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

Lookup NU author(s): Jamie Gibson, Professor Thomas Penfold

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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.

Publication metadata

Author(s): Huang R, Ward JS, Kukhta NA, Avó J, Gibson J, Penfold TJ, Lima JC, Batsanov AS, Berberan-Santos MN, Bryce MR, Dias FB

Publication type: Article

Publication status: Published

Journal: Journal of Material Chemistry C

Year: 2018

Volume: 6

Issue: 34

Pages: 9238-9247

Print publication date: 14/09/2018

Online publication date: 17/08/2018

Acceptance date: 05/08/2018

Date deposited: 19/08/2018

ISSN (print): 2050-7526

ISSN (electronic): 2050-7534

Publisher: Royal Society of Chemistry

URL: https://doi.org/10.1039/C8TC02987C

DOI: 10.1039/C8TC02987C

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