Synthesis and characterization of luminescent conjugated organoboron oligomers and macrocycles

Conjugated molecules have been explored as an important class of organic materials that are of paramount interest in organic electronics, such as organic light emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic solar cells. Although current studies frequently concentrate on conjugated polymers, small molecules are attractive in that they allow for facile fine-tuning of the HOMO and LUMO energy levels, which is crucial for enhancement of the overall performance of organic devices. Functionalization of conjugated organic systems with main group elements represents an active research area of current interest in the chemistry and matarial science community. One of the most often employed elements is the electron-deficient boron that features an empty p orbital that opens up a pathway to overlap with π orbitals of attached aryl groups. This interaction leads to unusual optical and electronic properties for organoborane compounds. The focus of this thesis is on the investigation of well-defined organoborane oligomers and macrocycles.Ph. D.Includes bibliographical referencesIncludes vitaby Pangkuan Che

Highly Emissive 9-Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication

A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m$^{-2}$. These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability

Highly Emissive 9‐Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication

A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m$^{-2}$. These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability

Dynamics of dual-junction-functionality associative polymer networks with ion and nanoparticle metal-coordinate cross-link junctions

We provide a canonical introduction to dual-junction-functionality associative polymer networks, which combine high and low functionality ( f) dynamic cross-link junctions to impart load-bearing, dissipation, and self-repairing ability to the network. This unique type of network configuration offers an alternative to traditional dual-junction networks consisting of covalent and reversible cross-links. The high- f junctions can provide load-bearing abilities similar to a covalent cross-link while retaining the ability to self-repair and concurrently confer stimuli-responsive properties arising from the high- f junction species. We demonstrate the mechanical properties of this design motif using metal-coordinating polymer hydrogel networks, which are dynamically cross-linked by different ratios of metal nanoparticle (high- f) and metal ion (low- f) cross-link junctions. We also demonstrate the spontaneous self-assembly of nanoparticle-cross-linked polymers into anisotropic sheets, which may be generalizable for designing dual-junction-functionality associative networks with low volume fraction percolated high- f networks. </jats:p

Synthesis of π‐Conjugated Chiral Aza/Boracyclophanes with a meta and para Substitution

We herein describe the synthesis of a new class of axially chiral aza/boracyclophanes (BDN1, BXN1, BDB1 and BXB1) using binaphthyls as chiral building blocks and the main-group (B/N) chemistry with tunable electronic effects. All macrocycles substituted with triarylamine donors or triarylborane acceptors are strongly luminescent. These macrocycles showed two distinct meta and para π-conjugation pathways, leading to the formation of quasi figure-of-eight and square-shaped conformations. Interestingly, comparison of such structural models revealed that the former type of macrocycles BXN1 and BXB1 gave higher racemization barriers relative to the other ones. The results reported here may provide a new approach to engineer the optical stability of π-conjugated chiral macrocycles by controlling π-substitution patterns. The ring constraints induced by macrocyclization were also demonstrated to contribute to the configurational persistence as compared with the open-chain analogues p-BTT and m-BTT

Changing the Nature of the Chelating Ligand of Tetracoordinate Boron-Containing PAH Multi-resonant Thermally Activated Delayed Fluorescence Emitters Tunes the Emission from Green to Deep Red

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have attracted considerable attention recently. The molecular design frequently incorporates cycloboration. However, to the best of our knowledge MR-TADF compounds containing nitrogen chelation to boron is still unknown. Reported herein is a new class of tetracoordinate boron-containing MR-TADF emitters bearing a C^N^C- and N^N^N-chelating ligands. We demonstrate that the replacement of B−C covalent bond in C^N^C-chelating ligand by B−N covalent bond affords a regioisomer, which dramatically influences the optoelectronic properties of the molecule. The resulting N^N^N-chelating compounds show bathochromically shifted absorption and emission spectra relative to C^N^C-chelating compounds. The incorporation of tert-butylcarbazole group to the 4-position of the pyridine significantly enhances both the thermal stability and the reverse intersystem crossing rate, yet has a negligible effect on the emission properties. Consequently, high-performance hyperfluorescence organic light-emitting diodes (HF-OLEDs) that utilize these molecules as green and yellow-green emitters show maximum external quantum efficiency (ηext) of 11.5% and 25.1%, and a suppressed efficiency roll-off with ηext of 10.2% and 18.7% at a luminance of 1000 cd m−2, respectively