Browsing by Author "Knöller, Julius A."

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Open Access
Isolable diaminophosphide boranes
(2020) Blum, Markus; Dunaj, Tobias; Knöller, Julius A.; Feil, Christoph M.; Nieger, Martin; Gudat, Dietrich
Metalation of secondary diaminophosphine boranes by alkali metal amides provides a robust and selective access route to a range of metal diaminophosphide boranes M[(R2N)2P(BH3)] (M=Li, Na, K; R=alkyl, aryl) with acyclic or heterocyclic molecular backbones, whereas reduction of a chlorodiaminophosphine borane gave less satisfactory results. The metalated species were characterized in situ by NMR spectroscopy and in two cases isolated as crystalline solids. Single‐crystal XRD studies revealed the presence of salt‐like structures with strongly interacting ions. Synthetic applications of K[(R2N)2P(BH3)] were studied in reactions with a 1,2‐dichlorodisilane and CS2, which afforded either mono‐ or difunctional phosphine boranes with a rare combination of electronegative amino and electropositive functional disilanyl groups on phosphorus, or a phosphinodithioformate. Spectroscopic studies gave a first hint that removal of the borane fragment may be feasible.
Open Access
Lumineszierende Flüssigkristalle auf Basis multiresonanter Bor-dotierter Heteroaromaten
(2025) Knöller, Julius A.; Laschat, Sabine (Prof. Dr.)
Open Access
MR-TADF liquid crystals : towards self assembling host-guest mixtures showing narrowband emission from the mesophase
(2024) Knöller, Julius A.; Müller, Franziska; Matulaitis, Tomas; dos Santos, John M.; Gupta, Abhishek Kumar; Zysman-Colman, Eli; Laschat, Sabine
Creating (room temperature) liquid crystalline TADF materials that retain the photophysical properties of the monomolecular TADF emitters remains a formidable challenge. The strong intramolecular interactions required for formation of a liquid crystal usually adversely affect the photophysical properties and balancing them is not yet possible. In this work, we present a novel host-guest approach enabling unperturbed, narrowband emission from an MR-TADF emissive core from strongly aggregated columnar hexagonal (Colh) liquid crystals. By modifying the DOBNA scaffold with mesogenic groups bearing alkoxy chains of different lengths, we created a library of Colh liquid crystals featuring phase ranges >100 K and room temperature mesomorphism. Expectedly, these exhibit broad excimer emission from their neat films, so we exploited their high singlet (S1 ∼2.9 eV) and triplet (T1 ∼2.5 eV) energies by doping them with the MR-TADF guest BCzBN. Upon excitation of the host, efficient Förster Resonance Energy Transfer (FRET) resulted in almost exclusive emission from BCzBN. The ability of the liquid crystallinity of the host to not be adversely affected by the presence of BCzBN is demonstrated as is the localization of the guest molecules within the aliphatic chain network of the host, resulting in extremely narrowband emission (FWHM = 14-15 nm). With this work we demonstrate a strategy for the self-assembly of materials with previously mutually incompatible properties in emissive liquid crystalline systems: strong aggregation in Colh mesophases, and narrowband emission from a MR-TADF core.
Open Access
A novel B,O,N-doped mesogen with narrowband MR-TADF emission
(2024) Knöller, Julius A.; Sönmez, Burcu; Matulaitis, Tomas; Gupta, Abhishek Kumar; Zysman-Colman, Eli; Laschat, Sabine
Modification of an unsymmetric B,O,N-doped aromatic core with peripheral mesogenic units triggers self-assembly into a columnar hexagonal mesophase, which is stable between 22 and 144 °C. The columnar assembly is preserved in a glassy state below 22 °C. The B,O,N-doped mesogen displays narrowband sky-blue multiresonance thermally activated delayed fluorescence (MR-TADF) under diluted conditions and bright excimer emission in condensed phase. Our combined experimental and theoretical approach provides insight into the development of strongly aggregating liquid crystalline MR-TADF emitters.