Triarylboron Compounds and Their Platinum(II) Complexes: Photophysical Properties and Applications in Optoelectronics
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This work concerns the development of π-conjugated materials for optoelectronic applications, with emphasis on organoboron- and organoplatinum-containing compounds. The preparation of a nonconjugated two-chromophore emissive material is described, containing both organoplatinum and organoboron units. This material exhibits simultaneous fluorescent and phosphorescent emission at ambient temperature. Both emission colours are switchable in the presence of fluoride, giving a dual-emissive compound with multiple observable luminescent colours. The preparation of a nonconjugated donor-acceptor triarylborane containing both Lewis acidic and basic receptor sites is also described. This highly fluorescent compound is reversibly switchable between three emissive states upon addition of acid or fluoride. Furthermore, platinum(II)-acetylacetonates with nonconjugated antenna chromophores were prepared, and their luminescent properties were investigated. A series of directly conjugated platinum(II)-acetylacetonates have been synthesized incorporating a triarylboron group. The presence of boron was found to enhance the electron-transporting capabilities, film-forming properties, and phosphorescent quantum yields of these complexes. Highly efficient OLEDs were prepared incorporating these materials as dopants, including the first example of a Pt(II)-based OLED with an external quantum efficiency >20%. Triarylboron-containing Pt(II) complexes of N-heterocyclic carbenes were also prepared. Using this design, blue to blue-green phosphorescence was achieved with high quantum yield, and their use in OLEDs was demonstrated. A new high-yield synthetic route has been developed to cyclometalated Pt(II)-β-diketonates, requiring stoichiometric reagents and short reaction times at ambient temperature. This methodology has broad substrate scope across a variety of N^C-chelate ligands, as well as P^C-chelate phosphines and C^C-chelate carbenes as well. The preparation of N-heterocyclic carbazole-based host materials for OLEDs is also described. These materials exhibit improved electron-transporting capabilities relative to the more commonly used host 4,4’-N,N’-dicarbazolylbiphenyl (CBP), and were used to fabricate the first single-layer electrophosphorescent devices with efficiencies competitive with conventional multilayer structures. Finally, the discovery of a triarylboron-based vapochromic material is described. This Pt(II)-alkyne complex was shown to change luminescent colour in response to a variety of volatile organic compounds, with distinct responses dependent on the nature of the analyte. The mechanism of vapochromism was investigated in detail by optical and multinuclear solid-state NMR spectroscopy, and differs in origin from all previously reported examples.