as key components for many applications. The most prominent physical feature of post-transition metal complexes of corroles is their outstandingly intense fluorescence. Prior to this work only two corroles that display long-lived emission at room temperature (RT) were reported, based on corresponding iridium(III) and gold(III) complexes. This motivated us to examine alternative approaches for the design of compounds based on abundant elements that will emit phosphorescence in the NIR region, at RT. The rationale behind the design was to exploit the low rate of non-radiative processes exhibited by highly fluorescent corrole complexes, while introducing heavy atoms on their periphery, which according to our hypothesis should result in efficient emission from the triplet state.
Our first target was chosen the most fluorescent corrole, Al(tpfc), whose photophysical properties were already explored. Facile iodination resulted in selective substitution of only the joined pyrrole rings, yielding the tetra-iodinated Al corrole. Emission of both the short- and the long-lived excited states was detected at RT, proving our hypothesis. Next, the iodination of Ga complex was also successfully performed, providing the tetra-iodinated Ga corrole. In addition, milder reaction conditions resulted in tris-iodinated derivatives for both the Al and Ga complexes. The RT photophysical and redox properties of partially iodinated complexes were investigated in detail and compared to the unsubstituted derivatives. In addition, all the iodinated complexes display NIR phosphorescence with relative long lifetimes. Surprisingly emission was also observed at wavelength characteristic for fluorescence but with long lifetimes; temperature dependent experiments proved that the case in study is thermally activated delayed fluorescence.
The successful work on the Al and Ga corrole complexes encouraged us to investigate the less explored phosphorus corroles. The presence of NMR/EPR active N, P and F atoms within one complex seemed advantages for facile characterization of the new derivatives. A series of phosphorus corrole complexes was prepared, differing in the identity of the aryls and the axial ligands on the central P atom. The identity of the meso-aryl substituents was found to have no effect on the positions of both the absorbance and the emission bands, but the fluorescence intensities and the redox potentials were strongly affected. The most dramatic changes in these properties were induced by changes in the axial ligands bound to the chelated phosphorous. Moreover, the pronounced coupling with the central-31P and axial-19F isotopes allowed for the first experimental insight on the nature of the corresponding corrole radicals. Iodination of the intensively fluorescent P(tpfc)(OH)2 complex yielded the tris-iodinated corrole, which displayed both fluorescence and phosphorescence emissions at RT.