Molecular engineering of functional materials for optoelectronic applications

Organic functional materials are indispensable components for the last generation of light-energy conversion devices. Photo- and electroactive small organic molecules constitute thin active (emitting, transporting, blocking, injecting etc.) layers of organic optoelectronics and often play a decisive role for efficiency of an operating device. Since desired optoelectronic and morphological properties of organic materials can be finely tuned at the molecular level, the relationships between molecular structure, physicochemical properties and, ultimately, performance of the corresponding bulk material in an operating device are subject of extensive research nowadays. Moreover, developing understanding of device operation and physics imposes newer stricter and more challenging requirements for organic functional materials urging the search for new molecular architectures with advanced properties. Thus, the work presented in this thesis is focused on synthesis, profound characterization and use of new organic functional materials for light-energy conversion devices. We aim eventually to find out the synthetic guidelines for judicious molecular design of organic low-molecular-weight materials with advanced properties for use in optoelectronic devices. In this work, we introduce rigid bulky symmetric 10H,10'H-9,9'-spirobi[acridine] (SBA) as a universal molecular platform to construct emitting dopants and HTMs for the last generation optoelectronics: thermally-activated delayed fluorescence light-emitting diodes (TADF OLEDS) and perovskite solar cells (PSCs) respectively. The compact SBABz4 TADF emitter exhibited pure blue emission via TADF channel and a significant hypsochromic shift as opposed to simpler DMABz4 with commonly used “monomeric” donor without the spiro-node. Moreover, stick-like elongated SBABz4 demonstrated increased light-outcoupling efficiency. As the next part of our work, we utilized SBA molecular platform to construct 4 novel HTMs that mimic simultaneously two benchmark materials: 2,2′,7,7′,-tetrakis-(N,N-dimethoxyphenyl-amine)-9,9′-spirobifluorine (spiro-MeOTAD) and poly(triaryl amine) (PTAA) monomer fragment. The new HTMs performed on par with spiro-MeOTAD reference, but the corresponding devices demonstrated no current density-voltage (J-V) hysteresis and excellent durability, strongly outperforming the etalon molecule. Finally, driven by our curiosity to new molecular scaffolds, we explored chemistry and optoelectronic properties of electron excessive polyaromatic heterocycle – ullazine. We performed synthetic optimization and elaborated a straightforward high-yielding protocol towards 3,9-disubstituted ullazine scaffold and a reactive monobromoullazine. Moreover, we developed synthetic approaches towards all possible ullazine monocarbaldehydes and studied the relationships between regioisomerism and photo-/electronic properties of the corresponding conjugates with malonate acceptor. One of the donor-acceptor (D-A) conjugates displayed a suitable energy level and was tested as a small-molecule dopant-free HTM for PSCs without conventional arylamine substituents.