The influence of molecular geometry on the efficiency of thermally activated delayed fluorescence
| Autor: | Beth Laidlaw, Jonathan S. Ward, Martin R. Bryce, Thomas J. Penfold, Andrei S. Batsanov, Zhongjie Ren, Jamie Gibson, Fernando B. Dias, Roberto S. Nobuyasu, Przemyslaw Data |
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| Rok vydání: | 2019 |
| Předmět: |
Materials science
Absorption spectroscopy Oscillator strength Electron donor 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology Photochemistry 01 natural sciences Acceptor 0104 chemical sciences chemistry.chemical_compound Condensed Matter::Materials Science Molecular geometry chemistry Materials Chemistry Singlet state Physics::Chemical Physics 0210 nano-technology Phosphorescence Luminescence |
| Zdroj: | Journal of materials chemistry C, 2019, Vol.7(22), pp.6672-6684 [Peer Reviewed Journal] Journal of Materials Chemistry C |
| Popis: | In this work we successfully developed a strategy for positively influencing the conformation of thermally activated delayed fluorescence (TADF) molecules containing phenothiazine as the electron donor (D) unit, and dibenzothiophene-S,S-dioxide as the acceptor (A), linked in D–A and D–A–D structures. In this strategy the effect of restricted molecular geometry is explored to maximize TADF emission. The presence of bulky substituents in different positions on the donor unit forces the molecules to adopt an axial conformer where the singlet charge transfer state is shifted to higher energy, resulting in the oscillator strength and luminescence efficiency decreasing. With bulky substituents on the acceptor unit, the molecules adopt an equatorial geometry, where the donor and acceptor units are locked in relative near-orthogonal geometry. In this case the individual signatures of the donor and acceptor units are evident in the absorption spectra, demonstrating that the substituent in the acceptor uncouples the electronic linkage between the donor and acceptor more effectively than with donor substitution. In contrast with the axial conformers that show very weak TADF, even with a small singlet triplet gap, molecules with equatorial geometry show stronger oscillator strength and luminescence efficiency and are excellent TADF emitters. Acceptor-substituted molecules 6 and 7 in particular show extremely high TADF efficiency in solution and solid film, even with a singlet–triplet energy gap around 0.2 eV. This extensive study provides important criteria for the design of novel TADF and room temperature phosphorescence (RTP) emitters with optimized geometry. |
| Databáze: | OpenAIRE |
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