The doctoral dissertation in the field of Chemistry will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus.
What is the topic of your doctoral research? Why is it important to study the topic?
My thesis explores a few approaches to diversify photophysical characteristics of polyaromatic hydrocarbon blocks by utilizing different organophosphorus functions. Three main directions to decorate conventional polyaromatic chromophores with P-derived groups were investigated, primarily aiming at low energy photoluminescence including organic phosphorescence. New photofunctional molecular materials with desired properties require flexible solutions to achieve structural tailorability and predictability of optical properties for a diversity of photonics applications. Phosphorus element appended to or incorporated into an organic dye can offer versatile options for structural and electronic modifications by means of additional covalent, coordination, and ionic bonding.
What are the key findings or observations of your doctoral research?
The first step was to modify anthracene-based donor-acceptor (D–A) dyes by altering D and A groups. A systematic analysis of cyclic and terminally phosphonium decorated compounds revealed the rare asymmetric phospha-spiro species to be the strongest electron acceptor in the study. This allowed to achieve charge transfer NIR fluorescence with maxima at 797 nm in solution and 860 nm in the solid state, highlighting the promising potential of phospha-bicyclic fragment for the design of low energy light absorbing and emitting D–A compounds. In the second part, easily accessible phosphonium iodide salts, composed of dicationic chromophores having conjugated backbones, were investigated. In crystals, these compounds tend to form ion pairs via efficient anion–π interactions, which bring heavy counter-anion in close proximity to the photoactive moieties. The combination of anion-cation charge transfer and external heavy atom effect resulted in efficient metal-free phosphorescence in the solid state with unusually fast radiative rate constants kr as high as 2.8 × 105 s–1, which are comparable to those of late transition metal phosphors and organic thermally activated delayed fluorophores. Lastly, anthracene-based phosphines, which allow for short non-covalent contacts between the metal center and PAH motif, were coordinated to selected metal fragments. While only the heavy atom effect was insufficient to induce anthracene-localized phosphorescence, the composite bichromophore molecules having platinum (II) pincer constituents, demonstrate efficient through-space energy transfer leading to NIR emission of the PAH component. This result illustrates a promising and feasible concept of molecular systems capable of low energy organic phosphorescence sensitized intramolecularly by simple organometallic groups.
What are the key research methods and materials used in your doctoral research?
Planning the molecular design and conducting synthesis of new compounds. Then the characterization of said compounds using spectroscopic and structural methods of analysis (NMR, IR and UV-vis spectroscopies, XRD study). Besides that, the photophysical measurements and theoretical studies by collaborating groups.
The doctoral dissertation of Iida Partanen, MSc, entitled Photofunctional phosphorus derivatives of polyaromatic hydrocarbons will be examined at the Faculty of Science, Forestry and Technology, Joensuu Campus. The opponent will be Professor Robert Podgajny, Jagiellonian University, and the custos will be Professor Igor Koshevoy, University of Eastern Finland. Language of the public defence is English.
