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The influence of molecular conformation on the photophysics of organic room temperature phosphorescent luminophores

Huang, Rongjuan; Ward, Jonathan S.; Kukhta, Nadzeya A.; Avó, João; Gibson, Jamie; Penfold, Thomas; Lima, João C.; Batsanov, Andrei S.; Berberan-Santos, Mário N.; Bryce, Martin R.; Dias, Fernando B.

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Authors

Rongjuan Huang

Jonathan S. Ward

Nadzeya A. Kukhta

João Avó

Jamie Gibson

Thomas Penfold

João C. Lima

Mário N. Berberan-Santos



Abstract

A series of novel donor–acceptor–donor (D–A–D) compounds featuring dibenzothiophene (DBT) and phenothiazine (PTZ) units are presented. A different degree of steric hindrance between the donor and acceptor fragments is achieved by the systematic changes of donor substituents (methyl, iso-propyl, tert-butyl groups). This leads to the tuning of photophysical properties by conformational control. The unsubstituted DPTZ–DBT molecule exists in both equatorial and axial forms in the ground state, due to the ability of PTZ to form H-extra and H-intra folded conformers that allow formation of parallel quasi-axial (ax) and perpendicular quasi-equatorial (eq) conformers, respectively. However, the equatorial conformer prevails in the excited state. This leads to strong room temperature phosphorescence (RTP) in the green region with high phosphorescence quantum yield (60 ± 8%). Under the influence of bulky substituents, the alkyl-DPTZ–DBT derivatives change molecular conformation, preventing formation of the excited charge transfer state. Hence, blue, but much weaker, phosphorescence is observed. The less bulky methyl substituent on the donor results in dual RTP (blue and green), apparently violating Kasha's rule imposed by the modulation of the barriers between excited states. The experimental results are supported by DFT calculations in the ground and excited state. Control of conformation with substituents is an effective strategy for tuning the excited state properties of D–A–D molecules for RTP emission.

Citation

Huang, R., Ward, J. S., Kukhta, N. A., Avó, J., Gibson, J., Penfold, T., …Dias, F. B. (2018). The influence of molecular conformation on the photophysics of organic room temperature phosphorescent luminophores. Journal of Materials Chemistry C Materials for optical and electronic devices, 10(34), 9238-9247. https://doi.org/10.1039/c8tc02987c

Journal Article Type Article
Acceptance Date Aug 5, 2018
Online Publication Date Aug 17, 2018
Publication Date Aug 17, 2018
Deposit Date Aug 23, 2018
Publicly Available Date Aug 23, 2018
Journal Journal of Materials Chemistry C Materials for optical and electronic devices
Print ISSN 2050-7526
Electronic ISSN 2050-7534
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 10
Issue 34
Pages 9238-9247
DOI https://doi.org/10.1039/c8tc02987c

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